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Biology for IGCSE & O level - Organisms And Their Environment (Section 3)

1
What are the key roles of the decomposers in an ecosystem?
Answer
A
C
2
In an ecosystem, where does the energy used by a primary consumer originally come from?
Answer
(A)
Sunlight
3
Which of these elements plays a crucial role in the carbon cycle?
Answer
(C)
Carbon
4
What is the main role of the bacteria in the nitrogen cycle?
Answer
(D)
All of the above
5
Which organisms are primarily responsible for nitrogen fixation?
Answer
(C)
Bacteria
6
What is the function of nitrogen-fixing bacteria?
Answer
(A)
To convert atmospheric nitrogen to a usable form.
7
What is the process by which plants take up nitrogen?
Answer
(C)
Taking up nitrates from soil
8
What is the significance of pyramids of biomass?
Answer
(B)
To show the total mass of living material at each trophic level.
9
Which of the following best describes the relationship between a producer and a primary consumer?
Answer
(B)
The primary consumer consumes the producer.
10
Which of these best explains why a pyramid of energy always has a pyramid shape?
Answer
(A)
Each trophic level uses up some energy.
11
Which of the following is a way that carbon enters the carbon cycle?
Answer
(D)
All of the above
12
Which of the following is NOT a step in the nitrogen cycle?
Answer
(D)
Eutrophication
13
What is the role of primary consumers in an ecosystem?
Answer
(B)
To eat producers.
14
Which of the following is an example of a primary consumer?
Answer
(B)
Grasshopper
15
Which type of organisms perform photosynthesis?
Answer
(C)
Producers
16
In the nitrogen cycle, what is the role of denitrification?
Answer
(B)
To convert nitrates back into nitrogen gas.
17
Which of the following are key elements in the nitrogen cycle?
Answer
A
B
C
18
What is the main goal of nitrogen fixation?
Answer
(B)
To convert nitrogen gas into usable forms for plants
19
What is the effect of excess use of fertilizers in agriculture on the nitrogen cycle?
Answer
(D)
It can lead to eutrophication in waterways.
20
What do the arrows in a food chain or web represent?
Answer
(B)
The flow of energy
21
What is the primary function of decomposers in an ecosystem?
Answer
(B)
To recycle nutrients from dead organisms.
22
Which organisms form the base of a food chain?
Answer
(C)
Producers
23
What happens to the amount of energy available as you move up a food chain?
Answer
(C)
It decreases.
24
What is the role of the sun in an ecosystem?
Answer
(B)
To provide energy for producers.
25
Which bacteria are involved in nitrogen fixation?
Answer
(D)
Nitrogen-fixing bacteria
26
What is the primary role of decomposers in an ecosystem?
Answer
(B)
To break down dead organisms and recycle nutrients.
27
What is the significance of energy transfer efficiency in ecosystems?
Answer
(A)
It determines the number of organisms that can be supported in the higher trophic levels.
28
Which process releases carbon dioxide back into the atmosphere?
Answer
(B)
Respiration
29
What are pyramids of numbers and biomass used for?
Answer
(C)
To represent the amount of energy at each trophic level.
30
Which of the following processes directly converts atmospheric nitrogen into a form usable by plants?
Answer
(C)
Nitrogen fixation
31
What is the source of energy for most ecosystems?
Answer
(C)
Sunlight
32
What is the role of photosynthesis in the carbon cycle?
Answer
(B)
To absorb carbon dioxide.
33
What is the process that converts nitrogen gas into ammonia?
Answer
(C)
Nitrogen fixation
34
Which of the following converts ammonia to nitrites and then nitrates?
Answer
(C)
Nitrifying bacteria
35
Which of the following is a producer?
Answer
(B)
A tree
36
What process converts atmospheric nitrogen into forms plants can use?
Answer
(C)
Nitrogen fixation
37
What is the primary function of nitrogen-fixing bacteria?
Answer
(A)
To convert atmospheric nitrogen into nitrates.
38
What are the units usually used when expressing the biomass?
Answer
(B)
Grams per square meter
39
What does the carbon cycle primarily involve?
Answer
(C)
The movement of carbon.
40
In the nitrogen cycle, what is the process of converting nitrates into nitrogen gas?
Answer
(B)
Denitrification
41
How does energy move through a food chain?
Answer
(C)
From producers to consumers.
42
Which of the following converts atmospheric nitrogen into a form usable by plants?
Answer
(D)
Nitrogen-fixing bacteria
43
What is the term for organisms that can produce their own food?
Answer
(B)
Producers
44
What do the arrows in a food web illustrate?
Answer
(B)
The direction of energy flow.
45
What is the main role of decomposers in the nutrient cycle?
Answer
(B)
To recycle nutrients back into the environment.
46
What are some of the main elements involved in nutrient cycles?
Answer
A
B
47
What is the role of respiration in the carbon cycle?
Answer
(B)
To release carbon dioxide.
48
What are the primary forms of nitrogen that plants can absorb?
Answer
B
C
49
In the nitrogen cycle, which bacteria convert ammonia into nitrites and nitrates?
Answer
(D)
Nitrifying bacteria
50
What does a pyramid of biomass measure?
Answer
(B)
The total weight of living matter at each trophic level.