A2 Biology Unit 5 Model Answers Flashcards

Question

Importance of reflex actions

Answer 1

Protect the body from harmful stimuli that do not have to be learned Fast because the neurone pathway is short Involuntary and do not require decision-making powers of the brain

Answer 2

Respiration produces increase in CO2 Blood pH is decreased This is detected by chemo-receptors in the carroted and aortic bodies Increased frequenct of impulses sent from medulla along the sympathetic nerve SAN increases heart rate

Answer 3

Pressure receptors in the carroted arteries and arota detect an increase in blood pressure Nervous impulses sent to the medulla Medulla sends more imoulses down the parasympathetic nerve SAN decreases heart rate

Answer 4

Pressure is applied The membrane around the neurone becomes stretched Stretch mediated sodium channels are widened NA+ ions diffuse into the neurone Membrane potential changes It becomes depolarised and proidueces a generator potential which then creates an action potential that is passed along the neurone

Answer 5

Several rods have connection with one bipolar neurone Uses spatial summation aka retinal convergence To allow impulses to exceed threshold for action potential

Answer 6

Rod cells contain rhodopsin Rhodopsin can be broken down in low-light intensity But a consequence of retinal convergence means that light received by red cells sharing the same neurone will only generate a single impulse, regardless of how many neurones are stimulated This results in low visual acuity

Answer 7

Cone cells respond to higher levels of light intensity Their pigment iodhopsin requires more light to break it down Cone cells can respond to colour and are connected to single neurones so they have have higher visual acuity Hence we can't see colours at night and can see much more detail in colour

Answer 8

Point directly behind the pupil Receives most light Only cone cells found here

Answer 9

Part of the eye where the optic nerve attaches and there are no rod or cone cells

Answer 10

Only red cells found Peripheral vision tends to be blurry Low visual acuity

Answer 11

Na+ ions actively transported out of the axon K+ ions actively transported into the axon Active transport of Na+ is greater Electrochemical gradient caused by inbalance of +ve ions Na+ begin to diffuse back into the axon K+ starts diffusing back out of the axon Na+ channels close so more K+ leaves than Na+ enters Equilibrium is established as outside of axon is more positive and K+ cannot diffuse out

Answer 12

Resting potential maintained by sodium and potassium ion pumps Depolarisation caused by sodium gates opening Repolarisation caused when potassium gates open Refractory period where sodium gates cannot open Resting potential re-established by ion pumps.

Answer 13

Energy of stimulus causes sodium voltage-gated channels to open Na+ ions diffused into axon along an electrochemical gradient This triggers a reversal in the potential difference across the membrane (depolarisation)

Answer 14

Voltage-gated sodium channels close, preventing further influx of Na+ ions Voltage-gated potassium channels open K+ diffsues out causing repolarisation Temporary overshoot of electrical charge (hyperpolarisation) causes K+ channels to close Resting potential is re-established

Answer 15

Presence of a myelin sheath - impulse jumps from node to node when the myelin sheath insulates rest of axon so impuse speeds up Diameter of axon - when larger conductance is faster as there is less resistance and less ion leakage Temperature - higher temps are faster to do faster diffusion of ions (higher resp. rate (inc. ATP production) and higher kinetic energy) Metabolic Poisons - Inhibit production of ATP during respiration meaning less energy for sodium/potassium ions to be pumped out/in and resting potential cannot be achieved

Answer 16

Where inward movement of Na+ ions is prevented due to closure of the sodium voltage-gated channels - impossible to create a further action potential during the time Ensures that action potentials are propagated in only one directions Ensure only discrete impulses are produced Limits the number of AP's

Answer 17

Below the threshold value there is no action potential and therefore no impulse will be generated Any stimulus above the threshold value will produce an action potential regardless of strength or size of the stimulus

Answer 18

Energy from stimulus causes calcium ion channels to open and Ca2+ ions enter the synaptic knob Synaptic vesicles fuse with presynaptic membrane and release acetylcholine into the synaptic cleft Acetylcholine fuses with complementary receptors on the postsynaptic neurone Sodium channels open and Na+ ions to diffuse in along a concentration gradient Depolarisation occurs and a new AP is generated on the post synaptic neurone

Answer 19

Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid The products diffuse across the synaptic cleft into the presynaptic neurone ATP is used to recombine the choline and ethanoic acid.

