Aqa a level biology paper 2 june 2023 question paper (7402-2), Exams of Biology

Download Aqa a level biology paper 2 june 2023 question paper (7402-2) and more Exams Biology in PDF only on Docsity! Aqa a level biology paper 2 june 2023 question paper (7402/2) acetylation of DNA - ansacetyl groups added to histones, so DNA is less tightly wound round it, making it easier for RNA polymerase and transcriptional factors to bind, so transcription can occur. allopatric speciation - ansWhen populations of a species become geographically isolated. Gene flow between them ceases (reproductive isolation). the new environment will trigger a change in the gene pool due to natural selection imposed on them. If the populations are relatively small, they may experience a founder effect. Selection and genetic drift will act differently on these two different genetic backgrounds, creating genetic differences between the two new species. codominance - ansoccurs where heterozygote has a phenotype that is different from both homozygotes. neither allele is dominant over the other; they both contribute equally to the phenotype. define biomass - ansthe total mass of organisms in a given area define community. - ansall the populations of different species living and interacting in a particular place at the same time. define niche. - ansthe role and position a species has in its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic factors of its environment. define population. - ansa group of individuals of one species that occupy the same habitat at the same time and are potentially able to interbreed. describe and explain the role of hormones in osmoregulation. - ans1.osmoreceptors in hypothalamus detect fall in water potential as they begin to shrink, causing hypothalamus to produce ADH. 2. ADH goes to posterior pituitary gland, where it is secreted into capillaries. 3. ADH goes from blood to kidneys, where it binds to receptors on the cells of of distil convoluted tubule and collecting duct. 4. this activates phosphorylase enzyme. 5. this causes vesicles, which contain water channel proteins, to fuse with cell surface membrane. hence, making it more permeable to water. 6. also increases permeability of collecting duct to urea so it passes out and lowers water potential, so more water can pass out by osmosis. describe and explain the steps in the light dependent reaction of photosynthesis - ans1. photoionisation: light reaches chlorophyll in PSII, which is absorbed by an electron, which becomes excited and moves to a higher energy level. 2. the electron passes to a carrier protein in the thylakoid membrane, and is passed down a series of carrier molecules called an electron transfer chain. 3. as the electron moves down, energy is lost from the electron and is released as ATP. 4. the loss of electron from PSII is 'refilled' by an electron produced by photolysis, which also produces hydrogen and oxygen. 5. the lost electron reaches PSI, which absorbs light energy and boosts another electron to a higher energy level (excitation). 6. this electron also goes down an electron transport chain. 7. this reaches the final electron acceptor which is a proton. they combine to form H and reduce NADP to NADPH. describe and explain the steps in the light independent reaction pf photosynthesis. - ans1. CO2 diffuses into stroma and combines with ribulose bisphosphate (RuBP) using the enzyme rubisco. 2. this forms an unstable 6 carbon molecule, which splits into 2 3 carbon molecules, glyercate-3- phosphate (G3P) . 3. G3P is reduced by NADPH to triose-phosphate (TP), which is aided by ATP for energy. 4. TP can be converted into useful organic substances. Aqa a level biology paper 2 june 2023 question paper (7402/2) 5. TP can also be reformed into RuBP using ATP. describe fast twitch fibres - anscontract more rapidly and more powerful but over a shorter period of time. adapted for intense exercise have thicker and more numerous myosin filament, have more glycogen, have more enzymes to carry out anaerobic respiration, has phosphocreatine. describe glycolysis in respiration. give net formation. - ans1. glucose is converted into phosphorylated glucose by 2ATP. this makes it very reactive, so it splits into 2 triose phosphate (TP). 2. 2TP is then oxidised by 2NAD and 4 ATP is formed to form pyruvate. 3. NET: 2ATP, 2Pyruvate, 2NADH, 2H+ describe krebs cycle in respiration. give net formation. - ans1. acetyl co-enzyme A combines with 4 carbon molecule (oxaloacetate) to form 6 carbon citric acid. 2. CO2 is lost (decarboxylation), molecule is oxidised by NAD and ATP is produce. this forms 5 carbon compound. 3. it is oxidised by 2NADH and FAD, and is decarboxylated. 4. this forms 4 carbon molecule again. describe links reaction in respiration. give net formation. - ans1. pyruvate diffuses into the matrix of mitochondria. 2. pyruvate is oxidised by NAD. CO2 is lost. this forms acetate. 3. acetate and co-enzyme A combine to form acetyl co-enzyme A. 4. NET: CO2, reduced NAD, acetyl co-enzyme A describe oxidative phosphorylation in respiration. - ans1. reduced coenzyme passes its H to a carrier protein in the ETC. this splits into a proton and electron. 2. the protons pass through the space between inner and outer mitochondrial membrane. 3. electrons pass through proteins on ETC. 4. protons return back via ATP synthase in the membrane, producing ATP. 5. the protons and electrons recombine to form H, which combines with O to form water. 6. oxygen is the last electron acceptor in the ETC. describe slow twitch fibres - anscontract more slowly and provide less powerful contractions but over a longer period. adapted for aerobic respiration to avoid lactic acid build up. adapted for endurance work. has lots of myoglobin, rich bloody supply and many mitochondria. describe the components of a reflex arc and give an example. - ans1. stimulus- heat 2. receptor- heat receptors to sensory neurone 3. sensory neurone- impulse to spinal cord 4. relay neurone- to motor neurone 5. motor neurone- spinal cord to muscle 6. effector- muscle in arm contracts 7. response- pulling hand away from heat describe the control of gravitropism by IAA. - ans1. root tip cells produce IAA, which is distributed evenly and down the root. 2. gravity causes IAA to accumulate on the LOWER side of the shoot than upper side, so there is a higher concentration on lower than upper. 