Topic 5 AQA A Level

Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested/2

1. amino acid / protein / polypeptide / peptide;

2. nucleic acid / nucleotide / base;

3. DNA;

4. RNA;

5. ATP / ADP;

6. NAD / NADP (reduced or not);

7. Cyclic AMP / cAMP;

8. Chlorophyll;

Explain the role of glycogen molecules in skeletal muscles/2

1. As a store of glucose

Ignore provide energy

OR

To be hydrolysed to glucose;

2. For respiration / to provide ATP;

Where precisely in a cell does the Calvin cycle take place?/1

Stroma (of chloroplasts);

In respiration glucose --> pyruvate --> ethanol and carbon dioxide. Where in the cell does the first stage happen converting glucose to pyruvate /1

Cytoplasm/cytosol;

In respiration glucose --> pyruvate --> ethanol and carbon dioxide.. Explain how stage 2 between pyruvate and ethanol and carbon dioxide enables stage 1 (converting glucose to pyruvate) to continue/2

1. Regenerates/produces NAD / oxidises reduced NAD;

2. NAD reduced in stage 1/glycolysis / NAD accepts hydrogen in stage 1/glycolysis;

Scientists took a large number of photographs of thin sections through neurones.

Using these photographs, they found that 40% of mitochondria had the unusual ultrastructure in damaged neurones. What sort of microscope would the scientists use to take the photographs? Give one reason for your answer./1

(Transmission) electron (microscope) - no mark

Need high resolution to see structure of mitochondria

Describe another process Iother than the nitrogen cycle) carried out by microorganisms which adds ammonium ions to soil./2

1. Protein / amino acids broken down (to ammonium ions / ammonia)

2. By saprobionts / saprobiotic (microorganisms).

Suggest appropriate units for gross productivity./1

Unit of energy / mass, per area, per year.

Explain the decrease in gross productivity as a woodland matures/2

1. Less light / more shading / more competition for light;

Neutral: references to animals

2. Reduced photosynthesis.

Accept: no photosynthesis

Describe how acetylcoenzyme A is formed in the link reaction./2

1. Oxidation of / hydrogen removed from pyruvate and carbon dioxide released; (Accept: NAD reduced for oxidation)

2. Addition of coenzyme A.

In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to form six-carbon citrate. This reaction is catalysed by the enzyme citrate synthase.

Oxaloacetate is the first substrate to bind with the enzyme citrate synthase. This induces a change in the enzyme, which enables the acetylcoenzyme A to bind.

Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme/2.

1. Change (in shape) of active site / active site moulds around the substrate;

Reject: reference to inhibitor

Accept: change in tertiary structure affecting active site

2. (Substrate / active site) now complementary.

Neutral: references to two active sites

Nitrates and phosphates are two nutrients. They provide a source of nitrogen and phosphorus for cells.

Give a biological molecule that contains:i) Nitrogen (1 mark) ii) phosphorus (1 mark)

1. Amino acid / protein / enzyme / urea / nucleic acid / chlorophyll / DNA / RNA / / ATP / ADP / AMP / NAD / NADP;

2. DNA / RNA / nucleic acid / ATP / ADP / AMP / NADP / TP / GP / RuBP / phospholipids;

Describe the role of microorganisms in producing nitrates from the remains of dead organisms./3

1. Saprobiotic microorganisms break down remains / dead material into ammonia

2. Ammonia converted into nitrite and then into nitrate

3. By nitrifying bacteria (nitrification)

Explain why CO2 uptake is a measure of net productivity./1

net productivity = (gross) photosynthesis - (minus) respiration.

State which of the following: Glycolysis, Link Reaction, Krebs cycle 1. Occurs in the mitochondria 2. Carbon dioxide is produced. 3. NAD is reduced (there can be more than one answer per Q)./3

1, Link and Krebs (1). 2. Link and Krebs (1). 3. All 3 (1)

In the nitrogen cycle name the process where ammonium ions convert to nitrite ions/1

Nitrification / oxidation

In the nitrogen cycle name the process where nitrate ions convert to nitrogen/1

Dentrification

State which of the following is true: 1. ATP produced. 2. Occurs in organelles. 3. Electron transport chain involved for a) photosynthesis, b) anaerobic respiration c) aerobic respiration / 3

a) all 3 b) only ATP produced c) all 3

Write a simple equation to show how ATP is synthesised from ADP./1

ADP + Pi → ATP;

Give two ways in which the properties of ATP make it a suitable source of energy in biological processes./2

