Biology A level Flashcards

Question

How is chloroplast adapted for photosynthesis?

Answer 1

- They contain stacks of thylakoid membranes called grana which contain the photosynthetic pigments such as chlorophyll. These are arranged as photosystems. - They contain stroma which is the fluid surrounding the grana, stroma contains all the enzymes required for the light independent stage of photosynthesis - Chloroplast appear as biconvex discs about 3-10 µm

Answer 2

Thylakoid membrane: where light-dependent reactions occur - Its membrane contains photosystems, inside which chlorophyll molecules are located. - It also has accessory pigments, ETC and ATP synthase

Answer 3

Grana: stacks of thylakoid membranes, increasing surface area for light dependent reactions. Its membrane: - Holds ATP synthase for chemiosmosis - Allows pigments to be arranged in light harvesting clusters (in funnel like structures) for efficient light absorption.

Answer 4

Stroma: contains enzymes for Calvin cycle (light independent reactions), 70S ribosomes, circular DNA, lipid droplets, starch grains

Answer 5

- Contain large numbers of chloroplasts - Large vacuole helps in pushing chloroplast to edge of cell for max light absorption and short diffusion pathway - Chloroplasts can move towards light and away from intense light to avoid damage - Elongated & arranged to intercept maximum light - Closely packed to absorb maximum light - Large surface area for diffusion of gases - Moist cell surfaces for diffusion of gases - Thin cell walls for maximum light penetration and diffusion of gases

Answer 6

The enzymes involved in photosynthesis have a higher optimum temperature, so are not damaged by the high temperatures.

Answer 7

Takes place in the thylakoid membranes

Answer 8

- Photosystems are required to trap wavelengths of light (photons) to energize the electron found in the primary pigment (chlorophyll α) - Photosystem I absorbs wavelengths of 700nm - Photosystem II absorbs wavelengths of 680nm

Answer 9

Photoactivation is the excitation of an e- to a higher energy level, causing it to escape a chlorophyll molecule

Answer 10

Accessory pigments are arranged in light harvesting clusters that pass on absorbed energy to the primary pigment at reaction centre

Answer 11

- thylakoid membranes - Photosystems - Photoactivation - Accessory pigments

Answer 12

1. Light energy excites electrons at the reaction centres of the photosystems (in the chlorophyll molecule in the thylakoid membrane), causing them to pass to an electron acceptor at the start of the electron transport chain. This is called photoionisation. 2. Electrons are released from photosystem II (PSII) and they pass down the chain from one electron carrier to the next in a series of redox reactions. ATP is produced via chemiosmosis. The electrons then leave PSII and enter photosystem I. Again they go down the electron transport chain and ATP is produced again. This process again generates ATP from ADP and inorganic phosphate. 3. Light splits water into protons (H+ ions), electrons and oxygen (waste). The electrons are used to replace the electrons that leave photosystem II. This process is called photolysis of water. The protons are pumped across the membrane using the ATP created in step 2 in a process called chemiosmosis. This creates a chemical potential gradient. 4. Reduced NADP is generated as the electrons in the electron transport chain are transferred to NADP along with a proton. 5. Protons return to the stroma through ATP synthase via facilitated diffusion which produces ATP. Approximately 4 protons make one ATP molecule. Both ATP and reduced NADP are used in the light-independent stage of photosynthesis.

Answer 13

- Only involves Photosystem I - E- is photoactivated and is accepted by e- acceptor rather than falling back into the photosystem and giving out thermal energy - It is then passed on via a chain of electron carriers, during which, enough energy is released to synthesize ATP by chemiosmosis - ATP is then passed on to light independent reactions - Electron then returns to Photosystem I

Answer 14

1. Accessory pigments in PSII absorb photons of light. The energy is passed onto primary pigment, exciting primary pigments e- to a higher energy level and causing them to escape the photosystem. - Photolysis: photosystem II contains a water splitting enzyme that catalyses the lysis of water in the presence of light: - Oxygen diffuses out of the chloroplast and into the air - The protons build up in the thylakoid lumen causing a gradient to be formed - The electrons in water replace the electrons that have left the primary pigment 2. The energized electrons are taken up by electron acceptors, and are passed down the ETC, which generates energy to pump protons from stroma to lumen. e- then travel to PS I, where more light is absorbed by the chlorophyll molecules and the e- are reenergised. H+NADP→NADPH 3. The combination of the water splitting and the proton pumping caused protons to build up inside the thylakoid lumen, generating a proton gradient across the thylakoid membrane. ATP is therefore photophosphorylated using the ATP synthase enzyme in exactly the same way as respiration.

Answer 15

Cyclic - Only photosystem I involved - e- emitted returns to same photosystem Non-cyclic - Both photosystems involved - e- emitted from PSII is absorbed by PSI - Reduced NADP produced - Photolysis of H2O, O2 by product

Answer 16

Light-independent reaction, also known as the Calvin cycle, is the final stage of photosynthesis which uses ATP and reduced NADP from the light dependent stage to produce glucose. These set of reactions take place in the stroma.

Answer 17

1) RuBP is combined with carbon dioxide in a reaction called carbon fixation, catalysed by the enzyme RUBISCO. 2) RuBP is converted into two glycerate 3-phosphate (GP) molecules 3) Reduced NADP and ATP are used to reduce each GP molecule to triose phosphate. In this process, the reduced NADP becomes oxidised. 4) Some of triose phosphate molecules are used to make glucose (every 6 cycles) which is then converted to essential organic compounds such as polysaccharides, lipids, amino acids and nucleic acids. 5) Remaining triose phosphate molecules are used to regenerate RuBP with the help of ATP

Answer 18

- 6C→2 X G3P (3C) - G3P is reduced and activated to form triose phosphate (TP or PGA). The ATP and NADPH from the light-dependent reactions is used in this step. The ADP and NADP return to the thylakoid membrane for recycling - Most of the triose phosphate regenerates the RuBP using ATP - Some of the triose phosphate molecules condense to hexose phosphates, to in turn form glucose, cellulose, sucrose and starch. - Others converted to amino acids, lipids, or acetyl coenzyme A (CoA)

Answer 19

if a process is affected by more than one factor, the rate will be limited by the factor which is nearest its lowest value

Answer 20

- Light intensity - As light intensity increases, ATP and reduced NADP are produced at a higher rate - Carbon dioxide concentration - As concentration increases, more carbon fixation takes place and an increased rate of TP production in the Calvin cycle - Temperature - The rate of enzyme-controlled reactions will also increase however when temperature goes above optimum the enzymes will denature, thus the rate is slowed

Answer 21

- A better understanding of the environmental factors on rate of photosynthesis allows us to manage the growth of plants in protected fields increasing yield of crop. - Sensors monitor light intensity, humidity and concentration of CO2 and control optimum conditions - Plants are grown hydroponically- in nutrient soil solution where its contents vary depending on the plants stage of growth - Pests and fungal diseases are fewer, further improving yield

Answer 22

- Higher optimum temperature than C3 plants (45 oC) - Mesophyll cells tightly packed so not allowing O2 to reach bundle sheath cells - Avoids photorespiration - Dimorphic nature of chloroplasts

Answer 23

- In C4 plants the Calvin cycle occurs in the bundle sheath - Carbon dioxide is absorbed by mesophyll cells that contain the enzyme PEP carboxylase which catalyses the combination of CO2 with PEP (3C) - Oxaloacetate (4C) is formed and is converted into malate (4C) - It is then passed onto the bundle sheath cells and CO2 is removed forming pyruvate (3C) - The CO2 continues normally like in the Calvin cycle

Answer 24

C3 plants forms a 3C molecule after splitting the 6C compound during the light independent stage of photosynthesis

Answer 25

C4 plants such as maize, sorghum and other tropical grasses

Answer 26

Photorespiration is the reaction when RuBP combines with oxygen instead of CO2 so Calvin cycle cannot occur. This usually happens in high temperatures (as stomata close to prevent water loss, causing O2 build up) and high light intensity.

Answer 27

- This can be done by extracting the pigments from a leaf and then carrying out chromatography.

Answer 28

Rf value = distance moved by solute / distance moved by solvent

Answer 29

Photosynthetic pigments are involved in absorbing light required for photosynthesis and subsequently convert it to chemical energy. The colour of pigments is determined by the light they reflect.

Answer 30

Absorption spectrum: is a graph that shows the absorbance at different wavelengths of light - A low absorption means that those wavelengths are not absorbed, but instead are reflected or transmitted therefore plants seem to be green as it is absorbed least - Carotenoids mainly absorb in the blue-violet region.

Answer 31

Action spectrum: graph shows the rate of photosynthesis at different wavelengths of light - Lowest absorbance corresponds to lowest rate of photosynthesis as slower light dependent reactions. - Note that rate is higher at lower wavelengths, this is not only due to greater absorption but also as lower wavelengths contains more energy

Answer 32

- Grind leaf using a mortar and pestle with solvent such as propanone - Leaf extract contains mixture of pigments - Allow the sample to evaporate to concentrate the pigment - Draw a pencil line and place extract on it using a capillary tube - Place paper vertically in jar of different solvent - Solvent rises up paper with each pigment traveling at different speeds hence pigments separated - Distance moved by each pigment is unique - Repeat with a different solvent, placing the chromatogram 90° to the original alignment

Answer 33

- Chlorophylls (Primary Pigments) - Carotenoids (Accessory Pigments)

Answer 34

Homeostasis is maintaining a relatively constant environment for the cells within the body, despite changes in external environment

Answer 35

Controlled by the composition of blood, and hence the tissue fluid

Answer 36

Homeostasis serves to ensure that a constant internal environment consisting of factors such as temperature, water potential, pH and blood glucose level is maintained, despite changes in the external environment of the organism.

Answer 37

- Temperature - low temp, slow metabolic reactions. High temp however denatures enzymes and proteins - Water potential - low water potential causes water to enter a cell and burst. High water potential causes water to leave and cell to shrink. - Water potential is the ability of water to move freely so if it is high water will leave not enter. - Concentration of glucose if too low, no energy for cell to respire, if too high would affect osmotic balance and disturb cells

Answer 38

This is done through two coordination systems: - Nervous system, electrical impulse along neurons - Endocrine system, in the form of chemical messengers (Hormones) that travel in the blood

Answer 39

A stimuli is a change in physiological factors, such as temperature, pH of blood, water potential etc

Answer 40

- Involves receptor that detects stimuli - Receptor sends information to the central control in the brain or the spinal cord - The input is processed and instructions are sent to the effector - Effectors such as muscles and glands cause the factor to return to its ideal value or set point

Answer 41

- Negative feedback keeps factors within narrow limits, making it close to set point as possible - When a factor is increased, an effector is stimulated that makes the factor decrease, and vice versa

Answer 42

- Is not used in keeping conditions constant as it increases effect when stimulus is increased -This is useful in other areas such as transmission of nerve impulses where the factor must be increased

Answer 43

- Deamination is the removal of an amino group (NH2) from a molecule. This is done in the liver when there is an excess of protein, rather than wasting a useful energy source. - The –NH2 and a hydrogen atom are removed leaving behind a keto acid

Answer 44

The liver is responsible for the breakdown of excess of amino acids coming from the digestion of protein.