3. IAA inhibits elongation in root cells, so inhibits elongation in lower side than upper side. so, the upper side of the shoot elongates further and bends towards gravity. Aqa a level biology paper 2 june 2023 question paper (7402/2) example of kinesis - answoodlice increase rate of movement/turning when they reach a dry area. this will allow them to reach a favourable damp area, where they don't turn as much. example of taxis - ansearthworms have negative phototaxis and so stay deeper in soil to aid their chances of survival, so they are more likely to find food, avoid predators, and conserve water. explain how chemoreceptors control heart rate. - ans1. chemoreceptors in the walls of the carotid arteries are sensitive in changes of pH. when they detect a lower pH (high CO2) then more impulses are sent to the specific heart rate increasing centre in the medulla oblongata. 2. this centre increases frequency of impulses to the sinoatrial node via sympathetic NS. this increases rate of electrical waves being produced. 3. increased heart rate results in increased blood flow, so more CO2 is removed by lungs and CO2 levels return to normal. pH rises to normal. 4. chemoreceptors reduce frequency of impulses, medulla oblongata reduces frequency of impulses. heart rate returns to normal. explain how the loop of henle acts as a counter current multiplier. - answater in the loop of henle meets water in the interstitial space which is of a lower water potential, and so water can pass out by osmosis for the whole length of the descending tube and collecting duct. explain how to produce DNA fragments with restriction endonucleases. - ans1. cuts gene at recognition site. this can result in blunt or sticky ends. 2. promotor gene and terminator gene also inserted. marker genes too. 3. same RE cut out complimentary recognition site in plasmid (vector). 4. DNA ligase is used to bind the nucleotides of the two DNA strands together. 5. plasmids introduced to host organisms. bacteria mixed with plasmids with calcium ions. explain how to produce DNA fragments with reverse transcriptase. - ans1. reverse transcriptase forms cDNA from an mRNA strand. 2. single stranded cDNA is isolated when mRNA is hydrolysed with an enzyme. 3. cDNA acts as a template for DNA nucleotides to bind to by complimentary base pairing. DNA polymerase joins them together. a copy of the gene is now formed. explain the role of hormones in osmoregulation - ans1. osmoreceptors in the hypothalamus detect fall in water potential. this causes water to be lost from osmoreceptors. 2. this makes them produce ADH, which goes to pituitary gland to pass into blood. 3. ADH goes to kidneys and binds to surface of DCT ad collecting duct, activating phosphorylase. this causes vesicles to fuse with membrane and form aquaporins. 4. ADH increases permeability to urea, which passes out and decreases WP in interstitial space. this causes water to leave by osmosis, so more water is reabsorbed. explain the steps of genetic fingerprinting. - ans1. extract DNA. quantity of DNA may be increased by PCR. 2. restriction endonucleases cut DNA into fragments. 3. gel electrophresis. dna put onto agar gel, voltage is applied across it. smaller fragments mover further than larger fragments. 4. DNA hybridisation- DNA probes have complimentary base sequences to non-coding DNA, and so bind under specific conditions. 5. X-ray film is exposed to radiation from probes. this film is put over a nylon membrane. a series of bars is shown which corresponds to the movement of the fragments. formula to calculate the mean density of individuals from quadrats - anstotal no of individuals counted ------------------------------------ no of quadrats x area of quadrat Aqa a level biology paper 2 june 2023 question paper (7402/2) gluconeogenesis - ansproduction of glucose from sources other than carbohydrates, such as glycerol or fatty acids. occurs when there's insufficient glycogen. glycogenesis - ansconversion of glucose to glycogen. this is when glucose levels are abnormally high. glycogenolysis - ansbreakdown of glycogen to glucose. this is when glucose levels are abnormally low. Hardy-Weinberg principle - ansp2 + 2pq + q2 p2 = homozygous dominant q2 = homozygous recessive 2pq = heterozygous In any hardy-weinberg problem, start with homozygous recessive individuals. homeostasis - ansthe maintenance of an internal environment within restricted limits in organisms. all cells are in an environment that meets their requirements and allows them to function normally despite external changes. how are DNA probes used to identify alleles? - ans1. DNA probes are made so that they are complimentary to part of the base sequence of the allele. 2. double-stranded DNA is treated so it becomes 2 separate strands. 3. the separated strands are mixed with the probes, which bind to the complimentary sites. this is DNA hybridisation. 4. the site at which it binds to can be identified as it will emit radioactivity or fluorescence. how can a population be separated and form different species? - ans1. Populations become separated. physical barriers may come between two groups. 2. Therefore they stop interbreeding. 3. Populations adapt to new environment. Selection pressures will be different in different areas. 4. Allele frequencies will change in the different populations. 5. Over time they become so different that they can no longer interbreed. how can you calculate the net primary production? - ansNPP = GPP - R how do drugs affect synaptic transmission and action potentials? - ans1. stimulate the nervous system by mimicking neurotransmitters, stimulating neurotransmitter release or inhibiting enzymes that break down neurotransmitters, and so create more action potentials. 2. inhibit the nervous system by inhibiting release of neurotransmitter or blocking Na+/K+ channels on postsynaptic neurone, hence creating less action potentials. how does glucagon and alpha cells in the pancreas affect glucose levels? - ans1. alpha cells detect a fall in blood glucose levels and so secrete glucagon. 2. glucagon attaches to receptors on cell surface membrane of liver cells. 3. this activates enzymes which convert glycogen to glucose. 4. also activates enzymes that convert amino acids to glucose. how does insulin and beta cells in the pancreas affect glucose levels? - ans1. the beta cells in the pancreas detect a rise in the blood glucose concentration and respond by secreting insulin into blood. 2. insulin binds to glycoprotein receptors on cells. 3. this causes a change in the tertiary structure of the glucose transport proteins, making them more permeable to glucose and so allowing more in by facilitated diffusion. 4. activates the enzymes that convert glucose to glycogen and fat. Aqa a level biology paper 2 june 2023 question paper (7402/2) how does the distil convoluted tubule reabsorb material from the filtrate? - ansthe cells lining the DCT have microvilli and mitochondria. it selects which ions to reabsorb. this controls the pH of the filtrate. how does the loop of henle concentrate urine? - ans1. filtrate enters descending limb. water passes out by osmosis and into the interstitial space as the walls are permeable. Na+ actively transported in. 2. this lowers water potential. lowest water potential is at the bottom of the hairpin. 