unit 3

Question 1

explain why ATP is sometimes called the universal energy currency [2]

Answer 1

• ATP is used by ALL ORGANISMS to PROVIDE ENERGY for many of their BIOCHEMICAL REACTIONS e.g active transport

Question 2

explain the importance of ATP in cells [3]

Answer 2

• ATP is used in cells for a number of FUNCTIONS including active transport, muscular contraction and protein synthesis
• ATP is the one molecule used to TRANSFER ENERGY TO CHEMICAL REACTIONS and the energy is supplied in small packages when a SINGLE BOND IS BROKEN

Question 3

explain how nitrate fertiliser leads to eutrophication and how this can lead to the death of fish [3]

Answer 3

• plants GROW MORE because of the extra nitrate fertiliser
• this means there is more competition for LIGHT and more of the plants DIE
• the extra dead plants are DECOMPOSED by BACTERIA whose population increases as they have a greater supply of organic material
• the decomposition process in bacteria requires OXYGEN for RESPIRATION which leads to a lowering of oxygen levels in the water and therefore the death of the fish

Question 4

questions related to ‘reabsorption of water in kidney’

Answer 4

• SOLUTES are REABSORBED from the FILTRATE in the proximal convoluted tubule
• this leads to OSMOSIS OF WATER from the proximal convoluted tubule into the CORTEX and then into the blood
• as the filtrate moves into the ASCENDING LIMB of the loop of Henle, SODIUM IONS are actively transported out of the ascending limb and into the MEDULLA
• this means that there is a high concentration of solutes and therefore a low water potential in this area of the medulla, the highest concentration of solutes and therefore the lowest water potential being found at the APEX of the loop of Henle
• the structure of the loop of Henle allows a COUNTERCURRENT MULTIPLIER SYSTEM to operate
• this leads to water being reabsorbed from the filtrate along the entire length of the descending limb of the loop of Henle into the medulla because of the water potential gradient that has been produced along its entire length
• water is also reabsorbed from the urine in the collecting duct into this area of the medulla again because of the water potential gradient that has been produced

Question 5

questions related to ‘how an action potential forms/refractory period/speeding up action potential conduction’

Answer 5

• an axon’s resting potential is maintained at -70mV by a sodium/potassium pump which moves sodium ions out of the axon and potassium ions into the axon
• this movement of ions requires energy in the form of ATP
• when the axon is depolarised to about -40mV (the threshold potential), voltage gated sodium channels open which allows sodium ions to flood into the axon down an electrochemical gradient, which leads to the axon becoming more depolarised
• when the potential difference gets to +40mV the voltage gated sodium channels close and the voltage gated potassium channels open
• this lead to the potassium ions flooding out of the axon down the electrochemical gradient which causes the axon to be repolarised
• when the potential difference gets to about -80mV, the sodium/potassium pump takes a little time to move the sodium ions out of the axon and the potassium ions back into the axon
• until this is achieved, and the resting potential is restored to -70mV no further action potential can form, this time period is called the refactory period
• action potentials conduction/transmission along a neurone can be sped up if the neurone is myelinated
• myelin electrically insulates the axon and prevents the movement of ions across the axon membrane
• action potentials can only form in the gaps between the myelin which are called Nodes of Ranvier
• this causes saltatory conduction to occur when action potentials form between the sections of myelin in the Nodes of Ranvier
• the action potentials ‘jump’ between Nodes of Ranvier which reduces the conduction time

Question 6

questions related to ‘the proton gradient can be maintained as long as reduced NAD is available in the mitochondrion. explain the reasons for reduced NAD being required to maintain a proton gradient’

Answer 6

• the reduced NAD in the mitochondrial matrix supplies both hydrogen ions (protons) and high energy electrons
• the high energy electrons are passed to electron carriers (proton pumps) in the inner mitochondrial matrix which use the energy provided to actively transport the hydrogen ions (protons) against their concentration gradient into the inter-membrane space from the mitochondrial matrix
• this means that a hydrogen ion (proton) gradient is maintained between the inter-membrane space and the mitochondria matrix

Question 7

questions related to ‘outline the pathway for the production of triose phosphate in glycolysis’

Answer 7

• glucose is phosphorylated twice using ATP to produce hexose bisphosphate (6C), then this splits to form 2 triose phosphate molecules (3C)

Question 8

questions related to ‘anaerobic respiration/regenerating oxidised NAD for aerobic respiration’

Answer 8

• as there is no oxygen available to act as the final electron acceptor, oxidative phosphorylation stops and no ATP can be produced in this way
• the link reaction and the Krebs cycle also stops because there are no oxidised BAD molecules available to act as hydrogen carriers
• some ATP (2 per glucose molecules) can be generated without oxygen (anaerobic respiration) during glycolysis because oxidised NAD can be regenerated to act as a hydrogen carrier for these reactions which allows them to continue
• the regeneration of oxidised NAD happens as a reduced NAD molecule is oxidised as it donates a hydrogen ion (proton) and high energy electrons to the reaction that converts pyruvate to lactate

Question 9

questions related to ‘the organic cycle to the Nitrogen cycle’

Answer 9

• nitrogen must be recycled as it is a component part of proteins which all organisms need
• nitrogen gas cannot be used to produce proteins by either plants or animals
• however, plants can use nitrates (which are chemicals that contain nitrogen) to produce proteins
• the nitrates are obtained by the plants from the soil
• for nitrates to be produced a number of steps are required
• decomposition of dead plants, dead animals and animal waste by decomposing bacteria which leads to the digestion of protein into amino acids and the deamination of amino acids to produce ammonia
• the ammonia is then converted into nitrates in a process called nitrification, this involves two different bacteria, Nitrosomonas converts ammonia to nitrite and Nitrobacter converts nitrite to nitrate
• the nitrogen in the nitrate is then available to the plant so that it can use it to make proteins
• animals obtain nitrogen to make their proteins by feeding on either plants or animals which contain protein

Question 10

questions related to ‘explain how carbon dioxide is used in the production of glycerate-3-phosphate during photosynthesis’

Answer 10

• RuBP (5 carbon compound) and carbon dioxide are linked together to produce a 6C compound in a chemical reaction catalysed by the enzyme RUBISCO
• the 6C compound is unstable and splits into two glycerate-3-phosphate (3C) molecules

Question 11

questions related to ‘osmoregulation/ADH’