1. Energy released in small / suitable amounts;

2. Soluble;

3. Involves a single / simple reaction;

Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP./2

1. ATP cannot be stored / is an immediate source of energy; 2. ATP only releases a small amount of energy at a time;

The over-application of fertiliser increases the rate of leaching. Explain the consequences of leaching of fertiliser into ponds and lakes./3

1. Increase algae / algal bloom causes light to be blocked out;

2. Plants can't photosynthesise / plants and / or algae die;

3. Bacteria / saprobionts breakdown dead organisms using up oxygen

Urea from animal waste can be used as a fertiliser. Some bacteria in the soil secrete the enzyme urease which hydrolyses urea into ammonia. Some of this ammonia is released into the atmosphere. NBPT is an inhibitor of urease and can be added to urea fertiliser to reduce the loss of ammonia to the atmosphere.A molecule of NBPT has a similar structure to a molecule of urea. Use this information to suggest how NBPT inhibits the enzyme urease./2

NBPT is complementary to the active site, binding to it.

Competitive inhibition, preventing urea attaching and enzyme-substrate complexes from forming.

When fertilisers are applied to fields next to a lake, nitrogen-containing substances from the fertilisers get into the lake. Describe how the nitrogen-containing substances get into the lake./1

dissolve (in soil water) / run-off / leaching; reject nitrogen dissolving

It takes longer for the nitrogen-containing substances to get into the lake when an organic fertiliser is used than when an inorganic fertiliser is used. Explain why it takes longer when an organic fertiliser is used./2

insoluble / less soluble;

(molecules) require breaking down so there is a slow release

Describe how the presence of nitrates in a lake may eventually lead to the death of fish./4

increased growth / algal bloom;

blocks light; less photosynthesis;

plants die;

increase in decomposers / bacteria; ignore growth of bacteria

bacteria respire;

less oxygen;

Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion./3

ATP formed as electrons pass along transport chain;

oxygen is terminal electron acceptor

electrons cannot be passed along electron transport

chain if no O2 to accept them;

forms H2O by accepting H+ from reduced NAD / FAD

Explain the roles of the decomposers and the nitrifying bacteria in converting nitrogen in organic compounds in the sewage into a soluble, inorganic form./3

decomposers convert (nitrogen in organic compounds) into ammonia / ammonium; suitable example of "organic nitrogen" - protein / urea / amino acid etc. (e.g. linked to process); nitrifying bacteria / correctly named convert ammonium to nitrate; via nitrite;

Nitrifying bacteria are one kind of bacteria that are important in the nitrogen cycle; nitrogen-fixing bacteria are another kind. Describe the part played by nitrogen-fixing bacteria in the nitrogen cycle./2

convert nitrogen (gas) into ammonium / ammonia / amino acids;

add usable / available nitrogen to an ecosystem / eq."

The kangaroo rat is a small desert mammal. It takes in very little water in its food and it rarely drinks. Its core body temperature is 38 °C.

The kangaroo rat takes in some water by feeding and drinking. Describe another method by which the kangaroo rat could obtain water./2

metabolic water / from respiration;

allow condensation reactions. Ignore 'oxidation'.

aerobic / use of oxygen; ('From aerobic respiration' = 2 marks)

In anaerobic respiration, what is the net yield of ATP molecules per molecule of glucose?/1

2 (molecules)

Give two advantages of ATP as an energy-storage molecule within a cell./2

Cannot pass out of cell;

Quickly / easily broken down (hydrolysed)

Stores / releases small amounts of energy

Do not credit "producing energy"

Describe how NAD is regenerated in anaerobic respiration in yeast cells./1

Formed when reduced NAD used to reduce pyruvate , converting it to ethanol;

The photolysis of water is an important part of the process of photosynthesis. Describe what happens in the photolysis of water./2

Water forms hydrogen ions and electrons

Oxygen formed

Light excites electrons to chlorophyll

Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 molecules of ATP for each molecule of nitrogen that is reduced. Nitrogen gas is the usual substrate for this enzyme. Name the product./1

Ammonia / ammonium / NH3 / NH4+;

ATP and reduced NADP are two products of the light-dependent reactions. Describe one function of each of these substances in the light-independent reactions. A) ATP b) Reduced NADP/2

ATP provides energy for GP → TP / provides P for RuP / TP → RuBP;

Reduced NADP provides H / electrons for GP → TP / reduces GP to TP

Apart from respiration, give three uses of ATP in a liver cell./3

Source of energy / of phosphate;

Active transport;

Phagocytosis / endo- / exocytosis / pinocytosis;

Bile production;

Cell division / mitosis;

Synthesis of: glycogen;

protein / enzymes;

DNA / RNA;

lipid / cholesterol;

urea;

Human skeletal muscle can respire both aerobically and anaerobically. Describe what happens to pyruvate in anaerobic conditions and explain why anaerobic respiration is advantageous to human skeletal muscle./4

Any four from:

Forms lactate;

Use of reduced NAD / NADH;

Regenerates NAD;

NAD can be re-used to oxidise more respiratory substrate / correct e.g.