Answer 20

Avoids build of transmitter in the synaptic cleft Allows the neurotransmitter to be reused Prevent the formation of continuous APs in the post synaptic neurone (because sodium gates would remain open and axon be constantly depolararised)

Answer 21

The same presynaptic neurone releases neurotransmitter over time in order for the concentration to accumulate exceeding the threshold.

Answer 22

Different presynaptic neurones release neurotransmitter into the same cleft in order for the concentration to accumulate exceeding the threshold

Answer 23

It takes time for enough neurotransmitter to be accumulated to exceed the threshold.

Answer 24

Cl- ion channels on postsynaptic neurone open Cl- ions diffuse into the axon Charge is made more negative than at resting (hyperpolarizing) New action potential is less likely to form. Sometimes inhibition is a good thing: natural chemical GABA causes most epilepsy and is treated with a drug that binds to receptors that binds receptors and inhibits nerve transmission

Answer 25

1. Stimulate by creating more AP's - mimic a neurotransmitter - stimulate release of neurotransmitter - inhibit enzymes that breakdown neurotransmitters - enhance the binding of neurotransmitters to its receptors 2. Inhibit by creating fewer action potentials - inhibit release of neurotransmitter - block receptors on postsynaptic neurone - e.g. painkillers block receptors in pain pathways reducing pain experienced - enhance the binding of neurotransmitters to its receptors - e.g. Valium enhances the effect of GABA which inhibits nerve transmissions

Answer 26

``` Sarcomere shortens Z lines move closer together H zone is shorter I band is shorter A band remains same size-size of Myocinn filaments do not change. ```

Answer 27

Calcium ions bind to Troponin This moves Tropomyocin This reveals the binding sites on the Actin This allows myocin heads to bind to the Actin-forming a crossbridge Myocin Head moves pulling the Actin along in a ratchet mechanism (power stroke). This activates ATPase-energy is released from ATP

Answer 28

Nerve impulses causes calcium ions enter the presynaptic membrane. Vesicles fuse with the membrane by exocytosis releasing acetylcholine (NT). NeuroTransmitter diffuses across the synapse. NeuroTransmitter binds to receptors in the post synaptic membrane. Depolarisation. Release of calcium ions from within the muscle. Calcium ions bind to Troponin This moves Tropomyocin This reveals the binding sites on the Actin This allows myocin heads to bind to the Actin-forming a crossbridge Myocin Head moves pulling the Actin along in a ratchet mechanism (power stroke). This activates ATPase-energy is released from ATP

Answer 29

ATP allows Myocin to detach from Actin. Phosphocreatine allows regeneration of ATP by providing inorganic phosphate to combine with ADP. This only happens in anaerobic conditions.

Answer 30

ACH stays bound to the receptors on the Post-synaptic membrane. Sodium channels will be permanently open. Cell will be continually depolarized. Continuous formation of action potentials. Muscle will be permanently contracted and unable to relax.

Answer 31

properties: - Contract more slowly - Less powerful - Adapted to endurance work - Adapted for aerobic respiration(avoiding build up of lactate) - Lots of Myoglobin (higher affinity for O2+appears darker - Good supply of Glycogen (can be hydrolysed into a glucose for respiration, production of ATP) - Good supply of blood vessels to circulate O2 and Glucose and remove Carbon Dioxide. - Numerous Mitochondria (more respiration-production of ATP)

Answer 32

Properties: - Contract more rapidly - Powerful contractions over a short period of time. - Adapted for intense exercise - Thicker and more umerousMyocin Filaments. - High concentration of enzymes that are involved in anaerobic respiration - Good store of phosphocreatine (generates ATP from ADP quickly to provide energy.

Answer 33

When stimulation ceases calcium ions actively transported into the sarcoplasmic reticulum using ATP Tropomyocin re-blocks Actin binding site. Myocin heads unable to bind Actin. No crossbridge is formed-contraction ceases.

Answer 34

``` No respiration. No ATP produced. Myocin Head unable to detach from Actin binding site. Crossbridges remain firmly bound. Muscles unable to relax. ```

Answer 35

1 - Formation of Crossbridges between Myocin Head & Actin binding site. 2- Powerstroke movement of Myocin Head 3 - Detachment of Myocin Head 4 - recovery stroke movement of Myocin Head (return to original position)

