Key Mechanisms Flashcards
1
Q
Transcription mechanism
A
- The DNA helix is unwound by helicase enzyme which separates the hydrogen bonds between bases
- One of the exposed strands is the coding strand, which acts as a template for mRNA synthesis
- RNA Polymerase lines up the complementary nucleotides C-G and A-U and joins them together by condensation reactions to form phosphodiester bonds
- The mRNA is spliced before leaving the nucleus. Non-coding introns are removed and the exons are joined together.
- The mature mRNA leaves through a nuclear pore and enters the cytoplasm
- The mRNA attaches to a ribosome and is translated
- Pieces of the RER pinch off to form vesicles carrying the polypeptide to the Golgi body, where it is processed and packaged.
- The mature protein is pancaked into vesicles for storage or exocytosis
2
Q
Translation mechanism
A
- The ribosome attaches to the mRNA strand
- The ribosome has two active sites into which tRNA molecules can enter
- The tRNA that enters the active site must have the correct anti-codon to match the codon being read.
- As the two tRNA are alongside each other, the amino acids they carry can be joined together by condensation reaction to form a peptide bond at the expense of ATP.
- One of the tRNA now exits the ribosome leaving a vacant active site. The ribosome moves along one codon, and then another tRNA brings the next amino acid and so on until the end of the mRNA strand, or until a STOP codon is reached.
3
Q
DNA replication mechanism
A
- Happens during the synthesis phase of interphase
- The DNA molecules uses a gyrase enzyme to unwind its double helix and then uses a DNA helicase enzyme to break the hydrogen bonds between the complementary base pairs on order to ‘unzip’ the molecule
- this results in two exposed strands of nucleotides which act as a template for semi-conservative replication
- Complementary nucleotides free in the nucleolus match up with the exposed bases on the original two strands by forming hydrogen bonds between them and DNA polymerase catalyses the formation of phosphodiester bonds between nucleotides in the 5’ to 3’ direction
- This happens continuously for the leading strand but for the lagging strand, it is built as Okazaki fragments due to it being opposite to the leading strand.
- The Okazaki fragments in the lagging strand are then joined by ligase enzymes
- This process forms 2 identical DNA molecules which each contain 1 strand of the original parent DNA
- this makes DNA replication semi-conservative
4
Q
Competitive inhibition mechanism
A
- The inhibitor has a shape similar to the substrate
- They both compete for the active site, consequently fewer Enzyme-Substrate complexes can be formed
- so the reaction rate is lower than normal
- at higher doses of substrate the inhibition can be overcome as the substrate will greatly outnumber the inhibitor molecule and most collisions will actually form Enzyme-Substrate complexes
5
Q
Non-competitive inhibition mechanism
A
- This binds to the allosteric site away from the active site
- this causes the tertiary structure of the enzyme to change
- this changes the shape of the active site so it is no longer complementary to the substrate
- fewer Enzyme-Substrate complexes can form
- reaction rate is lowered
- higher substrate concentrations cannot overcome the inhibition because the limiting factor is the number of active sites
6
Q
Cell Cycle and Division Mechanism
A
Interphase: (not part of mitosis)
Prophase:
- Chromosomes condense and become visible as DNA supercoils
- Nuclear envelope and nucleolus breaks down
- Centrioles divide and two new daughter centrioles move to opposite ends of the cell
- Mitotic spindle fibres form
Metaphase:
- pairs of chromatids attach to the spindle threads at equator region
- they attach by their centromeres
Anaphase:
- Centromere of each pair of chromatids splits
- Motor proteins pull each sister chromatid towards opposite poles
- Chromatids form chromosomes
Telophase:
- Separated chromosomes reach the poles
- New nuclear envelope forms around each set of chromosomes
- Cell now contains two new nuclei which are genetically identical to each other and to the parent cells they came from
Cytokinesis: (not part of mitosis)
- Cell splits into two
- each new cell contains a nucleus
- New plasma membrane forms around the two new cells
- Two daughter cells are formed
- They are genetically identical to each other and the parent cell
7
Q
Meiosis mechanism
A
Prophase 1:
- Chromatin condenses and each chromosome supercoils
- Nuclear envelope breaks down
- Centrioles form
- Chromosomes come together in homologous pairs
- Each member of the pair consists of two chromatids
- Crossing over occurs - where non-sister chromatids wrap around each other and swap sections so that alleles are shuffled
Metaphase 1:
- Pairs of homologous chromosomes attach along the equator of spindles
- Each attached to a spindle thread by its centromere
- Independent Assortment occurs
- Where homologous pairs are arranged randomly and face opposite poles of the cell
Anaphase 1:
- Chromatids in each pair of homologous chromosomes are pulled apart by motor proteins across the spindle
- Centromeres don’t divide
- Crossed-over areas separate from each other
- This results in swapped areas of chromosomes and allele shuffling
Telophase 1:
- Two new nuclear envelopes from around each set of chromosomes
- Cell divides by cytokinesis
- Chromosomes uncoil during interphase
- Each new nucleus contains half the original number of chromosomes
- Each chromosome consists of two chromatids
- In plant cells, cell goes from anaphase 1 into prophase 2
Prophase 2:
- If nuclear envelopes have reformed, they then break down
- Chromosomes coil and condense, each one consisting of two chromatids
- Chromatids of each chromosome are no longer identical
- This is due to crossing over in Prophase 1
- Spindles form
Metaphase 2:
- Chromosomes attach to equator of the spindle by the centromeres
- Chromatids of each chromosome are randomly arranged
Anaphase 2:
- Centromeres divide
- Chromatids of each chromosome are pulled apart by motor proteins towards opposite poles
- Chromatids are therefore randomly segregated
Telophase 2:
- Nuclear envelopes from around each of the four haploid nuclei
- In animals, two cells divide to give four haploid cells
- In plants, a tetras of four haploid cells is formed
8
Q
Interphase Mechanism
A
G1(Gateway 1)
Cells grow and increase in size. • Transcription of genes to make RNA occurs. • Organelles duplicate. • Biosynthesis, like protein synthesis, including making the enzymes needed for DNA replication in the S phase. • The p53 (tumour suppressor) gene helps control this phase.
