4.7.2.2 How Materials are Cycled

Question 1

Why are all materials in the living world recycled?

Answer 1

• to provide building blocks for future organisms

Question 2

What does the carbon cycle involve?

Answer 2

• carbon dioxide removed from air in photosynthesis by green plants and algae
• carbon dioxide returned to air when plants, algae and animals respire, as well as decomposers when returning mineral ions to soil
• carbon dioxide returned to air when wood and fossil fuels are burnt

Question 3

Why is carbon dioxide removed from the air in photosynthesis by green plants and algae?

Answer 3

• they use carbon to make carbohydrates, proteins and fats
• they are eaten and the carbon moves up the food chain

Question 4

What does the water cycle involve?

Answer 4

• sun’s energy causes water to evaporate from sea and lakes, forming water vapour
• water vapour is also formed as a result of transpiration in plants
• water vapour rises and condenses to form clouds
• water is returned to land by precipitation (rain, snow, hail) and runs into lakes to provide water for plants and animals
• then runs into seas and cycle repeats