Key Concepts: Populations live in habitats and form communities in ecosystems. Energy flows through trophic levels and only about 10% transfers between levels. Human activity can alter cycles and ecosystems.
Section A: Organisms in the Environment
1. Define: population, community, habitat, ecosystem. [4]
2. Describe how quadrats can be used to estimate population size in two areas. [4]
3. Give two abiotic factors and two biotic factors that affect population size and distribution. [4]
Section B: Feeding Relationships
4. In the food chain: grass → rabbit → fox, name the trophic level of each organism. [3]
5. Explain why only about 10% of energy is transferred between trophic levels. [3]
6. Compare pyramids of numbers, biomass and energy (one key feature each). [3]
Section C: Cycles in Ecosystems
7. Describe the main stages in the carbon cycle. [4]
Section D: Human Influences
8. Describe biological consequences of air pollution by sulfur dioxide and carbon monoxide. [4]
9. List five greenhouse gases and explain how human activities increase them. [6]
10. Explain how increased greenhouse gases cause global warming. [3]
11. Describe the effects of sewage pollution on aquatic ecosystems. [3]
Total marks: 37
Mark Scheme
1.
- Population: all members of one species in a given area. [1]
- Community: all the populations of different species in an area. [1]
- Habitat: the place where an organism lives. [1]
- Ecosystem: a community plus the abiotic environment. [1]
2.
- Place quadrats randomly or along a transect in each area. [1]
- Count the organisms in each quadrat. [1]
- Calculate the mean number per quadrat for each area. [1]
- Scale up by total area to estimate population size and compare the two areas. [1]
3.
- One abiotic factor, e.g. light, temperature, water, pH, wind. [1]
- Second abiotic factor (different from first). [1]
- One biotic factor, e.g. competition, predation, disease, food availability. [1]
- Second biotic factor (different from first). [1]
4.
- Grass is the producer. [1]
- Rabbit is the primary consumer. [1]
- Fox is the secondary consumer. [1]
5.
- Energy is lost as heat during respiration. [1]
- Energy is lost in movement/excretion/uneaten parts (any one). [1]
- Only a small amount remains stored as biomass for the next trophic level. [1]
6.
- Pyramid of numbers shows the number of organisms at each trophic level. [1]
- Pyramid of biomass shows the mass of living material at each level. [1]
- Pyramid of energy shows energy flow per unit time and is always upright. [1]
7.
- Photosynthesis removes CO₂ from the atmosphere. [1]
- Respiration by organisms releases CO₂. [1]
- Decomposers release CO₂ during decay. [1]
- Combustion of fuels/biomass releases CO₂. [1]
8.
- SO₂ irritates the respiratory system, causing breathing problems. [1]
- SO₂ leads to acid rain that damages plants and aquatic life. [1]
- CO binds to haemoglobin, reducing oxygen transport in blood. [1]
- Reduced oxygen transport lowers aerobic respiration and can cause tissue damage. [1]
9.
- Water vapour is a greenhouse gas. [1]
- Carbon dioxide is a greenhouse gas. [1]
- Methane is a greenhouse gas. [1]
- Nitrous oxide is a greenhouse gas. [1]
- CFCs are greenhouse gases. [1]
- Any valid human activity that increases greenhouse gases, e.g. burning fossil fuels, deforestation, livestock farming, industry, landfill. [1]
10.
- Earth emits infrared radiation. [1]
- Greenhouse gases absorb and re-radiate infrared energy. [1]
- More trapped heat increases global temperature. [1]
11.
- Sewage adds nutrients that increase bacterial growth. [1]
- Bacterial respiration reduces dissolved oxygen levels. [1]
- Low oxygen leads to death of fish and other aquatic organisms. [1]