S Phase(synthesis):
DNA replicates.
• When all chromosomes have been duplicated,
each one consists of a pair of identical sister
chromatids.
• This phase is rapid, and because the exposed
DNA base pairs are more susceptible to mutagenic agents, this reduces the chances of spontaneous mutations happening.
G2(Gateway 2):
Cells grow
M Phase(Mitosis):
Cell growth stops
Mitosis occurs
Cytokinesis follows to create two daughter cells identical to each other and the parent cell
9
Q
Phagocytosis and Antigen Presentation Mechanisms
A
Phagocytosis:
- Receptor on phagocyte’s cell surface membrane binds to antigen on pathogen’s cell surface membrane
- Pathogen engulfed by endocytosis
- This produces a phagosome
- Lysosomes fuse with phagosome, releasing enzymes(lysins) into it
- The pathogen is digested into amino acids and fatty acids
- Products are absorbed into cytoplasm by diffusion
- Phagocyte can incorporate antigens into cell membrane to become an antigen-presenting cell
Antigen Presentation:
Antigen presenting cells move around body where can come into contact with specific cells and activate the immune response
These are B and T lymphocytes
The antigen-presenting cells increase chances that the lymphocytes will come into contact with pathogen
10
Q
Pressure changes in mouth that cause water to move over gills mechanism
A
Fish opens its mouth, lowering the buccal cavity
The volume of the buccal cavity increases therefore decreasing the pressure causing water to be sucked in
When the fish closes its mouth, the buccal cavity is raised
This decreases the volume and increases the pressure
The increased pressure forces water out of the operculum cavity across gill filaments
This causes the operculum to open
This allows the water to move out of the gills down a pressure gradient.
11
Q
Adaptations in fish gas exchange
A
Large surface area provided by gill filaments
Rich blood supply from lamallae
Thin walls - shorter diffusion pathway
Countercurrent flow - concentration gradient maintained by counter flow of water in opposite direction to blood flow, oxygen constantly moving into blood by diffusion along a concentration gradient . Happens as oxygen concentration in the water is always higher than oxygen concentration in the blood
12
Q
Ventilation in insects
A
Air enters pores in their abdomen called spiracles
Air comes through a tube called trachea
These then split into tracheoles which branch very finely between all tissues
The ends of tracheoles are filled with tracheal fluid
The gases will diffuse in the tracheal fluid where it will diffuse into the cell
-When muscles use up oxygen they respire anaerobically
Lactic acid builds up ==> more negative water potential
Water moves by osmosis from tracheoles and into the muscle.
Increases the surface area of the exchange surface and so increased oxygen diffusion
13
Q
Inspiration in the lungs
A
Signal is sent from the medulla oblongata / brain stem along the phrenic nerve
Rib External intercostal muscles contract causing the ribs to move up
The diaphragm muscles contract which makes the diaphragm move down and out
The volume of the lungs increase
The pressure of air decreases below atmospheric pressure
Air enters the lungs to equalise the pressure.
14
Q
Expiration in the lungs
A
Ribs move down and in
Diaphragm muscles relax, causing diaphragm to move up from pressure of Liver
The volume of the lungs decreases
The pressure inside the lungs increases above atmospheric pressure and mainly
Elastic recoil of the lung tissue
15
Q
Adaptations of alveoli
A
Good blood supply so gases can easily diffuse in and out of the blood and maintain a steep concentration gradient by rapid removal of Oxygen
Well ventilated - maintain steep concentration gradient of Oxygen with blood
Moist lining - gases can dissolve first before entering blood
Folded - increases their surface area, more oxygen from bronchioles can diffuse into blood
Contain a lung surfacant - stops alveoli collapsing and sticking together
Contain collagen and elastic fibres that can stretch out and recoil to squeeze air out, stops alveoli exploding
Squamous epithelium of alveoli - thinner walls for a shorter diffusion distance for gases
Squamous endothelium of the capillary - thinner walls for a shorter diffusion distance for gases into alveoli
16
Q
Cardiac Cycle Mechanism
A
- SAN sends an electrical impulse across the atrial wall
- This causes the atria to contract
- The volume in the atria decreases and the pressure increases above ventricular pressure
- Blood is forced through the atrioventricular valves and into the ventricles
- A band of connective tissue is non-conductive and prevents the signal passing to the ventricles
- The AVN is stimulated and conveys signals to the apex of the heart through the Bundle of His
- These family into the purkyne fibres which rapidly and evenly disperse the impulse
- this causes a delayed ventricular contraction - Ventricular pressure increases
- Atrioventricular valves close and semi-lunar valves open - Blood leaves through the pulmonary artery and aorta
17
Q
Enzyme induced fit hypothesis mechanism
A
- Enzymes have active sites complementary to the substrate molecule
- When the substrate molecules fit into the enzyme’s active site, the active site changes shape slightly to mould itself around the substrate
- An enzyme-substrate complex is formed, and non-covalent forces such as hydrogen bonds, ionic attractions, van der Waals forces and hydrophobic interactions, bind the substrate molecule to the enzyme’s active site.
- When the substrate molecules have been converted to the product molecules and these are still in the active site, they form an enzyme-product complex.
- As the product molecules have a slightly different shape from the substrate molecule, they detach from the active site.