3. at the ascending limb, the walls are not permeable to water and so it cant leave. Na+ is actively transported out into the interstitial space. this creates a higher water potential. 4. interstitial space between collecting duct and ascending limb has a wp gradient, from high to low, and so any water left passes out. how is glucose reabsorbed in the proximal convoluted tubule? - ansNa+ actively transported out of cells lining the PCT, into blood capillaries, which carry them away. Na+ diffuse down concentration gradient from the PCT into the epithelium by facilitated diffusion- cotransport. the molecules in the PCT then diffuse into blood, so they are reabsorbed. how many types of rod and cone cells are there? - ansrod- 1 cone- 3, all responding to different wavelengths induced pluripotent stem cells - ansproduced from unipotent cells. genetically altered in labs (transcription factors) to make them have the characteristics of embryonic stem cells. they turn on the genes that were otherwise turned off. linked genes - ansgenes on the same chromosome list the parts of control mechanisms in homeostasis. - ans1. optimum temperature 2. receptor- detects any deviation from the optimum temperature 3. coordinator- info from receptor to effector 4. effector- often a muscle/gland, brings about change to return the system to optimum level 5. feedback mechanism list the steps in osmoregulation - ans1. Ultrafiltration in Bowmans capsule 2. reabsorption in the proximal convoluted tubule 3. concentration in the loop of henle distil convoluted tubule methylation of DNA - ansaddition of methyl groups to bases. added throughout life, sometimes in response to environmental factors e.g. diet. causes the DNA to wrap more tightly around histones, so transcriptional factors cannot bind to specific DNA sites and initiate transcription. multiple alleles - ansthis is where there are several different alleles of a gene e.g. blood type: IA, IB (codominant), and IO (recessive). multipotent cells - anscan divide into some, but not all, specialized cells. name the negative effects of using nitrogen containing fertilisers. - ans1. reduced species diversity 2. leaching 3. eutrophication oncogenes - ansmutated proto-oncogenes form oncogenes. oncogenes are permanently activated (switched off). pluripotent cells - anscan become any kind of specialized body cell, but cannot divide to form a whole organism. sex linkage - ansalleles carried on the X chromosome. Aqa a level biology paper 2 june 2023 question paper (7402/2) where are rod cells more highly distributed at? - ansperiphery of the retina which region of the brain controls the changes in heart rate? - ansmedulla oblongata why are sex linked diseases more common in males than females? - ansbecause males only have one X chromosome, and so if there is a recessive allele there, then there will be no dominant allele on Y chromosome to "hide" it. why do action potentials travel faster down a myelinated axon? - ansmyelin sheath prevents action potentials forming. action potentials form at the Nodes of Ranvier, and jump from node to node by saltatory conduction. in an unmyelinated axon, it takes longer as the events of depolarisation take place all the way along an axon. why do cone cells give high visual acuity? - anseach cell is connected to a separate bipolar cell. if 2 separate rod cells are stimulated by light, then 2 separate impulses will be sent to the brain. so, the brain can distinguish between two sources of light that stimulate two different rod cells, hence better resolution, hence better visual acuity. why do rod cells give poor visual acuity? - ansmany rod cells link to the same bipolar cells (spatial summation), so when light stimulates rod cells which share the same neurone, only 1 impulse will travel to the brain. so, the brain can't distinguish between separate sources of light that stimulated them. resolution is poor, hence low visual acuity. why does using nitrogen containing fertilisers result in reduced species diversity? - ansnitrogen rich soils favour the growth of grasses etc., which can outcompete other species, which die as a result. why is converting sunlight energy into biomass in producers inefficient? - anssome light isn't the correct wavelength to be absorbed some light doesnt hit chloroplast some light is converted into heat energy some light energy is reflected why is homeostasis important? - ans1. the enzymes that control biochemical reactions in cells are sensitive to change e.g. in pH or temperature, which can cause them to denature. homeostasis allows enzyme controlled reactions to take place at a suitable rate. 2. homeostasis allows a constant blood glucose concentration to ensure a constant water potential, so cells don't shrink or burst. 3. homeostasis allows organisms to be more independent of external changes. acetylation of DNA - ansacetyl groups added to histones, so DNA is less tightly wound round it, making it easier for RNA polymerase and transcriptional factors to bind, so transcription can occur. allopatric speciation - ansWhen populations of a species become geographically isolated. Gene flow between them ceases (reproductive isolation). the new environment will trigger a change in the gene pool due to natural selection imposed on them. If the populations are relatively small, they may experience a founder effect. Selection and genetic drift will act differently on these two different genetic backgrounds, creating genetic differences between the two new species. codominance - ansoccurs where heterozygote has a phenotype that is different from both homozygotes. neither allele is dominant over the other; they both contribute equally to the phenotype. define biomass - ansthe total mass of organisms in a given area Aqa a level biology paper 2 june 2023 question paper (7402/2) define community. - ansall the populations of different species living and interacting in a particular place at the same time. define niche. - ansthe role and position a species has in its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic factors of its environment. define population. - ansa group of individuals of one species that occupy the same habitat at the same time and are potentially able to interbreed. describe and explain the role of hormones in osmoregulation. - ans1.osmoreceptors in hypothalamus detect fall in water potential as they begin to shrink, causing hypothalamus to produce ADH. 2. ADH goes to posterior pituitary gland, where it is secreted into capillaries. 3. ADH goes from blood to kidneys, where it binds to receptors on the cells of of distil convoluted tubule and collecting duct. 4. this activates phosphorylase enzyme. 