In natural circumstances, accumulated reserves of carbon such as peat, coal and oil represent a sink or natural diversion from the cycle. Eventually, the carbon in these sinks returns to the cycle through the action of geological processes which return deposits to the surface for oxidation.

Describe the effect of human activity on atmospheric $\mathrm{CO}_2$ levels:

Match the body cavities in column A with the organs contained in the cavities in column B. Place the letter of your choice in the space provided.
Column A
a. Abdominal cavity
b. Cranial cavity
c. Pelvic cavity
d. Thoracic cavity
e. Vertebral canal (spinal cavity)
Column B
Liver _______

Explain what happens to light when it is refracted at the surface of water.

Under certain conditions, decomposition rates can be very low or even zero, allowing detritus to accumulate:

What are the consequences of this lack of decomposer activity to the energy flow?

The diagram shows a simple grassland food web. Decide whether the following statement is true or false:

The grasshopper is a herbivore:

In natural circumstances, accumulated reserves of carbon such as peat, coal and oil represent a sink or natural diversion from the cycle. Eventually, the carbon in these sinks returns to the cycle through the action of geological processes which return deposits to the surface for oxidation.

What is the effect of human activity on the amount of carbon stored in sinks?

Under certain conditions, decomposition rates can be very low or even zero, allowing detritus to accumulate:

From your knowledge of biological processes, what conditions might slow decomposition rates?

Explain how temperature and rainfall affect the distribution of biomes.

The diagram shows a simple grassland food web. Decide whether the following statement is true or false:

The grass is the only producer in this food web:

Why might farmers plough a crop of legumes into the ground rather than harvest it?

What would you need to know to determine the gross primary productivity of $B$. rapa?

What is happening to the NPP over time? Explain why this is happening:

How could detritus be removed or added to an ecosystem?

State the groups for which detritus is an energy source: