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Photosynthesis transfers carbon from carbon dioxide into organic molecules. Feeding moves it between organisms, while respiration and decomposition return carbon dioxide. Combustion releases carbon from fuels or biomass. The water cycle includes evaporation, condensation, precipitation and movement through organisms and the ground. Matter is conserved through these transfers; new atoms are not created when a plant grows.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Trace carbon and water through ecosystems
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Which process removes CO2 into biological material?
Photosynthesis. Carbon is incorporated into organic molecules.
After watching 2: What do decomposers help recycle?
Nutrients and materials. They break down organic remains.
What you'll be able to do
Photosynthesis transfers carbon from carbon dioxide into organic molecules. Feeding moves it between organisms, while respiration and decomposition return carbon dioxide. Combustion releases carbon from fuels or biomass. The water cycle includes evaporation, condensation, precipitation and movement through organisms and the ground. Matter is conserved through these transfers; new atoms are not created when a plant grows.
Microorganisms break down dead material and waste, recycling nutrients. Temperature, moisture and oxygen affect the rate of aerobic decomposition. Waterlogged low-oxygen conditions can slow it and store carbon in peat; draining or burning peat releases carbon and damages habitats. Nitrogen-containing compounds cycle through processes involving microbes and plant uptake. Conditions favourable for composting are not identical to conditions that preserve food or organic archaeological material.
Biodiversity includes variation within and between species and ecosystems. Habitat loss, pollution, climate change and invasive species can reduce it. Conservation measures include habitat protection, seed banks, breeding programmes and sustainable resource use. Food security depends on production, distribution, climate, disease and social factors. Intensive farming, fisheries management, biotechnology and alternative proteins each have benefits and trade-offs. Use evidence and specify which outcome a measure improves rather than calling it universally sustainable.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Why can draining peatland increase greenhouse-gas emissions?
Drainage can accelerate loss of a carbon store.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.