Answer 36

1- DNA contains Deoxribose sugar - RNA contains Ribose 2- DNA contains Thymine - RNA contains Uracil 3- DNA is double stranded - RNA is single stranded 1- Both contain Cytosine, Guanine & Adenine 2- Both contain Phosphate Groups 3- Both contain Pentose sugars

Answer 37

1- mRNA is a single helix linear molecule-tRNAis a clover leaf shaped molecule 2- mRNAis chemically unstable - tRNA is chemically more stable 3- mRNA does not have areas of complementary based pairing - tRNA does. 4- mRNA has no hydrogen bonding - tRNA does. 5- mRNA length is variable - tRNA length is specific and standard. 6- mRNA has no AA attachment sites - tRNA does. 1- mRNA has a Codon - tRNA also has a Codon however technically called AntiCodon. 2- Both have the same bases 3- Both contain Pentose sugar ribose

Answer 38

* DNA double helix unzips, hydrogen bonds are broken * Transcriptional factor binds promoter of gene * RNA polymerase binds to promoter * Free mRNA nucleotides complementary base pair with exposed DNA nucleotides (only on the template strand) * RNA polymerase seals the new backbone of mRNA (catalyses the formation of new phosphodiester bonds between adjacent nucleotides) * When RNA polymerase reaches a stop codon it detaches and pre-mRNA is formed * DNA strands rejoin

Answer 39

* Ribosome attaches to mRNA at start codon (AUG) * tRNA is activated in the cytoplasm by binding to a specific amino acid * This process requires ATP * tRNAs with complementary anticodon sequence base pair with mRNA codons * Ribosome moves along the mRNA bringing together two tRNAs at any one time * Two amino acids on the tRNA are joined by a peptide bond, this also requires ATP * tRNA is released from the amino acid and is recycled * Synthesis continues until the ribosome reaches a stop codon * The polypeptide chain then detaches and is folded into a functional protein

Answer 40

* Pre-mRNA copies whole section of a gene including non-coding regions * Introns are removed (spliced) from the mRNA by enzymes * Functional exons are joined together * Mature mRNA molecules leave nucleus via a nuclear pore

Answer 41

* to identify the role of genes in biological pathways | * to block the genes that cause genetic diseases

Answer 42

Cells that are able to differentiate into any body cell

Answer 43

1. Identify the gene using a DNA probe and cut it out using restriction enzymes 2. Artificially synthesise the gene, after working out its base sequence from knowing the primary protein structure 3. Using mRNA and reverse transcriptase to produce cDNA

Answer 44

* a cell that readily produces the required protein is selected * the large quantities of relevant mRNA are extracted from the nucleus * reverse transcriptase (isolated from retroviruses) enzyme catalyses the formation of cDNA from the mRNA * via complementary base pairing * DNA polymerase is used to build up the complementary DNA nucleotides

Answer 45

1. PCR (in vitro gene cloning) 2. In vivo gene cloning (inserting a gene into a plasmid and transforming bacteria) – this one gets you a desirable protein product!

Answer 46

Short single-stranded molecules of DNA, which complementary base pair with specific regions on the DNA molecule

Answer 47

* Primers prevent the single strands of DNA re-joining | * Provide a short double stranded section of DNA for the attachment of Taq polymerase

Answer 48

- extremely rapid - does not require living cells - can be v. inaccurate - cannot be used to make genes to be used in humans for things like gene therapy as it may give rise to further mutation

Answer 49

* DNA is heated to 95°C to separate the strands * By breaking the hydrogen bonds * Mixture is cooled to 55°C * Primers are added (see below) – lower temperature allows primers to anneal * Molecules are reheated to 72°C (optimum for Taq polymerase) * Taq polymerase (DNA pol) joins nucleotides together

Answer 50

* required gene is identified from DNA strand using a DNA probe and is isolated by cutting at specific recognition sequences using restriction endonucleases * the same restriction endonuclease is used to cut the plasmid vector * to produce complementary palindromic sticky ends * DNA ligase is used to seal the DNA of the required gene into the plasmid vector; this produces a recombinant plasmid * bacteria are then given an electric or thermal shock to encourage them to take up the recombined plasmid * successful recombinants are identified using a marker gene e.g. antibiotic resistance, luciferin / GFP, lactase * colonies containing bacteria possessing the recombined plasmid are selected and cultured in a batch fermenter; the required protein is extracted and purified