Answer 11

• when there is a low blood volume this is detected by osmoreceptors in the hypothalamus which causes the release of more antidiuretic hormone (ADH) from the posterior lobe of the pituitary gland
• the ADH is carried in the blood and affects target cells in the distal convoluted tubule and the collecting duct by causing them to become more permeable to water
• this results in water leaving the distal convoluted tubule and the collecting duct by osmosis as the water potential of the medulla is lower than that of the distal convoluted tubule and the collecting duct
• the water that enters the medulla is rapidly removed by the capillary network and water is therefore conserved
• the urine released from the collecting ducts would be concentrated and would have a small volume
• the reason for the low water potential in the medulla is because of the countercurrent multiplier system occurring in the Loop of Henle
• as the filtrate moves into the ascending limb of the loop of Henle sodium ions are actively transported out of the ascending limb and into the medulla
• this means that there is a high concentration of solutes and therefore a low water potential in this area of the medulla, the highest concentration of solutes and therefore the lowest water potential being found at the apex of the loop of Henle
• this leads to water being reabsorbed from the filtrate along the entire length of the descending limb of the loop of Henle into the medulla because of the water potential gradient that has been produced along its entire length
• water is also reabsorbed from the urine in the collecting duct into this area of the medulla again because of the water potential gradient that has been produced
• some animals are adapted to a dry environment by having a long loop of Henle which leads to more water being reabsorbed

Question 12

questions related to ‘describe how energy is released from ATP’ [3]

Answer 12

• ATP is hydrolysed into ADP and phosphate in a reaction catalysed by ATPase releasing 30.6kJ of energy

Question 13

questions related to ‘explain how impulses are transmitted across a synapse’ [3]

Answer 13

• when an impulse reaches the synaptic knob this depolarises the membrane which leads to an influx of calcium ions into the synaptic knob
• the presence of calcium ions causes the secretory vesicles containing the neurotransmitters to migrate towards the presynaptic membrane
• at the presynaptic membrane the secretory vesicles fuse with the membrane and the neurotransmitter is released into the synaptic cleft by exocytosis
• the neurotransmitter diffuses across the synaptic cleft and binds to receptors on the post synaptic membrane causing the depolarisation of the post synaptic membrane

Question 14

questions related to ‘describe what is meant by the term facultative anaerobes’ [2]

Answer 14

• facultative anaerobes GROW best when they use the available OXYGEN to carry out aerobic respiration but can also carry out anaerobic respiration if oxygen is not available

Question 15

questions related to ‘how would you use the dilutions produced to carry out a viable count’ [4]

Answer 15

• each dilution would require its own sterile nutrient agar plate
• 1cm^3 of the dilution would be transferred onto the nutrient agar plate and then spread with a sterile spreader
• the nutrient agar plate would then be re-covered and it would then be incubated at 30°C for 3 days
• colonies would then be counted on the assumption that one colony is equal to one original viable cell

Question 16

questions related to ‘explain the term carrying capacity’ [2]

Answer 16

• the MAXIMUM size of the population that can be SUPPORTED INDEFINITELY by a particular environment

Question 17

questions related to ‘describe how the principles of a batch culture fermenter are applied in the industrial production of penicillin’ [10]

Answer 17

• in batch culture fermenters, all of the materials are present at the start
• the fermenter must be kept sterile so when the Penicillium culture is added it will only be this microorganism that grows
• as well as the Penicillium culture, the fermenter will also contain a sterile nutrient medium the microorganisms can use and a pH buffer to maintain the optimum pH for the Penicillium
• optimum temperatures also need to be maintained using a water jacket to maximise the growth in the population of Penicillium and therefore the production of penicillin
• the penicillium also requires oxygen and this is obtained from the air outside the fermenter, the air passes through filters to ensure it is sterile
• finally, some form of mixing is required to ensure that all the penicillium has access to oxygen and nutrients
• during the growth phase the glucose in the sterile nutrient medium will be depleted
• as penicillin is a secondary metabolite it is produced during the stationary phase
• once the penicillin is produced it is isolated from the Penicillium by filtering
• the penicillin is then extracted from the solution

Question 18

questions related to ‘how do you accoubt for the low rate of population growth in the first three hours of the experiment’ [2]

Answer 18

• initially, the microorganism is switching on the genes required for the new nutrient source which will take time
• the synthesis of the proteins coded for by these genes will also take time
• the cells will then need to digest then absorb the nutrients; grow in size and their DNA will need to be replicated before mitosis can begin
• all of these steps require time

Question 19

questions related to ‘differences betwen primary and secondary succession’

Answer 19

• primary succession involves the colonisation of an area where no living organism has lived before
• while secondary succession involves the colonisation of an area where living organisms previously lived

Question 20

questions related to ‘problems of fish farming’

Answer 20

• eutrophication caused by the fishes waste products and the waste food
• as the fish are kept so closely together diseases are more likely to spread throughout the population and they may also infect wild fish
• to prevent diseases and parasites spreading through the population, the fish farmer can apply pesticides and treat the fish with antibiotics which cause their own problems
• as well as the high costs these treatments place on the fish farmers, they also cause other problems
• the introduction of pesticides can harm other marine organisms directly as well as entering food chains which can lead to bioaccumulation causing harm particularly to top predators
• the overuse of antibiotics can lead to the development of populations of antibiotic resistant bacteria
• finally some alleles from the farmed fish may find their way into the wild fish population leading to the genetic contamination of the wild fishes genome

Question 21

questions related to ‘crops to increase nitrate levels’

Answer 21

• leguminous plants could be planted as they contain the nitrogen fixing bacterium Rhizobium in their root nodules
• the Rhizobium converts nitrogen gas into ammonium
• the ammonium can be converted into amino acids and used for the growth of the plant
• these crops are then allowed to decay in the soil or ploughed into the soil

Question 22

questions related to ‘eutrophication’

Answer 22

• plants GROWING MORE because of the extra nitrate fertiliser
• this means there is more competition for LIGHT and more of the plants DIE
• the extra dead plants are decomposed by bacteria whose population increases as they have a greater supply of organic material
• the decomposition process in bacteria requires oxygen for respiration which leads to a lowering of oxygen levels in the water and therefore the death of the fish

Question 23

technical terms need to be used and spelt correctly

Question 24

many lost marks due to carelessness with ‘simple’ maths

Question 25

important to give detailed answers

Question 26

diagrams only get marks if they have been annotated in detail

Question 27

primary succession: - colonisation of an area where nothing has been before (no mark) - colonisation of an area where NO LIVING ORGANISM HAS LIVED BEFORE (mark)

Question 28

gross primary production: - the amount of energy produced by the plant (no mark) - the rate of conversion of light energy into chemical energy by photosynthesis (mark) - the rate at which the products of photosynthesis are formed (mark)

Question 29

understand the difference between egestion and excretion

Question 30

careful with language: - cellulose cannot be digested by herbivores (no mark) - herbivores are less efficient at digesting cellulose

Question 31

- conservation is the preservation of wildlife (no mark) - conservation is the PLANNED preservation if wildlife (mark)

Question 32

conservation can maintain the GENE POOL of a species

Question 33

conservation, if you are describing laws e.g conservation areas, fishing quotas etc then you must use the word LEGISLATION

Question 34

gram +ve purple (mark) gram -ve red (mark)

