AQA A level Biology Revision Exam Question & Answers 2024, Exams of Nursing

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Question & Answers 2024

Describe how you would use a biochemical test to show that a solution contained a non-reducing sugar, such as sucrose. [3] - Correct Answers ✅,first reducing sugars test; boil with dilute HCl acid then Neutralise with NaHCǑ, add benedict and heat to 95 degrees C brick red ppt forms if reducing sugar is present Describe a chemical test you could carry out to show that a piece of coconut contains lipids. [3] - Correct Answers ✅(Crush in) ethanol / alcohol; Add (to) water (Order of adding is critical for this point); Emulsion / white colour Explain what is meant by a polymer. [1] - Correct Answers ✅Molecule) made up of many identical/similar molecules/monomers/ subunits; Name the reaction which occurs when starch is broken down into maltose. [1] - Correct Answers ✅Hydrolysis What is the formula for lactose? [2] - Correct Answers ✅C12 ; H22Ō 1 Describe how β-glucose molecule differs from a molecule of α-glucose. [1] - Correct Answers ✅H at top right end (instead of OH) / OH at bottom (carbon 1)

Question & Answers 2024

Show two ways in which the structure of cellulose is different from the structure of starch. [2] - Correct Answers ✅Starch 1,4 and 1, bonds / branching Cellulose 1,4 bonds / no 1,6 bonds / straight; starch All glucoses /monomers same way up cellulose Alternate glucoses upside down; starch Helix / coiled/compact cellulose Straight; Starch monomer Alpha glucose Cellulose monomer Beta glucose Describe the structure of starch and explain how its structure is related to its function. [3] - Correct Answers ✅Formed from α glucose; Joined by condensation/ by the removal of a water molecule/ glycosidic bonds; Between (carbons) 1 and 4 (and 1 and 6); Coiled chain; compact; (Allows) storage of large amount in a small space; Insoluble so has no effect on osmosis/water potential; Branches; (Allows) rapid breakdown/release of glucose / hydrolysis; The structure of a phospholipid molecule is different from that of a triglyceride. Describe how. [2] - Correct Answers ✅triglyceride has three fatty acids and phospholipid has two; no phosphate group present in triglyceride but present in phospholipid. What is an unsaturated fatty acid? [1] - Correct Answers ✅Some / two carbons with only one hydrogen / (double bonds) between carbon atoms / not saturated with hydrogen;

Question & Answers 2024

Describe the structure of cellulose and explain how its structure is related to its function. [3] - Correct Answers ✅Alternate β-glucose rotated 180o, long straight chains, Many hydrogen bonds join (polysaccharide) chains/molecules to each other / makes microfibrils / gives tensile strength; Which elements are found in proteins? [1] - Correct Answers ✅Carbon, hydrogen, oxygen, nitrogen (sometimes sulphur) Describe how you would use a biochemical test to show that a solution contained protein. [2] - Correct Answers ✅Biuret / alkali + copper sulphate; Lilac/purple/mauve/violet; Which bonds are found in a)Primary structure [1]b)Secondary structure [1] c)Tertiary structure [2] - Correct Answers ✅a)Peptide b) Hydrogen (and peptide) c)Ionic, disulphide bridges, hydrophobic interactions (hydrogen and peptide) Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure. [3] - Correct Answers ✅Sequence of amino acids changes; tertiary structure changes/folds in a different way; bonds form in different places (not peptide);

Question & Answers 2024

Describe how two-way chromatography is carried out. [2] - Correct Answers ✅Run chromatogram then turn through 90/right angle; With a different solvent; Explain the advantage of using two-way chromatography to separate short polypeptides. [2] - Correct Answers ✅Spreads spots/polypeptides out more/ make sure spot only contains one substance; Explain how inhibitors affect the rate of enzyme-controlled reactions. [6] - Correct Answers ✅Statement about two types, competitive and non-competitive; Competitive: Similar shape to substrate;Inhibitor can enter/bind with active site (of enzyme);Non-competitive: Affect/bind to enzyme other than at active site; Distorts shape of active site; Inhibitors: Prevent entry of/binding of substrate to active site; Therefore fewer/no enzyme-substrate complexes formed; Describe and explain how an increase in temperature affects the rate of an enzyme controlled reaction. [5] - Correct Answers ✅Rate of reaction increases; Increasing temperature increases rate of movement of molecules/ kinetic energy; Collide more often/substrate enters active site more often/more enzyme-substrate complexes formed; Up to optimum; Rate of reaction decreases; High temperatures cause denaturation/loss of tertiary structure/3D structure; By breaking specified bonds (not peptide bond); Active site altered/substrate cannot bind/fit/

