Chapter 20 Ecosystems

Multiple-choice questions

[0320101]
* The following diagram shows part of a food web from Yellowstone Park.

elk
aspen grey wolf
moose

beaver

What would be the short-term effects on the populations of the other species if
the grey wolf were exterminated?
Beaver Moose Elk Aspen
A increase decrease increase increase
B decrease decrease decrease decrease
C increase increase decrease increase
D decrease increase increase decrease

[0320102]
* The diagram below shows a nitrogen cycle associated with soil.
Which arrow indicates the activity of denitrifying bacteria?

plant animal ammonium

protein protein compounds

atmospheric D
nitrogen
B
A
C
nitrates nitrites

[0320103]
* The graph below shows variation in biomass throughout one year in an aquatic
ecosystem.

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 producers

biomass of organic matter under

primary consumers
secondary consumers

1 m surface (g)
2

month of year

During which month of the year would the following pyramid of biomass be
applicable?

secondary consumers

primary consumers

producers

A June
B July
C August
D September

[0320104]
** Which of the following promotes the loss of nitrogen from soil due to the activity
of denitrifying bacteria?
A leaching of nitrate from soil in drainage water
B anaerobic conditions caused by water saturation
C high levels of phosphate from addition of fertilizers
D the presence of a leguminous crop such as clover
[0320105]
* A species of Latin American ant inhabits the thorns of a species of Acacia. The
ant receives nectar and shelter from the plant. The plant receives protection from
the ants.
This is an example of
A parasitism. B commensalism.
C mutualism. D predation.

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[0320106]
** Hydra is a small freshwater animal that uses its tentacles to catch food.
One variety (green hydra) has photosynthetic algae living in its tissues.
Another variety (colourless hydra) has no algae.
The relationship between Hydra and the algae is believed to be an example of
mutualism.
Under what conditions would a comparison of the growth rates of green and
colourless Hydra test this hypothesis?

mouth

tentacle

A light; food supplied B light; no food supplied

C dark; food supplied D dark; no food supplied
[0320107]
Which of the following processes reduces atmospheric carbon dioxide
concentrations?
A decomposition B nitrogen fixation
C respiration D photosynthesis
[0320108]
* Which organism(s) in the food web below is/are both secondary consumer(s) and
tertiary consumer(s)?

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 hawk fox

small birds badger hedgehog shrew

mice
beetles slugs

woodlice
rabbits

grass

A hawk and fox B hawk and hedgehog

C fox and badger D hawk only

[0320109]
* What is a community?
A A group of producers and consumers living and interacting in an area.
B A group of species living and interacting in an area.
C A group of organisms living and interacting in an area.
D A group of populations living and interacting in an area.
[0320110]
What are the main sources of carbon dioxide on earth?
A cellular respiration of consumers, producers and combustion of fossil fuels
B photosynthesis and cellular respiration of consumers
C cellular respiration of producers and combustion of fossil fuels
D photosynthesis and combustion of fossil fuels
[0320111]
What components are needed to make an ecosystem?
A a community and its abiotic environment
B a community and its source of energy and nutrients
C producers and consumers only
D producers, consumers and decomposers only

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[0320112]
* What is the ecological role of saprotrophic bacteria?
A To recycle energy in dead organic matter.
B To digest dead organic matter and release nutrients from it.
C To ingest dead organic matter and prevent it from accumulating.
D To produce dead organic matter by killing organisms.

[0320113]
* This diagram represents a simple food chain. In which ways is energy lost
between the trophic levels?

plant caterpillar frog snake owl

(1) heat loss through cell respiration

(2) material not consumed
(3) material not assimilated
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and (3)
[0320114]
How could a quadrat be used by an ecologist?
A To estimate rates of immigration and emigration of animals in a population.
B To estimate the sizes of plant populations by random sampling.
C To trap animals so that they can be marked and released.
D To estimate light intensity from the height of the sun above the horizon.

[0320115]
Which of the following processes is carried out by bacteria found in root
nodules?
A denitrification
B nitrification
C nitrogen fixation

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 D deamination
[0320116]
The diagram below shows a simplified version of the carbon cycle.

