Energy Flow (Cambridge (CIE) O Level Biology): Exam Questions

The dominant grass species in an African grassland ecosystem are star grass and red oat grass.

• Star grass is eaten by antelope species, such as topi and Thomson’s gazelle.

• Smaller animals such as mice and grasshoppers feed on red oat grass.

• Topi and Thomson’s gazelle are eaten by predators such as cheetahs, lions and serval cats.

• Grasshoppers and mice are eaten by serval cats and tawny eagles.

• Vultures feed on dead mammals.

Fig. 1 shows part of the food web for this ecosystem.

Fig. 1

Complete the food web by writing the names of the correct organisms in the boxes in Fig. 1.

Name the trophic level of the following species.

(i) Star grass

[1]

(ii) Topi

[1]

(i) State the principal source of energy for the food web shown in Fig. 1.

[1]

(ii) State what happens to energy when it leaves a food web.

[1]

Explain why there are no more than four trophic levels in the food web shown in Fig. 1.

Extended only

Fish such as salmon can be reared intensively in fish farms. They are fed on high protein food made from animals. When eating this food, the fish are feeding as secondary consumers.

Describe the disadvantages of intensive farming, such as salmon farming, for producing human food.

Fig. 1 shows a simple food web.

Fig. 1

(i) Table 1 shows some of the terms that can be used to describe the organisms in the food web in Fig. 1.

Place ticks (✓) in the boxes to show the terms that can be used to describe each organism.

Table 1

[3]

(ii) State the number of trophic levels in the food web in Fig. 1.

[1]

(iii) Identify one organism that feeds at more than one trophic level.

[1]

(iv) State the term used to describe an organism that gets its energy from dead or waste organic material.

[1]

(v) State the principal source of energy for food webs.

[1]

Wetlands are important ecosystems. Researchers studied the feeding relationships between the organisms in an area of coastal wetland.

Fig. 1 shows part of the food web that they studied.

Fig. 1

Complete Table 1 by giving the name of one organism from the food web in Fig. 1 for each row.

Table 1

A pyramid of numbers for the wetland ecosystem showed that there were very large numbers of organisms at the base of the pyramid and very few at the top.

Explain why.

(i) The sentences in the box describe the feeding relationships between four organisms. 

Use the information in the sentences to write a food chain containing these four organisms. Do not draw pictures of the organisms.

[3]

(ii) State the principal source of energy for this food chain.

[1]

(iii) State the type of organism that gains its energy from dead organic material.

[1]

Fig. 1 shows a food chain that is found in the sea.

Fig. 1

(i) State the name of the producer in this food chain.

[1]

(ii) Define the term producer.

[2]

(iii) State the name of the secondary consumer in this food chain.

[1]

(iv) State the name of the herbivore in this food chain.

[1]

(v) State what the arrows in a food chain represent.

[1]

In some countries humans eat crabs.

Explain how the over-harvesting of crabs could affect the other organisms in the food chain shown in Fig. 1.

Ecologists studied an area of woodland and estimated the biomass of each trophic level for one of the food chains in the woodland.

Some students wanted to use the data to draw a pyramid of biomass for the food chain.

Table 1 shows the students’ table.

The students added a column to calculate the width of the bars they would need to draw.

Table 1

(i) Complete Table 1 by calculating the missing value and writing it in the table.

[1]

(ii) Using the information in Table 1, draw a pyramid of biomass.

Label each bar with the trophic level.

[3]

(i) Outline how organisms in the first trophic level of the woodland food chain produce biomass using energy from the Sun.

[3]

(ii) Explain why the fourth trophic level has the least biomass in this food chain.

[3]

Fig. 1 shows a food chain in a mangrove forest.

mangrove tree → fiddler crab → seagull

Fig. 1

Table 1 gives the number of organisms and their biomass in a mangrove forest.

Table 1

(i) Estimate the biomass of one fiddler crab in grams.

Write your answer to two significant figures.

Show your working.

[2]

(ii) Sketch a pyramid of numbers, using the information in Table 1, for the food chain shown in Fig. 2.

Write the number of each trophic level on the appropriate part of your pyramid. 

[3]

(iii) Explain why the shape of a pyramid of biomass, for the information given in Table 1, would be different from the shape of your pyramid of numbers.

[4]