Question & Answers 2024

An enzyme catalyses only one reaction. Explain why [2] - Correct Answers ✅(Enzyme has) active site; Only substrate fits (the active site); Describe the induced fit model of enzyme action. [2] - Correct Answers ✅Active site / enzyme not complementary; Active site changes (shape) / is flexible; (Change in enzyme allows) substrate to fit / E-S complex to form; Describe one way that the lock and key model is different from the induced fit model. [1] - Correct Answers ✅Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around substrate / (already) fits the substrate / is complementary (before binding); Explain why the rate of reaction of an enzyme is low away from its optimum pH. [3] - Correct Answers ✅(change in pH) leads to breaking of bonds holding tertiary structure/ changes charge on amino acids; enzyme/protein/active site loses shape/denatured; substrate will not bind with/fit active site; fewer/no ES complexes formed; A protein molecule contains 150 amino acids. What is the total number of peptide bonds in this molecule? [1] - Correct Answers ✅ 149

Question & Answers 2024

How do you calculate magnification? [1] - Correct Answers ✅M= I (Image)/ A (actual size) Describe the ways in which prokaryotic cells and eukaryotic cells differ. [3] - Correct Answers ✅Prokaryotic cells do not have a nucleus / have genetic material in cytoplasm; DNA in loop / ring; Not associated with proteins / do not have chromosomes /chromatin / do not divide by mitosis; Smaller ribosomes; No membrane-bound organelles; Such as mitochondria / lysosomes / endoplasmic reticulum / Golgi / chloroplasts; Prokaryotic cells may have mesosomes; Prokaryotic cells smaller; May be enclosed by capsule; What is the function of: a)Ribosome b)Smooth ER c)Golgi apparatus d) Chloroplast e)Mitochondria [5] - Correct Answers ✅a)Protein synthesis b)Lipid synthesis and transport c)Processing and packaging proteins for secretion d)Photosynthesis e)Aerobic respiration to produce ATP Explain the advantages and limitations of using a transmission electron microscope [5] - Correct Answers ✅Advantages: Small objects can be seen; TEM has high resolution as wavelength of electrons shorter; Limitations: Cannot look at living cells as cells must be in a vacuum; must cut section / thin specimen; Preparation may create artefact; Does not produce 3D or colored image;

Question & Answers 2024

Why an electron microscope can be used to produce images [2] - Correct Answers ✅EM gives high resolution due to short wavelength of electrons; Explain how viruses cause damage to cells. [3] - Correct Answers ✅uses / breaks up / digests host nuclear / genetic material (allow references made to DNA /RNA instead of nuclear /genetic); virus DNA / genetic material inserted into hosts DNA / chromosome / genetic material; host cells amino acids are used to synthesize viral proteins; cell lysis; by enzyme (produced by expressing a virus gene); toxin production; Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells. [5] - Correct Answers ✅Cell homogenisation to break open cells; 1. Accept suitable method of breaking open cells. Filter to remove (large) debris / whole cells; 2. Reject removes cell walls. Use isotonic solution to prevent damage to mitochondria / organelles; Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation; Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments / heavy organelles; Re-spin (supernatant / after nuclei / pellet removed) at higher speed to get mitochondria in pellet / at bottom.