Answer 45

The reason why the excess amino acids need to be excreted is because nitrogenous substances are damaging to the body therefore if they are not used up, they must be excreted.

Answer 46

- Since ammonia is very soluble and highly toxic compound it is converted immediately to urea 2NH3 + CO2 CO(NH2)2+ H2O - Urea is the main nitrogenous excretory product, however we also produce creatinine and uric acid - Creatine is made in the liver from amino acids that is used as an energy store in muscles - Uric acid is made from the breakdown of purines

Answer 47

- Blood enters the kidney through the renal artery and subsequently passes through the capillaries in the cortex of the kidneys. - Blood enters the glomerulus through the afferent arteriole and exits through the efferent arteriole. The efferent arteriole is narrower, thus a high pressure is created. This pushes smaller molecules (glucose, urea, water and sodium) into the Bowman’s capsule from the blood. This process is known as ultrafiltration. - Selective reabsorption occurs in the proximal convoluted tubule. Here, useful substances such as amino acids, glucose, vitamins are reabsorbed back through the tubules in the medulla. Sodium ions and glucose are cotransported back into the blood through a sodium-potassium pump. Water moves down a water potential gradient into the blood. - The substances to be excreted pass along the tubules and ureter and finally reach the bladder where they’re disposed of as urine. - The filtered blood passes out of the kidneys through the renal vein.

Answer 48

- Bowman’s capsule - Proximal convoluted tubule - Distal convoluted tubule

Answer 49

- Collecting duct - Loop of Henle

Answer 50

Involves filtering small molecules out of the glomerulus and into the Bowman’s capsule due to hydrostatic pressure build up

Answer 51

- Hydrostatic pressure builds up in the glomerulus due to the wider afferent and narrower efferent arterioles - This causes the hydrostatic blood pressure in the glomerulus to rise above that of the Bowman’s capsule. - Water from blood therefore goes down its water potential gradient through the endothelium of the capillary walls, the basement membrane and podocytes, thus filtering substances.

Answer 52

- Endothelium: one cell thick cell with many holes - Basement Membrane: makes up inner lining of bowman’s capsule and acts as filter for large molecules eg large Mr proteins, WBC and RBC -Podocytes: inner lining of bowman’s capsule with large holes

Answer 53

- Microvilli to increase surface area for many co-transporters for maximum reabsorption - Tight junction between cells so that fluid can’t pass between them - Many mitochondria to provide ATP for (Na+–K+) pump on basal membrane - Folded basal membrane providing large surface area for (Na+–K+) pump

Answer 54

1. Removal of Na+ from the cell: Na+–K+ pumps in the basal membrane use ATP pumping 3 Na+ out and 2K+ in, lowering its concentration inside the cell 2. Passive movement of Na+/glucose/amino acid inside the cell - Na+ goes down its concentration gradient via a cotransporter that brings along glucose/amino acids. - This a secondary active transport as ATP was not used for pumping - Na+ into the PCT cell but has occurred as a result of actively transporting Na+ out of the cell - Glucose and amino acids diffuse down their gradient from cell into blood via transport proteins in the basal membrane 3. Reabsorption of water: - Removal of ions from the tubule increases its water potential, and increases the solute potential of the cell - Thus, water diffuses down its gradient into the cell, and is reabsorbed in the blood via osmosis 4. Reabsorption of urea: urea is a small molecule and passively gets reabsorbed

Answer 55

1. Na+ & Cl- are actively transported out of higher end of ascending limb into the tissue fluid 2. This increases concentration of ions in tissue fluid 3. Water is therefore lost from the descending limb 4. Loss of water concentrates Na+ and Cl− along the descending limb. 5. This concentrates the fluid inside the loop, so ions passively move down their concentration gradient, into the tissue fluid

Answer 56

- First part functions the same way as ascending limb - Second part functions the same way as collecting duct

Answer 57

- Fluid in ascending limb is dilute due to loss of ions and urea, concentrating tissue fluid in medulla - When fluid enters collecting duct from DCT, it returns to the concentrated medulla region, thus water moves out by osmosis into the tissue fluid and is reabsorbed, concentrating urine

Answer 58

Involves the control of water potential in body fluid

Answer 59

Osmoreceptors in the hypothalamus constantly monitor water potential in the blood

Answer 60

1. Osmoreceptors detect and send impulses to the posterior pituitary gland to secrete antidiuretic hormone (ADH) 2. ADH in the blood binds to receptors on the cells of collecting duct, activating intracellular enzymes 3. Vesicles that contain aquaporin in the cell are stimulated to fuse to membrane 4. This causes duct to become permeable to water hence water moves out, down its concentration gradient - Volume of urine decreases and becomes more concentration

Answer 61

- Osmoreceptors no longer stimulate ADH production, so aquaporins moved back into cytoplasm as vesicles, making cells impermeable to water again - This process is very slow because ADH molecules take 15-20 mins to be broken down in the blood and another 15-20 mins for aquaporins to be removed from the membrane

Answer 62

- The rise in glucose concentration is detected by the beta cells in the pancreas - Insulin, a hormone, is secreted by beta cells, inhibiting the action of alpha cells - Insulin travels to target cells known as hepatocytes in the liver, fat and muscle cells - Binding of insulin to the receptors on the plasma membrane of these cells causes adenyl cyclase to convert ATP into cyclic AMP (cAMP) - cAMP acts as a secondary messenger and activates certain enzyme controlled reactions in the cells to stimulate the opening of glucose channels in the surface membrane, thus causing more glucose to enter the cell, which is then converted to glycogen or fats (stored in the muscle) and subsequently used for respiration

Answer 63

- The rise in glucose concentration is detected by the beta cells in the pancreas - Insulin, a hormone, is secreted by beta cells, inhibiting the action of alpha cells - Insulin travels to target cells known as hepatocytes in the liver, fat and muscle cells - Binding of insulin to the receptors on the plasma membrane of these cells causes adenyl cyclase to convert ATP into cyclic AMP (cAMP) - cAMP acts as a secondary messenger and activates certain enzyme controlled reactions in the cells to stimulate the opening of glucose channels in the surface membrane, thus causing more glucose to enter the cell, which is then converted to glycogen or fats (stored in the muscle) and subsequently used for respiration

Answer 64

- Alpha cells detect change and secrete a hormone called glucagon - Glucagon secretion inhibits beta cell action - Glucagon binds to the receptors on the cell surface membrane which causes a conformational change - This activates G-proteins which activates adenylyl cyclase enzymes - cAMP (a secondary messenger) formation is initiated - This activates protein kinases which then leads to initiation of a cascade of enzymes - The final enzyme that is activated is

Answer 65

The homeostatic control is carried out in the pancreas by a tissue called the islets of Langerhans which consisting two types of cells: - α cells which secrete glucagon - β cells which secrete insulin

Answer 66

The α and β cells detect the change α responds by stopping secretion of glucagon β responds by secreting insulin into the blood

Answer 67

- When glucose is in low concentration our cells may not have enough glucose for respiration, hence might not be able to carry out its normal function - On the contrary, high concentrations can effect normal behaviour of cells as they may lose water due to the concentration gradient built (cells become flaccid)

Answer 68

Insulin is a signalling molecule that targets the liver and muscle cells and binds to a receptor

Answer 69

This stimulates the cells to increase rate of glucose absorption by making vesicles carrying glucose transporter proteins (GLUT) to bind onto cell membrane

Answer 70

Glycogenesis is the condensing of glucose molecules to glycogen which can later be converted to glucose in respiration.

Answer 71

- α responds by secreting glucagon into the blood - β responds by stopping secretion of insulin

Answer 72

Gluconeogenesis is a new glucose made from amino acid and lipid

Answer 73

It is important to keep the blood glucose concentration in the correct range of about 90mg per 100cm3.

Answer 74

Its insulin dependent diabetes, where the pancreas is incapable of secreting enough insulin due to

Answer 75

- Lack of gene that codes for insulin - Autoimmune disease Treatment : insulin injections and mini pumps, controlled diet

Answer 76

Non-insulin dependent diabetes is when the pancreas secretes insulin but liver and muscle cells do not respond properly.

Answer 77

- Hunger and thirst are a consequence as kidney cannot reabsorb glucose, which passes in urine along with extra water and salts - Instead cells metabolise fats and proteins instead which leads to build up of keto acid which is toxic. - Blood glucose levels may fall as there was no glycogen stored when glucose was in the blood.

Answer 78

- Diabetes: presence of excessive glucose and ketones in urine, as blood glucose level rises above renal threshold and so not all reabsorbed - High blood pressure/kidney infection: presence of proteins as they are too large to be filtered out

Answer 79

- Much easier to collect than blood samples - Urine tests can give early indications of health problems

Answer 80

- Urine analysis to measure: pH, glucose, ketones and proteins - Glucose dipsticks contain glucose oxidase and peroxidase

Answer 81

Positive test: glucose oxidase oxidises glucose to form gluconolactone and hydrogen peroxide - Peroxidase catalyses reaction of hydrogen peroxide and chromogen (colourless chemical) forming a brown compound - The colour formed is compared to a chart, the more glucose present, the darker the colour (semi- quantitative)

Answer 82

Allow people with diabetes to monitor their blood glucose concentration much quicker than dipsticks

Answer 83

- They also contain glucose oxidase which catalyses the same reaction - However, a current is generated, detected and amplified which gives a reading within seconds (quantitative) - The more the glucose present the greater the reading

Answer 84

- Increase in light intensity - Low CO2 concentrations

Answer 85

- Darkness - High CO2 concentrations - Low humidity - High temperature - Water stress

Answer 86

- Stomata has daily rhythms of opening and closing even if kept in constant light/dark - Opening during day maintains inward diffusion of CO2 and outward diffusion of O2 and water vapour - Closing during the night as it does not respire and conserves water

Answer 87

A stress hormone that causes the closure of stomata in difficult conditions

Answer 88

- ABA binds to receptors that inhibit proton pumps and stimulate movement of Ca2+ ions into the cell. - Ca2+ acts as a second messenger, activating channel proteins to allow negatively charged ions to move out - This causes potassium ions to move out and also closes K+ channels so that they can’t enter - Water potential increases inside the cells, which diffuses down its water potential gradient by osmosis. - The cell becomes flaccid and stomata closes

Answer 89

Stomata closes when hydrogen ion pumps stop and potassium ions leave the guard cells. Water then leaves the cells, causing it to become flaccid and closing the stomata

Answer 90

- ATP proton pumps actively move H+ ions out of the guard cells - This causes potassium channels to open & move into the cell due to the electrochemical gradient produced - Electrochemical gradient is the combination of an electrical gradient caused by the release of H+ ions (making inside more negative) and a concentration gradient due to low levels of K+ inside - Influx of K+ ions inside the cell increases the solute potential and reduces water potential, thus water enters by osmosis making cells turgid - The stomata has uneven cell wall thickening; walls adjacent to pore is very thick, whereas the walls furthest from pore is thin - When cells are turgid, the outer end cells lengthen, causing the guard cells open.

