Download public exam_ecosystems_R1 - ECF Saint Too Canaan College

ECF Saint Too Canaan College
Biology public exam exercise
Ecosystem
Name: ___________________
Class: _____ (
)
Date: _____________________
CE 2003_I_Q.1(c)(iv)
1.
The diagram below shows a simplified food web in Tai Mo Shan Country Park:
(a) With reference to the given food web, draw a food chain that consists of five trophic
levels.
(1 mark)
(b) Construct a pyramid of numbers for this food chain.
(2 marks)
(c) Explain the shape of this pyramid of numbers.
(4 marks)
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CE 2004_I_Q.4(b)
2.
Some industries produce mercury-containing wastes which may be discharged into the sea. The
table below shows the mercury levels in the seawater and the marine organisms around the area
of discharge:
(a) With reference to the mercury level in various marine organisms, construct a probable food
chain using these organisms.
(1 mark)
(b) Explain why tuna fish contains a much higher mercury level than shrimp.
(3 marks)
(c) After consuming seafood harvested in this area for years, people may develop the
symptom of shaky hands. This is a sign of mercury poisoning. Suggest which body system
is likely to have been affected.
(1 mark)
(d) Describe how the nitrogen in the shrimp can be made available to the microscopic algae
after the death of the shrimp.
(4 marks)
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CE 2005_I_Q.6(c)
3.
A piece of agricultural land can be used for growing crops, or for growing grass to raise cattle
for meat. Explain why crop-growing can provide more food for human consumption than
cattle-raising.
(4 marks)
CE 2005_I_Q.8
4.
The picture below shows a school garden with some tomato plants:
(a) Explain why continuous harvesting of tomatoes may lead to the depletion of nitrate in the
garden soil.
(1 mark)
(b) Which organism in the soil turns some of the nitrate into atmospheric nitrogen?
(1 mark)
(c) Suggest two ways to restore the nitrate content of the soil.
(1 mark)
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CE 2007_I_Q.9(a)
5. The photograph below shows an ecosphere:
(a) The ecosphere is a self-sustaining ecosystem sealed in a glass container. It contains
bacteria, microscopic algae, shrimps and branches of dead coral in filtered seawater.
Why is it essential to put algae into the ecosphere to make it self-sustaining?
(4 marks)
(b) How can the activity of the bacteria contribute to the growth of algae?
(2 marks)
(c) This ecosphere can only support two trophic levels. Suggest a possible explanation for this.
(2 marks)
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AL 1999_I_Q.4
6. In an experiment to study the interaction of organisms, a student introduced some zooplankton
X into a culture of zooplankton Y kept in a jar. The following graph shows the population
changes of X and Y in the jar based on the data obtained from this experiment. It is known that
these two zooplanktons are not competitors, and they have similar masses and similar turnover
rates.
(a) Identify the relationship between X and Y.
(1 mark)
(b) Sketch a graph to show what you would expect to find in the population pattern of X and Y
if they were allowed to interact in the natural environment.
(2 marks)
(c) Account for the difference in population pattern when X and Y were allowed to interact in
the natural environment compared to when they were kept in the jar.
(3 marks)
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DSE PP_IB_Q.3
7.
A sandy shore community has three species: a burrowing clam, a snail, and a crab.
(a) To determine the relative abundance of these species, a student placed a quadrat on the
shore and collected all the individuals on the sediment surface inside the quadrat. After
counting the number of individuals of each species collected from this quadrat, he
determined their relative abundance. Give three reasons why the student’s sampling
method may not reflect the actual relative abundance of these organisms.
(3 marks)
(b) The feeding relationship of these three species is shown below:
Suggest the effect on the population of crabs if a large number of clams are harvested by
visitors to the shore. Explain your answer.
(2 marks)
(Assume that the crabs have the same preference for snails and clams.)
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DSE PP_IB_Q.6
8.
Graph 1 shows the change in the soil nitrogen content in an area over 200 years. At the
beginning of Stage 1, the area was without vegetation. Table 1 shows the relative abundance of
three plant species found in this area at the different stages:
Graph 1
Table 1
(a) With reference to Table 1, state the process that accounts for the change in the relative
abundance of the plant species in this area.
(1 mark)
(b) The bacteria living symbiotically with plant species A and species B played an important
role in causing the increase in the soil nitrogen content in Stages 1 and 2.
(i)
Name the symbiotic bacteria living in plant species A and B.
(1 mark)
(ii)
Describe how the symbiotic bacteria and the two plant species caused the increase in
the soil nitrogen content in Stages 1 and 2.
(3 marks)
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DSE 2012_IB_Q.7
9.
The diagram below shows a food chain in an ocean. The energy content of each trophic level is
shown in the boxes:
(a) In the space below, calculate the percentage decrease in energy content from unicellular
phytoplankton to krill.