Question & Answers 2024

Name two structures present in eukaryotic cells that are not present in the cells of prokaryotes. [2] - Correct Answers ✅Nucleus; mitochondria; chloroplast, Golgi, RER; SER; centrioles Describe the fluid-mosaic structure of a cell surface membrane.(5/ marks) - Correct Answers ✅Phospholipids and proteins; Phospholipid bilayer; Arrangement of phospholipid molecules 'Tails to tails';'Floating'(protein) molecules / molecules can move in membrane;Intrinsic proteins extend through bilayer; Extrinsic proteins in outer layer only;(Ref. to intrinsic and extrinsic, unqualified, gains 1 mark);Detail of channel proteins / protein shapes / glycoproteins;Presence of cholesterol between phospholipids. Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells.(6/10 marks) - Correct Answers ✅1. Non-polar/lipid soluble molecules move through phospholipid layer/bilayer;2. Small molecules/water/gases move through phospholipid layer/bilayer;3. Ions/water soluble substances move through channels in proteins;4. Some proteins are gated;5. Reference to diffusion;6.Carriers identified as proteins;7. Carriers associated with facilitated diffusion;8. Carriers associated with active transport/transport with ATP/pumps;9. Different cells have different proteins;10. Correct reference to cytosis; Describe the role of the enzymes of the digestive system in the complete breakdown of starch. (6 marks) - Correct Answers ✅1.

Question & Answers 2024

Amylase;2. (Starch) to maltose:3. Maltase;4. Maltose to glucose;5. Hydrolysis;6. (Of) glycosidic bond; Explain how the small intestine is adapted to its function in the absorption of the products of digestion. (6/9 marks) 1. - Correct Answers ✅Large surface area provided by villi / microvilli;2. long / folds increase surface area / time for absorption;3. thin epithelium;4. short diffusion pathway;5. capillary network absorbs amino acids / sugars;6. lacteal for absorption of digested fats;7. Maintains a steep concentration gradient;8. mitochondria supply ATP / energy for active transport;9. carrier proteins (in membranes); Describe and explain the role of diffusion in the absorption of digested food by the ileum. (4 marks) - Correct Answers ✅1. movement along / down concentration gradient;2. monoglycerides / micelles/fatty acids move into epithelial cells;3. monoglycerides move from epithelium into blood;4. chylomicrons move into lacteals / lymph; Describe and explain the role of facilitated diffusion in the absorption of digested food by the ileum. (3 marks) - Correct Answers ✅1. movement along / down concentration gradient;2. reference to carrier / channel proteins;3. monosaccharides or named / amino acids move into epithelial cells;

Question & Answers 2024

Describe and explain the role active transport in the absorption of digested food by the ileum.(4/6 marks) - Correct Answers ✅1. movement against concentration gradient;2. energy / ATP required;3. reference to carrier proteins;4. monosaccharides or named / amino acids moved into epithelial cells;5. reference to co-diffusion e.g. glucose and NaCl;6. monosaccharides or named / amino acids move into blood Describe how the structure of DNA is related to its function (4/7marks)

• Correct Answers ✅1. Sugar-phosphate backbone: provides stability & protects bases 2. Double stranded: replication can occur semi-conservatively where each strand can act as template making replication more accurate 3. Complementary base pairing (A-T and G-C) makes replication more accurate 4. Individual hydrogen bonds are weak: easily unzip DNA for replication 5. Many hydrogen bonds in the DNA molecule: stable 6. Long molecule: can store lots of information7. Helix/coiled: compact; Compare DNA Vs RNA (6/ 10marks) - Correct Answers ✅Similarities: Contain phosphate Made up of nucleotides Contains organic bases (A, C and G) (not T as it is replaced by U in RNA) Pentose sugar (3 max) Differences RNA single stranded RNA has non-coding strands (introns) removed Ribose sugar in RNA deoxyribose in DNA U in ribose replaces the T 3 types of RNA, only one DNA Smaller than DNA ( max)

Question & Answers 2024

Explain why specific base pairing is important in DNA replication. ( marks) - Correct Answers ✅identical/exact copies made; same base sequence as original DNA; both strands act as template/complementary base pairing occurs on both strands; The events that take place during interphase and mitosis lead to the production of two genetically identical cells. Explain how. (4 marks) - Correct Answers ✅1. DNA replicated; Reject: DNA replication in the wrong stage 2. (Involving) specific / accurate / complementary base-pairing; Accept: semi conservative replication 3. (Ref to) two identical / sister chromatids; 4. Each chromatid / moves / is separated to (opposite) poles / ends of cell. Note: sister chromatids move to opposite poles / ends = 2 marks for mp 3 and mp 4 Reject: meiosis / homologous chromosomes / crossing over or events in wrong stage Describe the features which would help you to recognise when a cell is in i) metaphase of mitosis; ii) in anaphase of mitosis (4/6 marks) (i) - Correct Answers ✅Chromosomes or chromatids on equator / in middle of cell; Of spindle (once); No nuclear membrane (once only). (ii) Chromatids moving towards poles / centrioles;of spindle (once);Two centromeres per chromosome/ centromeres are being pulled; No nuclear membrane (once only). Describe what happens to the chromosomes during each of the following stages of mitosis. Prophase, Metaphase, Anaphase, Telophase (4 marks) - Correct Answers ✅prophase - coil