- The enzyme molecule is now free to catalyse another reaction with another substrate molecule of the same type.
18
Q
Formation of tissue fluid mechanism
A
Arteries branch into arterioles, and then into a network of capillaries
These link up with venules to carry blood to veins
Therefore blood flowing into an organ or tissue is contained in the capillaries
At arterial end of a capillary, blood is at relatively high hydrostatic pressure.
This pressure tends to push blood fluid out of capillaries through their walls - slit pores
The fluid can leave through tiny gaps between cells in capillary walls
Fluid that leaves the blood consists of plasma with dissolved nutrients and oxygen.
All RBCs, platelets and WBCs remain in the blood, as do the plasma proteins above RMM 69000
These are too large to be pushed out through the gaps in the capillary wall
Tissue fluid surrounds the body cells, so exchange of gases and and nutrients can occur across the plasma membrane.
Exchange occurs by diffusion, facilitated
diffusion, and active uptake
Oxygen and nutrients enter the cells; CO2 and other wastes leave the cells
19
Q
Tissue fluid returning to the blood mechanism
A
The blood pressure(hydrostatic pressure) at the venous end of the capillary is much lower than oncotic pressure
This allows some of the tissue fluid to return to the capillary carrying carbon dioxide and other waste substances into the blood.
The proteins that remained in the blood exert a high negative water potential
Osmosis of water from tissue fluid into lumen
Some tissue fluid directed to another tubular system called lymphatic system
This drains excess tissue fluid out of tissues and returns it to blood system in left subclavian vein in chest
Fluid in lymphatic system called “lymph” and is similar in composition to tissue fluid
Contains more lymphocytes, as they are produced in the lymph nodes
A* low protein in the blood ==> fluid accumulates in tissue (see Kwaskiokor syndrome)
A* parasites can block lymph vessesl and cause tissue swelling ==> see elephantiasis / filiariasis ==> affects over 1 million worldwide )
20
Q
How do xylem vessels form?
A
Lignin impregnates early xylem
Waterproofs and kills the cells
Long column of dead cells with no contents forms - called xylem vessel
This prevents vessel from collapsing
Lignin thickens and forms spiral in cell wall
This allows some flexibility to stem or branch
Where lignification is not complete, bordered pits form
These allow water to move sideways into cells
21
Q
Transpiration stream mechanism
A
H
22
Q
Translocation/Active loading mechanism
A
- H+ ions are actively pumped out of the companion cell
- This process requires the use of ATP
- This creates a concentration gradient outside the companion cell
- High concentration of H+ ions causes facilitated diffusion back into the companion cell
- Sucrose is carried with the H+ ions through cotransport proteins in the plasma membrane
- As the concentration of sucrose in the companion cell increases, facilitated diffusion occurs via contransport proteins in the membrane
- sucrose moves through the plasmodesmata into the sieve tube element
23
Q
Test for Reducing Sugars
A
- Benedict’s reagent is heated to 80Degrees Celsius with a solution of the sample
- Reagent test strips can be used for semi-quantitative results
- On heating, if a reducing sugar is present, there will be a red or orange precipitate
- Intensity of colour depends on concentration of reducing sugars. If there is little it will be green, if there is a high conc. if will turn intense red.
- Use colorimetry and a calibration curve to quantify reducing sugars in a sample
24
Q
Triggering immune response mechanism
A
- Antigens on pathogen’s surface communicate to body cells is foreign
- To initiate immune response, pathogens have to be detected by B and T lymphocytes with complementary receptors on pathogen’s antigens
- Infected cells sometimes get pathogen’s antigens on their surface - helps to select right B and T lymphocytes
- Macrophages in the lymph nodes engulf and digest pathogens. They separate the pathogen’s antigens and incorporate them into their own cell surface membrane. They are now antigen presenting cells ‐ they increase the chances of the correct T lymphocytes locating the foreign antigens.
• The selection of the correct lymphocytes with receptors complementary in shape to the antigens is call clonal selection.
• More of these lymphocytes are needed to fight the pathogens so they divide by mitosis in clonal expansion.
25
Inflammation mechanism
Microbes detected by mast cells which release histamines
Histamines cause vasodilation - makes capillaries more permeable so more WBCs can leave
More tissue fluid forms as more plasma leaves
This causes swelling(odoema)
Tissue fluid can drain into the lymph vessels so pathogens may come into contact with lymphocytes (WBCs) and cause a specific immune response
26
Blood clot and skin repair mechanism
Blood Clot:
Blood vessel is damaged
Platelets bind to exposed collagen to form temporary plug
Platelets also release clothing factors which activate an enzyme cascade
Enzymes cause fibrinogen to form insoluble fibres which attach to the plug
Red blood cells are also trapped, this forms a clot
Skin Repair:
Clot dries and forms a scab which pulls skin closer together
Under skin collagen is deposited
Stem cells in epidermis divide by mitosis and differentiate to form new skin cells at the edge of the cut
New blood vessels form
When edges of cut are drawn together the repair is complete
27
Clonal selection and proliferation mechanism
Clonal Selection:
- An invading pathogen has specific antigens
- These are detected by T and B lymphocytes with receptor molecule complementary to the shape of the antigen
Clonal Expansion:
- Once the correct lymphocytes have been activated they must increase in numbers to become effective
- This is achieved by mitotic cell division
- The correct B and T lymphocytes are replicated and develop into different types of B and T cells:
- T killer cells - attack infected host cells
- T memory cells - remain in the blood
- T helper cells - stimulate B cells to divide
- Plasma cells - make antibodies
- B memory cells - remain in blood
28
Bohr shift mechanism
- CO2 in the blood plasma diffuses into the red blood cells
- It combines with water to form carbonic acid
- This reaction is catalysed by carbonic anhydrase
- CO2 + H2O —> H2CO3
- The carbonic acid dissociates to release hydrogen ions(H+) and hydrogencarbonate ions(HCO3-)
- H2CO3 —> HCO3- + H+
- The hydrogencarbonate ions diffuse out of the red blood cell into the plasma
- The charge of the red blood cell is maintained by the movement of chloride ions(Cl-) from the plasma into the red blood cell.
