Decay and the carbon cycle Quiz

1. Which three conditions make microorganisms decay materials fastest?

• A. Cold, dry, anaerobic
• B. Warm, moist, aerobic
• C. Cold, moist, anaerobic
• D. Warm, dry, aerobic

2. A garden compost heap is kept damp and is turned regularly to let air in. Why does turning the heap speed up decay?

• A. It cools the compost down, slowing unwanted reactions
• B. It removes water, which microorganisms do not need
• C. It increases the oxygen available, supporting more active (aerobic) microorganisms
• D. It kills the microorganisms so the material breaks down chemically instead

3. A leaf takes up carbon dioxide during photosynthesis, and the carbon becomes part of a carbohydrate in the leaf. A caterpillar then eats the leaf. Which process is responsible for the carbon moving from the leaf into the caterpillar's body?

• A. Respiration
• B. Combustion
• C. Feeding
• D. Decay

4. A tree is cut down and burned as firewood, releasing carbon dioxide. Later, a different tree absorbs that carbon dioxide during photosynthesis. Which two processes together explain this carbon's journey out of the first tree and into the second?

• A. Respiration, then feeding
• B. Combustion, then photosynthesis
• C. Decay, then respiration
• D. Photosynthesis, then combustion

5. A dead animal is left on a forest floor. Over several weeks, microorganisms and detritus feeders break down its body, and its nutrients become available to plants again. Which statement best explains why this happens, applying the principles of the carbon cycle?

• A. Decay by microorganisms releases carbon dioxide by respiration, and returns other nutrients to the soil, keeping the community's materials in balance
• B. The animal's carbon disappears permanently and cannot be reused by any other organism
• C. The nutrients only become available once the animal's body is burned by combustion
• D. Only photosynthesis can return nutrients to the soil for other organisms to use