Question 35

facultative / obligate anaerobes must mention oxygen for the mark

Question 36

- anaerobic conditions encourage pathogenic bacteria (mark) - anaerobic condition encourages bacteria / bad bacteria (no mark)

Question 37

- body temperature encourages pathogenic bacteria (mark) - body temperature encourages bacteria / bad bacteria (no mark)

Question 38

ATP: - nitrogenous base (mark) - base (no mark) - ribose/pentose sugar (mark) - sugar (no mark)

Question 39

- ATP is used for ALL reactions/organisms (mark) - ATP is used for most reactions/organisms (no mark)

Question 40

- ATP supplies or releases energy (mark) - ATP produces energy (no mark)

Question 41

- ATP can be used for muscle contraction (mark) - ATP can be used for movement (no mark)

Question 42

- NADP in photosynthesis - NAD in respiration

Question 43

- photosynthesis produces organic material or organic compounds (mark) - produces nutrients (no mark) - produces food (no mark)

Question 44

- impulses move along neurones (mark) - signal moves along neurones (no mark) - prefer neurones rather than nerves

Question 45

- if asked to compare, compare in same sentence - remember comparison is similarities AND differences

Question 46

Loop of Henle, use correct terms i.e counter current mechanism, water potential, renal filtrate, medulla etc

Question 47

why does the urea concentration increase at bottom of loop of Henle?

Answer 47

- water reabsorbed into MEDULLA AND THEN BLOOD so concentration of urea increase

Question 48

- loop of Henle can be longer or shorter (mark) - smaller or larger (no mark)

Question 49

why do athletes produce more urea in their urine?

Answer 49

- high protein diet (no mark) - high protein diet = excess amino acids = more deamination = more urea

Question 50

collecting ducts, distal convoluted tubules - use correct terms i.e water potential gradient, osmosis, medulla etc

Question 51

- legumes have root NODULES containing … (mark) - legumes have roots containing … (no mark)

Question 52

- bacteria divide or reproduce (mark) - bacteria give birth (no mark)

Question 53

lag phase: - getting used to the environment (no mark) - time to switch on the appropriate genes and synthesise the appropriate proteins for the environment (mark)

Question 54

exponential growth: - population doubles per unit time

Question 55

decline phase: - if population has gone above the carrying capacity (no mark) - if population has exceeded the carrying capacity (mark)

Question 56

oxidative phosphorylation: - use correct terms: • inter-membrane space • H ions • chemiosmosis • electrochemical gradient

Question 57

- suitable temperature required (mark) - heat required

Question 58

- cyanide INHIBITS respiration (marks) - cyanide stops/blocks respiration (no marks)

Question 59

- haemoglobin absorbs or has affinity for oxygen (mark) - haemoglobin takes up oxygen (no mark)

Question 60

nitrogen cycle: - ‘nitrogen containing compounds’ is too vague (no marks) - be specific e.g ammonium ions/ammonia/nitrites/nitrates/urea/uric acid/proteins/amino acids etc

Question 61

- bacteria can be antibiotic resistant (mark) - bacteria can’t be immune

Question 62

- neurotransmitters are released by EXOCYTOSIS from the presynaptic membrane (mark) - neurotransmitters are released from the presynaptic membrane (no mark)

Question 63

- neurotransmitters DIFFUSE across the synaptic cleft (mark) - neurotransmitters move across the synaptic cleft (no mark)

Question 64

decarboxylation is the removal of carbon dioxide

Question 65

dehydrogenation is the removal of hydrogen

Question 66

action potentials: - sodium ions/potassium ions (mark) - sodium/potassium (no mark) - ions diffuse in (mark) - ions move in (no mark) - ions move along concentration gradient (mark)

Question 67

saltatory conduction: - detailed explanation using the following phrases, no myelin at nodes, depolarisation can only happen at nodes, action potential jump from one node to the next, nerve impulse transmission faster

Question 68

resting potential: - when a nerve impulse is not being conducted or no action potential is being produced

Question 69

- when discussing changes in the axon during action potential, use the term polarised and quote figures i.e -40mV

Question 70

50% increase calculations are common

Question 71

- pituitary (no mark) - posterior pituitary (mark)

Question 72

free living nitrogen fixing bacteria: - Azotobacter (spelling correct) (mark)

Question 73

- cell walls of bacteria affected by gram stain not cell membranes

Question 74

- bacillus (mark) - rod (no mark) - spirillum (mark) - spiral (no mark) - coccus (mark) - round (no mark)

Question 75

- ribulose bisphosphate is regenerated FROM triose phosphate (mark) - triose phosphate is regenerated into ribulose bisphosphate (no mark)

Question 76

carbon dioxide is FIXED during photosynthesis

Question 77

lidocaine is a local anaesthetic used by dentists to numb pain. it is believed that it blocks the sodium ion channels in a neurone membrane describe the function of sodium ion channels in a neurone membrane in response to a stimulus [2]

Answer 77

- allowing sodium IONS/Na+ to (rapidly diffuse/floss/rapid influx) INTO NEUTRON/AXON/CELL - brings about depolarisation of axon / inside of neurone becomes positive with respect to outside / generation of action potential

Question 78

lidocaine is a local anaesthetic used by dentists to numb pain. it is believed that it blocks the sodium ion channels in a neurone membrane explain how lidocaine acts as a local anaesthetic [4]

Answer 78

- (sodium IONS/Na+) can no longer enter/ fewer sodium ions enter the axon - threshold is not reached - there is no action potential / no depolarisation - along SENSORY neurone (to brain)

Question 79

the marine cone shell, Conus magus, releases a chemical which blocks calcium ion channels on the pre-synaptic membrane of a synapse. this has a potential use as an anaesthetic. with reference to the pre-synaptic neurone only, describe and explain the mechanism by which this chemical could work as an anaesthetic [3]

Answer 79

- calcium ions (dont DIFFUSE / DIFFUSE less) into the synaptic knob/presynaptic neurone/across the presynaptic membrane - prevent (synaptic) vesicles from fusing with presynaptic membrane - prevents (neurotransmitter / acetylcholine) (release into the synaptic cleft/synapse/exocytosis)

Question 80

using a diagram and your own knowledge, explain how the release of more ADH causes a smaller volume of concentrated urine to be produced [5]

Answer 80

- ADH makes membranes of (collecting duct / distal convoluted tubule) more permeable to water - ADH combines with receptor - vesicles fuse with membrane on COLLECTING DUCT side - inserting MORE aquaporins into membrane - water potential of filtrate is higher than water potential within (cell/tissue fluid / blood) - water moves into (epithelial cell / tissue fluid) by osmosis / water leaves filtrate) by osmosis

Question 81

diabetes insipidus is a condition that results in excessive thirst and production of large volumes of dilute urine. one cause of diabetes insipidus is the patient not releasing ADH suggest how this causes diabetes insipidus [1]