5. this causes vesicles, which contain water channel proteins, to fuse with cell surface membrane. hence, making it more permeable to water. 6. also increases permeability of collecting duct to urea so it passes out and lowers water potential, so more water can pass out by osmosis. describe and explain the steps in the light dependent reaction of photosynthesis - ans1. photoionisation: light reaches chlorophyll in PSII, which is absorbed by an electron, which becomes excited and moves to a higher energy level. 2. the electron passes to a carrier protein in the thylakoid membrane, and is passed down a series of carrier molecules called an electron transfer chain. 3. as the electron moves down, energy is lost from the electron and is released as ATP. 4. the loss of electron from PSII is 'refilled' by an electron produced by photolysis, which also produces hydrogen and oxygen. 5. the lost electron reaches PSI, which absorbs light energy and boosts another electron to a higher energy level (excitation). 6. this electron also goes down an electron transport chain. 7. this reaches the final electron acceptor which is a proton. they combine to form H and reduce NADP to NADPH. describe and explain the steps in the light independent reaction pf photosynthesis. - ans1. CO2 diffuses into stroma and combines with ribulose bisphosphate (RuBP) using the enzyme rubisco. 2. this forms an unstable 6 carbon molecule, which splits into 2 3 carbon molecules, glyercate-3- phosphate (G3P) . 3. G3P is reduced by NADPH to triose-phosphate (TP), which is aided by ATP for energy. 4. TP can be converted into useful organic substances. 5. TP can also be reformed into RuBP using ATP. describe fast twitch fibres - anscontract more rapidly and more powerful but over a shorter period of time. adapted for intense exercise have thicker and more numerous myosin filament, have more glycogen, have more enzymes to carry out anaerobic respiration, has phosphocreatine. describe glycolysis in respiration. give net formation. - ans1. glucose is converted into phosphorylated glucose by 2ATP. this makes it very reactive, so it splits into 2 triose phosphate (TP). 2. 2TP is then oxidised by 2NAD and 4 ATP is formed to form pyruvate. 3. NET: 2ATP, 2Pyruvate, 2NADH, 2H+ describe krebs cycle in respiration. give net formation. - ans1. acetyl co-enzyme A combines with 4 carbon molecule (oxaloacetate) to form 6 carbon citric acid. Aqa a level biology paper 2 june 2023 question paper (7402/2) 2. CO2 is lost (decarboxylation), molecule is oxidised by NAD and ATP is produce. this forms 5 carbon compound. 3. it is oxidised by 2NADH and FAD, and is decarboxylated. 4. this forms 4 carbon molecule again. describe links reaction in respiration. give net formation. - ans1. pyruvate diffuses into the matrix of mitochondria. 2. pyruvate is oxidised by NAD. CO2 is lost. this forms acetate. 3. acetate and co-enzyme A combine to form acetyl co-enzyme A. 4. NET: CO2, reduced NAD, acetyl co-enzyme A describe oxidative phosphorylation in respiration. - ans1. reduced coenzyme passes its H to a carrier protein in the ETC. this splits into a proton and electron. 2. the protons pass through the space between inner and outer mitochondrial membrane. 3. electrons pass through proteins on ETC. 4. protons return back via ATP synthase in the membrane, producing ATP. 5. the protons and electrons recombine to form H, which combines with O to form water. 6. oxygen is the last electron acceptor in the ETC. describe slow twitch fibres - anscontract more slowly and provide less powerful contractions but over a longer period. adapted for aerobic respiration to avoid lactic acid build up. adapted for endurance work. has lots of myoglobin, rich bloody supply and many mitochondria. describe the components of a reflex arc and give an example. - ans1. stimulus- heat 2. receptor- heat receptors to sensory neurone 3. sensory neurone- impulse to spinal cord 4. relay neurone- to motor neurone 5. motor neurone- spinal cord to muscle 6. effector- muscle in arm contracts 7. response- pulling hand away from heat describe the control of gravitropism by IAA. - ans1. root tip cells produce IAA, which is distributed evenly and down the root. 2. gravity causes IAA to accumulate on the LOWER side of the shoot than upper side, so there is a higher concentration on lower than upper. 3. IAA inhibits elongation in root cells, so inhibits elongation in lower side than upper side. so, the upper side of the shoot elongates further and bends towards gravity. describe the control of heart rate by pressure receptors. - ans1. when blood pressure is higher than normal, pressure receptors in carotid arteries send more impulses to centre in medulla oblongata that decreases heart rate via parasympathetic NS. 2. when blood pressure is lower than normal, pressure receptors send more impulses to the centre of the medulla oblongata that increases heart rate via sympathetic NS. describe the control of phototropism by IAA. - ans1. cells in shoot tip produce IAA which is transported evenly throughout all regions and then down the shoot. 2. light causes IAA to accumulate on the shaded side of the shoot, so much that there is a greater build up of IAA on shaded than unshaded side. 3. IAA causes the shaded side of the shoot to elongate further than the non shaded side. this causes the shoot to eventually grow and bend towards the light. describe the formation of glomerular filtrate by ultrafiltration - ansblood enters Bowmans capsule. the walls of glomerular capillaries are made up of epithelial cells. high hydrostatic pressure in glomerulus. Aqa a level biology paper 2 june 2023 question paper (7402/2) explain how the loop of henle acts as a counter current multiplier. - answater in the loop of henle meets water in the interstitial space which is of a lower water potential, and so water can pass out by osmosis for the whole length of the descending tube and collecting duct. explain how to produce DNA fragments with restriction endonucleases. - ans1. cuts gene at recognition site. this can result in blunt or sticky ends. 2. promotor gene and terminator gene also inserted. marker genes too. 3. same RE cut out complimentary recognition site in plasmid (vector). 4. DNA ligase is used to bind the nucleotides of the two DNA strands together. 5. plasmids introduced to host organisms. bacteria mixed with plasmids with calcium ions. explain how to produce DNA fragments with reverse transcriptase. - ans1. reverse transcriptase forms cDNA from an mRNA strand. 2. single stranded cDNA is isolated when mRNA is hydrolysed with an enzyme. 