CO2 in atmosphere
I

II
fuels plants
secondary
consumer
primary
consumer

What processes are involved in the transfer of carbon at stages I and II?
I II
A combustion photosynthesis
B photosynthesis respiration
C combustion respiration
D fossilization respiration

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[0320117]
* Which of the following comparisons between the primary succession and
secondary succession is not correct?
Primary succession Secondary succession
A occurs in areas with no organisms occurs in areas with some
organisms
B takes a longer time to reach a climax takes a shorter time to reach a
community climax community
C occurs in a new land formed by occurs in a woodland after hill fire
reclamation
D occurs in land with no soil occurs in land with soil

[0320118]
* Directions: The following two questions refer to the table below, which shows
the number of three species, X, Y and Z, in four habitats.

X Y Z
Habitat P 60 55 45
Habitat Q 130 6 4
Habitat R 0 60 0
Habitat S 16 4 140

Which habitat has the highest species diversity?

A P B Q
C R D S

[0320119]
* Which species is/are the dominant species in habitat Q?
A X B Y
C Z D Y and Z

[0320120]
Decomposers return carbon to the ecosystem in the form of
A urea. B carbon dioxide.
C protein. D fat.

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[0320121]
Which of the following is the function of a quadrat in ecological studies?
(1) To estimate the abundance of plants in a grassland.
(2) To estimate the number of fish in the freshwater stream.
(3) To estimate the number of barnacles in the rocky shore.
A (1) and (2) only B (1) and (3) only
C (2) and (3) only D (1), (2) and (3)

[0320122]
Which of the following matchings of the instruments used in ecological studies
and their functions is not correct?
Instrument Functions
A lux meter to measure light intensity
B thermohygrometer to measure relative humidity
C anemometer to measure wind speed
D conductivity meter to measure oxygen concentration in water

[0320123]
Directions: The following two questions refer to the food chain below.

grass ® grasshopper ® small bird ® eagle

Which organism(s) in the above food chain is/are (a) consumer(s)?

A grass only
B grasshopper only
C eagle only
D grasshopper, small bird and eagle

[0320124]
What is the ecological relationship between grasshopper and small bird?
A predation
B competition
C commensalism
D mutualism

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[0320125]
* An ecosystem is composed of
(1) a group of interacting populations.
(2) environmental factors affecting the populations.
(3) the plants in the area.
A (1) and (2) only B (1) and (3) only
C (2) and (3) only D (1), (2) and (3)

[0320126]
How is energy lost as it is transferred up trophic levels?
A through predation only
B through competition only
C through respiration only
D through respiration and uneaten organisms

[0320127]
* Which of the following statements are correct?
(1) Producers use light or chemical energy to make food from inorganic
substances.
(2) The population of producers is always larger than that of primary
consumers.
(3) Herbivores are secondary consumers.
A (1) and (2) only
B (1) and (3) only
C (2) and (3) only
D (1), (2) and (3)

[0320128]
* Which of the following statements about the nitrogen cycle is correct?
A Nitrogen fixing bacteria can change atmospheric nitrogen into nitrites.
B Denitrifying bacteria can change nitrites into nitrates.
C Nitrifying bacteria can change the nitrogen in dead bodies into nitrites.
D Producers absorb nitrogen in the form of nitrates.

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[0320129]
* Which of the following is the corresponding pyramid of biomass of the food
chain below?

oak tree ® caterpillar ® parasite inside the caterpillar

A B

C D

[0320130]
Which of the following pairs of organisms demonstrate commensalism?
A lion and human
B barnacle and crab
C tapeworm and pig
D bee and flower

[0320131]
Nitrogen can be added to the soil by
(1) combustion.
(2) lightning.
(3) nitrogen fixation.
A (1) only
B (1) and (2) only
C (2) and (3) only
D (1), (2) and (3)

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[0320205]
** Crayfish are crustaceans known for their aggressive behaviour. Researchers
observed this aggressive behaviour to determine what was most important to the
crayfish of genus Orconectes: shelter, dead food source, or live food source. The
researchers recorded the number of fights and the length of time pairs of crayfish
spent fighting in three different areas.
time spent fighting (%)

time spent fighting (s)

Key: sheltered areas areas rich in dead food areas rich in live food

Graph X
average length of fight (s)

N = number of fights observed

area

Graph Y

a Using the data in graph X, compare the percentage of time the crayfish
spent fighting in sheltered areas and areas rich in live food. (2 marks)
b i Identify the average length of a fight in sheltered areas and areas rich
in dead food. (1 mark)
ii Calculate the ratio of the average fight length in areas rich in dead food
to the average fight length in sheltered areas. (1 mark)
c Discuss which areas are preferred by the crayfish. (3 marks)