Question & Answers 2024

up/spiralise/condense; (allow shorter/contract/become visible) metaphase - move to equator or centre of cell / attach to spindle; (reject if reference to pairing) anaphase - chromatids separate/centromeres divide; (reject chromosomes move to poles without further explanation) telophase - uncoil; (allow lengthen/becomes less visible) 4 Mitosis is important in the life of an organism. Give reasons why. ( marks) - Correct Answers ✅1. Growth / increase in cell number; 2. Replace cells / repair tissue / organs /body; 3. Genetically identical cells;

4. Asexual reproduction /cloning; Explain the importance of meiosis in the life cycle of a sexually reproducing organism. (4 marks) - Correct Answers ✅Meiosis halves the number of chromosomes; Restoration of diploid number at fertilisation; Introduces variation;Correct reference to natural selection / survival; Suggest how the proportion of dividing cells in a thin section could be determined.(3 marks) - Correct Answers ✅count cells using microscope; count number of cells in cell division/where chromosomes visible; and then the total number of cells in field of view; Meiosis results in genetic variation in the gametes which leads to variation in the offspring formed by sexual reproduction. Describe how

Question & Answers 2024

meiosis causes this variation and explain the advantage of variation to the species. (6/8 marks) - Correct Answers ✅1. Crossing-over; [IGNORE any wrong ref. to timing] 2. Independent / random assortment / orientation / segregation of (homologous) chromosomes in meiosis I;

3. Independent / random assortment / orientation / segregation of chromatids in meiosis II; + Any three from: 4. Different adaptations / some better adapted; 5. Some survive / example described; 6. To reproduce; 7. Pass on gene / allele; 8. Allows for changing environment / different environment / example described; Describe what happens to chromosomes in meiosis. (6 marks) - Correct Answers ✅1. Chromosomes shorten / thicken / condense; 2. Chromosomes associate in homologous / (described) pairs / formation of bivalents / tetrads; 3. Crossing-over / chiasma formation; 4. Join to spindle (fibres) / moved by spindle;() 5. (At) equator / middle of cell; () 6. (join via) centromere / kinetochore;() 7. (Homologous) chromosomes move to opposite poles / chromosomes separate / move apart; (ALLOW 'are pulled apart') 8. (Pairs of) chromatids separated in 2nd division; () OR " independent assortment" If an organism has a diploid chromosome number of 28 (2n = 28) how many chromosomes will its gametes contain? (1 mark) - Correct Answers ✅ 14

Question & Answers 2024

What is non-disjunction? (1 mark) - Correct Answers ✅Failure of chromosomes to separate properly resulting in daughter cells with wrong number of chromosomes Calculate the possible number of different combinations of chromosomes following meiosis (without crossing over) if parent cell contains 22 chromosomes (1 mark) - Correct Answers ✅211 = 2048 formula 2n Name the lymphocyte present in the Cell-mediated response. - Correct Answers ✅T lymphocytes Name the lymphocyte present in the humoral response. - Correct Answers ✅B Lymphocytes Define the term antigen - Correct Answers ✅An antigen is a molecule (usually protein) that stimulates an immune response resulting in the production of specific antibodies. Describe how a microbe can be broken down by the process of Phagocytosis - Correct Answers ✅Pathogen is engulfed by the phagocyte. Forming a vesicle surrounding the pathogen (called a phagosome). Lysosomes fuse with this vesicle releasing digestive enzymes Lysosome enzymes hydrolyse the proteins and lipids in the