Answer 91

- Both involve cell signalling - Both involve signal molecule binding to receptor - Both involve chemicals

Answer 92

- Form of transmission - Electrical impulses - Formed at - Sensory neurone generates impulse - Travel in - Neurones - Speed - Instantaneous - Duration - Short-term - effects - Localised - receptor location - On cell surface membrane - Energy - Large amount

Answer 93

Form of transmission - Chemical messengers (Hormones) Formed at - Secretory gland Travel in - Blood (endocrine) Speed - Slow Duration - Long lasting effects - Widespread receptor location On cell surface membrane Cell surface membrane OR within cell Energy - Less required

Answer 94

Form of transmission - Chemical messengers (Hormones) Formed at - Secretory gland Travel in - Blood (endocrine) Speed - Slow Duration - Long lasting effects - Widespread receptor location - Cell surface membrane OR within cell Energy - Less required

Answer 95

There are three types of neurones, sensory, motor and relay with different functions which differ by the position of the cell body within the neurone.

Answer 96

- Swelling of spinal cord containing cell body known as ganglion - Sensory neurones transmit impulses from receptors to the central nervous system.

Answer 97

- Intermediate Neurone (Relay/Connector): transmit impulse from sensory to motor neurone - Relay neurones are located within the central nervous system and transmit the electrical impulses from sensory neurones to motor neurones - Found entirely in CNS

Answer 98

- Cell body lies within CNS and contains the nucleus - Dark specks in cytoplasm are rough ER regions - Motor neurones are involved in transmitting electrical signals from the central nervous system to muscles and glands in the body

Answer 99

- The structure of neurones is similar, as they all have a cell body composed of the nucleus as well as organelles such as mitochondria within the cytoplasm. - Apart from the essential components, they also contain extensions called dendrites involved in conducting impulses towards the cell body, as well as axons which conduct them in the opposite direction, that is away from the cell body

Answer 100

A reflex arc is the pathway along which impulses are transmitted from receptor to an effector without involving the ‘conscious’ regions of brain

Answer 101

- Impulses travel from sensory to relay (not always) and finally to motor neurone - The effector acts before the brain processes the impulse and produces any voluntary movement. - Hence, this is a reflex reaction, which is fast, automatic and is useful in response to danger

Answer 102

- Myelin is made when specialised cells called Schwann Cells which wrap themselves around the axon, enclosing it within many layers - About a third of axons on motor and sensory neurons are surrounded by myelin sheaths

Answer 103

The uncovered regions between Schwann cells are called Nodes of Ranvier

Answer 104

- Myelination stops depolarisation from occurring, greatly increasing the speed of conduction - It also prevents the leakage of ions and increases insulation, increasing speed of conduction. - Myelin also causes saltatory conduction which is when action potentials jump from one node to the next, which is about 50 times faster than unmyelinated axon - Diameter also affects speed of transmission; with thinner axons, there is greater resistance, hence, transmission is slower

Answer 105

The structure of neurones, that is the length of axons as well as the polarised nature of the neurone membrane in the resting state where the outside of the membrane is positively charged and the inside is negatively charged enables the neurones to carry electrical impulses called action potentials.

Answer 106

Nerve impulses are signals transmitted along the axon, consisting of waves of depolarisation, causing changes in the potential difference across the membrane (action potential)

Answer 107

- Plasma membrane being impermeable to Na+ /K+ - Sodium-potassium pumps that actively pump 3 Na+ out and 2K+ in, increasing the concentration of K+ inside, and Na+ outside - There are more K+ channels than there are Na+, therefore K+ diffuses down its concentration gradient (outside the cell) faster than Na+ diffuses in. - Many large negatively charged molecules inside cell

Answer 108

Resting axons have a slightly negative electrical potential inside, producing a potential difference of about -70mV inside compared to the outside

Answer 109

It is the change in potential difference across the membrane due to changes in permeability of the membrane to Na+/K+ ions

Answer 110

- An initial stimulus causes the opening of some voltage-gated channels causing Na+ to rush in, down its electrochemical gradient - This causes the potential difference across the membrane to become less negative and is called depolarisation.

Answer 111

- If this potential difference reaches -50mVV, then many more channels open, causing inside to become +30mVV - This wave of depolarisation is an example of positive feedback

Answer 112

- For an action potential to be produced, the potential must be raised to a minimum threshold potential of -50mVV. If lower than this, an action potential will not be generated - This is known as the all-or-nothing law as the neurones either transmit impulse or do not

Answer 113

- After 1ms, all Na+ voltage-gated channels close & K+ gated channels open, causing K+ to diffuse out, thus repolarising the membrane. - The sodium potassium pump continues pumping these ions and maintaining their concentration across the membrane, allowing more action potentials to occur. - Local circuits are set up, where the permeability of the neighbouring region of the axon is increased

Answer 114

- Action potentials do not merge and so are discrete - There is a minimum time between action potentials occurring at one place on neurone - Length of refractory period determines max frequency at which impulses are transmitted - Hyper polarisation occurs when the cell potential becomes more negative than resting potential as there is an excess outflow of K+

Answer 115

Axons have a refractory period after the action potential, where it is unresponsive to new stimulations.

Answer 116

- Action potentials do not change in size whether large or small stimulus & has constant peak value of +30mVV - The brain receives action potential from specific position of neurones and interprets the nature of the stimulus eg position: retina, nature: light

Answer 117

- The brain interprets this from the frequency of the action potential-stronger stimuli have larger frequency - Also strong stimuli cause more neurones to be stimulated hence the number of neurones carrying action potential can tell us about the strength

Answer 118

A receptor cell responds to stimulus by converting energy from one form to electrical impulse, initiating an action potential (acts as a transducer)

Answer 119

- Receptor cells are often found in sense organs and are specialised cells which detect specific type of stimulus - Some receptors are the ends of sensory neurones, thus there is no synapse between the receptor cells and sensory neurones.

Answer 120

1. Ensures one-way transmission as the receptors are only in post synaptic neurone and vesicles are only in presynaptic neurone 2. Decreases the overload of information in the brain as impulses with low frequencies do not reach the brain 3. Involved in memory and learning due to the formation of new synapses that links neurones involved 4. Interconnection of nerve pathways: sensory and relay have many dendrite increasing surface area for many synapses. This connects neurones from different parts of the body and spreads information throughout.

Answer 121

The tongue is covered in many papillae, each papilla has many taste buds over its surface and within each taste bud lies around 50-100 chemoreceptors that detect different chemicals, giving different sensations

Answer 122

- Na+ ions diffuse through highly selective channels of microvilli and cause depolarisation of the membrane: receptor potential. - If receptor potential is below the threshold, it causes a local depolarisation of the receptor cell and doesn’t stimulate the sensory neurone to send impulses.

Answer 123

- If sufficient stimulation is produced, voltage-gated Ca2+ channels open; Ca2+ then enters, causing exocytosis of neurotransmitter vesicles - Neurotransmitters cause action potential in the sensory neurone and eventually reaches the cortex of the brain

Answer 124

Region where two synapses meet, there is a small gap called the synaptic cleft

Answer 125

Synapses are junctions between two neurones.

Answer 126

- Action potential stimulates the opening of voltage gated Ca2+ channels at the presynaptic knob, causing an influx of Ca2+ into the cytoplasm - This causes exocytosis of ACh vesicles, which fuse with the pre synaptic membrane, then diffuse across the synaptic cleft - ACh has a complementary shape to the chemically gated receptor protein on the post synaptic membrane, and binds to it - This changes the shape of the protein and opens the channel for the entry of Na+ - Na+ depolarises that part of the membrane; if pd is above threshold, an action potential is generated - Acetylcholinesterase recycles Ach by breaking it into acetate and choline, preventing the permanent depolarisation of the membrane. - Choline returns to presynaptic neurone and combines with Acetyl coA to form Ach again.

Answer 127

Tendons – non-elastic tissue which connects muscles to bones

Answer 128

Ligaments – elastic tissue that joins bones together and determines the amount of movement possible at a joint

Answer 129

Joints – the area where two bones are attached for the purpose of permitting body parts to move, they’re made of fibrous connective tissue and cartilage

Answer 130

Skeletal muscles- muscles attached to bones, they are arranged in antagonistic pairs

Answer 131

Antagonistic muscle pairs- pairs of muscles which pull in opposite directions – as one muscle contracts, the other relaxes. Flexors and extensors are an antagonistic muscle pair such as triceps and biceps. When the triceps relaxes, the biceps contracts to lift the arm

Answer 132

Neuromuscular junction - the junction between a motor neurone and a skeletal muscle fibre

Answer 133

- Striated muscle is multinucleate (syncytium) and consists of several tissues eg connective, nerve, striated muscle, blood. - It is made up of bundles of muscle fibres/cells (fascicles) - Each muscle fibre is made up of regular arrangement of myofibrils, which produce the striated appearance of muscle fibres

Answer 134

1. An impulse arrives as a neuromuscular junction, Ca2+ is released from the sarcoplasmic reticulum. 2. Ca2+ binds to troponin, causing a shape change. Consequently, the tropomyosin moves away from the actin, uncovering binding sites 3. Myosin binds to the uncovered actin binding sites, forming an actomyosin cross bridge. 4. ADP and inorganic phosphate ions are released, causing the power stroke 5. After this, ATP binds, causing myosin to unbind from the actin 6. ATP breaks town to ADP and inorganic phosphate to return the myosin to its original position 7. Ca2+ ions are reabsorbed, troponin moves back to its original shape and tropomyosin re-covers the binding sites.