3. cDNA acts as a template for DNA nucleotides to bind to by complimentary base pairing. DNA polymerase joins them together. a copy of the gene is now formed. explain the role of hormones in osmoregulation - ans1. osmoreceptors in the hypothalamus detect fall in water potential. this causes water to be lost from osmoreceptors. 2. this makes them produce ADH, which goes to pituitary gland to pass into blood. 3. ADH goes to kidneys and binds to surface of DCT ad collecting duct, activating phosphorylase. this causes vesicles to fuse with membrane and form aquaporins. 4. ADH increases permeability to urea, which passes out and decreases WP in interstitial space. this causes water to leave by osmosis, so more water is reabsorbed. explain the steps of genetic fingerprinting. - ans1. extract DNA. quantity of DNA may be increased by PCR. 2. restriction endonucleases cut DNA into fragments. 3. gel electrophresis. dna put onto agar gel, voltage is applied across it. smaller fragments mover further than larger fragments. 4. DNA hybridisation- DNA probes have complimentary base sequences to non-coding DNA, and so bind under specific conditions. 5. X-ray film is exposed to radiation from probes. this film is put over a nylon membrane. a series of bars is shown which corresponds to the movement of the fragments. formula to calculate the mean density of individuals from quadrats - anstotal no of individuals counted ------------------------------------ no of quadrats x area of quadrat gluconeogenesis - ansproduction of glucose from sources other than carbohydrates, such as glycerol or fatty acids. occurs when there's insufficient glycogen. glycogenesis - ansconversion of glucose to glycogen. this is when glucose levels are abnormally high. glycogenolysis - ansbreakdown of glycogen to glucose. this is when glucose levels are abnormally low. Hardy-Weinberg principle - ansp2 + 2pq + q2 p2 = homozygous dominant q2 = homozygous recessive 2pq = heterozygous In any hardy-weinberg problem, start with homozygous recessive individuals. Aqa a level biology paper 2 june 2023 question paper (7402/2) homeostasis - ansthe maintenance of an internal environment within restricted limits in organisms. all cells are in an environment that meets their requirements and allows them to function normally despite external changes. how are DNA probes used to identify alleles? - ans1. DNA probes are made so that they are complimentary to part of the base sequence of the allele. 2. double-stranded DNA is treated so it becomes 2 separate strands. 3. the separated strands are mixed with the probes, which bind to the complimentary sites. this is DNA hybridisation. 4. the site at which it binds to can be identified as it will emit radioactivity or fluorescence. how can a population be separated and form different species? - ans1. Populations become separated. physical barriers may come between two groups. 2. Therefore they stop interbreeding. 3. Populations adapt to new environment. Selection pressures will be different in different areas. 4. Allele frequencies will change in the different populations. 5. Over time they become so different that they can no longer interbreed. how can you calculate the net primary production? - ansNPP = GPP - R how do drugs affect synaptic transmission and action potentials? - ans1. stimulate the nervous system by mimicking neurotransmitters, stimulating neurotransmitter release or inhibiting enzymes that break down neurotransmitters, and so create more action potentials. 2. inhibit the nervous system by inhibiting release of neurotransmitter or blocking Na+/K+ channels on postsynaptic neurone, hence creating less action potentials. how does glucagon and alpha cells in the pancreas affect glucose levels? - ans1. alpha cells detect a fall in blood glucose levels and so secrete glucagon. 2. glucagon attaches to receptors on cell surface membrane of liver cells. 3. this activates enzymes which convert glycogen to glucose. 4. also activates enzymes that convert amino acids to glucose. how does insulin and beta cells in the pancreas affect glucose levels? - ans1. the beta cells in the pancreas detect a rise in the blood glucose concentration and respond by secreting insulin into blood. 2. insulin binds to glycoprotein receptors on cells. 3. this causes a change in the tertiary structure of the glucose transport proteins, making them more permeable to glucose and so allowing more in by facilitated diffusion. 4. activates the enzymes that convert glucose to glycogen and fat. how does the distil convoluted tubule reabsorb material from the filtrate? - ansthe cells lining the DCT have microvilli and mitochondria. it selects which ions to reabsorb. this controls the pH of the filtrate. how does the loop of henle concentrate urine? - ans1. filtrate enters descending limb. water passes out by osmosis and into the interstitial space as the walls are permeable. Na+ actively transported in. 2. this lowers water potential. lowest water potential is at the bottom of the hairpin. 3. at the ascending limb, the walls are not permeable to water and so it cant leave. Na+ is actively transported out into the interstitial space. this creates a higher water potential. 4. interstitial space between collecting duct and ascending limb has a wp gradient, from high to low, and so any water left passes out. how is glucose reabsorbed in the proximal convoluted tubule? - ansNa+ actively transported out of cells lining the PCT, into blood capillaries, which carry them away. Na+ diffuse down concentration gradient from the PCT into the epithelium by facilitated diffusion- cotransport. the molecules in the PCT then diffuse into blood, so they are reabsorbed. Aqa a level biology paper 2 june 2023 question paper (7402/2) how many types of rod and cone cells are there? - ansrod- 1 cone- 3, all responding to different wavelengths induced pluripotent stem cells - ansproduced from unipotent cells. genetically altered in labs (transcription factors) to make them have the characteristics of embryonic stem cells. they turn on the genes that were otherwise turned off. linked genes - ansgenes on the same chromosome list the parts of control mechanisms in homeostasis. - ans1. optimum temperature 2. receptor- detects any deviation from the optimum temperature 3. coordinator- info from receptor to effector 4. effector- often a muscle/gland, brings about change to return the system to optimum level 5. feedback mechanism list the steps in osmoregulation - ans1. Ultrafiltration in Bowmans capsule 2. reabsorption in the proximal convoluted tubule 3. concentration in the loop of henle distil convoluted tubule methylation of DNA - ansaddition of methyl groups to bases. added throughout life, sometimes in response to environmental factors e.g. diet. causes the DNA to wrap more tightly around histones, so transcriptional factors cannot