Edexcel International A Level Biology Energy Flow, Ecosystems and the Environment Exam Questions

About Edexcel International A Level Biology Energy Flow, Ecosystems and the Environment

This topic is part of Unit 4 (Energy, Environment, Microbiology and Immunity) of Edexcel International A Level Biology. It starts with photosynthesis: the structure of chloroplasts, the light-dependent reactions on the thylakoid membranes and the Calvin cycle in the stroma. You then study energy flow through ecosystems, gross and net primary productivity and the efficiency of energy transfer. Ecosystems are described in terms of populations, communities, niches, biotic and abiotic factors and succession. The final section covers evidence for climate change, its causes and its effects on organisms, the reliability of the evidence and models, and how evolution and speciation occur. Calculations of productivity and efficiency are common.

What you need to know

• Light-dependent reactions Light energy excites electrons in chlorophyll; photolysis of water releases oxygen, protons and electrons; ATP is made by photophosphorylation and NADP is reduced.
• Calvin cycle CO2 combines with RuBP, catalysed by RUBISCO, to form GP. GP is reduced to GALP using ATP and reduced NADP. GALP is used to make carbohydrates, lipids and amino acids, and to regenerate RuBP.
• Productivity NPP = GPP - R. Efficiency of energy transfer = energy at higher trophic level / energy at lower level x 100.
• Ecosystems Distribution of organisms depends on biotic and abiotic factors. Succession leads from pioneer species to a climax community. Quadrats and transects are used to sample.
• Climate change Evidence includes temperature records, dendrochronology, pollen in peat bogs and CO2 from ice cores. Greenhouse gases such as CO2 and methane trap heat; effects include changes in species distribution and development rates.
• Evolution and speciation Natural selection changes allele frequencies; reproductive isolation leads to new species. Scientific evidence is evaluated by peer review.

Common mistakes in Energy Flow, Ecosystems and the Environment

• Saying GPP is available to consumers; only NPP is available.
• Writing that the Calvin cycle happens only in the dark.
• Claiming the greenhouse effect itself is harmful; the enhanced greenhouse effect causes global warming.
• Confusing weather with climate in data questions; climate refers to long-term trends.
• Forgetting that energy losses include heat from respiration as well as uneaten and undigested material.

Try three Energy Flow, Ecosystems and the Environment exam-style questions