Answer 81

MEMBRANE not made more permeable so more water stays in (filtrate/urine) / no aquaporins inserted into MEMBRANE so less water reabsorbed

Question 82

a scientist carrier out an experiment counting the living bacteria present each hour for 60 hours explain how the growth curve would differ if a total count had been used to measure the population density. suggest a disadvantage of this technique [2]

Answer 82

- dead cells are included therefore there (are higher numbers / numbers stay constant) - death phase cannot be identified

Question 83

a class of 20 students investigated respiration in maggots over a 5 minute time period explain the advantages of collecting results from the whole class [2]

Answer 83

- increase (reliability / reproducibility) (of mean) NOT ACCURATE/REPEATABILITY - increase confidence / (exclude/identify) anomalous results / allow use of statistical test

Question 84

the respiration of fat releases more energy than the respiration of glucose produced by the breakdown of glycogen explain why muscles use glycogen as an energy store rather than fat [2]

Answer 84

- glycogen does not need a large oxygen supply - and does not need to remove a large amount of CO2 / water

Question 85

- birdsfoot trefoil and restharrow are legumes - therefore they have root nodules that contain the bacterium Rhizobium - the scientists observed that they were two of the first plants to arrive in areas with nutrient poor soil - explain why they are able to survive in soils with low nitrogen levels [3]

Answer 85

- carry out nitrogen fixation - nitrogen gas converted to nitrogen containing compounds / ammonium ions - used by plants to make amino acids / proteins / DNA

Question 86

- Rhizobium contain the enzyme nitrogenase which is responsible for fixing atmospheric nitrogen - this enzyme is inhibited if oxygen levels are high - the root nodules of legumes contain a form of haemoglobin called leghaemoglobin - this has a very high affinity for oxygen - suggest why leghaemoglobin is present in the root nodules of restharrow and birdsfoot trefoil [3]

Answer 86

- (leghaemoglobin) (combines/binds) with the oxygen present NOT ABSORBS OXYGEN - leghaemoglobin gives (anaerobic/oxygen free / low oxygen) conditions (in the root nodule) - Rhizobium only fixes nitrogen in (anaerobic / oxygen free / low oxygen) conditions

Question 87

- close to Ynyslas is the peat bog of Cors Fochno - this is an area of poor drainage where soil is waterlogged - no trees grow on Cors Fochno - the climax community is bog, which is permanently dominated by the moss, Sphagnum explain why bog is described as the climax community [1]

Answer 87

- stable community / no further succession / final community / community has reached equilibrium

Question 88

- fish farming is an important industry in Scotland, producing almost 180,000 tonnes of fish in 2014 - it provides employment and financial gain for the areas where it is carried out - the number and size of fish farms has increased as one way of preventing overfishing - explain the possible ecological impacts of fish farming in the areas where it takes place. describe other ways to overcome the problem of overfishing. explain how these methods are used to prevent overfishing [9QER]

Answer 88

EUTROPHICATION - the nitrogen in the food fed to the fish may be lost as uneaten food, in faeces and as ammonia - the extra nitrogen and phosphorus in the water can be used by algae to grow - this algal bloom at the water surface can block light to the aquatic plants in the deeper water - with no light these plants cannot photosynthesise and so die - decomposers (bacteria and fungi) will then decompose the dead organic matter - they use aerobic respiration and so use oxygen from the water - the water becomes deoxygenated and fish and other oxygen requiring species die - anaerobic bacteria may start to reduce nitrates (denitrification) OTHER IMPACTS OF FISH FARMING - the farmed fish tend to be packed tightly into into a small area - this can lead to diseases passing through the population quickly and these can spread to the local wild fish population - to keep the stock healthy antibiotics are used - this can lead the antibiotic resistant bacteria developing - pesticides used to kill the parasites may also be toxic to some of the local marine invertebrates - farmed fish may have a selective advantage over wild species METHODS OF PREVENTING OVERFISHING - net mesh sizes may be restricted - larger mesh sizes allow immature fish to escape and they can go on to interbreed - closed seasons for fishing are also enforced - these will be at times of the year when fish are breeding so again the stocks are replenished - quotas - agreements which limit the catches brought ashore - around the coast there are exclusion zones where fishing is not allowed - these areas allow fish to reproduce without being caught - landing size regulations have been introduced which only allowing fish of a certain size to be caught - this allows some fish to return for breeding - fishing of non-traditional varieties e.g. coalfish has allowed stocks of other fish to recover

Question 89

- cytochrome c is an electron carrier involved in oxidative phosphorylation - it transfers electrons between two large proteins found in the electron transport chain suggest why cytochrome c detaches from the cytochrome oxidase molecule when the electrons it carries are removed [2]

Answer 89

- it changes shape - so no longer complimentary shape to the active site / does not fit into active site any more / can no longer form enzyme substrate complexes

Question 90

suggest why lactate begins to accumulate in the blood if high levels of reduced NAD form [2]

Answer 90

- (lactate is end product) of anaerobic respiration - pyruvate is reduced to regenerate NAD / pyruvate is reduced by using reduced NAD - for glycolysis to continue

Question 91

- in diseases such as diabetes mellitus and glomerulonephritis the membranes in the glomerulus and Bowman’s capsule are damaged and they become more permeable to proteins - suggest TWO reasons why the proteins are not usually reabsorbed back into the bloodstream [2]

Answer 91

- they are too large to (diffuse back in / pass though / to be reabsorbed) - there are no (specific carriers / transport proteins / carrier proteins / channel proteins) for them

Question 92

- a team of scientist from the Mara Cheetah Project estimated that the adult population of cheetahs in the Masai Mara Game Reserve in Kenya stood at 30 individuals in the summer of 2016 - the population between 1850 and 1900 has been estimated to have around 55 individuals in this area - the graph below shows the approximate number of adult cheetahs in this area from 1850 to 2016 - explain the factors affecting the population of cheetahs in region A of the graph - account for the drop in cheetah numbers in region B - describe and explain the strategies being used to overcome the problem of low cheetah numbers in region C [9QER]

Answer 92

REGION A: - carrying capacity determines maximum population size that can be supported - this will be determined by biotic and abiotic factors / environmental resistance - explanation of predator prey relationship - examples of biotic factors such as number of prey/disease/parasitism - examples of abiotic factors such as water availability - description of interspecific/intraspecific competition REGION B: - human influence due to Hunting/killing due to cheetahs destroying livestock - lack of food due to prey being hunted - habitat destruction + reasons - density dependent factors/example of e.g new disease - density independent factors/example of e.g bush fire/new predator REGION C: - (zoos / reintroduction / outbreeding) program - (embryo/sperm/egg) banks - education of locals - ecotourism - national parks/game reserves/prevention of poaching - political pressures / CITES / legislations

