OxfordAQA International GCSE Biology 3.3 Ecology Exam Questions

About OxfordAQA International GCSE Biology 3.3 Ecology

Ecology in OxfordAQA International GCSE Biology looks at how energy and materials move through ecosystems and how organisms depend on each other. You study the small fraction of light energy captured by plants, the roughly 10% of biomass passed on at each trophic level and pyramids of biomass drawn to scale. Then come adaptations, competition, extremophiles and parasites, decay and the carbon cycle. The separate Biology course adds pollution, eutrophication, deforestation and global warming. It links to photosynthesis and respiration in 3.2 Bioenergetics. Examiners regularly ask for efficiency calculations, carbon cycle explanations and step by step accounts of eutrophication.

What you need to know

• Energy from the Sun The Sun is the energy source for most communities. Green plants and algae transfer only about 1% of the light energy falling on them into photosynthesis.
• Biomass transfer Only about 10% of biomass is passed on to the next trophic level, because material and energy are lost in waste (faeces, urine) and much energy released by respiration is transferred to the surroundings. You must draw and interpret pyramids of biomass to scale; food webs and pyramids of numbers are not required.
• Competition and interdependence Plants compete for light, space, water and mineral ions; animals compete for food, mates and territory. Organisms need materials from their surroundings and from other living things.
• Adaptations Adaptations can be structural (shape, colour), behavioural (migration, huddling) or functional (reproduction, metabolism). Extremophiles live in very salty, hot or high pressure environments. Separate Biology adds parasite adaptations in fleas, tapeworms and the malaria parasite.
• Decay Microorganisms break down dead material and waste fastest in warm, moist, aerobic conditions. Decay returns mineral ions that plants need, and in a stable community removal and return balance.
• Carbon cycle Photosynthesis removes carbon dioxide and makes carbohydrates, fats and proteins. Carbon passes along food chains when animals eat. Respiration by plants, animals and decomposers (microorganisms and detritus feeders) returns carbon dioxide, and combustion of wood and fossil fuels releases it.
• Humans and the environment Sewage, fertilisers and toxic chemicals pollute water; smoke and sulfur dioxide (acid rain) pollute air; pesticides and herbicides pollute land. Large scale tropical deforestation reduces biodiversity. Carbon dioxide and methane add to global warming, causing climate change, sea level rise and changes in migration and species distribution.
• Eutrophication Mineral ions from sewage or fertiliser cause rapid algal and plant growth; plants below die when light is blocked; decomposers increase and their respiration uses up dissolved oxygen, so fish and other aerobic organisms die.

Common mistakes in 3.3 Ecology

• Saying energy is lost from food chains. Energy is transferred to the surroundings, mainly by respiration, and some is in waste; it is not destroyed.
• In eutrophication, saying the algae use up all the oxygen. It is the respiration of the decomposing microorganisms that depletes the oxygen.
• Drawing pyramids of biomass with equal bar widths or not to scale. The bars must be drawn to scale from the data.
• Leaving decomposers out of the carbon cycle. Microorganisms release carbon dioxide by respiration as they break down dead material.
• Confusing global warming with the ozone layer. Global warming is caused by greenhouse gases such as carbon dioxide and methane.

Try three 3.3 Ecology exam-style questions