Question & Answers 2024

pathogen. Waste materials are ejected from the cell or presented on cell surface memebrane. What is a monoclonal antibody? - Correct Answers ✅A hybrid cell from tumour/cancer and B-lymphocyte form a hybridoma; Antibodies produced are all the same / from one type of plasma cell; specific to / complementary to / fits only one antigen; Describe how B-lymphocytes respond when they are stimulated by antigens.(4 marks) - Correct Answers ✅divide by mitosis / form clones; produce plasma cells; (plasma cells) make antibodies; (plasma cells) produce memory cells; Describe how the MMR vaccine results in immunity (8 mark) - Correct Answers ✅1 Three different viruses (in vaccine);2 With antigen (on each virus);3 Different for each (virus);4 Macrophage/phagocyte presents antigen;5 Binds to/activates (receptor protein on) T-cells;6 T- cells activate B-cell;7 Antigen binds to receptor on B-cell;8 B-cell divides/ clonal selection;9 Different clone/antibody against each virus;10 Plasma cells/B cells secrete antibody;11 Memory cells formed (B and/or T);12 Vaccine stimuates (primary immune) response; Memory cells give rapid response in future (preventing development of disease/giving immunity);

Question & Answers 2024

Describe how new viruses are produced after HIV has infected a T cell. (4/6 marks) - Correct Answers ✅DNA copy made (of viral RNA);Inserted into host DNA / chromosomes;(Uses viral DNA to) make viral proteins/particles;Makes viral RNA;(Host) cell makes new viruses;"Budding off" / wrapped in cell membrane; Define Mass Flow - Correct Answers ✅Mass flow is the bulk movement of liquids (and gases) due to a pressure difference. Why do mammals have a double circulatory system? - Correct Answers ✅Blood passes twice through the heart for each complete circuit of the body. When blood passes through the lungs the pressure is reduced. Blood returns to the heart to increase the pressure before being circulated to the rest of the body. The thickness of the aorta wall changes all the time during each cardiac cycle. Explain why. (5 marks) - Correct Answers ✅1. (Aorta wall) stretches; 2. Because ventricle/heart contracts / systole / pressure increases; 3. (Aorta wall) recoils; 4. Because ventricle relaxes / heart relaxes /diastole / pressure falls; 5. Maintain smooth flow / pressure Describe how the structure of an artery wall differs from that of a capillary wall in relation to the functions of the two blood vessels. ( marks) - Correct Answers ✅artery has muscle artery has elastic

Question & Answers 2024

tissue to withstand pressure / capillary only one cell thick with pores for exchange Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue - Correct Answers ✅1.Permeable capillary wall/membrane;2. Single cell thick/thin walls, reduces diffusion distance;3. Flattened (endothelial) cells, reduces diffusion distance;4. Fenestrations, allows some larger molecules through; 5. Small diameter/ narrow, gives a large surface area to volume/ short diffusion distance;6. Narrow lumen, reduces flow rate giving more time for diffusion;7. Red blood cells in contact with wall/ pass in single file, gives short diffusion distance / more time for diffusion; Name the main chambers and valves within the heart - Correct Answers ✅Right Atrium, Right Ventricle, Left atrium, Left Ventricle, Atrioventricular valves, Semi-lunar valves. Explain how tissue fluid is formed and how it may be returned to the circulatory system. [5] - Correct Answers ✅1. (hydrostatic) pressure of blood high at arterial end;2. fluid/water/soluble molecules pass out (reject plasma);3. proteins/large molecules remain;4. this lowers the water potential / water potential becomes more negative (inside the capillary);5. water moves back into venous end of capillary (reject tissue fluid);6. by osmosis;7. lymph system collects any excess

Question & Answers 2024

tissue fluid;8. (lymph) returns to blood / circulatory system / link with vena cava/ returns tissue fluid to vein; Describe the events in the cardiac cycle (6marks) - Correct Answers ✅1) Blood enters atrium - Blood volume increases pressure in atrium- Pressure in atrium greater than in ventricl- atrioventricular valve opens.

• Atrium muscles contract- Further increases pressure- Remaining blood forced into ventricles2) Blood enters ventricle- increase in volume of blood increases the pressure in the ventricles- Pressure in ventricle greater than in atrium- atrioventricular valve closes. 3) Ventricle muscles contract- increasing pressure further in ventricle until greater than in aorta/ pulmonary artery- Semi Lunar valve opens.- Blood enters aorta/ pulmonary artery- Blood is pumped to body (left) or lungs (right)4) Ventricle muscles relax- Pressure in ventricle is less than in aorta/ pulmonary artery- Semi lunar valves close How is the cardiac cycle controlled? (6marks) - Correct Answers ✅(SAN) myogenic; Electrical Impulse (spreads over atria and) produces atrial contraction; Delay at AVN; Electrical impulse is prevented from passing to the ventricles by non-conducting tissue Allowing atria to empty before ventricles contract; Impulse to base of ventricles; Contraction of ventricles from base up Describe and explain the mechanism that causes forced expiration. ( marks) - Correct Answers ✅1. Contraction of internal intercostal muscles 2. Relaxation of diaphragm muscles/Relaxation of external