- This is called chloride shift
- The hydrogen ions building up in the red blood cell could cause the contents of the red blood cell to become acidic
- To prevent this, the hydrogen ions are taken out of solution by associating with haemoglobin to produce haemoglobinic acid(HHb).
- The haemoglobin is acting as a buffer(a compound that maintains a constant pH)
29
Test for non-reducing sugars
- If a reducing sugar is not present, heat with HCl to reduce the non-reducing sugar.
- Sodium hydrogencarbonate solution is added to neutralise the acid.
- Then the Benefict’s reagent is added before heating to 80 Degrees Celsius
- On heating, if a non-reducing sugar is present, there will be a red or orange precipitate
30
Water moving from soil to xylem mechanism
-Minerals actively transported into root hair cell (through carrier proteins)
• Water moves via osmosis from soil into root hair cells across cell surface membrane (through aquaporins) down the water potential gradient
• Water can move via cell walls in the apoplast pathway
• Water can move via the cytoplasm in the symplast pathway, through plasmodesmata, linking the cytoplasm in neighbouring cells
• Water also moves through vacuoles via the vacuolar pathway
• At the endodermis, the Casparian strip (made of suberin) blocks the apoplast pathway
• This makes the water enter the symplast pathway
• Water potential is most negative in the xylem due to the active transport of minerals into it
• This causes water to move into the xylem from the cells of the endodermis and cortex
31
How does transpiration result in the movement of water up a stem?
• Water evaporates from the surface of the mesophyll cells in the leaf and forms water vapour
• Water vapour diffuses from a high water potential to a lower water potential out of the leaf, through the stomata
• More water is drawn from the mesophyll cells via the symplast/apoplast pathways in the leaf replacing the water that has evaporated
• Bonus: This occurs via osmosis down the water potential gradient in the symplast pathway and mass flow in the apoplast pathway
• This water is replaced by water from the xylem vessels (moving out via osmosis)
• The loss of water from the xylem causes a low hydrostatic pressure at the top of the xylem
• Water moves from a higher pressure (roots) to a lower pressure (down the pressure gradient) under tension
• Water is therefore pulled up the xylem by mass flow
• The cohesion of water molecules due to the
hydrogen bonds between them causes them to stay as a long unbroken column of water during this process the transpiration stream
32
Sucrose moving across phloem at a source
* Sucrose is actively loaded into the sieve tube elements at the source
* This reduces the water potential in the sieve tube element
* Water enters the sieve tube elements by osmosis
* This increases the hydrostatic pressure in the sieve tube element near the source
33
How sucrose moves across phloem at a sink
* Sucrose is unloaded at the sink by diffusion/active transport and used in respiration/stored
* This increases the water potential in the sieve tube element
* Water moves out of the sieve tube element via osmosis down the water potential gradient
* This reduces the hydrostatic pressure in the sieve tube element
* Water in the sieve tube element at the source moves down the hydrostatic gradient from source to sink
* This creates a flow which carries the sucrose and other assimilates along the phloem via mass flow either up or down the plant
34
Transpiration stream - better?
- Minerals actively transported into xylem by the Endodermis cells and into the Xylem
- There is MORE NEGATIVE water pot in xylem
- Water follows by osmosis (through the Symplast pathway of the endodermis)
- The cell wall of the endorma cells have waxy Suberin (Casparian strip) which prevents water and mineral ions diffusing backwards through the Apoplast pathway
- Water moves by mass flow through cohesion
- Mesophyll cells dry out due to transpiration of water through the stomata
- Water potential becomes more negative
- Water moves out of the adjacent xylem by osmosis
- Due to water cohesion a column of water moves up through the Xylem from the roots
- Minerals such as nitrates are carried in solution to the leaves for biosynthesis
35
Active loading mechanism
- H+ ions are actively pumped out of the companion cell
- This process requires the use of ATP
- This creates a concentration gradient outside the companion cell
- High concentration of H+ ions causes facilitated diffusion back into the companion cell
- Sucrose is carried with the H+ ions through cotransport proteins in the plasma membrane
- As the concentration of sucrose in the companion cell increases, it diffuses through the plasmodesmata into the sieve tube element
- This causes the water potential to become more negative in the sieve element
36
Setting up a potometer mechanism
H
37
Translocation - better?
