May/June 2026 Paper 43

Figure 5.1 shows a food web from a marine ecosystem.

Using Figure 5.1, identify: an organism that only feeds as a secondary consumer an organism that consumes at three different trophic levels all of the quaternary consumers.

Figure 5.2 shows a food chain.

Table 5.1 shows the energy in the organisms shown in Figure 5.2.

Use the information in Figure 5.2 and Table 5.1 to construct a pyramid of energy on the grid. Label each trophic level.

State one reason for using a pyramid of energy rather than a pyramid of biomass.

Phytoplankton are aquatic producers. Scientists investigated the factors that affect their rate of population growth. A sample of phytoplankton was grown in a container with conditions similar to those found in the wild. The phytoplankton were provided with constant light. The population of phytoplankton was measured as the number of organisms per ${\mathrm{cm}}^3$. Figure 5.3 shows the results of the investigation.

Using Figure 5.3, calculate the population of phytoplankton in 0.5 ${\mathrm{dm}}^3$ on day 4. Give your answer in standard form.

Identify and explain the phases of growth shown by the phytoplankton in Figure 5.3.