The carbon and water cycles Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Explore the carbon cycle and how it returns carbon to the atmosphere, and understand the water cycle and how it provides fresh water through evaporation...

• Explain the importance of the carbon and water cycles to living organisms
• Describe how the carbon cycle returns carbon dioxide to the atmosphere for photosynthesis
• Describe how the water cycle provides fresh water for plants and animals on land
• Compare the processes of evaporation and precipitation in the water cycle

Key ideas to keep in view

Use this lesson to stay inside B4.1 Ecosystems while connecting the detail back to the wider B4: Community level systems topic.

• B4: Community level systems
• B4.1 Ecosystems
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from The carbon and water cycles before testing yourself from memory.

• Picture Earth without these cycles. Plants would run out of carbon dioxide for photosynthesis. Animals would die of thirst as water stayed locked in the oceans. Nothing would decompose, so dead material would pile up everywhere.
• The carbon and water cycles are Earth's recycling systems. They move essential materials between living things and the environment, keeping ecosystems running. Without them, life as we know it couldn't exist.
• 2. The Carbon Cycle - Nature's Recycling System
• Carbon moves in a giant loop. Plants take carbon dioxide from the air during photosynthesis, turning it into glucose and other compounds. Animals eat plants, getting this carbon into their bodies.
• When organisms respire, they release carbon dioxide back to the atmosphere. When they die and decompose, bacteria and fungi break them down, releasing more carbon dioxide. This completes the cycle.
• The breakdown of dead organisms by bacteria and fungi, releasing carbon dioxide and nutrients back to the environment.
• Trap: Many students think carbon 'disappears' when animals eat plants. Actually, the carbon atoms just move from one organism to another - they're never destroyed, only recycled.
• 3. The Water Cycle - Earth's Water Distribution System
• The sun drives the water cycle by providing energy for evaporation. Water evaporates from oceans, rivers and lakes, rising as invisible water vapour. As it rises higher, it cools and condenses into tiny droplets, forming clouds.
• When droplets in clouds get too heavy, they fall as precipitation - rain, snow, sleet or hail. This water flows into rivers and streams, eventually returning to the sea. Some soaks into the ground, providing fresh water for plant roots.

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.