The roots take up minerals from the soil
They are actively transported by the endodermal cells from the parenchyma and into the xylem
Water potential in the xylem vessel becomes more negative
Backwards flow of ions and water via the apoplast pathway is prevented by the waxy Suberin layer of the Casparian strip
38
Uses of stem cells
- Bone Marrow Transplants - to treat blood diseases like leukaemia, or restore blood after cancer treatment
- Drug and Medical Research
- Developmental Biology - study how organisms develop, grow and mature
- Repair damaged or lost tissues and organs - diabetes, Alzheimer’s or stem cells can grow into specific organs and tissues to treat degenerative diseases
39
Diastole Mechanism
* atria and ventricles relax and recoil
* blood flows from veins into atria
* pressure in ventricles is lower than in atria
* blood flows through open A‐V valves into ventricles • volume in atria and ventricles increase
* pressure in atria and ventricles slowly increases
40
Atrial Systole Mechanism
- both atria contract
• causes further increase in pressure in the atria
• increase in pressure causes blood to be pumped through the open A‐V valve into the ventricles (causing the volume in the ventricles to increase)
41
Ventricular Systole Mechanism
• When the ventricles are full, they begin to contract (from apex upwards)
• The pressure in the ventricles increases above the pressure in the atria A‐V valves snap shut ‐ stops blood returning to atria
• At this point the semilunar valves are also shut as the pressure in the
major arteries is higher than in the ventricles
• The pressure in the ventricles increases quickly as the blood can't escape
• When the pressure in the ventricles exceeds the pressure in the major
arteries, the semilunar valves open and the blood is pumped out the
heart due to this pressure
• The volume in the ventricles drops quickly
• This causes pressure to drop in the ventricles, below the pressure of the
major arteries ‐ semilunar valves pushed closed by blood in arteries and stop blood flowing back into ventricles
42
Uses of different mineral ions in plants
Nitrates - synthesis of amino acids and nucleotides
Phosphates - synthesis of Nucleic acids, ATP and phospholipids
Magnesium - production of chlorophyll
Iron - synthesis of mitochondria
43
Differences between meiosis and mitosis
Mitosis:
- produce 2 diploid cells
- daughter cells genetically identical to parent cell
- etc.
Meiosis:
- produce 4 haploid cells
- produce gentically daughter different cells to parent
- etc
44
Differences between bacterial and eukaryotic cells
H
45
Sampling for PLANTS model answer mechanism
• set grid/area to be sampled
• use belt transect to sample
• use 50cmx50cm quadrats
• at regular 5m intervals ‐ systematic sampling
• identify plant species using keys
• record the presence/absence of sp. in each quadrat
• estimate the % cover of each species in your quadrat
• repeat this using several different transects to show repeatability and identify
anomalies
• extrapolate the data to estimate biodiversity in the entire habitat
46
Sampling ANIMALS model answer mechanism
• set grid/area to be sampled
• use random numbers generated by a computer to locate the areas you will
randomly sample
• pick appropriate capture method CHOSE ONE e.g. sweep nets, pooters,
pitfalls etc
• identify each sp. using a key and count the numbers of each sp.
• repeat this several times in each habitat, using the same technique each
time to show repeatability and identify anomalies
extrapolate the data to estimate biodiversity in the entire habitat
47
Factors affecting biodiversity
- Human Population Growth:
- more food and land needed = alter ecosystems and destroy habitats
- Using up more natural resources, e.g. crude oil is finite
- More energy sources and materials needed = more pollution
- Over hunting/fishing decreases biodiversity
- Agriculture and monoculture:
- monoculture will have reduced genetic diversity
- More land and natural habitats are cleared for land monoculture - reduces size of habitats and of wild species populations
- reducing population sizes reduces genetic diversity - less able to survive changes in conditions and leads to extinction
- Climate Change:
- Species with low genetic diversity are unable to adapt to the climate changes
- So species may have to migrate, which is risky as it is not always possible and could lead to extinction of a species
48
Reasons for maintaining biodiversity
Ecological reasons:
Economical Reasons:
Aesthetic reasons:
50
Definition of a tissue
A collective group of specialised cells that work together to achieve a common function
51
Test for proteins
A solution is made of the protein
Biuret test is added to the sample in solution.
Leave to warm gently in water bath for 5 minutes and observe for a colour change
Positive result is colour change from blue to purple
52
Test for lipids
- Take a sample and mix it thoroughly with ethanol
- Filter the solution
- Pour solution into water
- shake the sample
- if a milky white emulsion is produced, lipids are present.
53
Test for starch
- Iodine(iodine solution is dripped on to a sample(solid or liquid)
- positive test turns solution from orange/yellow to blue/black
54
Test for reducing sugars
| -What type of sugars does it test for?
- Benedict’s reagent is heated to 80 Degrees Celsius with a solution of the sample
- Reagent test strips can be used for semi-quantitative results
- On heating, if a reducing sugar is present, there will be a red or orange precipitate
- Intensity of colour depends on concentration of reducing sugars. If there is little it will be green, if there is a high conc. if will turn intense red.
- Use colorimetry and a calibration curve to quantify reducing sugars in a sample
- (this shows positive for all monosaccharides AND Maltose)
55
Test for non-reducing sugars
- If a reducing sugar is not present, heat with HCl to reduce the non-reducing sugar.
- Sodium hydrogencarbonate solution is added to neutralise the acid.
- Then the Benefict’s reagent is added before heating to 80 Degrees Celsius
- On heating, if a non-reducing sugar is present, there will be a red or orange precipitate
56
Organ def
A collection of tissues that work together to achieve a certain(named, e.g. gas exchange for lungs) function in body
57
Processing of budding in fungi(yeast cells)
- Nucleus divides by mitosis
- Cells swell at the side and form a bulge
- Nucleus moves into the swell
- Nucleus pinches off to form a new cell
58
Evolution mechanism
- Variation and overproduction of offspring
- Competition and selection pressure
- E.g. abiotic and biotic factors (disease, natural disasters etc.)