Answer 135

- The sarcolemma (cell membrane) splits into many infoldings called T-tubules - Sacroplasm (cytoplasm) contains many mitochondria that generate ATP for muscle contraction - The sarcoplasmic reticulum (SR) (endoplasmic reticulum) have many protein pumps that transport Ca2+ into the cisternae of SR

Answer 136

Actin: globular protein; two chains of actin overlap to make up thin filament

Answer 137

Myosin: fibrous protein with globular head that makes up thick filament

Answer 138

Tropomyosin: fibrous protein twisted around actin chain

Answer 139

Troponin: protein that is attached to the actin chain at regular intervals

Answer 140

Z line: where actin filaments are attached to

Answer 141

M line: where myosin filaments are attached to

Answer 142

A band: includes the darker parts in the centre where actin and myosin overlap

Answer 143

H band: the grey area within the A band where only myosin is present

Answer 144

I band: the white area next to the Z line where only actin is present

Answer 145

- Myosin - Actin - Tropomyosin - Troponin - Z line - M line - A band - H band - I band

Answer 146

Myofibrils are made of contractile units called sacromeres (between two Z discs) which are made of thin and thick protein filaments

Answer 147

- ATP can be provided from little ATP found in muscle by respiration and lactic fermentation - Creatine phosphate stores is an immediate source of energy that regenerates ATP in the absence of respiration creatine phosphate + ADP creatine + ATP - When demand for energy has reduced, creatine is recharged to form creatine phosphate in the presence of ATP from respiration - When there is an energy demand and not enough ATP to regenerate creatine phosphate, creatine is converted to creatinine and excreted

Answer 148

- Allows actomyosin cross bridge to detach and is hydrolysed so that the myosin can return to its original position. (Allows muscle to relax). - Allows reabsorption of Calcium ions via active transport.

Answer 149

- Sarcolemma is depolarised by an incoming action potential which spreads along membrane and down the T-tubule - Calcium ions are released from sarcoplasmic reticulum (using ATP) and bind to troponin, causing it to change shape - This in turn causes tropomyosin to move, exposing myosin binding sites on actin filament - Myosin heads bind with this site forming cross-bridges - Myosin heads tilt, pulling actin filaments towards centre of sarcomere (M line) - The heads hydrolyse ATP, providing energy for heads to let go of actin and return to original position so that it can bind again to exposed site - This process continues as long as binding sites are open and ATP is in excess - It can be reversed by relaxation of muscle (no cross bridge) and contraction of antagonist muscle that pulls filaments further away, lengthening sarcomere - During contraction, the A band is unaffected however both H and I bands decrease in length

Answer 150

Hormones are made in endocrine glands (ductless) and are secreted into the blood

Answer 151

Birth control pills can contain progesterone only or both progesterone and oestrogen (combined)

Answer 152

The progesterone pill may not prevent ovulation to occur but they reduce the ability of sperm to reach the egg cell by increasing mucus levels in the cervix

Answer 153

The combined pill supresses secretion of FSH and LH due to the negative feedback from high levels of progesterone and oestrogen

Answer 154

- During the 7 days of menstruation pills are not taken to drop progesterone levels and cause menstruation, reassuring that woman is not pregnant - pills must be taken daily to be effective as missing a single day could cause ovulation

Answer 155

The menstrual cycle is coordinated by the anterior pituitary gland and by the ovaries

Answer 156

The anterior pituitary gland secretes Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH)

Answer 157

The corpus luteum (follicle after releasing gamete) secretes both oestrogen (stimulates endometrium to grow, thicken and develop numerous blood capillaries) and progesterone (to maintain endometrium)

Answer 158

- FSH and LH are in relatively high concentrations during menstruation (4-8 days) and so cause one follicle to mature - The presence of FSH and LH stimulates oestrogen to be produced by the cells surrounding the follicle - Oestrogen however, has a negative feedback on FSH and LH so their concentrations decrease - When oestrogen reaches a level 2-4 times initial value, it stimulates a surge of LH, causing the ovarian follicle to burst and ovulation occurs (14-36 hours after the surge) - The corpus luteum is now formed, releasing progesterone and some oestrogen - Progesterone inhibits secretion of FSH and LH so that no more follicles develop - Corpus luteum begins to degenerate, decreasing progesterone and causing menstruation

Answer 159

A carnivorous plant that obtains nitrogen compounds by digesting small animals

Answer 160

- Nectar secreting glands attract insects - Each lobe has three sensory/ trigger hairs that respond when deflected - Outer edges have stiff hairs that interlock to trap insect - Surface of lobes has glands that secrete digestive enzymes

Answer 161

- Stimulation of single hair doesn’t trigger closure eg rain or debris - Gaps between stiff hairs allow tiny insects to crawl out, so plant doesn’t waste energy to consume small meals

Answer 162

- The deflection of a sensory hair opens Ca2+ channels at cells at the base of hair, causing inflow of Ca2+ and generating receptor potential (depolarisation) - If two hairs (or one hair touched twice) are stimulated within 20-35s, action potentials travel across the lobe to close it. - H+ ions are pumped into the cell walls, breaking cross links (acid growth hypothesis) - Calcium pectate ‘glue’ in middle lamella dissolves - Ca2+ enters the hinge cells causing water to enter by osmosis hence expanding the hinge cells - Lobes of the leaves flip from convex to concave rapidly (change in elastic tension) - Further deflection of hairs stimulate entry of Ca2+ into gland cells, causing exocytosis of vesicles containing digestive enzymes. - Mechanical energy converted to electrical energy

Answer 163

- Auxins: influence elongation of roots and shoots - Gibberellins: seed germination and stem internode elongation

Answer 164

- Plants make several chemicals known as auxins, of which the main one is IAA - Auxins bind to a protein receptor which stimulates ATPase to pump in H+ into cell walls, reducing its pH. - Proteins called expansins are activated at low pH, loosening cellulose microfibril linkages - Water is absorbed by osmosis and pressure potential causes the wall to stretch, elongating the cell - Auxins also inhibit lateral growth so that plant grows taller

Answer 165

- Auxins are synthesised in growing tips/meristems

Answer 166

Seeds are in a state of dormancy; this allows it to survive through cold winters and is only activated when enough water is present

Answer 167

- The dominant allele Le causes the synthesis of the last enzyme that produces active form of gibberellin, GA1 - Active gibberellin stimulates cell division and cell elongation whilst interacting with auxin, causing the plant to grow tall

Answer 168

- Plants that are homozygous and have the recessive allele le produce a non-functional enzyme (due to substitution mutation in its primary structure) - Thus, active gibberellin is not produced and so the plant is genetically dwarf

Answer 169

Applying active gibberellin to plants that would remain short can stimulate them to grow tall

Answer 170

FSH is involved in stimulation the development of eggs and release of oestrogen

Answer 171

LH stimulates egg release, oestrogen and progesterone production

Answer 172

Oestrogen stimulates uterine lining growth and egg release, inhibits FSH and LH after ovulation

Answer 173

Progesterone maintains the lining of the uterus, involved in inhibiting LH after ovulation

Answer 174

- Involved in osmoregulation which is the maintenance of the water potential balance in the blood. - When the bloods water content is low, ADH is released by the posterior pituitary gland - Increases the DCT and collecting duct wall’s permeability to water - Increases reabsorption of water from the tubules into the blood

Answer 175

- Involved in the control of blood glucose concentration - When glucose concentration is too low, glucagon is released from the alpha cells of the islets of langerhans - Stimulates hepatocytes to convert glycogen to glucose which diffuses out of hepatocytes into the blood

Answer 176

- Involved in the control of blood glucose concentration - When glucose concentration is too high, insulin is released from the beta cells of the islets of langerhans - Stimulates hepatocytes to convert glucose into glycogen which is stored in the muscle until needed for respiration

Answer 177

Homologous chromosomes are a pair of chromosomes in diploid cell that have same structure as each other, with the same genes (may not be same allele) at the same loci, which pair up to form a bivalent

Answer 178

Locus is a position at which a particular gene is found on a particular chromosome

Answer 179

A Gene is a length of DNA that codes for a particular protein

Answer 180

Chromosomes can be distinguished by staining it; each pair has distinctive banding patterns

Answer 181

There are 22 pairs of autosomal homologous chromosomes, wherein one chromosome of each pair is maternal, and the other is paternal

Answer 182

Meiosis is a form of cell division that gives rise to genetic variation

Answer 183

The main role of meiosis is production of haploid gametes as cells produced by meiosis have half the number of chromosomes.

Answer 184

-Crossing over of chromatids where pairs of chromosomes line up and exchange some of their genetic material - Independent assortment of chromosomes – there are various combinations of chromosome arrangement - During fertilisation the random fusion of gametes also increases genetic variation in offspring

Answer 185

- In prophase I, homologous chromosomes pair up to form bivalent in a process called synapsis. - At the end of Telophase II, 4 haploid daughter cells are produced

Answer 186

- During late prophase II, crossing over takes place: homologous chromosomes (bivalents) attach to each other forming chiasma and switch genetic information - During metaphase II, independent assortment of genes occurs: pairs of homologous chromosomes lie independently of each other and randomly at the equator - When genetically different gametes fuse at random

Answer 187

Chiasma is a point of contact between two non-sister chromatids belonging to homologous chromosomes

Answer 188

- Takes place in the tubules of the testes - Germinal epithelial cells divide by mitosis to produce diploid spermatogonia which grow to form primary spermatocytes - These divide by meiosis II to form 2 haploid secondary spermatocytes which continue with meiosis II forming 4 spermatids that mature into spermatozoa

Answer 189

- Takes place in the ovules - Diploid spore mother cell divides by meiosis to produce four haploid cells - All but one degenerates; this cell develops into an embryo sac - Embryo sac divides by mitosis 3 times forming 8 haploid nuclei, of which one becomes the female gamete

Answer 190

Unequal distribution of cytoplasm: the resulting zygote receives all of its cytoplasm from the egg, so the egg needs to have as much cytoplasm as possible.

Answer 191

- Produces sperm - Division of cytoplasm is equal - Four gametes produced - No polar bodies - Complete meiosis

Answer 192

- Produces oocyte - Division of cytoplasm is unequal - One gamete produced - Polar bodies - Incomplete meiosis

Answer 193

In plants, gametes are not formed directly from meiosis, instead meiosis is used in producing the pollen grains and embryo sac which then form gametes by mitosis

Answer 194

- Takes place in the anther - Diploid pollen mother cells divide by meiosis forming 4 haploid cells. - The nuclei of these cells divide by mitosis (cytokinesis does not take place) resulting in cells with two haploid nuclei - These cells mature into pollen grains

Answer 195

One of the nuclei is the tube nucleus and the other is generative nucleus. The generative nucleus divides by mitosis to give 2 nuclei, which are the male gametes.