Question & Answers 2024

intercostal muscles; 3. Causes decrease in volume of chest/thoracic cavity; 4. Air pushed down pressure gradient; Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them. (5 marks) - Correct Answers ✅1 Many alveoli/ alveoli walls folded provide a large surface area;2 Many capillaries provide a large surface area;3 (So) fast diffusion;4 Alveoli or capillary walls/ epithelium/ lining are thin/one cell thick/short distance between alveoli and blood; 5 Flattened/ squamous epithelium6(So) short diffusion distance/ pathway;7 (So) fast diffusion;8 Ventilation / circulation; 9 Maintains a diffusion / concentration gradient; Explain how two features of gills allow efficient gas exchange. - Correct Answers ✅Filaments/lamellae provide large surface area; Thin/flattened epithelium/ one/two cell layers so short diffusion pathway (between water and blood); Countercurrent/blood flow maintains concentration/diffusion gradient; Describe how the insect is adapted to ensure minimal water loss and explain how these adaptations help minimise water loss. (4 marks) - Correct Answers ✅1 Exoskeleton / cuticle / outer covering of insect; 2 is waterproof;3 Insect has a small surface area to volume ratio;

4. which reduces the area over which water can be lost;5 Spiracles can be closed; 6 to prevent water loss from the spiracles;

Question & Answers 2024

Explain how a concentration gradient occurs and how this ensures efficient gas exchange in insects (3 marks) - Correct Answers ✅1. Respiring cells use up oxygen; 2. Oxygen concentration decreases towards the end of the tracheoles; 3. So oxygen diffuses down a concentration gradient from the tracheae along the tracheoles to the respiring cells. Haemoglobin is described as a quaternary protein, what is meant by this? - Correct Answers ✅composed of four polypeptide chains, each containing a haem group. Describe how the structure of haemoglobin makes it effective in the transport of oxygen. (4 marks) - Correct Answers ✅quaternary structure, haem groups bind oxygen, four polypeptide chains so four haem groups ,one haemoglobin molecule can bind 4 oxygen molecules / 8 oxygen atoms ,Bohr effect / oxygen release in the presence of carbon dioxide/acidic pH Describe how haemoglobin is involved in absorbing oxygen in the lungs and transporting it to respiring tissues. (6 marks ) - Correct Answers ✅1. diffusion of oxygen into haemoglobin in red blood cells; 2. high affinity of haemoglobin in high partial pressure of oxygen 3. loads / becomes saturated in lungs / at high ppÓ oxygen; 4. oxyhaemoglobin formed; 5. unloads / low affinity in low partial pressure of oxygen; 6.

Question & Answers 2024

respiration in tissues gives high CÓ concentration / high temperature/ high H+ concentration / low pH 7. dissociation curve shifts to right / 8. oxyhaemoglobin dissociation at higher partial pressure of carbon dioxide. During exercise the oxygen-haemoglobin dissociation curve moves to the right, describe the advantage of this change - Correct Answers ✅(Haemoglobin) releases more oxygen; For respiration; The tissues of a mouse have a higher rate of oxygen consumption per gram of body tissue than an elephant. Sketch the oxygen dissociation curve for both animals and explain the advantage of the position of the mouse curve. - Correct Answers ✅Both curves drawn as sigmoidal curves with the mouse to the right. (at the tissues at low pp oxygen) the mouse haemoglobin is less saturated with oxygen / has reduced affinity; oxyhaemoglobin dissociates more readily / haemoglobin releases oxygen more readily / more oxygen released; allowing greater demand /respiration rate; Describe how a high pressure is produced in the phloem near photosynthesising leaves (3 marks) - Correct Answers ✅Sucrose AT into sieve tube, water potential becomes lower , water enters phloem by osmosis from xylem and increased volume increases pressure

