12.1Chapter 12: The Carbon Cycle and Climate Change

The carbon cycle — Alhussan Biology - Stage 9 Revision Notes & Topical Questions

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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 8The carbon cycle and why it matters

Carbon

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

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 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)

Section 2 of 8Photosynthesis

1Process

Process green plants, algae and some bacteria use light energy trapped by chlorophyll to combine carbon dioxide and water into glucose and oxygen.

2Effect on carbon

Effect on carbon carbon is removed from the atmosphere and builds the biomass of plants as sugars, starch and cellulose.

3Oceans

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 8Feeding

Passing on carbon

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

Losses at each stage some carbon is released as carbon dioxide by respiration.

Remaining carbon

Remaining carbon some stays in the body until the organism dies, when it passes to decomposers.

Section 4 of 8Respiration and decomposition

Respiration

Respiration all living things, plants, animals and microorganisms, break down glucose using oxygen,
- producing carbon dioxide and water and releasing energy.

Decomposition

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 8Combustion and fossil fuels

Combustion

Combustion 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.

Fossil fuel formation

Fossil fuel formation 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 8Effect 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.

Section 7 of 8Key terms

Term	Meaning
Carbon cycle	The movement of carbon between living things and the environment.
Photosynthesis	Making glucose from carbon dioxide and water using light.
Respiration	Breaking down glucose to release energy, producing carbon dioxide.
Decomposition	Breakdown of dead material by bacteria and fungi.
Combustion	Burning a substance in oxygen.
Fossil fuel	A fuel formed from the buried remains of ancient organisms.