Answer 196

Takes place in the ovaries

Answer 197

- Germinal epithelial cells divide by mitosis to produce diploid oogonia - Oogonia start meiosis and become primary oocytes (still diploid), but meiosis stops at prophase I - All this occurs before a baby girl is born and at birth has around 400 000 primary oocytes - At puberty, primary oocyte continues to finish meiosis I to produce secondary oocyte and first polar body (small haploid cell with less cytoplasm; degenerates; gets rid of half of the chromosomes) - Each month one secondary oocyte is released into the oviduct to get fertilised - If fertilisation occurs, secondary oocyte undergoes meiosis II to form an ovum and second polar body - If ovum is fertilised, then a diploid cell is formed called a zygote embryo fetus

Answer 198

Alleles are different varieties of the same gene

Answer 199

Genotype: the genetic composition of an organism formed by alleles eg the alleles HbA HbS form the genotype: HbAHbS, HbSHbS, HbAHbA

Answer 200

A dominant allele is one whose effect on the phenotype of a heterozygous is identical to one of a homozygote

Answer 201

A recessive allele is one who does not express itself when a dominant gene is present

Answer 202

Codominant alleles have both the phenotypes of each allele in a heterozygous organism

Answer 203

A test cross is a genetic cross in which a dominant allele is crossed with a homozygous recessive organism; the offspring phenotypes can determine whether the parent is homo/hetro dominant

Answer 204

- Used to predict the ratios of inherited characteristics in a population - A monohybrid cross is a mating between two individuals with different alleles at one genetic locus of interest

Answer 205

Dihybrid crosses are used to determine the outcome of two genes, each of which have two alleles.

Answer 206

- Y chromosome is much shorter than X and contains fewer genes - A person with XX chromosomes is female and XY is male - Your gender is determined by the father’s sperm as mother always gives the X chromosome (1:1 chance)

Answer 207

Sex linkage is the phenotypic expression of an allele that is dependent on the gender of the individual and is directly tied to the sex chromosomes

Answer 208

- X chromosomes contain a gene that codes for blood clotting: the factor VIII. - The recessive allele (h) causes the disease haemophilia (blood fails to clot) - This is considered to be a sex-linked gene as it is found on the X chromosome but not found on the Y (thus it is expressed in males despite being a recessive allele) - When inherited, females will have 2 copies of this gene and males would have - Males always express it in their phenotype if it is present in their genotype (XhY) whereas women require 2 recessive alleles to show expression (homozygous XhXh). Therefore women can only be effected if both her mother and father contain the allele.

Answer 209

Genotypes of sex-linked genes are always represented by symbols that are on the X chromosome e.g. XHXh (carrier)

Answer 210

Dihybrid crosses are used to determine the outcome of two genes, each of which have two alleles. When cells undergo meiosis to produce gametes, the homologous pairs line up independently of each other

Answer 211

The effect on phenotypic character by interaction between different gene loci; one gene locus could mask the phenotypic expression of another.

Answer 212

Linkage: the presence of two genes on the same chromosome, so that they are inherited together and do not assort independently

Answer 213

Linked gene written in brackets to indicate that they are on the same chromosome e.g. (EA)(EA) instead of EEAA

Answer 214

Total linkage is very rare, almost always links are broken due to crossing over during meiosis

Answer 215

Occurs during prophase I where chiasmata formed between bivalents

Answer 216

Chiasmata connects with a non-sister chromatid so maternal and paternal genes are exchanged

Answer 217

When linked genes exchange genes they form offspring they are said to be recombinant offspring

Answer 218

- Cross over value is calculated by adding the percentage of offspring that belong to recombinant classes - This value can be used to measure the distance apart of the two gene loci - Chance of cross over ∝ distance apart

Answer 219

Mutation is a unpredictable change of the nucleotide sequence in DNA

Answer 220

Mutagen is a substance that increases chances of mutation eg. ionising radiation

Answer 221

- Gene mutation: change in the structure of DNA molecule producing different allele of a gene - Chromosome mutation: changes in structure or number of whole chromosomes in cell

Answer 222

- Base substitution where simply one base takes another base’s place - Base addition where on/more extra bases are added - Base deletion where bases are lost from sequence

Answer 223

A silent mutation is a codon change which does not affect the amino acid sequence produced.

Answer 224

A missense mutation is a codon change which results in the production of a different amino acid, thus resulting in altered tertiary structure of the protein. The extent of the effect of this is determined by which amino acid is replaced

Answer 225

A nonsense mutation is one where a translation is stopped early thus giving rise to a truncated polypeptide due to premature introduction of a stop codon

Answer 226

Point mutation/substitution occurs where one base pair is replaced by another (this may have no effect).

Answer 227

Insertion/deletion mutations where one or more nucleotide pairs are inserted or deleted from the sequence. This type of mutation alters the sequence of nucleotides after the insertion/deletion point known as a frameshift.

Answer 228

All mutations can cause a STOP codon to form, causing the polypeptide production to be halted.

Answer 229

- A condition where a person is deficient in the amount of healthy red blood cells it has. If a person has sickle cell anaemia they have crescent-shaped red blood cells. - This means they have abnormal hemoglobin which can’t carry sufficient oxygen. The HBB gene is responsible for producing a protein which is a subunit of haemoglobin. - If a mutation occurs in the HBB gene then the red blood cell’s haemoglobin will be altered leading to sickle cell anemia

Answer 230

Caused by a missense mutation in the beta-haemoglobin gene. This causes red blood cells to become sickle shaped. Sickle cells carry less oxygen and can block blood vessels.

Answer 231

Albinism is a result of a mutation in a gene that causes the production of melanin. This causes little or no melanin to be produced, resulting in light hair and skin colour, and vision impairment.

Answer 232

Caused by a mutation in the FVII or FIX genes located on the X chromosome, which code for proteins that are important in blood clotting. The result is that blood cannot clot correctly

Answer 233

Huntington’s is caused by a mutation to the HTT gene, which makes a protein called huntingtin. It leads to the degeneration of nerve cells in the brain, causing cognitive and movement problems.

Answer 234

- Albinism is a condition that affects a person's melanin production in the skin and leads to them having white hair, light eyes (may affect their eyesight) and pale skin. - The TYR gene is responsible for the production of tyrosinase. This is the enzyme that controls melanin production. - If a mutation in the TYR gene occurs, tyrosinase production is hindered resulting in the person developing albinism.

Answer 235

- A sex-linked recessive disorder which only affects males. It is carried on the X chromosome and females can be carriers of the disorder. - It is when a person's blood doesn’t clot normally due to the lack of the blood-clotting factor. If this isn’t treated it can lead to prolonged bleeding which can be fatal. - A mutation in the FB gene leads to a factor VIII deficiency causing haemophilia.

Answer 236

A neurodegenerative disease which affects the brain and the spinal cord (central nervous system). The HTT gene codes for a protein called huntingtin which plays a role in normal functioning of neurones. A mutation in the HTT gene causes Huntington's disease.

Answer 237

A Chi-squared test: to test whether the difference between observed and expected results has arisen due to chance (used for categorical variables eg colour and shape of leaf)

Answer 238

- It can be used if the sample size is sufficiently large, that is over 20. It can only be used for discontinuous variation data in the form of raw counts. - The chi squared test can be used to determine whether the null hypothesis is correct or not. The null hypothesis is the assumption that there is no difference between observed and expected results. - The value obtained is compared to the critical value, and in a case where the value obtained is less than the critical value, the null hypothesis is accepted as the difference due to chance is not significant - Whereas in a case where the x2 value is greater than critical value, the null hypothesis is rejected meaning that the difference between observed and expected results is not due to chance, as is significant.

Answer 239

Null hypothesis: there is no significant difference between observed and expected results x2 = Σ(O−E)2 / E

Answer 240

Structural genes are genes that code for proteins or enzymes required by a cell

Answer 241

Regulatory genes are genes that code for proteins that regulate the expression of other genes

Answer 242

Repressible enzymes are produced continuously unless production is repressed by binding a repressor protein to the operator

Answer 243

Inducible enzymes are only produced when its substrate is present. Transcription of the structural gene occurs as a result of the inducer (the enzyme’s substrate) interacting with the protein produced by the regulatory gene

Answer 244

- An Operon is a length of DNA containing a cluster of genes including structural genes and regulatory gene controlled by a single promoter - The enzyme β-galactosidase (inducible enzyme) hydrolyses lactose to glucose and galactose

Answer 245

- The lac operon consists of promoter, operator and 3 structural genes which are: - lacZ which codes for β-galactosidase. - lacY which allows lactose to enter cell - lacA which codes for transacetylase

Answer 246

- Lactose is taken up by bacterium - And binds to repressor protein, distorting its shape and preventing it from binding to DNA at operator - Transcription is no longer inhibited and RNA is produced

Answer 247

- Transcription factors: regulate transcription - Proteins that bind to a specific DNA sequence and control the flow of information from DNA to RNA by controlling mRNA formation

Answer 248

- Form part of protein complex that binds with promoter region - Activate appropriate genes in sequence allowing correct pattern for body development - Responsible for the determination of sex in mammals - Allows responses to environmental stimuli, such as switching on correct genes in high temp - Regulate cell cycle, growth and apoptosis (cell death)

Answer 249

- The plant hormone, gibberellin controls seed germination by stimulating the increase in transcription of mRNA coding for amylase - Gibberellin does this by breaking down DELLA proteins which inhibit the binding of transcription factor, PIF to a promoter - Transcription can then take place resulting in increase of amylase production

Answer 250

Phenotype – the characteristics of an organism, which result from the interaction of the genes of the organism with the environment in which it lives

Answer 251

- Independent assortment of chromosomes and therefore alleles - Crossing over between chromatids of homologous chromosomes - Random mating between organisms - Random fertilisation - Mutation

Answer 252

Continuous variation is variation within a range and it includes mass and height

Answer 253

Discontinuous variation can only take particular values – such as gender or shoe size.

Answer 254

- Height for example can be influenced by environmental factors such as nutrition - Cats can change their fur colour in extremities according to external temperature eg: dark pigment at low temp

Answer 255

- A qualitative difference that has clear distinguishable categories with no intermediates - It is usually a one to one relation between genotype and phenotype - E.g. Blood groups, there is only 4 possible groups - Different genes have different effect on phenotype - One or few genes control the characteristic, so alleles on single gene locus have large effects

Answer 256

- A quantitative difference that has a wide range of phenotypes - Intermediate phenotypes are usually what is observed - Plotting a frequency graph usually gives a bell-shaped distribution curve - E.g. Height and weight as these do not have distinguishable classes but are in a range - Different alleles at a single gene locus have small effects on the phenotype - Polygenes genes have an additive effect on a particular trait

Answer 257

- The t-test is used to assess whether the means of two normally distributed sets of data are significantly different from one another - Similar to the chi-squared test, you always start with a null hypothesis stating that there is no significant difference between the two samples

Answer 258

t = (− x̄1 x̄2) / √(s1 /n1) s2 /n2) - X1/2 is the mean of samples 1 and 2 - s^2 1/2 is the standard deviation of samples 1 and 2 - n1 /2 is the no. of individual measurements in 1 and 2 - Degrees of freedom: total number of samples−2

Answer 259

From the probability table we take 0.05 (5% confidence level) as our critical value - If probability lower than critical value, null hypothesis accepted, so difference is due to chance - If greater or equal, difference is significant and not due to chance, so reject null hypothesis

Answer 260

Natural selection: the effects of selection pressures on the frequency of alleles in a population.

