Unit 5 Exam Questions

Question 1

In the light-dependent reaction of photosynthesis, light energy generates ATP.Describe how 5 marks

Answer 1

1.Light (energy) excites / raises energy level of electrons in chlorophyll;

2.Electrons pass down electron transfer chain;Q Accept any reasonable alternative for electron transfer chain.

3.(Electrons) reduce carriers / passage involves redox reactions;

4.Electron transfer chain / role of chain associated with chloroplastmembranes / in thylakoids / grana;Example such as chemiosmosis;

5.Energy released / carriers at decreasing energy levels;

6.ATP generated from ADP and phosphate / Pi / phosphorylation of ATP;

Question 2

the role of chlorophyll in photolysis;

Answer 2

Absorbs light / energy;Loses electrons / becomes positively charged / is oxidised;

Question 3

Describe the role of electron transport chains in the light-dependent reactions of photosynthes

Answer 3

1 electron transport chain accepts excited electrons
2 from chlorophyll / photosystem;
3 electrons lose energy along chain;
4 ATP produced;
5 from ADP and Pi;
6 reduced NADP formed;
7 when electrons (from transport chain) and H+combine with NADP;
8 H+from photolysis

Question 4

Crops use light energy to produce photosynthetic products.Describe how crop plants use light energy during the light-dependent reaction 5 marks

Answer 4

1. Excites electrons / electrons removed (from chlorophyll) ;Accept: higher energy level as ‘excites’.
2. Electrons move along carriers/electron transfer chain releasing energy;
3. Energy used to join ADP and Pi to form ATP
4. Photolysis of water produces protons, electrons and oxygen;
   5.NADP reduced by electrons / electrons and protons / hydrogen;

Question 5

After harvesting, the remains of crop plants are often ploughed into the soil.Explain how microorganisms in the soil produce a source of nitrates from these remains

Answer 5

1. Protein/amino acids/DNA into ammonium compounds / ammonia
   2.By saprobionts
2. Ammonium/ammonia into nitrite;
   4.Nitrite into nitrate;
   5.By nitrifying bacteria/microorganisms

Question 6

Explain why converting pyruvate to ethanol is important in allowing the continued production of ATP in anaerobic respiration

Answer 6

allows NAD to be recycled / re-formed;so that glycolysis / described / candidates answer to (i) can proceed / so that (more) glucose can be converted to pyruvate

Question 7

Describe the part played by the inner membrane of a mitochondrion in producing ATP. 3 marks

Answer 7

Electrons transferred down electron transport chain;
Provide energy to take protons / H+into space between membranes
Protons / H+pass back, through membrane / into matrix / throughATPase;
Energy used to combine ADP and phosphate / to produce ATP;

Question 8

The scientist measured the uptake of oxygen by the mitochondria during the investigation. The uptake of oxygen decreased when malonate was added. Explain why 2 marks

Answer 8

1.Krebs cycle inhibited as NAD / Coenzyme / FAD not / less reduced;
2.Hydrogens not passed to ETC therefore oxygen not used as (much as a) final / terminal (electron) acceptor;

Question 9

Describe how ATP is made in mitochondria

Answer 9

1.Substrate level phosphorylation / ATP produced in Krebs cycle;
2.Krebs cycle / link reaction produces reduced coenzyme / reduced NAD / reduced FAD;
3.Electrons released from reduced / coenzymes / NAD / FAD
4.(Electrons) pass along carriers / through electron transport chain / through series of redox reactions;
5.Energy released;
6. ADP / ADP + Pi;
7. Protons move into intermembrane space;
8. ATP synthase;

Question 10

Why is it important that plants respire to make ATP and not just photosynthesise?

Answer 10

1.In the dark no ATP production in photosynthesis;1. In context of in photosynthetic tissue / leaves
2.Some tissues unable to photosynthesise / produce ATP;
3.ATP cannot be moved from cell to cell / stored;
4.Plant uses more ATP than produced in photosynthesis;
5.ATP for active transport / synthesis (of named substanc

Question 11

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

Answer 11

Any two from:
(Water) forms H+/ hydrogen ions andelectrons / e–;
O2/ oxygen formed; [NOT‘O’, NOT‘O–’]
(Light) excites electrons / raises energy level of electrons / electrons to chlorophyll / to photosystem;

Question 12

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.

Answer 12

(ATP) Provides energyfor GP →TP / provides Pfor RuP / TP →RuBP;
(Reduced NADP) Provides H / electronsfor GP →TP / reducesGP to TP;

Question 13

Some bacteria use hydrogen sulfide, H2S, to produce organic compounds.The hydrogen sulfide has a similar role to that of water in photosynthesis.A simple equation for this process in bacteria is shown below:hydrogen sulfide + carbon dioxide →glucose + sulfur + waterSuggest what the hydrogen sulfide is used for in these bacteria.

Answer 13

1.(Provides) hydrogen / protons/H+andelectrons/e-;
2.For reduction;
3.Source of electrons for chlorophyll/electron transfer chain;

Question 14

Describe how acetylcoenzyme A is formed in the link reaction.

Answer 14

1. Oxidation of / hydrogen removed from pyruvate andcarbon dioxide released;
2. Addition of coenzyme A.