- Many individuals die
- Survivors pass on their alleles
- Speciation - due to isolation
- Speciation due to ancestral population - becomes into two or more isolated groups -Due to geography or behavioural
- Physical size
- Timing - e.g. trees blossoming at different times or seasons, or animals being oestrous at different times
59
Properties of fibrous proteins
- insoluble
- strong - high tensile strength
- unreactive/inert
- Structural role in body
- Metabolically inactive
- Form fibres - fibrils and macrofibrils - high tensile strength
- Flexible
60
Properties of globular proteins
- Tertiary structure rolls up into a spherical shape - due to folding of hydrophobic and hydrophilic R groups
- Specific shapes
- Soluble in water
- Have metabolic roles within the organism
- E.g. enzymes, hormones, haemoglobin
- May have prosthetic groups
- Have complementary shape to other molecules, like enzymes
61
Primary structure mechanism
H
62
Secondary structure mechanism
H
63
Tertiary structure
H
64
Quaternary structure mechanism
Separate twisted or folded polypeptide subunits linked together
Prosthetic groups may be attached to the quaternary structure of a protein
E.g. haem group into haemoglobin
Each protein subunit has its own primary, secondary, and tertiary structure
65
Different components of antibodies and their functions
Constant region - allows agglutination - constant region binds to
Variable region -
Hinge region - flexibility to variable regions so can bind to more than one pathogen
Two strands - one light and one heavy connected by disulfide bonds
66
Potometer Practical Mechanism
- Cut a shoot underwater
- AND CUT DIAGONALLY TO PREVENT AIRBLOCKS
- This is done to prevent air from entering the xylem
- Place the shoot in the tube
- Make sure it is airtight, using vaseline/petroleum jelly to seal any gaps
- If air enters the apparatus the readings will be affected
- Dry the leaves of the shoot
- Any moisture present on the leaves will affect the rate of transpiration
- Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water
- Set up the environmental factor you are investigating
- Allow the plant to adapt/acclimatise to the new environment for 5 minutes
- Record the starting location of the air bubble
- Leave for a set period of time
- Record the end location of the air bubble
- Change the light intensity or wind speed or level of humidity or temperature (only one – whichever factor is being investigated)
- Reset the bubble by opening the tap below the reservoir
- Repeat the experiment THREE TIMES TAKE MEAN AND REMOVE OUTLIERS
- The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa
- THE MEASURE OF TRANSPIRATION IS AN ESTIMATE AS SOME WATER IS USED FOR PHOTOSYNTHESIS AND METABOLISM
67
What could affect the rate of transpiration?
H
68
Three variables that need to be controlled during chromatography(TLC)
- Temperature of system/lab
- Humidity of the lab/conditions
- Volume of the mobile phase solvent
69
How to work out retention factor(Rf value)
Rf = distance travelled by pigment/distance travelled by solvent
-Always leave as a decimal/number(not a percentage)
70
Outline a method to carry out a thin layer chromatography experiment
H - on SnapRevise video on Chromatography
71
Autoimmune disease def
Abnormal immune response against tissues normally in the body
-Antigens on cell surface membrane of body cells aren’t recognised by immune system, so is attacked by leukocytes
72
TEM info.
Mag: 500000x / 2,000,000x
Res: 0.5 nm
- only shows 2D images
-Specimen has to be dead - vacuum
73
SEM info
Mag: 500000x
Res: 3-10 nm (5nm)
- only shows 3D images
-Specimen has to be dead - vacuum
74
Optical microscope info
Mag: 2000x
Res:
-
75
Advantages + disadvantages of optical microscopes
H
76
Advantages + disadvantages of electron microscopes
H
77
Info about cytoskeleton
H
78
Reasons for staining specimens
- To identify differences between organelles
- To identify differences between cells
- Greater contrast between different cell types
79
Independent assortment mechanism
- Occurs in metaphase 1
- Independent assortment of homologous chromosomes
- homologous chromosomes line up across the equator of the cell
- maternal or paternal chromosomes in the homologous pair face either pole in either daughter cell
- each chromosome of the homologous pair is genetically different, as they each contain different alleles
80
Crossing over of non-sister chromatids in prophase 1 mechanism
H
81
Differences between phloem and xylem
H
82
Similarities between phloem and xylem
H
83
Methods/practices to reduce chances of infection
H
84
Species def
-A group of organisms similar in appearance, physiology and genetics whose members are able to interbreed to produce fertile offspring
85
Adaptations of xerophytes
| How do they help reduce water loss?
```
thick waxy cuticle -
few stomata -
stomata sunken or in pits -
hairs on leaves/ hairy -
leaf curled / rolled -
dense spongy mesophyll -
closure of stomata during day / when water availability low -
```
86
Adaptations of hydrophytes
| How do these help?
H
87
What is meant by a homologous pair of chromosomes?
```
one maternal and one paternal
carry same genes
carry same alleles
(usually) same similar, length
centromere in same position
same banding pattern
pair up in meiosis to form bivalent
```
88
How are monoclonal antibodies synthesised in the context of pregnancy tests?
1. HCG is injected into an animal - a horse as more blood is produced (more WBCs)
2. Horse plasma cells will produce antibodies against HCG
3. Those plasma cells are isolated
4. Plasma cells are fused with cancer cells
5. This produces a hybridoma - immortalises the plasma cell
6. This allows the HCG antibody to be made forever
89
Main uses of monoclonal antibodies
- Pregnancy tests
- Screening tests - prostate cancer etc.
- Treatments - e.g. cancer treatment shuttling
- Antibody tests - COVID tests/HIV tests
90
How do pregnancy tests work?
1. Tip of strip dipped in urine
2. Monoclonal antibodies diffuse into and move with urine
3. Monoclonal antibodies are specific to HCG and have a coloured marker/pigment
4. The results window contains immobilised monoclonal antibody which will stick to HCG
5. The immobilised monoclonal antibodies will only capture the HCG antibodies if they both stick to the HCG
6. So we see a coloured line
7. In both cases some of the HCG antibody will diffuse all the way to the control window
8. This can be proved by the presence of an immobilised antibody which is specific to the pigment molecule
9. This shows the antibodies are moving through the results window (control window)
91
Roles of the cytoskeleton
- cell support and stability
- movement of flagella and cilia
- changing shape of cell - phagocytosis/exocytosis
- movement of organelles e.g. movement of vesicles
- movement of chromosomes and mRNA to ribosomes
92
Roles of the cytoskeleton
- cell support and stability
- movement of flagella and cilia
- changing shape of cell - phagocytosis/exocytosis
- movement of organelles e.g. movement of vesicles
- movement of chromosomes and mRNA to ribosomes
93
If error bars/standard deviation bars overlap, what is the significance?