Answer 261

- Anatomical adaptations are physical adaptations, either external or internal e.g. presence of loops of Henlé which allow desert mammals to produce concentrated urine and minimise water loss - Behavioural adaptations are changes in behaviour which improve the organism’s chance of survival e.g. mating calls - Physiological adaptations are processes inside an organism’s body that increase its chance of survival e.g. regulation of blood flow through the skin

Answer 262

- Genetic drift is a phenomenon where there is a small change in allele frequency which occurs as a result of the fact that not all the individuals in a population reproduce. This effect is amplified in very small groups, isolated from the rest of the population. - Genetic bottleneck – rapid reduction in population size which has an effect on the population size and genetic variation in future generations - Founder effect – decrease in genetic diversity which occurs when the population descends from a small number of ancestors

Answer 263

- There are a variety of phenotypes within a population - An environmental change occurs and as a result of that the selection pressure changes - Some individuals possess advantageous alleles which give them a selective advantage and allow them to survive and reproduce - The advantageous alleles are passed on to their offspring - Over time, the frequency of alleles in a population changes and this leads to evolution

Answer 264

- due to genetic variation, individuals that are best adapted are likely to breed and pass on advantageous alleles to next generations - Thus, selection pressure causes changes in allele frequency and gene pool which overtime leads to evolution.

Answer 265

Stabilising selection: when natural selection keeps the variety of the population the same.

Answer 266

- Directional selection: when a new environmental factor or a new allele appears, causing different allele frequencies to be produced - Selection acts against one extreme, results in change in a characteristic in a particular direction

Answer 267

Disruptive selection: when conditions favour both extremes of a population (this selection maintains different phenotypes)

Answer 268

Genetic drift is a change in allele frequency due to chance and is most noticeable in small populations.

Answer 269

- The small sample is unrepresentative of the allele frequency of the larger population and leads to loss of genetic variation. - Further genetic drift of the small population leads to further alteration of the allele frequency, leading to evolution and a new species – Founder’s effect

Answer 270

- Used to calculate allele, genotype and phenotype frequencies within a large randomly mating population. p + q = 1 p+q=1 p^2 + 2pq + q^2 = 1 - p represents dominant allele frequency - q represents recessive allele frequency

Answer 271

- Significant selective pressure against a genotype - Migration into or out of population - Non-random mating - Limited population

Answer 272

- Selection pressure applied is by humans - Genetic diversity is lowered - Inbreeding is common - Inbreeding depression - Increased homozygosity - No isolation mechanisms operating - Usually faster - Selected feature is for human benefit - Not for survival/evolution

Answer 273

- Individuals showing desired features are chosen to breed - Some of the alleles conferring these features are passed on to the offspring - Again, most desired features are chosen for breeding - This process is continued for many generations causing the frequency of the desired alleles to increase

Answer 274

- Introduction of disease resistance as there is a great loss of yield resulting from infections - Incorporation of mutant alleles: These genes code for DELLA proteins that reduce the effect of gibberellin and produce shorter stems. This allows more energy to be used for producing more seeds/grains instead of growing tall. - Inbreeding and hybridization

Answer 275

Inbreeding: mating between two genetically closely related species, sharing common ancestry

Answer 276

Out breeding produces heterozygous plants that are healthier and grow taller

Answer 277

- The aim is to get heterozygous and uniformity in genes thus out breeding cannot be used - Therefore, hybrid plants are used instead. Seeds are taken from companies which inbreed to Produce homozygous plants. These are crossed with different homozygous varieties to produce different hybrid offspring.

Answer 278

Charles Darwin forwarded the original theory that natural selection might be a mechanism by which evolution is formed

Answer 279

- Organisms produce more offspring than what is needed to replace the parents (reproductive potential) - Variation amongst individuals of a given species - Natural populations tend to remain stable in size

Answer 280

- There is a competition for survival - The best adapted variants will be selected by natural conditions, these are the variants that have a selective advantage and so ‘survival of the fittest’ occurs - This theory was put forward in the past, where they knew nothing about genes and alleles so now we can improve it by saying that, natural selection picks particular alleles or groups of alleles

Answer 281

- When amino acid sequence is compared the number of differences gives a measure of how closely related the species are - Differences in primary structure can cause dramatic change in structure and function however small changes can leave the overall structure and function same

Answer 282

- Difference in mtDNA can be used to study the origin and spread of species - mtDNA is inherited through the mother only - mtDNA is circular and not protected by histone proteins, so they cannot undergo crossing over hence the only possible way of change is through mutation - mtDNA mutates at around one mutation in 25000 years - This has provided us with evidence that the origin of H.sapiens was from Africa around 200 000 years ago

Answer 283

Living organisms are dependent on the environment and other species for their survival. When the environment changes, organisms that cannot adapt become extinct

Answer 284

There are many factors that can cause extinction: competition for food and resources, climate change, habitat loss, hunting, diseases, etc

Answer 285

Speciation is the evolutionary process by which new biological species arise

Answer 286

The main feature biologists use to decide whether two organisms belong to different species is their inability to interbreed successfully (reproductive isolation)

Answer 287

- Prezygotic is when individuals don’t recognise each other as mates or don’t respond to mating behaviour - Physically being unable to mate - Inability to fuse male and female gametes - Incompatibility of pollen and stigma in plants

Answer 288

- Failure of cell division in the zygote - Non-viable offspring (dies soon) - Viable but sterile offspring

Answer 289

Allopatric speciation: when speciation occurs where two populations are separated from each other geographically

Answer 290

- Mixing of the two is prevented, and each have different selection pressures acting on the populations - This results in different alleles being selected for, and soon the morphological, physiological and behavioural features become so different that the two populations can no longer interbreed even if the barrier is removed

Answer 291

Sympatric speciation: is when a new species is evolved from a species that inhabits the same geographic region

Answer 292

The most common way in which sympatric speciation occurs is by polyploidy - A polyploidy is an organism with more than two complete sets of chromosomes in its cell - This can happen if meiosis is abnormal during gamete formation, resulting in a gamete with 2 sets of chromosomes (diploid)

Answer 293

If two diploid gametes fuse, it results in 4 complete sets of chromosomes - tetraploid zygote

Answer 294

If a diploid gamete joins with a haploid gamete, they form a triploid zygote

Answer 295

- Polyploidys are often sterile as they can’t divide during meiosis. This is because all the sets try to pair up at once and end up in a muddle. - However, they can grow perfectly well & reproduce asexually

Answer 296

Autopolyploid are polyploidys that are derived from a single species and are infertile.

Answer 297

Allopolyploid are polyploidys that are derived from different species. Note that meiosis happens more easily here as the sets of chromosomes are from different species and can pair up. They are fertile, but cannot breed with parent species (self-fertile).

Answer 298

Species: a group of organisms with similar morphological and physiological features, which can interbreed to produce fertile offspring and are reproductively isolated from other species

Answer 299

Ecosystem: a relatively self-contained, interacting community of organisms, and the environment in which they live and with which they interact. Consists of biotic and abiotic parts

Answer 300

Niche: is the role of an organism in an ecosystem (it is how an organism fits into the ecosystem).

Answer 301

- Variation in ecosystems or habitats - Number of different species in the ecosystem and their relative abundance - Genetic variation within each species

Answer 302

Biodiversity: The variety of species in an area along with their variation within species and the genetic diversity between them.

Answer 303

- Maintains stability of ecosystem; preventing extinction - Maintains large gene pool (genetic variation) - Ecosystems provide ‘services’ for humans - Species can be source of new medicines - Resource such as food and wood - Leisure for humans to see in zoos; ecotourism - Climate stability

Answer 304

- Is the diversity of the alleles within the genes in the genome of a single species - A species can all have the same genes, but different alleles for those genes. Genetic diversity is assessed by finding proportion of genes with different alleles and how many alleles there are per gene.

Answer 305

Species diversity takes species richness into account, but also includes evenness of abundance of each species

Answer 306

The number of species in a community is known as species richness

Answer 307

In species diversity there are two points that need to be found: distribution and abundance of species.

Answer 308

To do this we use means of Random sampling such as: - Quadrat - Mark and release - Simpson’s Index of Biodiversity - The importance of random sampling is that a habitat may be too large for actual counting so a sample is quick and gives a representation of the whole habitat.

Answer 309

- Decide size of quadrat and number of samples - Mark a specific area - Samples are taken randomly eg by using random number generator to give coordinates of sampling points in the area to avoid any bias and increase accuracy of estimate - Take measurement of abundance of specific species - usually used with species that are stationary

Answer 310

2 ways to use your results: - Species frequency: is the measure of the chance of a particular species being found in any one quadrant. No. of Appearance / No. of Quadrats ×100 - Species density: is a measure of how many individuals there are per unit area. Total No. of individuals Calculated / Total Area of All Quadrats Units: m-2 - When unable to count, use percentage cover

Answer 311

Mark-release and recapture: Used with mobile animals - As many individuals possible are caught - Each individual is marked in a way that would not affect its chance of survival or reproduction - The marked individuals are counted and returned to their habitat to mix randomly - After enough time elapses for mixing to take place, capture another sample - Number of marked and unmarked counted and used to calculate estimate of population

Answer 312

N= n1 × n∗2 / m∗2 - N = population estimate - n1 = number of marked individuals released - n2 = total number of individuals (both marked and unmarked) captured - m2 = number of marked individuals recaptured

Answer 313

Used to determine species distribution in areas where conditions such as altitude, soil moisture content, pH or exposure to light intensity varies

Answer 314

Using transacts: to detect changes in community composition along a line across one or more habitats.

Answer 315

Line transect is the number of organisms found at regular points along a line are noted

Answer 316

Belt transect is the abundance of organisms within quadrats placed at regular intervals

Answer 317

- Find the highest value from the table e.g. 6 in this case - Give each species 6 spaces on y axis - Draw a straight line of 0 through the middle - Divide the number you are plotting by two, plot it above and below the line (from 0)

Answer 318

- Interval data that must be distributed normally- you can see this if the graph does not appear skewed or has obvious outliers - Must have linear correlation - The two variables can be on either axis - r= Σxy−n (overline(xy)) / nsxsy n = sample size (number of observations) x,y = number of species x, number of species y overline x,y = mean sx,sy = standard deviation of x and y - The value of r is always between -1 and 1, where -1 indicates a negative correlation, 1 indicates positive correlation, and 0 indicates no correlation.