Question 93

- it has been found that organophosphates, which are used in some pesticides, can cause the myelin sheath to become damaged - in people who handle organophosphates, the myelin sheath may degenerate and leave the membrane of the axon exposed - suggest what would happen to the rate of oxygen consumption for the demyelinated neurone. explain your answer [4]

Answer 93

- rate would increase - because more AEROBIC respiration - saltatory conduction would not occur/whole membrane would need to be depolarised / action potentials would occur at more places along neurone / shorter local circuits occur - so more (Na+ / K+) pumps (have to work across whole length of exposed membrane) / more active transport - more ATP needed (to maintain resting potential)

Question 94

- planetary boundaries are designed to define a safe operating space for humanity to control the stability of the land, atmosphere and the sea - one such boundary that has been crossed is the Biodiversity Boundary. - this is measured in the number of species becoming extinct per million species per year - the boundary is 10 species but the current loss is over 100 species per year - in this area of Peru, the rainforest trees are harvested using the strip felling technique - this involves harvesting the trees in an area 50 m wide - that area is then left uncut for 40 years allowing natural regeneration of the rainforest - this is a suitable alternative of felling trees on a mass scale - a photograph below shows an area of strip felling five years after harvesting - explain why this method of tree harvesting is helping to reduce the extinction rate whereas mass felling of trees is not [4]

Answer 94

- soil erosion less likely - allows light to reach ground level to stimulate growth - seeds from neighbouring trees reach cut area - (secondary) succession can take place - habitat maintained / (new/more) niches available - dead leaves / material from trees in the adjoining areas can add nutrients to the soil - soil not as wet as in mass felling (therefore more oxygen available for root growth / maintains higher temp / less denitrification) - accept reverse argument for all points

Question 95

- describe a method that could be used to produce a range of dilutions from the original sample of bacteria to a 10^-5 dilution [3]

Answer 95

- serial dilution description (of tenfold/hundredfold) e.g 1cm^3 of sample and 9 cm³ of (water/growth medium) mixed (gives 10^-1) or equivalent - water/saline/equipment must be sterile / reference to aseptic technique - repeated four more times / method to achieve a 10^-5 dilution

Question 96

- a group of scientists investigated the rate of respiration in brown adipose tissue - there is a high proportion of this tissue in newborn babies - the cells in brown adipose tissue contain a much higher number of mitochondria than the cells of white adipose tissue; this gives the brown adipose tissue its colour - the scientists isolated mitochondria from brown adipose tissue cells and used them to investigate some aspects of respiration - the mitochondria were placed in a solution with pyruvate as the respiratory substrate - an oxygen electrode was used to monitor the concentration of oxygen present in the solution . - explain why pyruvate was used as a respiratory substrate rather than glucose [3]

Answer 96

- glucose is used in glycolysis takes place in the cytoplasm - glucose cannot enter mitochondria / pyruvate can enter the mitochondria - pyruvate used in link reaction and takes place in the mitochondria - no enzymes for glycolysis in mitochondria

Question 97

- a group of scientists investigated the rate of respiration in brown adipose tissue - there is a high proportion of this tissue in newborn babies - the cells in brown adipose tissue contain a much higher number of mitochondria than the cells of white adipose tissue; this gives the brown adipose tissue its colour - the scientists isolated mitochondria from brown adipose tissue cells and used them to investigate some aspects of respiration - the mitochondria were placed in a solution with pyruvate as the respiratory substrate - an oxygen electrode was used to monitor the concentration of oxygen present in the solution . - when ADP was added to the solution, the concentration oxygen present dropped to 40%. explain the observation [2]

Answer 97

- ADP required to generate ATP - oxygen is (final electron acceptor / terminal electron acceptor / converted to water)

Question 98

state what happens to the energy that is not incorporated into ATP during respiration and the benefit of this to a newborn baby [2]

Answer 98

- released as heat - keeps baby warm / maintains body temp / counteracts high surface area to volume ratio

Question 99

- barnacles are marine animals related to crabs and lobsters - they live in shallow tidal waters and the adults are attached permanently to a hard surface - they feed by filtering particles from the water using their modified feathery legs - a rocky shore was studied and the distribution of two barnacle species: Semibalanus balanoides and Chthamalus stellatus recorded. - near the maximum high tide level only Chthamalus barnacle larvae develop into adults - scientists removed Chthamalus from the upper area continually for several weeks and observed that Semibalanus did not colonise this area. - scientists removed Semibalanus from the lower area continually for several weeks and observed that Chthamalus were found in this cleared area. - give an explanation for this observation [2]

Answer 99

- Semibalanus is a more successful competitor in the lower zone / Chthamalus is outcompeted in this area - there is INTERSPECIFIC competition normally / a lack of INTERSPECIFIC competition after clearing

Question 100

- if there is a decrease salinity in the surrounding water, barnacles are able to carry out active transport to remove sodium ions from their cells - explain why they would be unable to survive if this is not occur [3]

Answer 100

- due to water potential in the cell being lowER than the surrounding water - water would MOVE IN BY OSMOSIS - cells would lyse / burst

Question 101

- two varieties of Austrominius were found on one of the sculptures - a sample of DNA was taken from each of the varieties - state the technique that could be used to show the relatedness of the two varieties of barnacles [1]

Answer 101

- (genetic / DNA) (fingerprinting / profiling) - /DNA base sequencing - DNA hybridisation

Question 102

- Austrominius modestus is a species of barnacle that was found only in Australasia up to 100 years ago - the first recorded sighting of it in the UK was in 1946 - in 2014, a survey of 16 harbours in Wales found Austrominius barnacles in each of the harbours - it is now classified as an ‘invasive species’ - at the time of the survey there were just a few Austrominius barnacles in each of the harbours - state why the welsh government is concerned about the presence of Austrominius in the harbours - your answer should include environmental and economic concerns [4]

Answer 102

- could outcompete (native /other) species - may not have a natural predator in this area - this will reduce the biodiversity (around the coast)/impact on food chains - could cause damage to the (harbours/boats) (more friction so more fuel costs)/boats use more fuel so higher economic impact - economic impact of removal of barnacles from (boats/harbour) / prevention of barnacle growth - introduction of disease

Question 103

- chlorophyll a, chlorophyll be and other accessory pigments, absorb light energy for use in photosynthesis - why are accessory pigments present in the chloroplast [1]

Answer 103

to absorb a greater range of wavelengths of light

Question 104

- the kidneys have an important role to play in the removal of urea and homeostasis in the body - along the length of a nephron there are mechanisms which regulate the balance of water and dissolved solutes in the blood - a graph illustrates the changes in the % of sodium ions, glucose and water remaining in the filtrate as it passes from the start of the proximal convoluted tubule to the end of the loop of Henle - use the information from the graph to explain the changes in the filtrate as it passes through a nephron from the proximal convoluted tubule to the end of the loop of Henle [9QER]