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[0320206]
** Fishing activities in marine ecosystems often result in catching unwanted species
in addition to the target species. Together with undersize fish, this unwanted
catch is often discarded. Discarded fish are a key food resource for many seabird
species. The great skua (Stercorarius skua) is a scavenger which feeds on other
birds, sand eels and discarded fish.
The graph below shows the effect of the size of the sand eel population and the
estimated amount of discarded fish on the proportion of birds in the great skua
diet.

proportion of
birds in the great
skua diet

estimates of
discarded fish sand eel
6
(10 kg) 6
biomass (10 kg)

a State the relationship between the amount of discarded fish and the
proportion of birds in the great skua diet when sand eel biomass is low.
(1 mark)
b Outline the relationship between sand eel biomass and the proportion of
birds in the great skua diet when the estimated amount of discarded fish is
high. (2 marks)
c Suggest one reason why the amount of discarded fish may decrease in the
future. (1 mark)
d Predict two possible consequences on the ecological community structure if
the amount of discarded fish decreases. (2 marks)

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[0320208]
* Mining activities often affect the pH of nearby lakes. Data was collected on the
observed and expected average number of species of zooplankton (small aquatic
animals) and fish in lakes from a mining area. The expected numbers of species
are based on values observed in lakes of a similar size in the same area but more
distant from the mines.
Zooplankton

average number
of species

pH categories

Key: expected observed

Fish

average number
of species

pH categories

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 a Identify which type of animal and pH range showed the highest difference
between the expected and observed numbers. (1 mark)
b Compare the expected and observed values for fish. (2 marks)
c Analyse the effect of pH on zooplankton and fish. (3 marks)
(0320210]
** The diagram below shows energy flow through a deciduous forest ecosystem.
Units are kJ m-2 day-1.

a Calculate the percentage of light energy that is captured in photosynthesis

by the forest plants. (1 mark)
b Ten percent is often quoted as a typical value for ecological efficiency. Use
the data to show that this value does not always apply to energy transfer
between trophic levels. (1 mark)
c In what form is the energy lost from metabolism? (1 mark)

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Structured questions

[0320301]
* Two species of sea snakes, Laticauda laticaudata and Laticauda colubrina,
spend most of their lives living in the sea. They must be able to move, hunt and
survive in the water, but for short periods they need to come ashore to breed.
They inhabit some of the Pacific islands which have low coral cliffs that the
snakes need to climb in order to get onto dry land for courtship, mating and
laying eggs.

Diagram to show a cross-sectional view of cliff used in the study

height

The scientists studied the ability of snakes to climb the low cliff. They measured
the body mass of the snakes and relative strength of the snakes. The mean results
are shown in the bar charts below.
muscle strength
body mass (g)

(arbitrary unit)

females males females males

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a State which sex of snake has the greater mean mass. (1 mark)
b State which species of snake is the strongest. (1 mark)
c The error bars represent standard deviation. Deduce which groups of snakes
show the greatest variability in body mass. (1 mark)
d For L. colubrina calculate the difference between the strength of the male
and the female snakes. (1 mark)

The scientists placed male snakes onto the coral cliff near its base. They
measured their ability to hold onto the coral cliff. The L. colubrina males
climbed much faster than the males of L. laticaudata. The graph below shows
the ability of snakes to cling to the coral cliff.

snakes still
clinging to the
cliff (%)

time (s)

e i Compare the ability of the two species of snake to cling to the cliff.
(2 marks)
ii Suggest two reasons for the difference in the ability of the snakes to
cling to the cliffs for 120 seconds. (2 marks)
f Discuss the advantages and disadvantages of body mass in these two
species of snake. (3 marks)

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[0320303]
* a Explain the meaning of the terms population and community. (4 marks)
b Different organisms in the same community interact with one another. The
graph below shows the numbers of four species of plants in a certain area of
a forest in a 40-year period after the introduction of species W.

100 W
90 X
80
number of plants

70
60
50
40
30
20
10
Y
0
0 10 20 30 40 Z
year

i Describe the change in the numbers of different species in these 40

years. (4 marks)
ii Explain why the population of species W increases rapidly in the first
25 years. (1 mark)
iii Why the number of species W becomes steady after year 25?
(1 mark)
iv What is the relationship between species W and Y? Explain your
answer with reference to the graph. (2 mark)

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