Basic 8 · Science · The Carbon Cycle
The Carbon Cycle
In this topic you will describe the process of the carbon cycle, explain how carbon moves between living things, the air, soil and oceans, and discuss human effects on the cycle.
By the end of these notes you should be able to:
- State where carbon is found
- Explain the processes that move carbon
- Explain human effects on the carbon cycle
What you already know
- Photosynthesis and respiration
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Cycles
- Sub-strand
- The Carbon Cycle
- Indicator
- B8.2.1.1.1 – Explain the process of the carbon cycle
Introduction
Carbon is in your body, your food and the air you breathe out. All life on Earth is built around this one element.
1. Carbon, the Element of Life
Carbon forms compounds that make up living things, including carbohydrates, fats, proteins and DNA. Carbon atoms can bond with many other atoms, including other carbon atoms, to form long chains. No other element is as versatile, which is why carbon is called the basis of life. Diamond and graphite are pure forms of carbon. Charcoal is mostly carbon too.
2. Carbon Stores
| Store | Form of carbon |
|---|---|
| atmosphere | carbon dioxide (CO₂) and methane |
| living things | carbohydrates, fats, proteins |
| soil | dead plant and animal matter |
| oceans | dissolved CO₂ and shells |
| rocks | limestone and fossil fuels |
These stores are called reservoirs. The carbon cycle describes how carbon moves between them. The total amount of carbon on Earth stays almost the same, but it keeps changing places and forms.
3. Fast and Slow Parts of the Cycle
Some carbon moves fast. A plant may take in carbon dioxide and release it within days. Other carbon moves slowly. Coal and crude oil formed from dead plants and sea creatures over millions of years, and limestone formed from shells. Burning these fossil fuels releases in a short time carbon that has been stored for millions of years.
4. Why the Cycle Matters
Carbon dioxide helps to keep the Earth warm by trapping heat in the atmosphere. Without it, the planet would be too cold for most life. Too much of it, however, makes the Earth warmer. The carbon cycle needs to stay in balance so that the climate stays stable.
New words
- carbon cycle
- The movement of carbon through nature.
- reservoir
- A place where carbon is stored.
- carbon dioxide
- A gas made of carbon and oxygen.
- fossil fuel
- Fuel formed from ancient living things.
Summary
- Carbon is the basis of life and is found in many forms.
- Carbon is stored in the air, living things, soil, oceans and rocks.
- The cycle moves carbon between stores at different speeds.
Class activity: Carbon Hunt
- List ten things around you that contain carbon.
- Group them by store.
- Discuss which stores change quickly.
You need: Potted maize plant, Charcoal pieces, Printed carbon-cycle diagram
Exercises
Answer in your exercise book first, then check your answers.
1. Which gas contains carbon?
- A. carbon dioxide
- B. oxygen
- C. nitrogen
- D. hydrogen
Show answer
Answer: carbon dioxideCO₂.2. Fossil fuels formed from…
- A. ancient plants and sea creatures
- B. sand
- C. metals
- D. rain
Show answer
Answer: ancient plants and sea creaturesMillions of years.3. Diamond is a form of carbon.
- A. True
- B. False
Show answer
Answer: TruePure carbon.4. A place where carbon is stored is a ______.
Show answer
Answer: reservoirStore.5. Name three stores of carbon.
Show answer
Answer: The atmosphere, oceans and rocks.Any three.6. Why is carbon called the basis of life?
Show answer
Answer: It forms the compounds in living things, thanks to its ability to bond in chains.Biology.
Lesson 2
- Strand
- Cycles
- Sub-strand
- The Carbon Cycle
- Indicator
- B8.2.1.1.1 – Explain the process of the carbon cycle
Introduction
Carbon travels around the planet through a few key processes. Your breathing is one of them.
1. Main Processes
| Process | What happens | Direction |
|---|---|---|
| photosynthesis | plants take in CO₂ to make food | air to plants |
| respiration | living things release CO₂ | organisms to air |
| feeding | animals eat plants or animals | plants to animals |
| decomposition | decomposers break down dead matter | dead matter to air and soil |
| combustion | fuels burn and release CO₂ | fuels to air |
| ocean exchange | CO₂ dissolves in or escapes from the sea | both ways |
2. Photosynthesis and Respiration
Green plants use sunlight, water and carbon dioxide to make glucose, and they give out oxygen. The equation in words is: carbon dioxide + water → glucose + oxygen. Respiration is basically the reverse: glucose + oxygen → carbon dioxide + water + energy. Plants and animals both respire. Trees therefore both remove and release carbon, but they take in more than they give out as they grow.
3. Decomposers
When a tree falls in a forest, bacteria and fungi feed on it, and carbon returns to the air and soil. Without these decomposers, dead things would pile up, and nutrients would be locked away. Compost heaps show this process at work. Under some conditions, such as deep mud without oxygen, dead matter does not fully decay, and over millions of years it can become coal or oil.