- SD shows how far data values deviate from the mean
| - there is no statistical significance between the two data values
94
Structure of a collagen molecule
| 6 Marks
- Peptide bonds between adjacent amino acids
- Every 3rd amino acid in the primary structure of polypeptide chains is glycine
- It is coiled to provide more structural support and integrity to the molecule
- No hydrophilic R groups on outside of the molecule so is insoluble
- Adjacent molecules joined by cross links (by covalent bonds)
- Cross links at the end of molecules are staggered
- Short polypeptide chains are fibrils, and cross linking of chains forms macrofibrils for structural support of the molecule
95
Structure of haemoglobin
Sjjsj
96
Structure of keratin
Sjjsj
| - Cysteine etc.
97
Any other biological molecules?
Ndjs
98
Definition of health (WHO)
- The physical and mental wellbeing of an individual
| - With the absence of disease or illness
99
Insect gas exchange - better?
1. Oxygen diffuses through the wall of the abdomen through spiracles
2. The spiracles can open and close to minimise water loss and entry of pathogens
3. The air passes into a main tube running longitudinally - the trachea - and
4. This then divides into many tracheoles which penetrate the tissues
5. When tissue is deprived of oxygen, the insect and the tissues will start to respire anaerobically
6. This causes a buildup of lactate, which causes a more negative water potential
7. Water will move by osmosis from the tracheoles and into the tissue
8. The increases the surface area for gas exchange
9. All gas movement is diffusion
10. Larger insects can help air circulation by abdominal pumping
100
Steps involved in replication of HIV
1
The glycoproteins on the surface of HIV bind to receptor proteins on the cell surface membrane of TH cells
2
The capsid is released and injected into the TH cells. The RNA and enzymes are released from the capsid. The enzymes are reverse transcriptase and integrase.
3
Reverse transcriptase converts the single-stranded RNA from the HIV into double-stranded DNA. The DNA moves into the nucleus of the TH cells.
4
Integrase is an enzyme that inserts the HIV DNA into the TH cells DNA.
5
The genes in the HIV DNA are expressed in the TH cells. The HIV proteins are synthesised and new HIV RNA is made
101
Explain how the structure of DNA is releated to its functions.
(6 Marks)
1. Sugar-phosphate (backbone) / double stranded / helix so provides strength / stability / protects bases / protects hydrogen bonds;
Must be a direct link / obvious to get the mark
Neutral: reference to histones
2. Long / large molecule so can store lots of information;
3. Helix / coiled so compact;
Accept: can store in a small amount of space for ‘compact’
4. Base sequence allows information to be stored / base sequence codes for amino acids / protein;
Accept: base sequence allows transcription
5. Double stranded so replication can occur semi-conservatively / strands can act as templates / complementary base pairing / A-T and G-C so accurate replication / identical copies can be made;
6. (Weak) hydrogen bonds for replication / unzipping / strand separation / many hydrogen bonds so stable / strong;
Accept: 'H-bonds' for ‘hydrogen bonds’
102
Vascularisation occurs in bodybuilders because blood vessels are pushed to the surface by increased muscle mass. They can also become more visible due to reduced body fat and dehydration.
Explain why the visible blood vessels are likely to be veins.
(3 Marks)
- Veins have thin walls so will bulge out more
- Veins have a large lumen - contains larger volume of slow-moving blood
- Veins found closer to skin surface than arteries
103
What is meant by the term ‘conjugated protein’?
| 3 Marks
- Contains non-protein groups
- has prosthetic groups
- this prosthetic group is (named ion if given a diagram, e.g. iron ion in haemoglobin
- prosthetic group is attached via covalent bonds/ionic bonds/hydrogen bonds
104
Suggest why reduced heart rate is sometimes seen in people who are very aerobically fit.
(2 Marks)
- increased stroke volume
- increased volume of ventricle
- increased thickness/strength of heart muscle
105
Explain how mass flow phloem sap occurs in plants with a vascular system.
(3 Marks)
- Sucrose and assimilates collect in the sieve tube elements
- Assimilates enter sieve tube at source and lowers water potential inside
- Water enters sieve tube by osmosis - down water potential gradient
- hydrostatic pressure increases
- assimilates leave sieve tube at the sink
- increases water potential in sieve tubes at sink
- water leaves sieve tube by osmosis
- lowers hydrostatic pressure
- assimilates move from high to low hydrostatic pressure/down pressure gradient
- moves from source to sink
106
Give three properties of cellulose that make it suitable as the basis of plant cell walls.
(3 Marks)
- high tensile strength
- insoluble - no effect on plant cell water potential
- Unreactive/inert
- Flexible
- Can form hydrogen bonds with neighbouring cellulose chains (macrofibrils)
107
Adaptations of xerophytes
- Stomata closed during day - open during night - prvenets water loss
- leaves curled or rolled when flaccid
- leaves may have spines or hairs on them - traps water vapour vapour - reduces water potential concentration gradient - decreased transpiration
- Reduced numbers of stomata - less transpiration can occur as lower SA to lose water
- thick waxy cuticle on leaves - water loss reduced from leaf surface
- stomata in pits - increases water vapour trapped - reduces water vapour conc. gradient - increased humidity reduces water loss.