Answer 51

* useful for delivering a gene into another organism * involves no risk of contamination (due to matching of sticky ends) * very accurate (mutations are very rare) * cuts out specific genes * produces transformed bacteria, which can be used to produce large quantities of gene products

Answer 52

3 types: • antibiotic resistance e.g. ampicillin, tetracycline • makes a fluorescent protein e.g. luciferin / GFP • produces an enzyme with an identifiable action e.g. lactase turns a particular substrate blue

Answer 53

* bacteria are cultured on a plate containing ampicillin – those that survive are known to have taken up the recombinant plasmid * a sterile gauze is used to transfer the colonies onto a second plate containing tetracycline * the colonies of bacteria containing the recombinant plasmid will not survive on the second plate * as the gene for tetracycline resistance will have been disrupted due to insertion and subsequent ligation of the required gene * the colonies transferred are in the same position as the originals * so comparison of the plates can identify the required colonies (i.e. the colonies that appear on the first plate but not on the second plate)

Answer 54

* tomatoes that do not soften (the enzyme causing softening has its expression blocked, as the mRNA cannot be translated) * herbicide-resistant crops * disease-resistant crops e.g. modified rice to withstand a particular virus * pest-resistant crops e.g. maize produces a toxin, killing the beetles that feed on it * plants that produce plastics * rice that expresses beta-carotene to avoid the deficiency problems in some Asian countries

Answer 55

* disease-resistance * transfer of growth hormone genes to increase yield e.g. salmon * sheep/goats with modified milk that can express useful proteins e.g. spider silk or anticoagulants such as factor IX (antithrombin)

Answer 56

The replacement or supplementation of defective genes in an individual with genes cloned from healthy individuals (or with DOMINANT ALLELES in the case of gene supplementation – but only useful if the disease-causing gene is a recessive allele)

Answer 57

* mutant recessive allele with 3 bases missing (deletion mutation) * amino acid left out of protein for chloride ion channels (CFTR protein) * chloride ions are not transported out of epithelial cells * so water does not move out cells by osmosis (water potential gradient not produced) * so epithelial membranes dry out and produce a sticky mucus, which blocks the airways

Answer 58

• adenoviruses made harmless by interfering with a gene involved in their replication • adenoviruses grown in epithelial cells along with recombinant plasmids containing the normal CFTR gene • gene becomes incorporated into the DNA of the viruses • viruses are isolated from the cells and purified • viruses containing the gene are introduced into the patient’s nostrils viruses inject their DNA into epithelial cells of the lungs

Answer 59

* CFTR genes isolated and inserted into plasmid vectors * vectors are reintroduced into host cells and gene markers used to detect successful recombinants * bacteria are cloned to produce multiple copies of the CFTR gene * plasmids extracted and wrapped in lipid molecules to form a liposome * liposomes sprayed into nostrils as an aerosol and are drawn into the lungs * liposomes pass across the phospholipid portion of the cell membrane of lung epithelial cells

Answer 60

- patient could become resistant to the viral vectors - patient’s immune system could recognize the viral vectors as non-self antigens and destroy it - effects are only short term - viral vectors may cause infections - protein may not be expressed

Answer 61

* normal ADA gene isolated from human tissue and cut using restriction endonuclease * ADA gene inserted into a retrovirus * Retroviruses are grown with host cells to increase their number * Retroviruses mixed with patient’s T cells * Retroviruses inject a copy of the normal ADA gene into the T cells * T cells are reintroduced into the patient’s blood to provide the code needed to make ADA ONLY EFFECTIVE FOR 6-12 MONTHS

Answer 62

Disease caused by a defective version of a gene coding for adenosine deaminase (ADA). The normal enzyme destroys toxins that kill white blood cells. The mutant enzyme cannot destroy the toxins and therefore white blood cells are affected and are unable to produce antibodies.

