CCEA GCSE Biology 1.7 Ecological Relationships and Energy Flow Exam Questions

About CCEA GCSE Biology 1.7 Ecological Relationships and Energy Flow

Ecological Relationships and Energy Flow is the final topic of CCEA GCSE Biology Unit 1 and has a lot of fieldwork and data analysis. You need the key ecological terms, how to sample organisms with quadrats, how organisms compete, and how energy passes along food chains. The topic then covers decomposition, the carbon and nitrogen cycles, global warming, the effects of fertilisers and eutrophication, and human impacts on biodiversity. It links back to photosynthesis and respiration. Examiners often ask for percentage energy transfer calculations, population estimates from quadrat data, explanations of why energy is lost between trophic levels and the sequence of events in eutrophication.

What you need to know

• Key terms A habitat is where an organism lives; a population is all the organisms of one species in an area; a community is all the populations in an area; an ecosystem is the community plus its physical environment. Biodiversity is the variety of living organisms in an area.
• Prescribed practical: quadrats Place quadrats randomly (for example using coordinates from random numbers) to avoid bias and count organisms or estimate percentage cover. Estimated population = mean number per quadrat x (total area / quadrat area). Use many quadrats to improve reliability.
• Competition Plants compete for light, water, space and minerals; animals compete for food, mates and territory. Competition can be within a species or between species.
• Energy flow and pyramids Only about 10% of energy passes to the next trophic level because energy is lost in respiration (as heat), movement, and in undigested waste and parts not eaten. Percentage efficiency = energy transferred to the next level / energy at the previous level x 100. Pyramids of biomass are almost always pyramid-shaped; pyramids of numbers may not be.
• Decomposition and cycles Bacteria and fungi decompose dead material, fastest when warm, moist and with oxygen. In the carbon cycle, photosynthesis removes carbon dioxide; respiration, decomposition and combustion return it. In the nitrogen cycle, nitrogen-fixing bacteria convert nitrogen gas into nitrogen compounds, nitrifying bacteria turn ammonium into nitrates and denitrifying bacteria return nitrogen to the air.
• Eutrophication Fertiliser runs into water, causing rapid algal growth. Algae block light so plants below die. Decomposers break down the dead plants and use up oxygen in respiration, so fish and other animals die.
• Human impact Burning fossil fuels and deforestation increase carbon dioxide, adding to the greenhouse effect and global warming. Deforestation, pollution and habitat loss reduce biodiversity; conservation measures and protected areas help maintain it.

Common mistakes in 1.7 Ecological Relationships and Energy Flow

• Saying energy is used up or destroyed at each trophic level. Energy is transferred to the surroundings, mainly as heat from respiration.
• Explaining eutrophication by saying the algae use up the oxygen. Most oxygen is used by bacteria decomposing the dead plants and algae.
• Placing quadrats where there are lots of organisms. Quadrats must be placed randomly to avoid bias.
• Mixing up nitrifying and denitrifying bacteria. Nitrifying bacteria make nitrates; denitrifying bacteria convert nitrates back to nitrogen gas.
• Forgetting to scale up quadrat data to the whole area. Multiply the mean per quadrat by the number of quadrats that would fit in the area.

Try three 1.7 Ecological Relationships and Energy Flow exam-style questions