108
Adaptations of hydropytes
- Many large air spaces in leaf - keeps leaves afloat - so are in air and can absorb sunlight for photosynthesis
- The stomata are on the upper epidermis - so that they are exposed to the air to allow gaseous exchange
- leaf stem has many large air spaces - helps with buoyancy - also allows oxygen to
diffuse quickly to the roots for aerobic respiration
109
An increase in respiration in the tissues of a mammal affects the oxygen dissociation curve of haemoglobin. Describe and explain how.
(2 Marks)
rgdgrg
110
There is less oxygen at high altitudes than at sea level.
People living at high altitudes have more red blood cells than people living at sea level. Explain the advantage of this to people living at high altitude.
(2 Marks)
dioq3doiq3joie
111
Precautions that should be taken when using a spirometer
| - 5 points
- subject should be healthy - free form asthma especially
- soda lime should be fresh and functioning
- no air leaks in apparatus - give inaccurate or invalid results
- mouthpiece should be sterilised - protect against infection
- water chamber must not be overfilled - or water may enter the air tubes
112
Tidal volume def
The volume of air inhaled or exhaled in one breath, usually at rest
113
Vital capacity def
The greatest volume of air that can be expelled form the lungs after the deepest possible breath
114
Residual volume def
the volume of air that remains in the lungs even after forced expiration
115
Outline the reasons why insects and other animals have well-developed transport systems.
(3 Marks)
ddjjdjdjdj
116
Guidlines to be used when drawing a dissection.
```
Use a sharp pencil
Use ruled label lines
include a scale bar
Include a title/heading
no labels outside diagram
label lines should not cross over others
continuous lines
no shading
use plain paper
state magnification
correct proportions
large size - at least 50% of available space
```
117
```
Parasite def
(3 Marks)
```
- organism that lives in/on host
- gains nutrition from the host
- at expense of the host/harms host
118
Explain why the human body's primary defences do not prevent the entry of PLasmodium into the body.
(2 Marks)
- Female anopheles mosquito feeds on blood
| - bites and pierces skin - bypasses primary defences
119
Describe how the structure of antibodies allows them to perform their function.
(7 Marks)
- 2 light and 2 heavy chains
- variable region allows binding to antigen
- two variable regions allow binding of more than one of the same antigen
- variable region on different antibodies are specific to different antigens - allows specificity to certain antigens
- constant region allows binding to phagocytes
- hinge region allows flexibility of the variable regions to attach to specific antigens
- disulfide bridges hold heavy and light chains together
120
Outline the model of neutralisation and agglutination.
| 4 Marks
- Neutralisation:
- Variable region binds to antigen on pathogen and blocks it
- prevents entry into host cell
- binds to toxins that could be released
Agglutination:
- Variable regions bind to many antigens on pathogens
- Clump pathogens together
- Clump is too large to enter the host cell
- Clumping together increases likelihood of being engulfed by a phagocyte
121
Describe how the infective agent that causes TB is transmitted from one individual to another.
(2 Marks)
- Droplets containing pathogen
- Released by coughing/sneezing
- Inhaled by uninfected individual
122
Factors that may affect transmission of a disease within a population.
- overcrowding
- poorly ventilated
- poor diet
- poor health/immune system
- homelessness
- more difficult to access proper medical care
123
Plant physical defences
hdhdhd
124
plant chemical defences
aeuhauwh
125
Random assortment mechanism.
| 3 Marks
i) The process takes place during Anaphase II
ii) Only one of each pair of homologous chromosomes can go into the gamete
iii) which of each pair goes into the gamete is random and generates variants
126
An important aspect of Oxygen binding is that it must be a relatively weak and reversible bond which is formed.
With reference to the function of Haemoglobin within the human circulation, explain why it is important that this is a weak AND reversible bond
(4 Marks)
sdjnsf
127
What are processed results in data?
| 1 Mark
Percentages have been calculated.
| Data provided has been calulated from results
128
Explain the difference between species richness and species evenness and why both measurements are needed to assess biodiversity.
(4 Marks)
- Species richness - number of species within a habitat
- Species evenness - abundance of each species within a habitat
- Both species richness and evenness are needed to reveal dominance of each species within the habitat
- high biodiversity associated with a species richness and high species evenness
129
Define the term phylogeny and explain how phylogeny is related to classification.
Use the two lynx species as examples (context maybe needed?)
(4 Marks)
- Phylogeny is the evolutionay relationhsip between organisms/species
- Phylogeny is the basis of classification
- (example of molecular evidence to classify) - e.g. base sequences, DNA
- species within the same group have a shared phylogeny - so have a common ancestor
- phylogeny of both lynx may be sufficiently different to be placed in seperate species/suffciently similar to be placed in same genus
130
Explain why meiosis has twice as many stages as mitosis.
| 2 Marks
- To halve the chromosome number
- to separate homologous pairs of chromosomes and sister chromatids
- because DNA has been previously replicated - chromosomes are two chromatids at start
131
Evolution mechanism and acronyms - VOSARM
V - populations contain genetic variation - caused by mutations
O - Overproduction of offspring
S - Selection Pressure - human impact(?)
S - Survive - organism better adapted more likely to survive
A - Allele variation gives adaptation to current environment
R - Alleles more likely to be passed on by reproduction - organism more likely to reproduce
M - Mutation cases genetic variation
132
The student stained a sago pondweed sample to improve the contrast between cellular
components when viewed under a microscope.
The student used the following procedure to stain the sample:
• Use forceps to place the sample on a glass slide.
• Use a pipette to place two drops of the stain in the centre of the sample.
• Carefully lower a cover slip onto the sample, ensuring that the cover slip is
parallel with the slide as it is lowered.
Describe two improvements the student should make to their staining procedure.
(2 Marks)
- lower slip at an angle
- use blotting paper to remove excess stain
- use more than one stain to improve contrast
- place stain at edge of sample (not at centre)
- ensure stain covers whole sample