Answer 104

PCT: - all glucose and some sodium ions (selectively) reabsorbed (back into the blood) - using co-transport with Na+ - lowers the water potential of the blood - so water out of filtrate into blood by OSMOSIS - so less water in filtrate DESCENDING LIMB OF LOOP OF HENLE - drop in water due to: - permeable to water - water moves out of filtrate by OSMOSIS into (tissue/interstitial fluid) - due to high concentration of Na+ ions there - sodium ions increase in descending limb due to DIFFUSION back in from interstitial fluid/medulla ASCENDING LIMB OF LOOP OF HENLE - impermeable to water - so water does not move out so levels stay same - Na+ actively transported out (into interstitial fluid) - so drop in ascending - makes filtrate more concentrated with Na+ at bottom of loop / reference to counter current multiplier

Question 105

- list the main steps of a method of counting bacteria that would allow the stationary phase (where no. of cells undergoing division is equal to no. of cell deaths) to be seen - details of aseptic technique are NOT required [4]

Answer 105

- take sample / transfer (a volume) of (culture / bacteria / E. coli) - serial dilution / description of - plate out / description of adding dilution to (agar / growth medium) - ignore put on/in a petri dish - incubate / description of being left for (suitable) time (at suitable temperature) - count (bacterial) COLONIES

Question 106

what is the shape of a gram negative cocci? [1]

Answer 106

spherical

Question 107

apart from habitat loss, name TWO other causes of species extinction [2]

Answer 107

- pollution - hunting/fishing - introduction/ competition of alien species - competition from domestic animals - natural selection - global warming / climate change

Question 108

- following a forest fire, given time, the forest will regenerate - using relevant technical terms, describe and explain the process of forest regeneration [3]

Answer 108

- secondary succession - presence of (soil / spore / seeds) - pioneer species are the first to return - (presence alters conditions) allowing other species to grow - seres / seral stages + the sequential progression of species to form intermediate communities / or description of - climax community + remain (stable / in equilibrium) / final stage of succession

Question 109

- human activity has resulted in the forest landscapes of Europe existing as a mixture of fragments of different ages and sizes - an image shows the fragmentation of forests surrounded by developed land - the Hardy-Weinberg principle states that allele frequencies remain constant from generation to generation - explain TWO reasons why this would not apply to the gene pool of species in fragments of land [2]

Answer 109

- (population / gene pool) in fragment would be small (HW would not apply) - genetic drift will cause changes in allele frequencies

Question 110

- osmoregulation is carried out

Question 111

- explain how ADH affects the target cells and how it prevents excessive water loss [3]

Answer 111

- (hormone) makes (the target cells) MORE permeable (to water) - correct reference to (more) aquaporins being inserted into membrane - (medulla / tissue) as a (lower potential) - so water moves (into the tissue / out of the filtrate) by osmosis - and a small volume of (concentrated/ hypertonic) urine released

Question 112

- the release of a hormone is brought about by the arrival of a nerve impulse - this is similar to the way in which neurotransmitters are released - describe how the hormone molecules are released from the end of the neurosecretory cell [5]

Answer 112

- impulses (arrive at tip and) open (voltage gated) Na+ channels - Na+ ions (rapidly pass / flood) into neurosecretory cell - (axon/membrane) is depolarised - which causes opening of (voltage gated) Ca2+ channels - Ca2+ ions diffuse into neurosecretory cell - and cause hormone containing vesicles to (move to/ fuse with) the membrane / correct reference to exocytosis

Question 113

- haemodialysis is one method of treating kidney failure - between dialysis sessions patients retain fluid and gain weight - excess fluid is removed during the next dialysis session to return the patient to their target weight - explain why it is important to remove excess fluid during haemodialysis [2]

Answer 113

- (body fluids) (will become too dilute / have a high water potential / will accumulate / build up) / correct reference to oedema - (entry of) water (lyses cells / causes cells to burst)

Question 114

- in addition to RuBisCO, carboxysomes contain the enzyme carbonic anhydrase - having carbonic anhydrase inside ENHANCES UPTAKE OF CARBON DIOXIDE by catalysing its combination with water - predict the effect that widespread use of crops engineered to contain carboxysomes might have on the carbon cycle and explain the impact this effect might have on the prospects for endangered species [3]

Answer 114

- increased photosynthesis / decreased atmospheric CO2 / more CO2 absorbed - will improve prospects for endangered species - (because less CO2 results in) less greenhouse effect / less climate change / global warming / higher yield leading to less habitat destruction

Question 115

what are some cell activities that require ATP?

Answer 115

- active transport - cell division - synthesis of (large / biological) molecules / proteins / complex carbohydrates / lipids / nucleic acids

Question 116

- in the conversion of pyruvate to lactate name the type of chemical reaction the pyruvate undergoes [1]

Answer 116

reduction

Question 117

- in the conversion of pyruvate of lactate - describe the part played by the coenzyme NAD [1]

Answer 117

provides the (electron/H) / reduces the pyruvate / acts as a (hydrogen/electron) (donor/carrier)

Question 118

- in the conversion of pyruvate of lactate - name the type of chemical reaction the coenzyme undergoes [1]

Answer 118

oxidation

Question 119

- an image shows ball and stick models of another Krebs cycle intermediate, succinic acid, and a molecule that is believed to act as a respiratory poison - using the info from the picture and your knowledge of enzymes suggest how malonic acid could act as a respiratory poison - explain your answer [2]

Answer 119

- competitive inhibitor - similar shape to succinic acid could act/ (fits into/complementary to) active site - prevents the succinic acid from binding to the active site / forms an enzyme substrate complex / prevents the formation of an enzyme substrate complex

Question 120

how are chloroplasts normally distributed in a typical leaf? [1]

Answer 120

- (in a layer) near upper epidermis / most chloroplasts are in the palisade (layer / cells / mesophyll)

Question 121

- describe and explain the changes in relative electron energy levels in non-cyclic photophosphorylation [5]

Answer 121

- in PS II (light/photons) (increase electron energy / excite electrons) - (higher energy electrons emitted and) accepted by electron acceptor - (energy decreases / electrons lose energy) as pass through (ETC / electron carriers) - (energy used to) (pump protons / for ATP production / photophosphorylation) -PS I (electrons raised to higher energy level / excited) and accepted by electron acceptor

Question 122

- NO2 dissolves in rainwater to form nitrous acids which break down to form nitrite ions and wash into the soil - name the soil bacteria that are act in nitrite ions and explain how the soil bacteria change the nitrite ions so they are able to continue to circulate in the nitrogen cycle [3]

Answer 122

- Nitrobacter - (converts nitrite) to (nitrates / NO3 -) - (nitrate) can be (absorbed / converted into amino acids) by (plants / producers) / broken down by (denitrification / Pseudomonas)

