1.3 The Carbon cycle

• Biology
• Secondary Education

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Unit 1 - Photosynthesis and the Carbon Cycle

The Carbon Cycle

17 November 2025

How do you feel today?

😒🙁😐🙂😃

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• I will know how carbon atoms move between the air, living organisms, and fossil fuels.

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What is CarbFix?

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Carbfix - How it works

Complete the statement:

CarbFix is a method of _________________

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Carbon, C

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Carbon, C

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diamond

coal

pencil 'lead'

Carbon, C

Give at least ONE thing that contains the carbon atom.

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Carbon, C, is found in...

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Carbon, C, is found in...

0.04% carbon dioxide in air

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Carbon, C, is found in...

0.04% carbon dioxide in air

plants

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Carbon, C, is found in...

0.04% carbon dioxide in air

food

plants

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Carbon, C, is found in the...

0.04% carbon dioxide in air

food

plants

animals

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Carbon, C, is found in the...

fossil fuels

0.04% carbon dioxide in air

food

plants

animals

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In the air

In plants

In animals

In decomposers

In fossil fuels

burning

decomposition

• photosynthesis
• feeding
• respiration
• decomposition
• combustion (burning)

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Work in groups: 

How a carbon atom moves in a cycle

photosynthesis

respiration

combustion

feeding

decomposition

TEAM

TOP 1

C.J.

C.L.

Penguins

Stay Young Beautiful And Unique

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Story:

Vortey decided to have a healthy lunch. She wanted to eat green leafy vegetables with carbs and proteins.

After a few hours, she went to the gym and exercised. 

"Everyone dies one day", she said, so enjoying it now makes a big difference.

She walked back home and noticed a car releasing smoke.

In the air

In plants

In animals

In decomposers

In fossil fuels

burning

decomposition

The Carbon in CO₂ moves from the air to the plant and 

is used for ______________________.

1. respiration
2. photosynthesis
3. feeding
4. decomposition

The Carbon in carbon compounds (CHO) moves from the plant to animals through _________________.

1. respiration
2. photosynthesis
3. feeding
4. decomposition

The Carbon in carbon compounds (CHO) moves from the plant to the decomposers through _________________.

1. respiration
2. photosynthesis
3. feeding
4. decomposition

The Carbon in carbon dioxide (CO₂) moves from plants 

to the air _________________.

1. respiration
2. photosynthesis
3. feeding
4. decomposition

The Carbon in carbon dioxide (CO₂) moves from animals

to the air _________________.

1. respiration
2. photosynthesis
3. feeding
4. decomposition

The Carbon in fossil fuels is released

to the air as CO₂ through_________________.

1. respiration
2. burning
3. feeding
4. decomposition

The Carbon in plants or animals is released into the air as CO₂ by bacteria or fungi through ___________________.

1. respiration
2. burning
3. feeding
4. decomposition

__________ are formed slowly from 

the remains of dead plants and animals.

1. Fossil fuels
2. Fossils
3. Glucose molecules
4. Carbon dioxide molecules

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• I will know how carbon atoms move between the air, living organisms, and fossil fuels.

How well did you participate 

in the lesson today?

05

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Unit 1 - Photosynthesis and the Carbon Cycle

The Carbon Cycle

18 November 2025

How do you feel today?

😒🙁😐🙂😃

TEMPLATE

• I will understand why respiration and photosynthesis affect the amount of carbon dioxide in the air.
• I will be able to draw the Carbon Cycle using a graphic organiser.

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Have you ever wondered how a coal-fired power plant works to provide electricity to our homes?

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Electricity Production – Burning Fossil Fuels

Do you agree or disagree?

Burning fossil fuels harms 

you and the environment. Explain your response.

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in the air

Photosynthesis

in plants

CO₂

CHO/CHON

in animals

Feeding

decomposers

Feeding

Feeding

Decomposition

Respiration

Respiration

CHO/CHON

CHO/CHON

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Work in groups: 

Explain each process in the carbon cycle

Rehearse

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in the air

CO₂

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in the air

Photosynthesis

in plants

CO₂

C₆H₁₂O₆

proteins

fats

converted to

converted to

Team 1

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in the air

Photosynthesis

in plants

CO₂

C₆H₁₂O₆

proteins

fats

converted to

converted to

Feeding

C₆H₁₂O₆

in animals

Team 2

TEMPLATE

in the air

Photosynthesis

in plants

CO₂

in animals

Feeding

decomposers

Feeding

Feeding

Decomposition

Team 3

CHO/CHON

CHO/CHON

CHO/CHON

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in the air

Photosynthesis

in plants

CO₂

in animals

Feeding

decomposers

Feeding

Feeding

Respiration

Respiration

Respiration

Team 4

CHO/CHON

CHO/CHON

CHO/CHON

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Combustion (burning)

in plants

in animals

in the air

CO₂

High Pressure and Heat

Team 5

CHO/CHON

CHO/CHON

The amount of carbon dioxide in the air rises due to burning fossil fuels and overpopulation. Explain how planting more trees helps in reducing the amount of CO₂.

The population of Cambodia in 2022 was 17,201,724, compared to 17,423,880 in 2024. Explain how the increase in population increases the amount of CO₂.

Coal-fired power plants provide electricity in Cambodia. The combustion of coal releases carbon dioxide to the atmosphere. Explain how YOU can help reduce carbon dioxide in the air.

respiration

decomposition

combustion

feeding

photosynthesis

How well did you enjoy the lesson today?

05

TEMPLATE

• I will know how carbon atoms move between the air, living organisms, and fossil fuels.
• I will understand why respiration and photosynthesis affect the amount of carbon dioxide in the air.
• I will be able to draw the Carbon Cycle using a graphic organiser.