Question & Answers 2024

How could you measure water uptake in mm3 per minute by a plant? (3 marks) - Correct Answers ✅Potometer, as water moves up plant, an air bubble is moved along scale, need to measure distance, diameter of capillary tube and time. What factors effect transpiration rate? (4 marks) - Correct Answers ✅Light intensity, temperature, humidity and wind speed. Give the names of experiments which support mass flow hypothesis - Correct Answers ✅Ringing, radioactive tracers Describe the mass flow hypothesis for the mechanism of translocation in plants. (4/5 marks) - Correct Answers ✅1. In source / leaf sugars actively transported into phloem; 2. By companion cells; 3. Lowers water potential of sieve cell / tube and water enters by osmosis;

4. Increase in pressure causes mass movement (towards sink / root); 5. Sugars used / converted in root for respiration for storage. Explain why the diameter of the trunk is smallest at midday. (6 marks) - Correct Answers ✅. Diameter of trunk minimal at warmest / brightest time of day / midday = warmest / brightest; 2. Stomata open in light → more water loss; 3. Water evaporates more when warm / more heat energy for water evaporation; 4. Hydrogen-bonding between water molecules / cohesion ( / described) between water molecules; 5. Adhesion (described) between water molecules and walls

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of xylem vessels; 6. (Xylem) pulled inwards by faster flow of water / pulled in by tension; Give three difference between prokaryotic DNA and eukaryotic DNA (3 marks) - Correct Answers ✅DNA of prokaryotes, is short, circular and not associated with protein. What are exons? (1 mark) - Correct Answers ✅Base sequences which code for amino acid sequence in polypeptides Give four features of the genetic code (4 marks) - Correct Answers ✅Triplet, universal, non-overlapping and degenerate Describe how the structure of tRNA differs from mRNA (2 marks) - Correct Answers ✅tRNA has amino acid binding site, complementary base pairing holding folds and it is shorter Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell. (6 marks) - Correct Answers ✅1. Helicase; 2. Breaks hydrogen bonds; 3. Only one DNA strand acts as template; 4. RNA nucleotides attracted to exposed bases; 5. (Attraction) according to base pairing rule; 6. RNA polymerase joins (RNA) nucleotides together; 7. Pre-mRNA spliced to remove introns.

Question & Answers 2024

How are new alleles of a gene produced? (1 mark) - Correct Answers ✅Mutation What is directional selection? (1 mark) - Correct Answers ✅Selection for ONE extreme/mean shifts over time Explain how antibiotic resistant strains of bacteria are produced? (3 marks) - Correct Answers ✅Mutation occurs producing resistance allele, bacteria with this allele survive and reproduce, passing on this allele. Frequency of allele increases over time. What is genetic diversity? (1 mark) - Correct Answers ✅All the different alleles of all genes in a population What type of variation is shown by human height? (1 mark) - Correct Answers ✅Continuous variation - range of values/not discrete categories/ many categories/no gaps; Give two possible causes of this variation that result from meiosis during gamete formation.(2 marks) - Correct Answers ✅Crossing over / chiasmata; Random segregation / independent assortment; In meiosis I and meiosis II;

Question & Answers 2024

When comparing variation in size between two groups of organisms, it is often considered more useful to compare standard deviations rather than ranges. Explain why.(2 marks) - Correct Answers ✅Range influenced by single 'outlier' (accept anomaly) / converse for S.D.; S.D. shows dispersion/spread about mean; Range only shows highest and lowest values/extremes; S.D. allows statistical use; Tests whether or not differences are significant; Describe how you would investigate the effect of antibacterial chemicals on the growth of E coli (6 marks) - Correct Answers ✅Aseptic technique/sterile agar plate, flame neck of culture bottle; Spread plate/controlled volume of bacteria transferred to plate and spread equally across the surface; Controlled volume of antibacterial chemical on to filter paper disc; Disc plated on inoculated agar plate and incubated at 25 degrees C for 2 days; Diameter of the zone of inhibition measured; Repeat measurements and mean calculated; Student T test to investigate significance of any difference between means. Give the hierarchical order of taxa in our classification system (1 mark) - Correct Answers ✅Domain, kingdom, phylum, class, order, family, genus, species How can you tell if two organisms belong to the same species grouping? (1 mark) - Correct Answers ✅Reproduce and produce fertile offspring