Question 123

- name the type of nervous system in Hydra and explain why its movements take a relatively long time [2]

Answer 123

- nerve net - unmyelinated / branched / impulses travel in many directions

Question 124

- an image shows an electron micrograph of the tip of a specialised nerve cell together with part of an adjacent cell (synaptic knob) - name the type of vesicle labelled and describe its function [1]

Answer 124

- synaptic (accept secretory / excretory) - transports (neurotransmitter / acetyl choline)

Question 125

- some drugs are described as acetylcholinesterase inhibitors - the site of action if these drugs are labelled (synaptic cleft) - suggest why these drugs cause over-stimulation of the membrane of the adjacent cell [2]

Answer 125

- (acetylcholine / neurotransmitter) (not broken down / remains in synaptic cleft) - continues to stimulate (post synaptic membrane /adjacent cell) / continuous (depolarisation/ action potentials) in (adjacent cell / neurone) / more (acetylcholine/neurotransmitter) binding to receptor on post-synaptic membrane

Question 126

explain how voltage-gated sodium ion channels bring about depolarisation [2]

Answer 126

- (Na+) channel opens - (Na+ / sodium ions) rush (into axon / into neurone / through membrane) - accept flood / rapidly diffuse in

Question 127

- the speed at which nerve impulses are conducted along nerve fibres depends on a number of factors, including myelination - graph 4.5 shows the results of a computer stimulation to investigate the effect of length of myelin internode on conduction speed - describe the relationship between internode length and conduction speed and use your knowledge of nerve impulse transmission to explain the results [4]

Answer 127

- increase (up to maximum / 60µm) and then decreases - depolarisation only takes place at the nodes / correct reference to saltatory conduction - less membrane needs to be depolarised / action potential does not have to travel the whole length of the neurone - (the longer the internode the conduction speed increases) due to less ‘jumps’ from node to node - when internodes are too long (impulses not able to jump from node to node / local currents are unable to extend to next node / no saltatory conduction

Question 128

- in culturing of bacteria, describe two precautions that should have been taken to prevent contamination of the samples of bacteria as they were transferred to the agar plates [2]

Answer 128

- flame (mouth of tubes / pipette) - hold lid above base of petri dish / lift lid (slightly / at an angle) - use a sterile pipette / pipette tip - work close to (the updraft of) a Bunsen burner

Question 129

- during an experiment, the number of bacterial cells was monitored by continuously measuring the optical density (cloudiness) of the culture using a colourimetry - a graph shows the population growth curve in the fermenter over a 4 hour period using the optical density method - explain the period of slow growth over the first 30minutes [1]

Answer 129

- (to give time to) synthesise (enzymes / proteins / DNA) / activating genes

Question 130

- for the first 40 minutes, the number of cells per cm^3 calculated from the agar plates was not significantly different from the number of cells per cm^3 calculated using optical density - however, as time passed the number calculated from the agar plates was significantly lower than the number calculated using optical density . - explain why there was no difference between the values from the two methods over the first 40 minutes but an increasing difference over the remaining time [3]

Answer 130

- (OD method) counts dead cells as well as living / total count for OD and viable count for the plates - for the first 40 minutes (no / few) dead cells - as time passes there are more dead cells

Question 131

- wetland ecosystems are increasingly threatened as land is drained for agriculture - an image shows some of the results of a survey carried out at Valley wetlands Centre, Anglesey - in order to carry out this survey, the team laid to rope across the area from north to south and identified the plant species that touched the rope - state the name given to the type of sampling technique used in the survey [1]

Answer 131

(line) transect

Question 132

- the swamp in this survey could be correctly termed as both a habitat and an ecosystem - distinguish between the terms habitat and ecosystem [2]

Answer 132

- habitat is the location - ecosystem (interaction between organisms in the community AND their environment / or description of) / ecosystem comprises biotic AND abiotic elements

Question 133

- name two nutrients for which plants will compete AND explain what each nutrient is used for in plants [3]

Answer 133

- nitrate / magnesium / phosphate - (nitrate to make) (amino acid/protein/chlorophyll/nucleic acids) - (magnesium to make) chlorophyll (molecules) - (phosphates to make) nucleic acids/phospholipids

Question 134

- explain why the concentration of nutrients is likely to be greater at the bottom of a pool of water and suggest a hypothesis to explain why pondweed (that grows at the bottom) outcompetes duckweed (grows at surface) in the deeper water [3]

Answer 134

- (plants/animals) die and bodied sink to form SEDIMENT / nutrients are present in the SEDIMENT - (organic matter and sediment is) decayed to release nutrients - duckweed (cannot reach the nutrients at the bottom / don’t have roots in the sediment)

Question 135

- two snails were found you in a survey - state how biologists would determine that snails belong to the same species [1]

Answer 135

- they can interbreed and produce fertile offspring (accept DNA (sequencing / profiling / fingerprinting) / amino acid sequencing)

Question 136

- suggest the advantage of bands to snails which live amongst twigs and leaves on the floor of the birch wood [2]

Answer 136

- better camouflage/less easily seen - less risk of (predation/being eaten) less easily seen by predators = 2 marks

Question 137

- feedback loops are essential to homeostasis - one image shows a generalised feedback loop and another image is a photograph of a person suffering from a condition caused by excessive alcohol conception - oedema: excess fluid retention: this condition can occur if the solute concentration of blood is too low, meaning that the water potential is not negative enough. this means the water cannot be drawn back into the blood from the surrounding tissue fluid . - explain the functions of each of the three components of a generalised feedback loop (detector, coordinator, effector) - with reference to the generalised feedback loop, describe the role of ADH in osmoregulation - long-term alcohol use has been shown to cause thickening of the basement membrane of glomeruli. explain how this change could cause oedema (details of tissue fluid formation are not required) [9QER]

Answer 137

FEEDBACK LOOP - detector (sensitive/reacts) to change in (set/normal) (point/level) - coordinator receives input from detector - and responds by sending an impulse to effector - effector bring about a change that corrects deviation OSMOREGULATION: - (hypothalamus/osmoreceptors) detects change in (water potential/body fluid concentration/concentration of blood) - hypothalamus sends a signal to the posterior pituitary gland - posterior pituitary gland releases (more) ADH if (water potential decreases/body fluid concentration increases) - walls of DCT and collecting ducts act as effectors - ADH makes walls of (DCT/collecting duct) more permeable to water (accept more aquaporins incorporated into membranes of (DCT/CD)) - MORE water (diffuses out of collecting duct/reabsorbed) into (medulla/blood) EXCESSIVE ALCOHOL USE - it is more difficult for fluid to pass through/less ultrafiltration occurs/ultrafiltration is more difficult - less fluid will leave the blood/more water remains in the blood/less filtrate is formed - blood is (more dilute/less concentrated)/blood has a higher water potential - fluid will accumulate (in tissues/reference to oedema) /stops water being drawn back into the blood h

Question 138

what happens to the carbon atoms that are lost in the krebs cycle? [1]

Answer 138

(released as) CO2

Question 139

describe the role of the two coenzymes in aerobic respiration and explain why they result in different yields of ATP [3]

Answer 139

- (transport/donate) (H atom/electrons/H+/protons) to (ETC/inner mitochondrial membrane/electron carriers - NAD delivers to first proton pump and FAD to second / NAD uses 3 (types of) proton pumps and FAD uses 2 - (reduced) NAD results in more protons being pumped (across membrane) than reduced FAD / reduced NAD leads to a steeper proton gradient - NAD gives 3 ATP FAD gives 2 ATP - NAD involved in glycolysis and link and krebs, but FAD only krebs

Question 140

state the term used to describe the role of oxygen in aerobic respiration [1]

Answer 140

FINAL (hydrogen / electron) acceptor

Question 141

what is the inside of the thylakoid called?