bind to specific DNA sites and initiate transcription. multiple alleles - ansthis is where there are several different alleles of a gene e.g. blood type: IA, IB (codominant), and IO (recessive). multipotent cells - anscan divide into some, but not all, specialized cells. name the negative effects of using nitrogen containing fertilisers. - ans1. reduced species diversity 2. leaching 3. eutrophication oncogenes - ansmutated proto-oncogenes form oncogenes. oncogenes are permanently activated (switched off). pluripotent cells - anscan become any kind of specialized body cell, but cannot divide to form a whole organism. sex linkage - ansalleles carried on the X chromosome. spatial summation - ansa number of different presynaptic neurones collectively release enough neurotransmitters to exceed the threshold value of the postsynaptic neurone, triggering a new action potential. sympatric speciation - ansbecome reproductively isolated from each other even though they occupy the same geographic range. Factors that could lead to them becoming reproductively isolated from each other are things like changes in courtship behavior, changes in feeding behavior, changes in coloration. The most common way this occurs is polyploidy. Rapid genetic changes can alter morphology, behavior, and habitat preferences. temporal summation - ansa single presynaptic neurone releases neurotransmitters many times over a short period. this exceeds the threshold value, triggering a new action potential. Aqa a level biology paper 2 june 2023 question paper (7402/2) can distinguish between two sources of light that stimulate two different rod cells, hence better resolution, hence better visual acuity. why do rod cells give poor visual acuity? - ansmany rod cells link to the same bipolar cells (spatial summation), so when light stimulates rod cells which share the same neurone, only 1 impulse will travel to the brain. so, the brain can't distinguish between separate sources of light that stimulated them. resolution is poor, hence low visual acuity. why does using nitrogen containing fertilisers result in reduced species diversity? - ansnitrogen rich soils favour the growth of grasses etc., which can outcompete other species, which die as a result. why is converting sunlight energy into biomass in producers inefficient? - anssome light isn't the correct wavelength to be absorbed some light doesnt hit chloroplast some light is converted into heat energy some light energy is reflected why is homeostasis important? - ans1. the enzymes that control biochemical reactions in cells are sensitive to change e.g. in pH or temperature, which can cause them to denature. homeostasis allows enzyme controlled reactions to take place at a suitable rate. 2. homeostasis allows a constant blood glucose concentration to ensure a constant water potential, so cells don't shrink or burst. 3. homeostasis allows organisms to be more independent of external changes. acetylation of DNA - ansacetyl groups added to histones, so DNA is less tightly wound round it, making it easier for RNA polymerase and transcriptional factors to bind, so transcription can occur. allopatric speciation - ansWhen populations of a species become geographically isolated. Gene flow between them ceases (reproductive isolation). the new environment will trigger a change in the gene pool due to natural selection imposed on them. If the populations are relatively small, they may experience a founder effect. Selection and genetic drift will act differently on these two different genetic backgrounds, creating genetic differences between the two new species. codominance - ansoccurs where heterozygote has a phenotype that is different from both homozygotes. neither allele is dominant over the other; they both contribute equally to the phenotype. define biomass - ansthe total mass of organisms in a given area define community. - ansall the populations of different species living and interacting in a particular place at the same time. define niche. - ansthe role and position a species has in its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces. A species' niche includes all of its interactions with the biotic and abiotic factors of its environment. define population. - ansa group of individuals of one species that occupy the same habitat at the same time and are potentially able to interbreed. describe and explain the role of hormones in osmoregulation. - ans1.osmoreceptors in hypothalamus detect fall in water potential as they begin to shrink, causing hypothalamus to produce ADH. 2. ADH goes to posterior pituitary gland, where it is secreted into capillaries. Aqa a level biology paper 2 june 2023 question paper (7402/2) 3. ADH goes from blood to kidneys, where it binds to receptors on the cells of of distil convoluted tubule and collecting duct. 4. this activates phosphorylase enzyme. 5. this causes vesicles, which contain water channel proteins, to fuse with cell surface membrane. hence, making it more permeable to water. 6. also increases permeability of collecting duct to urea so it passes out and lowers water potential, so more water can pass out by osmosis. describe and explain the steps in the light dependent reaction of photosynthesis - ans1. photoionisation: light reaches chlorophyll in PSII, which is absorbed by an electron, which becomes excited and moves to a higher energy level. 2. the electron passes to a carrier protein in the thylakoid membrane, and is passed down a series of carrier molecules called an electron transfer chain. 3. as the electron moves down, energy is lost from the electron and is released as ATP. 4. the loss of electron from PSII is 'refilled' by an electron produced by photolysis, which also produces hydrogen and oxygen. 5. the lost electron reaches PSI, which absorbs light energy and boosts another electron to a higher energy level (excitation). 6. this electron also goes down an electron transport chain. 7. this reaches the final electron acceptor which is a proton. they combine to form H and reduce NADP to NADPH. describe and explain the steps in the light independent reaction pf photosynthesis. - ans1. CO2 diffuses into stroma and combines with ribulose bisphosphate (RuBP) using the enzyme rubisco. 2. this forms an unstable 6 carbon molecule, which splits into 2 3 carbon molecules, glyercate-3- phosphate (G3P) . 3. G3P is reduced by NADPH to triose-phosphate (TP), which is aided by ATP for energy. 4. TP can be converted into useful organic substances. 5. TP can also be reformed into RuBP using ATP. describe fast twitch fibres - anscontract more rapidly and more powerful but over a shorter period of time. adapted for intense exercise have thicker and more numerous myosin filament, have more glycogen, have more enzymes to carry out anaerobic respiration, has phosphocreatine. describe glycolysis in respiration. give net formation. - ans1. glucose is converted into phosphorylated glucose by 2ATP. this makes it very reactive, so it splits into 2 triose phosphate (TP). 