Can still release energy when oxygen in short supply

Pyruvate is formed in the breakdown of glucose during respiration. When there is sufficient oxygen, this pyruvate is fully broken down. Name two substances formed from the pyruvate./1

CO2, water, ATP, reduced NAD / FAD;

If there is a shortage of oxygen in muscle cells during exercise, some pyruvate is converted into lactate. Explain why muscles become fatigued when insufficient oxygen is available./2

1. increased concentration of lactate lowers pH

2. enzymes / named protein inhibited (not denatured);

Some of the lactate is oxidised to pyruvate by muscles when they are well-supplied with oxygen. Suggest an advantage of the lactate being oxidised in the muscles./2

lactate / pyruvate is an energy source;

muscles have increased / immediate energy or ATP supply;

Name the type of bacteria which convert i) nitrogen in the air into ammonium compounds;ii) nitrites into nitrates /2

(i) nitrogen-fixing;

(ii) nitrifying;

Other than spreading fertilisers, describe and explain how one farming practice results in addition of nitrogen-containing compounds to a field./2

growing legumes / named legume;

ploughed in / allowed to decompose / nitrogen-fixing (bacteria in nodules);

OR

allow cattle / named species / (farm) animals (to graze);

add dung / urine;

OR

spread / add manure / slurry;

decomposed to release nitrates / ammonia / nitrites;

Describe and explain how one farming practice results in the removal of nitrogen-containing compounds from a field./2

bare soil / fallow in winter / hedge removal; leaching

(of nitrates) / soil erosion;

OR

uptake of nitrates / ammonium compounds by crop;

harvesting crop / named crop which would be harvested;

OR

(farm) animals eat plants

(in field); (then) animals removed;

Name the two substances produced by anaerobic respiration in humans./2

lactate / lactic acid / pyruvate; ATP;

When an athlete runs in a 100 metre race, 90% of the energy needed is provided by anaerobic respiration. Explain why most of the energy is provided by anaerobic respiration rather than aerobic respiration./2

energy demand is very high ;

unable to supply enough oxygen to muscles / tissues

The athlete continues to breathe deeply for several minutes after a 100m race ends. Explain why this is necessary./2

oxidise lactate into pyruvate / glucose / glycogen / CO2 + water;

by aerobic respiration;

In which part of the mitochondrion does the Krebs cycle take place?/1

matrix

Name two substances for which there would be net movement into the mitochondrion./2

pyruvate;

ADP;

P / inorganic phosphate;

reduced NAD;

oxygen;

The mitochondria in muscles contain many cristae. Explain the advantage of this./2

larger surface area for electron carrier system / oxidative phosphorylation;

provide ATP / energy for contraction;

The producers in a marine ecosystem are seaweeds, which have a large surface area to volume ratio. Give two advantages to seaweeds of having a large surface area to volume ratio./2

(larger area) to absorb light;

(larger surface area) to absorb carbon dioxide;

short diffusion pathway for gases / oxygen / CO2;

light able to penetrate to all cells;

Pea plants respire aerobically, producing ATP which can be used for amino acid synthesis. Describe the role of oxygen in aerobic respiration./2

final acceptor for hydrogen:

to form water;

Some bacteria respire anaerobically. This produces hydrogen and ATP used in nitrogen fixation. The hydrogen comes from reduced NAD. Explain how the regeneration of NAD in this way allows ATP production to continue./2

glycolysis can continue;

NAD can accept more hydrogen;

The enzyme nitrogenase is specific to its reaction. Explain how one feature of the enzyme would contribute to this specificity./2

secondary / tertiary structure;

produces particular shape of active site;

or

(shape of) active site;

complementary to shape of substrate;

Other substances are produced in the Krebs cycle in addition to the carbon dioxide and the 4 5 and 6 carbon compounds. Name three of these other products/3

reduced NAD / NADH

reduced FAD / FADH

ATP;

In which part of a chloroplast does the light-independent reaction occur?/1

stroma

Which process is the source of the ATP used in the conversion of glycerate 3-phosphate (GP) to triose phosphate?/1

light-dependent reaction / (photo)phosphorylation;

(accept photolysis)