Answer 141

thylakoid space

Question 142

describe how the components in the membrane of mitochondria are involved in the synthesis of ATP by chemiosmosis [5]

Answer 142

- proton pump pumps protons (into intermembrane space/across membrane) - to create (proton/H+/electrochemical) gradient - (ATP synthase/stalked particle) allows (protons/H+) (through membrane/down gradient) - (convert/combine) ADP (+Pi) to ATP - correct reference to (electron carriers/electron transport chain - ref to: proton pump AND ATP synthase

Question 143

- the capture-recapture method was used to determine the number of adult frogs - they were marked by clipping off one toe - explain why the chosen method of marking the frogs might have affected the estimate of the frog population [1]

Answer 143

- removing part of toe might affect (ability to survive / increase chance of recapture)

Question 144

what are some density-dependent factors that might change a tadpole population [1]

Answer 144

- COMPETITION for food - predation - disease - accumulation of toxic waste

Question 145

use a graph to explain the change in concentration for urea and chloride ions along the proximal convoluted tubule [2]

Answer 145

- (conc of urea increases because) (little/no) urea is reabsorbed but water is reabsorbed - (conc of chloride decreases because) chloride is (reabsorbed / diffuses out / actively transported out) (faster than water)

Question 146

explain the change in concentration of glucose with a respiratory inhibitor along the proximal convoluted tubule [3]

Answer 146

- with inhibitor no respiration and therefore (no/less) ATP - no active transport of Na+ out of PCT - therefore no concentration gradient of Na+ - for the co-transport of glucose

Question 147

- the Na+ concentration in the sample taken from the start of the descending limb of the loop of Henley was higher than the sample taken at the end of the ascending limb - use your knowledge of the function of both limbs of the structure to explain this result [4]

Answer 147

- descending limb water leaves by osmosis - Na+ concentration increases (as it moves down the descendent limb/as it gets closer to the (hairpin/apex) /as it moves deeper into the medulla) - ascending limb Na+ pumped out - ascending limb is impermeable to water - Na+ concentration decreases as it moves up the ascending limb

Question 148

- name the two reactants involved in the fixation of carbon in green plants and the enzyme that catalyses this process [2]

Answer 148

- RuBP / ribulose bisphosphate + carbon dioxide - RuBisCO

Question 149

- planetary boundaries: - state what is meant by the safe operating space for humanity - describe where that is shown on a circular graph - describe the consequences of exceeding planetary boundaries [3]

Answer 149

- (safe operating space is) where (planetary/global) systems are stable/changes are reversible/there is no detrimental impact on global systems - (shown by the) (central circle/threshold/ dashed circle) - (exceeding boundary) results in small changes having extreme effect/causes (irreversible/unpredictable) (damage/change) / given example example e.g. extinction m

Question 150

- an image shows the pathway from a tooth to an area of the brain which generates the sensation of pain - it also shows the site of action of two local anaesthetics used in dentistry - site of action of local anaesthetic A which prevents the passage of sodium ions into neurones - site of action of local anaesthetic B, which prevents the entry of calcium ions into the presynaptic membrane . - compare and contrast the pathway shown in the first image with a reflex arc in the second image - using your knowledge of the generation of action potentials, suggest how anaesthetic A will prevent pain - using your knowledge of synaptic transmission, suggest how anaesthetic B could also prevent pain [9QER]

Answer 150

ANAESTHETIC a - anaesthetic A (blocks Na+ channels/ Na+ channels don’t open) - threshold (potential) is not met / ref to all or nothing (member) not depolarised - action potential is not generated - so impulse doesn’t reach (pain centre/brain) ANAESTHETIC B - anaesthetic B block Ca2+ channels/ Ca2+ channels do not open - (Ca2+ can’t enter) so synaptic vehicles don’t fuse with presynaptic membrane - neurotransmitter not released into synaptic left / no exocytosis - postsynaptic membrane not depolarised - no action potential generated - so impulse does not reach (pain centre/brain) COMPARE WITH REFLEX ARC - both have sensory neurones / both have 3 neurones - (with cell bodies) in ganglia - outside CNS - pain pathway has no motor neurones /shorter motor neurones /motor neurone in brain - accept reverse answer for reflex - pain pathway has no relay neurone/relay neurone in brain/longer relay neurone - pain pathway has no effector/effector is located in the brain - involves brain not spinal cord

Question 151

suggest why the mean values for the first two dilutions were so close despite there being a 100 times difference in the dilutions [1]

Answer 151

clumping of bacteria / overlapping colonies / difficult to count large colony numbers

Question 152

dilution - SD 10^-3 - 50.5 10^-5 - 17.7 state what the standard deviations of the l two dilutions tell u about the data [1]

Answer 152

- data range is very large / 10^-3 is less reliable than 10^-15 / both unreliable as they have a large SD / data is very variable

Question 153

describe the effect of heat in the process of pasteurisation on the proteins in bacteria [3]

Answer 153

- increased kinetic energy + (breaks hydrogen bonds / denatures protein) - holding together the specific (3-D) shape/shape of active site changes - protein can no longer carry out function/enzyme-substrate complexes (can no longer form/reduced £

Question 154

- selective reabsorption occurs in the proximal convoluted tubule - describe two ways in which the cells of the proximal convoluted tubule are adapted for reabsorption [2]

Answer 154

- microvilli so large surface area for diffusion - many mitochondria for active transport / co-transport

Question 155

state two problems associated with kidney transplants [2]

Answer 155

- organ rejection - shortage of donors - immunosuppressants

Question 156

is the reaction of ADP + Pi —> ATP endergonic or exergonic? explain ur answer [1]

Answer 156

endergonic - energy (being stored / taken in / gained) / HIGH ENERGY BONDS (created / formed)

Question 157

why is ATP needed for endocytosis/exocytosis?

Answer 157

- ATP needed as source of energy to change shape of cell membrane / form the vesicle