AQA Bio A Level Unit 5

Question 1

What is the role of chlorophyll in photosynthesis?

Answer 1

Chlorophyll absorbs light energy, which excites electrons and drives the process of photophosphorylation during the light-dependent reactions of photosynthesis.

Question 2

What are the two main stages of photosynthesis?

Answer 2

The two main stages are the light-dependent reactions (which produce ATP and NADPH) and the light-independent reactions (Calvin cycle, where glucose is synthesised).

Question 3

Where does the light-dependent reaction of photosynthesis take place?

Answer 3

The light-dependent reaction takes place in the thylakoid membranes of the chloroplasts

Question 4

What is photolysis, and why is it important in photosynthesis?

Answer 4

Photolysis is the splitting of water using light energy to produce electrons, protons, and oxygen. The electrons replace those lost from chlorophyll in photosystem II, and the protons contribute to ATP synthesis

Question 5

What are the products of the light-dependent reactions of photosynthesis?

Answer 5

The products are ATP, NADPH, and oxygen (O₂).

Question 6

Where does the Calvin cycle take place?

Answer 6

The Calvin cycle takes place in the stroma of the chloroplasts.

Question 7

What is the role of RuBP and RuBisCO in the Calvin cycle?

Answer 7

RuBP (ribulose bisphosphate) reacts with CO₂ in a reaction catalyzed by the enzyme RuBisCO, forming two molecules of GP (glycerate-3-phosphate), which are then used to produce glucose.

Question 8

What is oxidative phosphorylation, and where does it occur?

Answer 8

Oxidative phosphorylation is the process of ATP production using energy derived from electron transfer in the mitochondrial inner membrane, involving the electron transport chain and chemiosmosis.

Question 9

What are the main stages of aerobic respiration?

Answer 9

The main stages are glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation.

Question 10

What is the net gain of ATP molecules in glycolysis?

Answer 10

The net gain of ATP in glycolysis is 2 ATP molecules per molecule of glucose.

Question 11

What is the purpose of the Krebs cycle?

Answer 11

The Krebs cycle generates reduced coenzymes (NADH and FADH₂), ATP, and carbon dioxide, which are used in oxidative phosphorylation to produce more ATP.

Question 12

How is ATP synthesized during chemiosmosis in respiration?

Answer 12

Protons are pumped into the intermembrane space of the mitochondria, creating a proton gradient. ATP is synthesised as protons flow back into the mitochondrial matrix through ATP synthase.

Question 13

What is anaerobic respiration and what are its products in animal cells?

Answer 13

Anaerobic respiration occurs without oxygen, producing lactic acid and a small amount of ATP in animal cells.

Question 14

What is the difference between gross primary production (GPP) and net primary production (NPP)?

Answer 14

GPP is the total amount of energy captured by producers through photosynthesis, while NPP is the energy remaining after respiration, available to consumers in the ecosystem.

Question 15

How do energy transfers between trophic levels affect the energy available in an ecosystem?

Answer 15

Only about 10% of energy is transferred to the next trophic level, with the rest lost as heat, through respiration, or in waste, limiting the number of trophic levels in an ecosystem.

Question 16

What is a pyramid of biomass, and what does it represent?

Answer 16

A pyramid of biomass represents the total mass of organisms at each trophic level in an ecosystem, showing the decrease in biomass at higher levels.

Question 17

What is the nitrogen cycle, and why is it important for ecosystems?

Answer 17

The nitrogen cycle involves the conversion of nitrogen between its various chemical forms (e.g., nitrogen fixation, nitrification, and denitrification), making nitrogen available for organisms to synthesize proteins and nucleic acids.

Question 18

What role do saprobionts play in nutrient cycles?

Answer 18

Saprobionts (decomposers) break down organic material from dead organisms, releasing nutrients like nitrogen and phosphorus back into the soil for reuse by plants.

Question 19

What is eutrophication, and how is it caused?

Answer 19

Eutrophication is the excessive growth of algae and aquatic plants due to increased nutrient levels (often from agricultural runoff), leading to oxygen depletion and harm to aquatic life.

Question 20

What is the role of NADP in photosynthesis?

Answer 20

NADP acts as an electron carrier. In the light-dependent reactions, it is reduced to NADPH, which then carries high-energy electrons and protons to the Calvin cycle for the synthesis of carbohydrates.