BIOLOGY · Stage 9 · Chapter 12: The Carbon Cycle and Climate Change
Biology 12.1 The carbon cycle — Photosynthesis, Respiration, Feeding and Decomposition
5 min read 6 parts Lesson 1 of 6
Lesson summary
12.1 The carbon cycle — Photosynthesis, Respiration, Feeding and Decomposition — Alhussan International Academy — Biology (Stages 7–9) notes: Describe how carbon moves between the atmosphere, living things, soil, oceans and fossil fuels through photosynthesis, feeding, respiratio…
- Carbon stores
- Effect on carbon
- Passing on carbon
- Remaining carbon
- Combustion
- Fossil fuel formation
Section 1 of 6The carbon cycle and why it matters
- Carbon
- it is an important element in the carbohydrate, protein and lipid molecules that make up cells, and in the DNA passed from parents to offspring.
- Carbon cycle = a series of processes that move carbon between living organisms and the physical environment.
- It returns carbon dioxide from organisms to the atmosphere to be used again in photosynthesis.
- It makes sure the carbon needed for life is always available.
- Carbon stores
- carbon dioxide in the atmosphere, dissolved carbon dioxide and carbonates in the oceans, living organisms, dead material in the soil,
- and fossil fuels and limestone rocks.
- (about 0.04% of air)
- carbon dioxide in the atmosphere, dissolved carbon dioxide and carbonates in the oceans, living organisms, dead material in the soil,
Section 2 of 6Photosynthesis
- Process
- green plants, algae and some bacteria use light energy trapped by chlorophyll to combine carbon dioxide and water into glucose and oxygen.
- Effect on carbon
- carbon is removed from the atmosphere and builds the biomass of plants as sugars, starch and cellulose.
- Oceans
- carbon dioxide also dissolves in the oceans, where marine organisms use it to make calcium carbonate shells that eventually form limestone.
Section 3 of 6Feeding
- Passing on carbon
- animals eat plants or other animals, break down the biomass and rebuild it as animal biomass.
- Herbivores take in carbon compounds from plants and carnivores eat herbivores.
- Losses
- at each stage some carbon is released as carbon dioxide by respiration.
- Remaining carbon
- some stays in the body until the organism dies, when it passes to decomposers.
Section 4 of 6Respiration and decomposition
- Respiration
- all living things, plants, animals and microorganisms, break down glucose using oxygen, producing carbon dioxide and water and releasing energy.
- Decomposition
- bacteria and fungi feed on animal waste, dead leaves and the dead bodies of animals and plants.
- They break these down and release carbon dioxide into the atmosphere by respiration.
Section 5 of 6Combustion and fossil fuels
1Combustion1 point
= burning, in which a substance reacts with oxygen and the energy transferred heats the surroundings and produces light.
- Wood and fossil fuels are carbon compounds, so burning them produces carbon dioxide and water, released quickly into the air.
2Fossil fuel formation2 points
- dead material buried and compressed without oxygen for millions of years forms coal, oil and gas.
- The carbon is locked away for a very long time.
Section 6 of 6Effect of each process on atmospheric carbon dioxide
| Process | Effect on atmospheric CO2 |
|---|---|
| Photosynthesis | Decreases |
| Respiration | Increases |
| Decomposition | Increases |
| Combustion | Increases |
| Dissolving in oceans | Decreases |
- Balance
- over a long time the processes balance, so the proportion of carbon dioxide in the air stays steady until human activity upsets it.
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