Organisms and Their EnvironmentCambridge IGCSE Biology: Topic test

20 questions, 54 marks

Cambridge IGCSE Biology

Organisms and Their Environment topic test

Total 54 marks

Name

Class

Date

1
In a desert ecosystem, cactus plants are eaten by kangaroo rats, which are in turn eaten by rattlesnakes, and rattlesnakes are eaten by owls.
(a)
Which organism in this food chain is the producer?
[1 mark]
ACactus
BKangaroo rat
CRattlesnake
DOwl
(b)
Which term describes the rattlesnake's position in this food chain?
[1 mark]
AProducer
BSecondary consumer
CPrimary consumer
DDecomposer
(c)
Explain why the cactus is described as a producer in this food chain.
[2 marks]
Total for question 1: 4 marks
2
On a coral reef, algae are eaten by parrotfish and by sea urchins. Parrotfish are eaten by reef sharks. Sea urchins are eaten by triggerfish, and triggerfish are also eaten by reef sharks.
(a)
Based on this coral reef food web, which of the following organisms is a primary consumer?
[1 mark]
AReef shark
BAlgae
CParrotfish
DTriggerfish
(b)
If a disease caused the sea urchin population on the reef to fall sharply, what would you expect to happen to the population of triggerfish, at least in the short term?
[1 mark]
AIt would increase, because they would face less competition for algae
BIt would stay exactly the same, because triggerfish do not depend on sea urchins
CIt would decrease because triggerfish would be eaten by sea urchins
DIt would decrease, because sea urchins are one of their food sources
(c)
Explain one advantage of representing these feeding relationships as a food web, such as the one described above, rather than as a single food chain.
[2 marks]
Total for question 2: 4 marks
3
In a tropical rainforest, leaves are eaten by leaf-cutter ants, and leaf-cutter ants are eaten by giant anteaters. Only a small proportion of the energy stored in the leaves is eventually transferred to, and stored in, the tissues of the giant anteaters.
(a)
State three ways in which energy is lost between the leaves and the leaf-cutter ants that feed on them, meaning that not all of the energy in the leaves is transferred to the ants.
[3 marks]
(b)
Using the idea of energy loss at each stage of a food chain, explain why food chains such as this one usually have no more than about four or five trophic levels.
[4 marks]
Total for question 3: 7 marks
4
A large tree falls in a forest and its trunk begins to decompose. A population of a single species of decomposer fungus colonises the dead wood, and ecologists monitor both the size of the fungus population over several months and the release of nutrients from the decaying wood back into the forest soil.
(a)
Describe the pattern of growth you would expect to see in the fungus population over several months as it colonises the dead wood, referring to the different phases of a typical population growth curve, and explain what limits the fungus population's growth in the later stages.
[6 marks]
(b)
Explain how the decomposition of the tree trunk by the fungus population releases nutrients back into the forest soil, and explain why this process is essential for the continued growth of other plants in the forest.
[6 marks]
Total for question 4: 12 marks
5
In a garden pond, pondweed is eaten by water fleas, water fleas are eaten by minnows (small fish), and minnows are eaten by herons. Only about 10% of the energy present at one stage of this food chain is typically transferred to, and stored in, the next stage.
(a)
Approximately what percentage of the energy present in the water fleas would you expect to be transferred to, and stored in, the minnows that eat them?
[1 mark]
A10%
B100%
C50%
D1%
(b)
Which diagram-based representation of this food chain would take into account the amount of energy transferred at each stage, rather than simply the number of organisms present?
[1 mark]
AA pyramid of numbers
BA pyramid of energy
CA food web
DA dichotomous key
(c)
Explain one advantage of using a pyramid of energy, rather than a pyramid of numbers, to represent this pond food chain.
[2 marks]
Total for question 5: 4 marks
6
A wildfire burns through an area of forest, releasing large amounts of carbon dioxide into the atmosphere as the wood and other plant material combust. In the years that follow, new trees grow in the burnt area, absorbing carbon dioxide from the atmosphere.
(a)
Which process do the new trees use to absorb carbon dioxide from the atmosphere as they grow?
[1 mark]
ARespiration
BCombustion
CPhotosynthesis
DDecomposition
(b)
Which of the following processes, other than combustion during the wildfire, also releases carbon dioxide into the atmosphere as part of the carbon cycle?
[1 mark]
APhotosynthesis
BNitrogen fixation
CDenitrification
DRespiration
(c)
Explain why the carbon released as carbon dioxide during the wildfire can be described as part of a cycle, rather than simply being lost from the ecosystem.
[2 marks]
Total for question 6: 4 marks
7
After unusually heavy rainfall in a normally dry region, plant growth becomes very abundant, providing a large new source of food. A small population of desert locusts that survived the dry period begins to grow rapidly in number, and scientists monitor the locust population size over the following weeks.
(a)
Identify and describe the phase of population growth that the locust population would be expected to show immediately after the heavy rainfall, while food is abundant and few predators or competitors are present.
[3 marks]
(b)
Explain what would be expected to happen to the locust population once the abundant plant food supply eventually becomes depleted by the rapidly growing swarm, describing the resulting phase(s) of population growth.
[4 marks]
Total for question 7: 7 marks
8
The brown tree snake is not native to the Pacific island of Guam, but was accidentally introduced there by ships in the mid-20th century. The island had no similar snake predator before this, and the native bird species had not evolved effective defences against this new predator. Within a few decades, the brown tree snake had caused the near-total extinction of Guam's native forest bird species.
(a)
Using ideas about food webs and populations, explain why the introduction of the brown tree snake to Guam caused such a dramatic decline in the island's native bird populations, and suggest one likely effect of this bird population collapse on the rest of Guam's forest food web.
[6 marks]
(b)
Explain how the near-total loss of Guam's native bird populations could also disrupt the flow of energy and the cycling of nutrients through the forest ecosystem, even for organisms not directly connected to the birds in the food web.
[6 marks]
Total for question 8: 12 marks

End of questions