Give one reason why not all the light energy falling on producers is used in photosynthesis./1

transmission / reflected / misses chlorophyll / chloroplasts / wrong wavelength;

Some species of seaweed are submerged in water for most of the time. Explain how being under water might affect the rate of photosynthesis./2

effect; (more than one effect give 1 mark only)

detail;

effect on photosynthesis;

some effects are less light / light absorbed by water

different wavelength of light

temperature

availability of carbon dioxide

availability of water

Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the advantage of mitochondria in muscle cells having more cristae./2

1. larger surface area for electron transport chain /

more enzymes for ATP production / oxidative phosphorylation;

2. muscle cells use more ATP than skin cells (not just more respiration);

Substance X enters the mitochondrion from the cytoplasm. Each molecule of substance X has three carbon atoms. Name substance X / 1

pyruvate

Substance X enters the mitochondrion from the cytoplasm. Each molecule of substance X has three carbon atoms.In the link reaction substance X is converted to a substance with molecules effectively containing only two carbon atoms. Describe what happens in this process./2

carbon dioxide formed / decarboxylation;

hydrogen released / reduced NAD formed;

acetyl coenzyme A produced;

The Krebs cycle, which takes place in the matrix, releases hydrogen ions. These hydrogen ions provide a source of energy for the synthesis of ATP, using coenzymes and carrier proteins in the inner membrane of the mitochondrion.

Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP./3

1. NAD / FAD reduced / hydrogen attached to NAD / FAD;

2. H+ ions / electrons transferred from coenzyme to coenzyme in a series of redox reactions;

3. energy made available as electrons passed on;

4. energy used to synthesise ATP from ADP and phosphate using ATPase;

5. H+ passed into intermembrane space

6. H+ / protons flow back through stalked particles / enzyme;

In autumn when there is no crop, farm land may be used to grow mustard. The mustard absorbs nitrates which otherwise can leach out of the soil at this time of the year. The mustard is ploughed back into the soil just before sowing of the main crop in the spring.

Nitrogen compounds in the mustard plants are made available for the main crop after ploughing in spring. Describe the role of microorganisms in this process./5

proteins / amino acids broken down;

deamination / ammonification / release of ammonium compounds;

conversion to nitrates;

by nitrifying bacteria / named bacterium;

nitrates absorbed into roots;

Explain why it is important for the farmer to reduce the leaching of nitrates./2

fewer nitrates in the soil for the next crop / plants grow less well

because of lack of nitrates;

requiring application of more fertiliser / economic reason for using less fertiliser / valid environmental reason explained e.g. nitrates leaching into water / eutrophication / explanation / health related e.g drinking water;

Plants absorb a number of other nutrients from the soil including phosphates. Describe why phosphates are needed by a growing plant./4

production of phospholipids;

in cell membranes;

synthesis of ATP;

production of DNA;

production of RNA;

production of NADP;

When one mole of glucose is burned, 2800 kJ of energy are released. However, when one mole of glucose is respired aerobically, only 40% of the energy released is incorporated into ATP. Each mole of glucose respired aerobically produces 38 moles of ATP.

Calculate how much energy is incorporated into each mole of ATP. Show your working./2

29.47(29.5);

(2 marks for correct answer)

40% / 0.4 of 2800 / 38;

When glucose is respired what happens to the energy which is not incorporated into ATP?/1

released as heat;

When one mole of glucose is respired anaerobically, only 2 moles of ATP are produced. Explain why less energy is released in anaerobic respiration./1

glucose only partly broken down / only broken down to lactate;

At the end of a sprint race, a runner continues to breathe rapidly for some time. Explain the advantage of this./2

lactate / lactic acid has built up ;

oxygen used to break down lactate / convert it back to pyruvate / glucose / glycogen;

During respiration where, exactly, in a cell does each of the following occur? i) glycolysis ii) electron transport chain/2

Cytoplasm ii) Inner membrane of mitochondrion Icristae; Reject ‒ crista/ particle

Without oxygen, less ATP is produced by respiration. Explain why./2

Oxygen is the termina/ acceptor;

(No) electron transfer chain / proton transfer / no oxidative phosphorylation;

Which produces most of the ATP (in aerobic respiration);

Only glycolysis takes place;

Pyruvate used to make lactate;

Only produces (net) 2 ATP per molecule of glucose;

Give two products of the light-dependent stage of photosynthesis./2

Reduced NADP;

ATP;

Accept oxygen

The products of the light-dependent stage are used in the light-independent stage of photosynthesis. What are these products used for?/1

To incorporate carbon dioxide to make sugars/glucose/fructose;