Transfer of biomass

Land can be used for producing food for human populations.

A 50 m² field can support a larger human population if used for growing crops for plant-based foods than if it was used for grazing animals, such as cows, for meat production.

Which option explains why the same field supports a larger human population if plant crops are grown?

A Biomass is lost between trophic levels in a food chain.

B Less energy is lost during respiration when humans eat plant-based foods.

C Plant-based foods are more easily digested than meat.

D The risk of heart disease is likely to be lower if humans eat plant-based foods rather than meat.

Biomass is transferred through ecosystems.

What process makes biomass available for transfer to the next trophic level in the food chain?

A Excretion

B Growth

C Removal of undigested food

D Respiration

What explains why food chains rarely have more than five trophic levels?

A Parts of the food organism are not eaten by organisms higher in the food chain.

B Plants absorb only a small proportion of the Sun’s energy.

C There is a limit to the size to which a predator can grow.

D Transfer of biomass between trophic levels is inefficient.

The rate at which plants produce biomass is known as productivity.

What is a suitable unit with which to measure productivity at different depths in the ocean?

kg day^–1 m^–2 A

kg day^–1 m^–3 B

kg year^–1 m² C

m kg^–1 year^–1 D

Accurate analysis of an ecosystem’s biodiversity requires a detailed classification of organisms.

The spruce pine plant is given the binomial name Pinus glabra.

Place a tick (✓) in the box next to the species most closely related to Pinus glabra.

Explain why Pinus glabra and humans, Homo sapiens, are classified in the same domain but in different kingdoms.

A scientist sampled the species of trees present in two different habitats containing Pinus glabra.

The results of the sampling are shown in Table 5.

Using Simpson’s Index of Diversity, the scientist calculated the biodiversity (D) of Habitat A as 0.71.

Use the formula given to calculate the biodiversity of Habitat B.

Show your working.

State which habitat, A or B, has the greater biodiversity.

D ( Habitat A ) = 0.71

Habitat B was situated beside a lake and showed evidence of ecological succession.

The scientist planned to investigate how the biodiversity changed from the edge of the lake to the other side of habitat B.

State the collective name of the animal and plant populations that are present at the end of primary succession.

Suggest how the scientist could achieve the following during their investigation:

Sample all stages of succession in the habitat........

Minimise sampling bias........

Sample insect biodiversity........

The scientist also measured primary production in both the woodland and lake habitats.

Suggest the units the scientist should use to measure primary production in the two habitats.

Nitrogen cycling within ecosystems is controlled by various bacterial species. The table below lists four groups of bacterium that are involved in the nitrogen cycle.

Complete the table to show the locations of each type of bacterium in the cycle and the reactions they perform.

Nitrogen fixation is an important part of the nitrogen cycle.

The rate of nitrogen fixation is reduced by the presence of oxygen.

Rhizobium uses the enzyme nitrogenase to fix atmospheric nitrogen.

Fig. 4 shows a simplified representation of the structure of nitrogenase and the reaction that it

Overall reaction: N₂ + 8H⁺ + 8e^– + 16ATP 2NH₃ + H₂ + 16ADP + 16P_i

Fig. 4

What can you conclude from Fig. 4 about the molecules or ions that affect the functioning of the nitrogenase enzyme?

Leghaemoglobin is a molecule that improves the performance of nitrogenase. It has very similar properties to mammalian haemoglobin.

Suggest two ways in which leghaemoglobin improves the performance of the nitrogenase enzyme.

Many species of bacteria act as decomposers within ecosystems by breaking down organic material.

Scientists analysed the energy flow within a grassland ecosystem.

They estimated that the energy in the decomposers’ trophic level was 950 000 J m^–2 yr^–1.

The energy within the producers’ trophic level was 800% greater than that of the decomposers.

Calculate the energy in the producers’ trophic level in kJ m^–2 yr^–1.

Answer:........ kJ m^–2 yr^–1

Calculate the percentage efficiency of the energy transfer from producers to decomposers.

Give your answer to two significant figures.