Question 1: Define a food web and explain how it differs from a food chain.

Answer: A food web is a complex network of interconnected food chains showing how different organisms obtain energy; unlike a food chain, it illustrates multiple feeding relationships in an ecosystem.

Question 2: Describe the role of primary producers in a food web.

Answer: Primary producers, such as plants and algae, convert energy from sunlight into chemical energy via photosynthesis, forming the base of the food web.

Question 3: Explain what is meant by 'energy transfer efficiency' in a food web.

Answer: Energy transfer efficiency refers to the percentage of energy passed from one organism to the next in a food web, generally around 10% per trophic level.

Question 1: A primary producer provides 1000 kJ of energy. Assuming an energy transfer efficiency of 10%, calculate the energy available to the secondary consumer.

Answer: Energy to secondary consumer = 1000 kJ × 0.10 (10%) = 100 kJ

Question 2: If a tertiary consumer receives 5 kJ of energy, estimate the energy input at the level of the primary producer, assuming a 10% transfer efficiency at each level.

Answer: Energy at primary producer = 5 kJ / (0.10)^3 = 5 kJ / 0.001 = 5000 kJ

Question 1: Design a simple experiment to investigate the effect of removing a keystone predator on the stability of a food web. Include variables and safety precautions.

Answer: Students should propose setting up a controlled environment with specific organisms, identify the independent variable as the presence or absence of the predator, the dependent variable as the diversity or biomass of prey species, control variables such as temperature and light, and safety precautions including proper handling and disposal of organisms.

Question 1: In a forest food web, the biomass of primary consumers is 200 kg, and the biomass of secondary consumers is 20 kg. Discuss what this indicates about energy flow and ecosystem stability.

Answer: The biomass ratio suggests that only about 10% of energy is transferred between these levels, indicating typical energy loss and a stable energy flow within the ecosystem.

Question 1: Explain how the removal of a top predator can lead to changes in the overall structure of a food web, and discuss the potential ecological consequences. (6 marks)

Answer: Removing a top predator can cause prey populations to increase, which might lead to overconsumption of primary producers, reducing biodiversity, and destabilising the ecosystem. This can result in trophic cascades affecting multiple species and ecosystem functions.

Question 1: Describe how knowledge of food webs can be used in fisheries management to prevent overfishing and maintain ecosystem balance.

Answer: Fisheries management uses food web data to set sustainable catch limits, protect key species, and ensure that removal of certain species does not disrupt the ecological balance, thereby preventing overfishing and supporting biodiversity.