Energy transfers in and between organisms

Question 1

3 marks

What structural features of the thylakoids increase rate of photosynthesis

Answer 1

1. Contain photosynthetic pigments to absorb light energy
2. Large SA as discs stacked into grana to increase light absorption
3. Contain ATP synthase enzymes required to make ATP in LIR

Question 2

6 marks

Desribe the role of electron trasnport chains in the light- dependent reactions of photosynthesis

Answer 2

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

Question 3

6 marks

Absorption of light energy and electron transfer chain

Answer 3

• Chlorophyll molecule absorbs light energy
• Pair of electrons become excited and move to higher energy level
• Electrons leave, chlorophyll molecule = oxidised
• Taken up by electron carrier molecule = reduced
• Move down chain in series of oxidation-reduction reactions
• Losing energy at each stage - used to combine ADP+Pi = ATP

Question 4

5 marks

Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP

Answer 4

Excitation of electrons raised to higher energy level
Electrons emimted from chlorophyll molecule
Electrons to electron transport chain
Loss of energy by electrons along electron transport chain
Energy lost by electrons is used to synthesise ATP; From ADP + Pi

Question 5

6 marks

Describe the light- independent reaction of photosynthesis

Answer 5

1. Carbon dioxide reacts with RuBP
2. Produces two GP using Rubisco
3. GP reduced to TP
4. Using reduced NADP
5. Using energy from ATP
6. TP converted to useful organic substances like glucose

Question 6

4 marks

Describe process of glycolysis

Answer 6

1. Glucose is phosphorylated using Pi from ATP
2. NAD is reduced
3. As TP is oxidised to form pyruvate
4. Net gain of 2 ATP molecules- 4 ATP molecules are produced

Question 7

2 marks

Describe how acetylcoenzyme A is formed in the link reaction

Answer 7

1. Oxidation of pyruvate and CO2 released
2. Addition of coenzyme A

Question 8

2 marks

Malonate inhibits the Krebs cycles
Explain why malonate would decrease the uptake of oxygen in a respiring cell

Answer 8

1. Less reduced NAD and reduced FAD made
2. Less oxidative phosphorylation
3. Less oxygen is used as a final electron acceptor

Question 9

Give ways in which the properties of ATP make it a suitbale source of energy in biological processes

Answer 9

• Immediate source of energy
• Soluble
• Involves in a simple reaction
• Energy released in small amounts

Question 10

2 marks

Explain why it is necessary for humans to synthesise a large amount of ATP

Answer 10

• Immediate source of energy
• ATP only releases a small amount of energy at a time

Question 11

3 marks

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

Answer 11

• Electrons transferred down electron transport chain
• Electrons transfer energy to proteins which actively trasnport protons from matrix to intermemembrane space
• Protons diffuse down proton gradient and back into matrix via ATP synthase
• Energy used to combine ADP + Pi to produce ATP

Question 12

6 marks

Describe how ATP is made in mitochondria

Answer 12

1. Substrate level phosphorylation
2. Krebs cycle produces reduced coenzyme- reduced NAD and reduced FAD
3. Electrons released from reduced coenzymes
4. Electrons pass along electron transport chain
5. Energy released
6. ADP+Pi –> ATP
7. Protons move to intermembrane space via ATP synthase

Question 13

5 marks

Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis

Answer 13

1. In the dark no ATP production in photosynthesis
2. Some tissues unable to photosynthesise —> produce ATP
3. ATP cannot be stored
4. Plants uses more ATP than produced in photosynthesis
5. ATP for active transport

Question 14

2 marks

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

Answer 14

1. Lactate has built up
2. Oxygen used to break down lactate to pyruvate

Question 15

2 marks

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

Answer 15

• More cristae = larger surface area for electron transport chain –> more enzymes for ATP production / oxidative phosphorylation
• Muscle cells use more ATP than skin cells

Question 16

6 marks

Oxidative phosphorylation

Answer 16

• Reduced NAD and reduced FAD are oxidised, and they donate elctrons to membrane protein
• This forms protons, NAD and FAD
• Electrons move along along membrane proteins through a series of redox reaction along ETC
• Electrons transfer energy to the proteins, which is used to actively trasnport protons from the matrix to intermembrane space
• Ptrotons in intermebrane space diffuse down proton gradient and back into matric via ATP synthase
• ADP+Pi–> ATP, catalysed by ATP synthase/ ATPase
• Oxygen is final electron acceptor
• Over 30 ATP molecules can be made

Question 17

What is nitrogen fixation

Answer 17

• Atmospheric nitrogen gas is converted into nitrogen-containing compounds
• This biological nitrogen fixation is carried out by nitrogen-fixing bacteria
• The bacteria convert nitrogen into ammonia, which forms ammonium ions that can then be used by plants
• These nitrogen-fixing bacteria are found inside the root nodules of leguminous plants such as peas, beans and clover
• The bacteria have a symbiotic (mutually beneficial) relationship with these plants - the bacteria provide the plants with nitrogen-containing compounds and the plants provide the bacteria with organic compounds such as carbohydrates