2. 2TP is then oxidised by 2NAD and 4 ATP is formed to form pyruvate. 3. NET: 2ATP, 2Pyruvate, 2NADH, 2H+ describe krebs cycle in respiration. give net formation. - ans1. acetyl co-enzyme A combines with 4 carbon molecule (oxaloacetate) to form 6 carbon citric acid. 2. CO2 is lost (decarboxylation), molecule is oxidised by NAD and ATP is produce. this forms 5 carbon compound. 3. it is oxidised by 2NADH and FAD, and is decarboxylated. 4. this forms 4 carbon molecule again. describe links reaction in respiration. give net formation. - ans1. pyruvate diffuses into the matrix of mitochondria. 2. pyruvate is oxidised by NAD. CO2 is lost. this forms acetate. 3. acetate and co-enzyme A combine to form acetyl co-enzyme A. 4. NET: CO2, reduced NAD, acetyl co-enzyme A describe oxidative phosphorylation in respiration. - ans1. reduced coenzyme passes its H to a carrier protein in the ETC. this splits into a proton and electron. 2. the protons pass through the space between inner and outer mitochondrial membrane. Aqa a level biology paper 2 june 2023 question paper (7402/2) 3. electrons pass through proteins on ETC. 4. protons return back via ATP synthase in the membrane, producing ATP. 5. the protons and electrons recombine to form H, which combines with O to form water. 6. oxygen is the last electron acceptor in the ETC. describe slow twitch fibres - anscontract more slowly and provide less powerful contractions but over a longer period. adapted for aerobic respiration to avoid lactic acid build up. adapted for endurance work. has lots of myoglobin, rich bloody supply and many mitochondria. describe the components of a reflex arc and give an example. - ans1. stimulus- heat 2. receptor- heat receptors to sensory neurone 3. sensory neurone- impulse to spinal cord 4. relay neurone- to motor neurone 5. motor neurone- spinal cord to muscle 6. effector- muscle in arm contracts 7. response- pulling hand away from heat describe the control of gravitropism by IAA. - ans1. root tip cells produce IAA, which is distributed evenly and down the root. 2. gravity causes IAA to accumulate on the LOWER side of the shoot than upper side, so there is a higher concentration on lower than upper. 3. IAA inhibits elongation in root cells, so inhibits elongation in lower side than upper side. so, the upper side of the shoot elongates further and bends towards gravity. describe the control of heart rate by pressure receptors. - ans1. when blood pressure is higher than normal, pressure receptors in carotid arteries send more impulses to centre in medulla oblongata that decreases heart rate via parasympathetic NS. 2. when blood pressure is lower than normal, pressure receptors send more impulses to the centre of the medulla oblongata that increases heart rate via sympathetic NS. describe the control of phototropism by IAA. - ans1. cells in shoot tip produce IAA which is transported evenly throughout all regions and then down the shoot. 2. light causes IAA to accumulate on the shaded side of the shoot, so much that there is a greater build up of IAA on shaded than unshaded side. 3. IAA causes the shaded side of the shoot to elongate further than the non shaded side. this causes the shoot to eventually grow and bend towards the light. describe the formation of glomerular filtrate by ultrafiltration - ansblood enters Bowmans capsule. the walls of glomerular capillaries are made up of epithelial cells. high hydrostatic pressure in glomerulus. water, glucose and other ions are forced out, forming glomerular filtrate. leaves behind blood cells and proteins. describe the nitrogen cycle. - ansfixation: atmospheric nitrogen can be fixed by rhizbium bacteria. if struck by lightning, it becomes reactive and combines with oxygen to form NO. ammonification: saprobionts feed on organic matter and release ammonia, which then forms ammonium ions in the soil. nitrification: nitrifying bacteria convert ammonium ions into nitrite ions and then to nirate ions. denitrification: Aqa a level biology paper 2 june 2023 question paper (7402/2) 3. cDNA acts as a template for DNA nucleotides to bind to by complimentary base pairing. DNA polymerase joins them together. a copy of the gene is now formed. explain the role of hormones in osmoregulation - ans1. osmoreceptors in the hypothalamus detect fall in water potential. this causes water to be lost from osmoreceptors. 2. this makes them produce ADH, which goes to pituitary gland to pass into blood. 3. ADH goes to kidneys and binds to surface of DCT ad collecting duct, activating phosphorylase. this causes vesicles to fuse with membrane and form aquaporins. 4. ADH increases permeability to urea, which passes out and decreases WP in interstitial space. this causes water to leave by osmosis, so more water is reabsorbed. explain the steps of genetic fingerprinting. - ans1. extract DNA. quantity of DNA may be increased by PCR. 2. restriction endonucleases cut DNA into fragments. 3. gel electrophresis. dna put onto agar gel, voltage is applied across it. smaller fragments mover further than larger fragments. 4. DNA hybridisation- DNA probes have complimentary base sequences to non-coding DNA, and so bind under specific conditions. 5. X-ray film is exposed to radiation from probes. this film is put over a nylon membrane. a series of bars is shown which corresponds to the movement of the fragments. formula to calculate the mean density of individuals from quadrats - anstotal no of individuals counted ------------------------------------ no of quadrats x area of quadrat gluconeogenesis - ansproduction of glucose from sources other than carbohydrates, such as glycerol or fatty acids. occurs when there's insufficient glycogen. glycogenesis - ansconversion of glucose to glycogen. this is when glucose levels are abnormally high. glycogenolysis - ansbreakdown of glycogen to glucose. this is when glucose levels are abnormally low. Hardy-Weinberg principle - ansp2 + 2pq + q2 p2 = homozygous dominant q2 = homozygous recessive 2pq = heterozygous In any hardy-weinberg problem, start with homozygous recessive individuals. homeostasis - ansthe maintenance of an internal environment within restricted limits in organisms. all cells are in an environment that meets their requirements and allows them to function normally despite external changes. how are DNA probes used to identify alleles? - ans1. DNA probes are made so that they are complimentary to part of the base sequence of the allele. 2. double-stranded DNA is treated so it becomes 2 separate strands. 