Energy transfer through ecosystems: Practice Questions

Why is a pyramid of energy for a stable ecosystem always upright and never inverted?

Biological agents, such as parasitic wasps, are often used in integrated systems to increase crop yield. How does this practice increase the efficiency of energy transfer to humans?

In certain marine ecosystems, a snapshot measurement shows that the biomass of primary consumers (zooplankton) is larger than the biomass of the producers (phytoplankton).
Which of the following explains how this ecosystem remains sustainable despite the inverted pyramid of biomass?

In an ecosystem, the total amount of chemical energy stored in plant biomass in a specific area and time, before any losses, is known as the:

A field of maize has a recorded gross primary production (GPP) of \(55,000\text{ kJ m}^{-2}\text{ yr}^{-1}\). The respiration of the maize plants is calculated to be \(24,500\text{ kJ m}^{-2}\text{ yr}^{-1}\).
What is the net primary production (NPP) of this field?

Using the equation \(N = I - (F + U + R)\), state the term that represents the chemical energy stored in faeces and describe why this energy is lost from the consumer's net production.

In the equation for the net production of consumers, \(N = I - (F + U + R)\), explain what the term \(F + U\) represents.

Explain why the Net Primary Production (NPP) available to consumers in a climax community is often lower than in the earlier seral stages of ecological succession, despite the climax community having a higher Gross Primary Production (GPP).

(a) Define the term Gross Primary Production (GPP).
(b) In a tropical rainforest, the GPP was measured as \(35,000 \text{ kJ m}^{-2} \text{ yr}^{-1}\). If the respiratory losses (\(R\)) of the plants were \(21,500 \text{ kJ m}^{-2} \text{ yr}^{-1}\), calculate the Net Primary Production (NPP). Include the appropriate units in your answer.
(c) Explain why NPP is a more useful measurement than GPP when assessing the energy available to the rest of the ecosystem.

A researcher investigated the energy flow within a controlled agricultural ecosystem containing a specific variety of wheat and a population of grain beetles (primary consumers).

The following data were obtained for the wheat crop over one growing season:
- Total chemical energy stored by photosynthesis: \(48,000\text{ kJ m}^{-2}\)
- Energy used by the wheat for cellular respiration: \(19,500\text{ kJ m}^{-2}\)

(a) Calculate the Net Primary Production (NPP) of the wheat crop. Show your working.
(b) The grain beetles ingested \(2,400\text{ kJ m}^{-2}\) of the wheat biomass. The beetles lost \(850\text{ kJ m}^{-2}\) in faeces and urine, and \(1,150\text{ kJ m}^{-2}\) through respiration. Calculate the net production (N) for the beetle population.
(c) Calculate the percentage efficiency of energy transfer from the NPP of the wheat to the net production of the beetles. Give your answer to two decimal places.