Ecosystems (OCR A Level Biology)

Algae are photosynthetic organisms that live in water.

A rapid increase in the population of algae is known as an algal bloom.

Scientists studied the population of algae in a river in the UK at different times of year. Their results are shown in Fig. 21.1.

percentage decrease = .......................................................... [2]

 [2]

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

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

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.

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 = 1 - 

D (Habitat A) = 0.71
D (Habitat B) = .........
Habitat with the greater biodiversity = ..........

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.

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 catalyses.

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 Jm^-2 yr^-1.

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

Answer: ................. kJm^-2 yr ^-1 [2]

Answer: ................% [1]

This Question is about ecosystems in the Southern (Antarctic) Ocean.

Observe the food chain:

phytoplankton (producers) → krill (shrimps etc.) → small fish → large fish → seals

Table 21.1 shows the transfers of energy and the quantities of energy stored as biomasses for the food chain. Magnitudes are given in kilojoules per square metre of sea surface per year.

Table 21.1

• Suggest two measures that an international treaty might impose, to prevent fishing from causing permanent damage to the Southern Ocean.
• Identify the practical difficulties that might prevent your two measures from being effective.

First measure .............................................................

Difficulty.........................................................

Second measure................................................

Difficulty..................................................

[4]

A small, permanent pond is the habitat for a climax community of producers (aquatic plants and algae) and consumers (bacteria, protoctista, worms, snails, arthropods and small vertebrates like newts and fish).

Why might ecologists call this a ‘climax community’?

The protoctist Paramecium caudatum is usually between 200 and 300 μm in length. An accurate measurement would help in the correct identification of a specimen from this pond.

What laboratory equipment would you select to make an accurate measurement of the length of Paramecium caudatum?

An animal fell into the pond. It drowned and decayed. Within a year the biological compounds in its body had been completely recycled.