Answer 63

1. Four tubes set up containing ssDNA fragments (of the gene to be sequenced) – these act as a template for synthesis of the complementary strand 2. Mixture of nucleotides added (ATCG) plus a small quantity of modified nucleotide terminators added to each tube (A* to tube 1, T* to tube 2 etc) 3. Primer added (as DNA polymerase only works on short sections of dsDNA) – the primer is labeled with a fluorescent dye or is radioactively tagged 4. DNA polymerase added to synthesise new DNA * addition of a modified nucleotide to the sequence (which is a random process) truncates the synthesis  depending on where this happens, different size fragments are produced * the fragments from tube 1 all have one thing in common – they all end in A (for example) and all the fragments from tube 2 end in T etc. Fragments can be identified due to the radioactive or fluorescent labeling. * The fragments are then separated using gel electrophoresis (based on density)

Answer 64

* DNA is extracted from the sample and restriction endonucleases cut the DNA into fragments; this is inserted into wells on an agar jelly * Fragments are separated using gel electrophoresis where an electrical charge is applied to the gel * DNA moves to the positive end as it is negatively charged * Smaller, lighter fragments move the furthest up the gel * Southern blotting occurs to transfer the DNA fragments from the gel to a nylon membrane * DNA probes are added to radioactively label the fragments * The membrane is placed onto an x-ray film and developed – a banding pattern is revealed

Answer 65

Changes the nucleotide base sequence on DNA. Changes the sequence of mRNA codons. tRNA brings different Amino Acids to the Ribosome (incorrect). Changes in the primary sequence of AAs may changer the tertiary structure of the protein. Bonds form in diff places and therefore the folding pattern is different. CONTEXT Enzyme-active site changes shape. ABS-AGS complexes do not form. Hb-Quaternary structure changes shape-Haem group can no longer transport O2

Answer 66

Pluripotent-power to differentiate into a limited number of type of cells- i.e. bone marrow stem cells. Totipotent-power to differentiate into all types of cells. Stem Cells are constantly replicated and replaced. Totipotent cells are only found in the unborn foetus. Plants have meristem cells-totipotent-throughout life.

Answer 67

Normal role is to stimulate cell division. Mutation causes the formation of an Oncogene. This can permanently activate the membrane receptor protein so: 1- Cell division is switched on even in the absence of growth factors. 2- Oncogene may code for a growth factor which would then be produced in excessive amounts.

Answer 68

Normal role is to inhibit cell division. Mutation can cause inactivation. Cell division is no longer inhibited and becomes uncontrollable.

Answer 69

In the cytoplasm, Oestrogen combines with a receptor on the transcriptional factor molecule (due to its complementary shape). Oestrogen changes the shape of the receptor molecule (non competitive inhibition) Inhibitor molecule is released from the transcriptional factor. Transcriptional factor can then enter the nucleus and bind to the DNA. This stimulates transcription of a particular gene. CONTEXT Gene that causes mutations in Oncogenes - Angelina Jolie

Answer 70

dsRNA is broken up by an enzyme dicer into siRNA (small interfering) 1 strand of siRNA combines with an enzyme. siRNA strand (within the RISC Complex) pairs with complementary bases on a mRNA strand (which has just left the nuclear pore). The RISC Complex (bound with the siRNA) cleaves the mRNA into smaller sections. translation cannot take place fully because the full sequence of AAs would not join.

Answer 71

PCR uses heat to separate the strands-DNA uses the enzyme Helicase to separate the strands. PCR uses primers to attach DNA Polymerase-DNA does not. PCR uses TAQ Polymerase which works at 72c - DNa uses a Polymerase which works at body optimum temperature (36.5c) Both involve breaking hydrogen bonds. Both use Polymerase. Both involve complementary base pairing.

Answer 72

A DNA probe is a short single stranded section of DNA with a radioactive or fluorescent marker label. The probe is designed in the lab so that the bases are complementary to part of the genetic sequence in the target gene. Usually used to screen for genetic diseases or identify sequences in DNA samples (criminal/paternity)

Answer 73

blood glucose level increases detected by beta-cells of pancreas insulin is produced which causes: -increased cellular respiration -conversion of glucose to glycogen (glycogenesis) -conversion of glucose to fat -absorption of glucose into cells lowering of blood glucose causes beta-cells to reduce insulin secretion (negative feedback) adrenaline also raises blood glucose by activating an enzyme that causes the breakdown of glycogen to glucose in the liver (glycogenolysis) and by inactivating an enzyme that synthesizes glycogen from glucose (glycogenesis)

Answer 74

An organism that relies on environmental/external heat sources to maintain a constant core body temperature.

Answer 75

An organism that has internal temperature regulation, and metabolic process responses to ensure the maintenance of core body temperatures.

A2 Biology Unit 5 Model Answers Flashcards

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