3. the separated strands are mixed with the probes, which bind to the complimentary sites. this is DNA hybridisation. 4. the site at which it binds to can be identified as it will emit radioactivity or fluorescence. how can a population be separated and form different species? - ans1. Populations become separated. physical barriers may come between two groups. 2. Therefore they stop interbreeding. Aqa a level biology paper 2 june 2023 question paper (7402/2) 3. Populations adapt to new environment. Selection pressures will be different in different areas. 4. Allele frequencies will change in the different populations. 5. Over time they become so different that they can no longer interbreed. how can you calculate the net primary production? - ansNPP = GPP - R how do drugs affect synaptic transmission and action potentials? - ans1. stimulate the nervous system by mimicking neurotransmitters, stimulating neurotransmitter release or inhibiting enzymes that break down neurotransmitters, and so create more action potentials. 2. inhibit the nervous system by inhibiting release of neurotransmitter or blocking Na+/K+ channels on postsynaptic neurone, hence creating less action potentials. how does glucagon and alpha cells in the pancreas affect glucose levels? - ans1. alpha cells detect a fall in blood glucose levels and so secrete glucagon. 2. glucagon attaches to receptors on cell surface membrane of liver cells. 3. this activates enzymes which convert glycogen to glucose. 4. also activates enzymes that convert amino acids to glucose. how does insulin and beta cells in the pancreas affect glucose levels? - ans1. the beta cells in the pancreas detect a rise in the blood glucose concentration and respond by secreting insulin into blood. 2. insulin binds to glycoprotein receptors on cells. 3. this causes a change in the tertiary structure of the glucose transport proteins, making them more permeable to glucose and so allowing more in by facilitated diffusion. 4. activates the enzymes that convert glucose to glycogen and fat. how does the distil convoluted tubule reabsorb material from the filtrate? - ansthe cells lining the DCT have microvilli and mitochondria. it selects which ions to reabsorb. this controls the pH of the filtrate. how does the loop of henle concentrate urine? - ans1. filtrate enters descending limb. water passes out by osmosis and into the interstitial space as the walls are permeable. Na+ actively transported in. 2. this lowers water potential. lowest water potential is at the bottom of the hairpin. 3. at the ascending limb, the walls are not permeable to water and so it cant leave. Na+ is actively transported out into the interstitial space. this creates a higher water potential. 4. interstitial space between collecting duct and ascending limb has a wp gradient, from high to low, and so any water left passes out. how is glucose reabsorbed in the proximal convoluted tubule? - ansNa+ actively transported out of cells lining the PCT, into blood capillaries, which carry them away. Na+ diffuse down concentration gradient from the PCT into the epithelium by facilitated diffusion- cotransport. the molecules in the PCT then diffuse into blood, so they are reabsorbed. how many types of rod and cone cells are there? - ansrod- 1 cone- 3, all responding to different wavelengths induced pluripotent stem cells - ansproduced from unipotent cells. genetically altered in labs (transcription factors) to make them have the characteristics of embryonic stem cells. they turn on the genes that were otherwise turned off. linked genes - ansgenes on the same chromosome list the parts of control mechanisms in homeostasis. - ans1. optimum temperature 2. receptor- detects any deviation from the optimum temperature 3. coordinator- info from receptor to effector 4. effector- often a muscle/gland, brings about change to return the system to optimum level 5. feedback mechanism Aqa a level biology paper 2 june 2023 question paper (7402/2) list the steps in osmoregulation - ans1. Ultrafiltration in Bowmans capsule 2. reabsorption in the proximal convoluted tubule 3. concentration in the loop of henle distil convoluted tubule methylation of DNA - ansaddition of methyl groups to bases. added throughout life, sometimes in response to environmental factors e.g. diet. causes the DNA to wrap more tightly around histones, so transcriptional factors cannot bind to specific DNA sites and initiate transcription. multiple alleles - ansthis is where there are several different alleles of a gene e.g. blood type: IA, IB (codominant), and IO (recessive). multipotent cells - anscan divide into some, but not all, specialized cells. name the negative effects of using nitrogen containing fertilisers. - ans1. reduced species diversity 2. leaching 3. eutrophication oncogenes - ansmutated proto-oncogenes form oncogenes. oncogenes are permanently activated (switched off). pluripotent cells - anscan become any kind of specialized body cell, but cannot divide to form a whole organism. sex linkage - ansalleles carried on the X chromosome. spatial summation - ansa number of different presynaptic neurones collectively release enough neurotransmitters to exceed the threshold value of the postsynaptic neurone, triggering a new action potential. sympatric speciation - ansbecome reproductively isolated from each other even though they occupy the same geographic range. Factors that could lead to them becoming reproductively isolated from each other are things like changes in courtship behavior, changes in feeding behavior, changes in coloration. The most common way this occurs is polyploidy. Rapid genetic changes can alter morphology, behavior, and habitat preferences. temporal summation - ansa single presynaptic neurone releases neurotransmitters many times over a short period. this exceeds the threshold value, triggering a new action potential. totipotent cells - anscells that can mature into any kind of specialized body cell. can divide to form a whole organism. they are found in very early mammalian embryos. after this stage, some of the genes become switched off and so are not translated into RNA, hence specialized. transcription factors - anstranscription factors bind to the DNA sequence at specific target sequences. RNA polymerase recognizes the complex formed and so transcribes the gene. unipotent cells - ansdivide to form just one type of cell. what are factors that affect the speed of an action potential? - ans1. myelin sheath 2. diameter of axon: the greater the diameter, the faster the speed, because there's less leakage of ions from a large axon, so membrane potentials are easier to maintain. 3. temperature: the higher the temperature, the greater the rate of diffusion of ions, and hence the faster the impulse.