4. Following a Carbon Atom
Picture one carbon atom in the air. A maize plant takes it in and stores it in a grain. A chicken eats the grain, and you eat the chicken. You breathe the atom back out as carbon dioxide. A tree absorbs it. Years later the tree is cut, made into charcoal and burned, and the atom returns to the air once again. This is the carbon cycle in action.
New words
- photosynthesis
- Plants making food using sunlight.
- respiration
- Releasing energy from food.
- decomposer
- An organism that breaks down dead matter.
- combustion
- Burning a substance in oxygen.
Summary
- Photosynthesis removes CO₂ from the air.
- Respiration, decomposition and combustion return CO₂.
- Carbon moves through food chains and oceans too.
Class activity: Carbon Journey
- Make a large poster of the carbon cycle.
- Follow one carbon atom through it.
- Tell the story to the class.
You need: Potted maize plant, Charcoal pieces, Printed carbon-cycle diagram
Exercises
Answer in your exercise book first, then check your answers.
1. Which process removes CO₂ from air?
- A. photosynthesis
- B. combustion
- C. respiration
- D. decomposition
Show answer
Answer: photosynthesisPlants.2. Which organisms break down dead matter?
- A. decomposers
- B. producers
- C. carnivores
- D. herbivores
Show answer
Answer: decomposersBacteria and fungi.3. Burning charcoal releases carbon dioxide.
- A. True
- B. False
Show answer
Answer: TrueCombustion.4. Burning a substance in oxygen is ______.
Show answer
Answer: combustionFire.5. Write the word equation for photosynthesis.
Show answer
Answer: Carbon dioxide + water → glucose + oxygen.Plants.6. How does carbon in a tree get back to the air?
Show answer
Answer: Through respiration, decomposition or burning.Cycle.
Lesson 3
- Strand
- Cycles
- Sub-strand
- The Carbon Cycle
- Indicator
- B8.2.1.1.1 – Explain the process of the carbon cycle
Introduction
For thousands of years, the carbon cycle stayed roughly balanced. Human activity is now changing that balance.
1. Human Activities
| Activity | Effect |
|---|---|
| burning fossil fuels | adds CO₂ to the air |
| deforestation | fewer trees to absorb CO₂ |
| bush burning | releases CO₂ and destroys plants |
| cement making | releases CO₂ |
| rice farming and cattle | release methane |
2. Enhanced Greenhouse Effect
Gases such as carbon dioxide and methane trap heat in the atmosphere, in a similar way to the glass of a greenhouse. This natural greenhouse effect makes life possible. Adding more greenhouse gases traps more heat, and the Earth's average temperature rises. This is known as global warming, and the wider changes it causes are called climate change.
3. Effects in Ghana
Climate change may bring less reliable rains, longer dry seasons, stronger floods and heat stress. Northern farmers are affected by unpredictable rainfall. Rising seas and erosion threaten coastal communities like Keta, where the sea has already destroyed many homes. Warmer oceans can harm fish, on which many Ghanaians rely. People who did little to cause the problem often suffer the most.
4. Solutions
- Plant trees and protect forests.
- Use solar and other clean energy.
- Use energy-efficient stoves and lights.
- Walk, cycle or share transport.
- Reduce waste and compost it.
- Stop bush burning.
Ghana's Green Ghana Day, begun in 2021, encourages tree planting across the country. Young people can make a difference by sharing facts and setting good examples.
New words
- greenhouse gas
- A gas that traps heat in the atmosphere.
- global warming
- The rise in the Earth's average temperature.
- deforestation
- Clearing forests.
- climate change
- Long-term change in weather patterns.
Summary
- Burning fuels and deforestation add CO₂ to the air.
- Extra greenhouse gases cause global warming.
- Tree planting and clean energy can reduce harm.
Class activity: Climate Action Plan
- List ways your school adds carbon to the air.
- Plan three actions to reduce this.
- Present your plan to the class.
You need: Potted maize plant, Charcoal pieces, Printed carbon-cycle diagram
Exercises
Answer in your exercise book first, then check your answers.
1. Which helps reduce CO₂?
- A. planting trees
- B. bush burning
- C. cutting forests
- D. burning tyres
Show answer
Answer: planting treesPhotosynthesis.2. The rise in Earth's average temperature is…
- A. global warming
- B. photosynthesis
- C. respiration
- D. erosion
Show answer
Answer: global warmingGreenhouse gases.3. Carbon dioxide is a greenhouse gas.
- A. True
- B. False
Show answer
Answer: TrueTraps heat.4. Clearing forests is called ______.
Show answer
Answer: deforestationTrees.5. Give two human activities that add carbon to the air.
Show answer
Answer: Burning fossil fuels and bush burning.Any two.6. Give two effects of climate change in Ghana.
Show answer
Answer: Unreliable rains and coastal erosion.Local impact.
Homework
- Draw the carbon cycle and write a paragraph explaining it.