Answer 319

- Used to find out if there’s a correlation when data is not normally distributed rs =1−( 6×ΣD^2 / n^3 - n) 1. Rank both species (where the highest data is ranked 1 and so on) 2. Calculate the difference in rank in each quadrat, D 3. Square the difference 4. Find the sum of D^2 , and proceed with formula. - The closer the value rs is to 1, the more likely it is that there is a correlation between the two sets of data - The rs value you calculated is then compared with the critical value- if rs is greater than the critical value, then null hypothesis is rejected, meaning there is a significant correlation

Answer 320

- After abundance of species is calculated in the area you are studying, use this formula to calculate the diversity D = 1 - Σ(N/n)^ 2 where n is the total number of organisms of a particular species, and N is the number of all species - Value of D ranges from 0 to 1(1 being highly diverse) Advantage: do not have to identify organisms to calculate diversity

Answer 321

Classification is the process of naming and organising organisms into groups based on their characteristics

Answer 322

Organisms can be grouped into one of the five kingdoms: animals, plants, fungi, prokaryotes and protoctista.

Answer 323

- They can then be grouped into phylum, class, order, family, genus and species. - Each species is named according to the binomial system, the first part of the name is the genus and the second part of the name is the species.

Answer 324

- Multicellular - Presence of a nucleus and other membrane bound organelles - No cell wall - No chloroplasts - Are able to move - with the help of contractile proteins, flagella or cilia - They are heterotrophic feeders hence nutrients are acquired by ingestion - They store food in the form of glycogen

Answer 325

- Multicellular - Presence of a nucleus and other membrane bound organelles - Contain a cellulose cell wall - Contain chloroplasts as well as chlorophyll - Mostly unable to move - Autotrophic feeders - acquire food via photosynthesis - Store food in the form of starch

Answer 326

- Mostly unicellular - Presence of a nucleus and other membrane bound organelles - Some contain chloroplasts - Some can move due to the presence of cilia or flagella - Autotrophic feeders - acquire food via photosynthesis - Some can be heterotrophic feeders - Some can be both autotrophic and heterotrophic feeders - Some may be parasitic

Answer 327

- Mostly unicellular - Presence of a nucleus and other membrane bound organelles - Some contain chloroplasts - Some can move due to the presence of cilia or flagella - Autotrophic feeders - acquire food via photosynthesis - Some can be heterotrophic feeders - Some can be both autotrophic and heterotrophic feeders - Some may be parasitic

Answer 328

- Mostly unicellular - Presence of a nucleus and other membrane bound organelles - Some contain chloroplasts - Some can move due to the presence of cilia or flagella - Autotrophic feeders - acquire food via photosynthesis - Some can be heterotrophic feeders - Some can be both autotrophic and heterotrophic feeders - Some may be parasitic

Answer 329

- Can be multicellular or unicellular - Presence of a nucleus and other membrane bound organelles - Contain a chitin cell wall - Contain no chloroplasts or chlorophyll - Cannot move - Most of them have a body or a mycelium composed of thread-like hyphae - Saprophytic feeders - acquire nutrients from dead or decaying matter - Some can be parasitic - Mostly store food in the form of glycogen

Answer 330

- Mostly unicellular - Divided into two domains: Bacteria and Archaea - Lack an envelope-enclosed nucleus, mitochondria or any other eukaryotic membrane-bound organelles - They can move through liquids or over moist surfaces by swimming, swarming, gliding, twitching or floating. - To aid movement, they may have flagella that spin, pili that pull or Mycoplasma 'legs' that walk. - They can store food in the form of lipid molecules or glycogen granules

Answer 331

- All organisms can be separated into one of the three domains: Bacteria, Archaea and Eukarya. - Archaea and bacteria are both prokaryotes with a few differences in between them.

Answer 332

- All organisms can be separated into one of the three domains: Bacteria, Archaea and Eukarya. - Archaea and bacteria are both prokaryotes with a few differences in between them.

Answer 333

- All organisms can be separated into one of the three domains: Bacteria, Archaea and Eukarya. - Archaea and bacteria are both prokaryotes with a few differences in between them.

Answer 334

- All organisms can be separated into one of the three domains: Bacteria, Archaea and Eukarya. - Archaea and bacteria are both prokaryotes with a few differences in between them.

Answer 335

- All organisms can be separated into one of the three domains: Bacteria, Archaea and Eukarya. - Viruses are not included in the three domains as they are non-living and are not classed as cells.

Answer 336

- Is based on the diseases which they cause - Type of nucleic acid they contain (DNA or RNA) - Whether nucleic acid is double/single stranded - In cellular organism’s DNA is double stranded and RNA is single stranded but in viruses both can be either single or double.

Answer 337

- Structure only visible by electron microscope - Acellular- they do not have cellular structure like bacteria and fungi however they have particles made of proteins and nucleic acids similar to cellular organisms. - Infectious but have no metabolism when they are free - When they infect cells, they use the biochemical machinery of the host cells to copy their nucleic acids and make their proteins destruction of host cell. - Energy for these processes is obtained by host cells’ respiration

Answer 338

- Present sometimes (cellulose) and has cell membrane - 80S ribosomes in the cytosol, but also has 70S in mito/chloro

Answer 339

- Present, with DNA arranged as linear chromosomes with histone proteins - Membrane bound organelle - 70S ribosomes smaller than eukaryote but have features that are similar to eukaryotic ribosome - Cell divides by mitosis - Many forms: unicellular, colonial(group mutual benefit) and multicellular - cell wall is no present -Archaea’s metabolism is similar to that of bacteria, but the way transcription occurs much in common with eukarya

Answer 340

- No nucleus, DNA exists as circular chromosomes without histones, along with small circular Plasmids - No membrane bound organelle - 70S ribosomes, smaller than eukaryotic ribosome - Cell divides by binary fission - Cell wall always present and contains peptidoglycan - Usually single cell or small groups of cells

Answer 341

- No nucleus, DNA exists as circular chromosomes without histones, along with small circular Plasmids - No membrane bound organelle - 70S ribosomes, smaller than eukaryotic ribosome - Cell divides by binary fission - Cell wall always present and contains peptidoglycan - Usually single cell or small groups of cells

Answer 342

Genetic engineering: the transfer of genes from one organism into another (of the same/different species) to express the gene into its new host.

Answer 343

Recombinant DNA (rDNA): is DNA made by joining lengths of nucleotide from two or more different sources

Answer 344

1. Plasmid and gene are cut with the same restriction enzymes called restriction endonucleases to create complementary ends. If sticky ends are missing, they can be added. Plasmids are used as vectors because they exist naturally and are small and easy to use. 2. The fragments are incubated with the plasmids. If a plasmid takes up the insert, base pairing takes place between the complementary ends which are then sealed with the use of DNA ligase which forms phosphodiester linkages. 3. A recombinant DNA molecule is created. Recombinant DNA is a combination of DNA from 2 different organisms.

Answer 345

- It can be extracted from the donor’s DNA - It can be synthesised from the donor organisms mRNA - Could chemically synthesise it from nucleotides

Answer 346

- Plasmids - Viruses - Liposomes- tiny spherical sacs made of phospholipid molecules - Insert vector with new gene into the cell - Cells with the new gene are identified and cloned

Answer 347

- By using the reverse transcriptase enzyme, free nucleotides, mRNA and DNA polymerase, we could obtain a cDNA strand (complementary DNA) - This process, however requires you to find the mRNA molecules in a cell cytoplasm

Answer 348

- Since proteins have now been sequenced, we can synthesise DNA artificially from nucleotides. - The sequence of nucleotides is held in a computer that directs the synthesis of short fragments of DNA. The fragments are then joined to make longer nucleotides that can be inserted into plasmids.

Answer 349

Restriction Endonuclease: enzyme that comes from bacteria which can breakdown DNA of invading virus (bacteriophages)

Answer 350

- ‘Endonucleases’ as they cut the DNA from the sugar phosphate backbone - These enzymes bind to specific target site on the DNA molecule which has a specific base sequence - Usually they bind to (inverted) palindromic sites, sites in which the sequence reads the same in complementary strands when read from 5’ to 3’

Answer 351

- blunt ends: straight cut across sugar phosphate - Sticky ends: short unpaired, staggered ends that can easily form H bonds with complementary bases cut using same restriction enzyme.

Answer 352

- Low molecular mass: can be taken up by bacteria easily - Polylinker: a short length of DNA containing several target sites for different restriction enzymes - One or more marker genes can be added, allowing cells that take up recombinant plasmid to be identified, making it easy to screen - An origin of replication so that they can be copied - Resistant to shearing - Easy to isolate in large quantities

Answer 353

- To obtain plasmids, bacteria are treated with enzymes to break their cell walls and are then centrifuged to separate chromosomes from plasmids. - Plasmid is then cut open using same restriction enzyme used for the DNA so that sticky ends are complimentary - Plasmid and DNA are mixed together - DNA ligase then links sugar phosphate backbone of DNA with plasmid, forming rDNA.

Answer 354

Plasmids: small, circular, double-stranded DNA that is used as a type of vector, which transfers new genes into a recipient cell

Answer 355

- A technique used to separate different molecules. - A mixture of molecules is placed into wells cut into agarose gel and applying an electric field.

Answer 356

Net charge: +ve molecules move towards anode (+), -ve molecules move towards cathode (-); highly charged molecules move faster. Size: smaller molecules move faster

Answer 357

- A gene from jellyfish codes for an enzyme that produces GFP (green fluorescent protein) needs to be inserted into the rDNA (with its promoter), which fluoresces in UV light. - If an organism contains GUS assay enzyme and is incubated with some specific colourless/non-florescent substrates, it can transform them into coloured or fluorescent substances. - These are easier methods to identify bacteria and also more economical than using antibiotic resistance genes

Answer 358

- Bacteria are put into solution with high Ca2+ conc, are cooled and then given electric shock to increase chances of plasmid passing through cell membrane - Only about 1% take up the plasmid and are said to be transformed - In the past, we used to use agar plates containing an antibiotic to identify the bacterium with the plasmid, but this causes unnecessary resistant strains to be formed

Answer 359

- Promoters: controls the expression of genes - Region of DNA to which RNA polymerase binds as it starts transcription of the template strand. - Promoters only allow synthesis of genes that are required & so waste less energy on unwanted proteins - Eg B-galactosidase is made only when the bacteria is growing in a medium containing lactose, in the absence of glucose. - In order for gene inserted into bacteria to be expressed, appropriate promoter needs to be added.

