Energy Transfers in and between Organisms

Question 1

Explain why the light independent stage of photosynthesis stops in the absence of light
(2 marks)

Answer 1

Supply of the products from the light dependent stage would stop.
Therefore no ATP and reduced NADP are passed into the light independent stage.

Question 2

Explain why at 25c raising the level of carbon dioxide from 0.04% to 0.1% increases the amount of glucose produced
(3 marks)

Answer 2

More carbon dioxide would be available to combine with ribulose bisphosphate (RuBP).
This forms more glycerate 3 phosphate (GP) which more triose phosphate and more hexose sugars such as glucose are formed.

Question 3

In the light-dependent stage of photosynthesis explain the role of protons in supplying intermediate products to the light dependent stage
(5 marks)

Answer 3

Protons are yielded by photolysis of water
Protons build up in the thylakoid space
Protons only pass out to the stroma via ATP synthase
Proton flow through ATP synthase drives the synthesis of ATP from ADP and Pi
Protons reduce NADP to NADPH

Question 4

Describe the exact role of ribulose biphosphate in the Calvin cycle
(3 marks)

Answer 4

RuBP’s role is to combine with a molecule of carbon dioxide. This produces 2 molecules of GP

Question 5

Describe the formation of acetyl coenzyme A in the link reaction
(3 marks)

Answer 5

It is formed by oxidation of pyruvate (hydrogen is removed from pyruvate and carbon dioxide is released.
The accompanying reduction reaction is the formation of reduced NAD from NAD.
Coenzyme A binds to the 2 carbon acetyl group forming acetyl CoA.

Question 6

Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP
(4 marks)

Answer 6

NAD/FAD are reduced
Electrons transferred in a series of redox reactions
Energy made available as electrons passed on
Energy used to synthesise ATP from ADP and phosphate
Protons are passed into the intermembrane space

Question 7

When measuring the rate of aerobic respiration why did the drop of coloured liquid move to the left?
(2 marks)

Answer 7

Oxygen is take up
Carbon dioxide is absorbed by the solution
There is a decrease in pressure

Question 8

Explain why oxygen is referred to as the ‘terminal electron acceptor’ in the process of aerobic respiration
(3 marks)

Answer 8

Oxygen has a high electronegativity meaning it attracts electrons.
Oxygen combines with protons and electrons to form water
Protons produced in glycolysis and Krebs cycle
Electrons passed down the electron transport chain

Question 9

Name two main groups of molecules (other than carbohydrates) that are used as respiratory substrates and describe how their catabolic products join the main pathways of respiration
(6 marks)

Answer 9

LIPIDS
- glycerol from lipids are converted to triose phosphate
- fatty acids are broken down and converted to CoA
PROTEINS
- amino acids deaminated
- 3C and 5C compounds are converted to pyruvate

Question 10

Describe the production of ATP in aerobic respiration
(6 marks)

Answer 10

ATP is produced in the Krebs cycle.
The Krebs cycle produces reduced coenzymes (reduced NAD and reduced FAD).
Electrons are released from the reduced coenzymes.
Electrons pass along the electron transport chain via a series of redox reactions.
Energy is released.
Protons move into the intermembrane space via ATP synthase.

Question 11

Define the term trophic level
(2 marks)

Answer 11

A trophic level is a step in a food chain based on the feeding behaviour of an organism

Question 12

Explain why the energy content of biomass measured in a calorimeter can only be an estimate
(2 marks)

Answer 12

Different organs have different energy contents
Difficult to quantify the energy content of a large organism from a small calorimeter sample
Not all the biomass will combust fully in a calorimeter
Not all the energy given out as heat will be transferred to the water

Question 13

Describe the nature of mycorrhizae and their role in facilitating the uptake of water and inorganic ions by plants
(3 marks)

Answer 13

Mycorrhizae are associations between fungi and roots of certain plants.
Mycorrhizae form mutualistic relationships with host plants.
Fungus receives sugar for respiration and amino acids in return for water and minerals

Question 14

Describe and explain how 2 different farming practices can result in the removal of nitrogen containing compounds from a field
(4 marks)

Answer 14

Leaving bare soil = nitrate leach away
Removal of hedges = soil erosion
Growing a high protein crop = nitrogen is taken up by the crop
Grazing animals in the field = nitrogen is taken up by the animals

Question 15

Explain the roles of the decomposers and the nitrifying bacteria in converting nitrogen from organic compounds in the sewage into a soluble inorganic form
(3 marks)

Answer 15

Decomposers convert nitrogen into ammonia
Nitrifying bacteria converts ammonium to nitrate via nitrite

Question 16

Describe the important to ecosystems of the role played by nitrogen fixing bacteria in the nitrogen cycle
(3 marks)

Answer 16

They convert nitrogen gas into ammonium and ammonia.
They provide nitrogen in usable forms to other organisms on all trophic levels for protein synthesis