Answer 360

- Proteins are made up of amino acids and the charges on these amino acids depend on R groups present and pH - In acidic pH, NH2 R groups (bases) gain a proton and become NH3+, hence net charge becomes positive therefore moves towards cathode - In basic pH, the COOH R groups (acids) lose their protons and become COO–, hence net charge becomes negative therefore moves towards anode - In neutral conditions, the NH3+ is cancelled by the COO– so it depends solely on the R group - E.g. haemoglobin in sickle cells contains slightly lower negative charge than normal as it’s R group is non-polar (valine) hence when separated sickle cell moves less than that of normal (non-polar valine replaces polar glutamic acid)

Answer 361

- DNA extracted from anything that contains cells such as, root of hair, blood splatter, saliva and so on - PCR is used to increase number of DNA - DNA cut into fragments using restriction endonuclease - DNA is placed on agarose gel and current is applied - Fragments travel towards anode, shorter fragments traveling further/faster, than longer ones

Answer 362

Genetic profiling (fingerprinting): sequencing a length of DNA of one organism and comparing it to another by looking at the ‘variable number tandem repeats’ (VNTRs)

Answer 363

- Place absorbent paper (nitrocellulose paper) on gel to transfer fragment on it - Heat the paper to separate both DNA strands - Add probes (short sequence of single strand), which form complementary base pairing with VNTR regions - Probes also contain radioactive isotope which, when placed on an X-ray film, emits radiation, making the film go dark - The dark strips on the film match position of fragment on gel - Alternatively, label probes with fluorescent stains that fluoresce when UV light is shone

Answer 364

Is a method for rapid production of a particular fragment of DNA to produce a very large number of copies

Answer 365

- DNA is denatured by heating to 95C and double helix splits into two strands - Annealing: Attaching primer onto ends of DNA after cooling to about 65C (primer is short sequence of complimentary DNA) - Elongation: Taq polymerase adds free nucleotides onto primer at 72C to complete new DNA strand - This process is then repeated many times, at each time doubling amount of DNA produced (exponential inc.)

Answer 366

- It is not easily destroyed by denaturing so doesn’t have to be replaced every cycle - High optimum temperature: so temp. does not have to be below (65C), hence faster rate of reaction

Answer 367

- DNA is collected from each species, cut up into different fragments and denatured to give lengths of single-stranded DNA - DNAs are labelled with fluorescent (eg species A = red, species B = green) and mixed together allowing to hybridise with the probes on the microarray - DNA that does not bind to the microarray is washed off - Microarray is inspected using UV light - Microarray is then scanned using laser scanner and read using a computer. Data stored in computer indicates which genes are present in which species.

Answer 368

- Fluorescent patches show hybridisation has taken place - Red tags indicate the gene probe is present in species A - Green tag indicates the gene is present in species B - Yellow tag indicates the gene is present in both species

Answer 369

- Tool to identify the genes present in an organism’s genome, which genes are being expressed and the level of activity - It could also be used to compare genes present in two different species - Microarray is a collection of genes, each in placed in depressions on a small chip/ slide

Answer 370

- The mRNA is reverse transcribed to form cDNA - PCR can be done if cDNA is in low quantity - The same process as above can be used - The fluorescence in the microarray indicates that those genes were being transcribed and their intensities indicate the activity of each gene

Answer 371

- Simple nutritional requirement - Large volume of product produced - Production facilities do not require much space and so can take place all around the world - No risk of infection e.g. HIV from blood donation - Less ethical issues as blood need not be extracted from animals or donors.

Answer 372

- mRNA is only from gene coding for insulin, whereas DNA has all genes and so you must locate and extract gene - Restriction enzyme would be needed for DNA extraction - Large number of mRNA that code for insulin

Answer 373

bacteria don’t modify their proteins the same way eukaryotes do since Golgi bodies are absent.

Answer 374

- mRNA from human pancreatic β cells are extracted - mRNA is incubated with reverse transcriptase producing single stranded cDNA - DNA polymerase is used to convert into double strand - Insulin gene (cDNA) is then inserted into a plasmid to transform the bacterium - The bacteria can now produce insulin, so they are grown in large fermenters and insulin is extracted and purified

Answer 375

- Human gene inserted into hamster kidney and ovary cells - They are then cultured in fermenters, and so they produce the protein - Protein is extracted, purified and regularly injected to patients - Before recombinant factor VIII, it came from blood donors and caused risk of infections eg HIV

Answer 376

- In the past, diabetics were treated with insulin extracted from pancreases of pigs or cattle - Gene technology made it possible to synthetically make our own insulin - So the advantage is that we now have a reliable supply of insulin available to the increasing demand - GF insulin is identical to human insulin unlike insulin previously extracted from cows

Answer 377

This is a protein that is essential for blood clotting, people who do not have it are said to be haemophilic

Answer 378

Bioinformatics is the collection, processing and analysing of biological information & data using computer software

Answer 379

- Bioinformatics combines biological data with computer technology and makes links - Databases hold gene sequences, complete genomes, amino acid sequences and protein structures - Gene sequencing is the order of base pairs in sections of DNA, allowing genomes of many species to be published - Researches can use these databases to find similarities between the sequence of what they are studying and of saved sequences in the databases - Sequences can be matched and degree of similarity calculated, this can show if there is common ancestry - Information stored in database about plasmodium allows us to find new methods to control it eg providing valuable information in the development of vaccines

Answer 380

- Viruses - Naked DNA - Liposomes

Answer 381

Retroviruses insert their genes into host randomly, so they may insert it within a gene, or even worse into the regulatory gene and so can cause cancer

Answer 382

Lentiviruses also insert genes randomly, however, they can be modified to inactivate replication

Answer 383

Preimplantation genetic diagnosis (PGD): At the 8 cell stage during an IVF, one cell can be removed and checked for diseases; if embryo healthy, then implanted, if not it is discarded

Answer 384

Amniocentesis: performed at 15 weeks, a sample of amniotic fluid obtained and cells checked for any genetic abnormalities

Answer 385

Therapeutic abortion is terminating pregnancies for medical reasons and having advice from professionals

Answer 386

- Parents also abort due to the sex of their child, and use PDG to select the sex of the embryo. This preselection, amongst others mentioned above, are considered unethical. - Could lead to the birth of designer babies where parents select other aesthetically pleasing traits, also unethical

Answer 387

- Modified crop plants can become agricultural weeds - Introduced genes may be transferred by pollen to wild offspring and so become more invasive - Can be transferred by pollen to organic certified farms - Hazard to humans as they can produce allergies - The herbicide can leave toxic residue on the crop - Growers need to buy seeds each season which is expensive - Can lose traditional varieties with their desirable background genes, hence would have to make programmes of growing and harvesting them. Also forcing us to setup seed bank to preserve them - No bioaccumulation - Allows non-leguminous plants to fix nitrogen - Increased yield in insecticide and herbicide resistant crops - Increased quality/ taste

Answer 388

- GM seed could be difficult for farmers in developing countries to obtain, as it cannot be replanted - High cost of buying GM seed, so also expensive for people to buy -May not grow well in all conditions - Might reduce efforts to relieve poverty

Answer 389

- This is another important development that allows plants to be protected against attack by insects - Vector used: Bt (a Bacillus bacterium) - Bt gene is inserted into the plant. It produces crystal proteins which kill insects when taken up - Examples: Bt maize, Bt cotton

Answer 390

- Growing herbicide resistant crops allows you to spray herbicide after seed has germinated, killing weeds that would otherwise compete for space, light and water - Vector used: Agrobacterium plasmids - Gene is taken up by plant cells to form a callus. The callus is then grown under ideal conditions to form a GMO plant - Example: sugar beet

Answer 391

- Evolution of resistance by insect pests - A damaging effect on other species of insects - The transfer of the added gene to other species of plant

Answer 392

- Genetically modified plants become agricultural weeds - Pollen will transfer into the wild, producing off-spring that are invasive weeds - Herbicide resistant weeds will evolve due to the usage of same herbicide and so mutate

Answer 393

- Golden rice is meant to be healthier than white rice due to increased Vitamin A content, as its deficiency can cause blindness and the immune deficiency syndrome that in turn causes a high level of mortality in children in developing countries - Pro-vitamin A carotenoids are present in the aleuronic layer of normal rice grains however; this layer is usually removed so that it does not go rancid quickly - Therefore, projects to produce rice that contain carotene in the endosperm were undertaken producing genetically modified golden rice - Vector used: Agrobacterium - First generation of golden rice used genes from daffodils - Second generation of golden rice uses genes from maize

Answer 394

- Is the altering of a genotype and inserting the normal allele into the appropriate cells using a vector, producing a functional recombinant DNA - Eg the CFTR gene in cystic fibrosis is usually the cause of a mutation of a deletion of 3 bases, so in theory inserting normal dominant allele would transcribe the normal protein

Answer 395

Severe combined immunodeficiency (SCID): the inability to produce the enzyme adenosine deaminase (ADA) which helps detoxify the immune system. Without it, the immune system is crippled, and sufferers usually die in infancy from common infections.

Answer 396

The CFTR gene normally codes for a transport protein that allows chloride ions to pass out of cell - Chloride ions are essential to be transported out so that they cause concentration gradient outside, hence causing water to move out of cells by osmosis - The water mixes with the mucus making it easy for removal by the sweeping movement of cilia - The recessive allele codes for a faulty version of this protein, not allowing cl- ions to pass out of the cell, so water doesn’t move out and mucus remains thick.

Answer 397

- Due to mucus not moving effectively by cilia, bacteria and dust accumulate, causing infections - Reduces gaseous exchange, by making it a longer diffusion pathway - Causes difficulty in breathing - Lungs may be scarred

Answer 398

- Allele needs to get into as many cells throughout respiratory system, including cells that divide. - Short natural lifespan; effects only last for a few days - Low uptake by target cells - Only target lung cells at this time - Side effects such as infections caused by the virus - However naked DNA is used (DNA directly inserted into tissues) to prevent problems associated with vectors

Answer 399

- Liposomes in aerosol sprays - Viral delivery by retrovirus/ adenovirus - Naked DNA for direct delivery

Answer 400

- No physiotherapy/antibiotics are needed - Less time consuming than other types of treatments

Answer 401

- Cystic fibrosis is caused by a recessive allele that codes for a transport protein called CFTR, causing the production of abnormal thick mucus that is difficult to be removed - Other body parts such as pancreatic duct can become blocked as well as reproductive ducts causing infertility

Biology A level Flashcards

(425 cards)