(2 marks)
(b) Give two reasons why there is a decrease in energy content from a lower trophic level to a
higher one.
(2 marks)
(c) In another food chain, the producer is tree and the primary consumer is caterpillar. Would
the percentage decrease in energy content be greater or smaller than the value found in (a)?
Explain your answer.
(2 marks)
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DSE 2013_IB_Q.5
10. Knowing that the nitrogen cycle is important to the healthy growth of fish, Tom purchased
testing kits to monitor the levels of ammonia, nitrite and nitrate in his aquarium. He kept the
aquarium aerated with an air pump. The graph below shows the changes in the concentrations of
the three compounds over 50 days:
(a) Name the process that led to the changes shown in the graph.
(1 mark)
(b) After three weeks, Tom observed a high concentration of nitrite in the water and the fish
were showing symptoms of nitrite poisoning. Therefore, Tom added a suspension of a
bacterial culture to the water to lower the nitrite concentration. Suggest the type of bacteria
he added and explain how it lowered the nitrite concentration.
(2 marks)
(c) To prevent the accumulation of nitrate, Tom regularly replaced some water in the
aquarium with fresh water. What else could Tom do to lower the nitrate concentration?
(2 marks)
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DSE 2013_IB_Q.8
11. A study was carried out to investigate the distribution and abundance of animal species A and B
on a rocky shore. The table below shows the results obtained from the back of the shore to the
waterfront:
Abundance (number of individuals m-2)
Distance from the back
of the shore (m)
Species A
Species B
1
10
0
2
25
2
3
40
8
4
38
10
5
20
20
6
18
35
7
15
33
8 (waterfront)
11
28
(a) Using the graph paper on the opposite page, plot a graph to show the results.
(5 marks)
(b) Based on the information in the graph, suggest which species would have a higher
tolerance to desiccation. Explain your answer.
(4 marks)
(c) Briefly describe the sampling procedure used to obtain the above data.
(3 marks)
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DSE 2015_IB_Q.3
12. The diagram below shows the feeding relationships among some organisms in a marine
ecosystem:
(a) Write down the shortest food chain found in the diagram.
(1 mark)
(b) In the space provided below, draw the pyramid of numbers for the food chain in (a).
(2 marks)
(c) Explain the shape of the pyramid of numbers drawn in (b).
(3 marks)
(d) Suggest two practical methods that allow you to confirm the feeding relationships among
various organisms in this ecosystem.
(2 marks)
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ECF Saint Too Canaan College
Biology public exam exercise – Ecosystems answer
1.
(a)
wild fruit tree → caterpillar → lizard → bird → snake
(b)
Drawing of the pyramid: upright pyramid, with inverted bottom
1
1, 1
Deduct 1 mark if any one of the trophic levels is not labeled.
(c)
Energy is lost along the food chain
1
due to respiration / excretion / incomplete ingestion and digestion of food / death
Thus the number of organisms in each trophic level decreases from caterpillar to
snake.
However, the biomass / energy / size of the fruit tree is much greater than that of a
caterpillar
so a fruit tree can support many caterpillars.
1
1
1
(7)
2.
(a)
microscopic algae → shrimp → squid → tuna fish
1
(b)
Tuna fish feed on a large number of squids, which in turn feed on a large number of
1
shrimps.
As mercury cannot be broken down or excreted by the organisms,
it accumulates along the food chain and reaches a high level in tuna fish.
1
1
(c)
nervous system
1
(d)
Protein in shrimp is broken down into ammonium compounds
by putrefying bacteria.
1
1
The ammonium compounds are in turn converted into nitrates
by nitrifying bacteria.
1
1
(9)
3.
In the first way, humans feed directly on the crops grown, while in the second way humans
feeds on cattle which in turn feeds on grass / In the first way, humans obtain food through
a shorter food chain / a smaller number of trophic levels.
Since energy is lost along the food chain
through respiration, death, excretory products, faeces.
1
1
1
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More energy in the form of organic matter will be available to humans in the first way.
1
(4)
4.
(a)
The nitrate in the soil is absorbed by the tomato plant for growth.
When tomatoes are harvested, the nitrogen in the tomatoes is not recycled to the soil.
1
1
(b)
denitrifying bacteria
1
(c)
add chemical fertilizer
bury leaves / organic matter into the soil
grow leguminous plants
)
) any two
)
1, 1
(5)
5.
(a)
It converts light energy to chemical energy
which is passed along the food chain to support other organisms.
It also maintains a steady air composition
by releasing oxygen and absorbing carbon dioxide.
1
1
1
1
(b)
Bacteria break down the organic matter to inorganic matter
which is then absorbed and used by algae for growth.
1
1
(c)
The biomass of algae is limited in the ecosphere.
1
Energy is lost along food chain
and cannot support more trophic levels.
1
(8)
6.
6.
(a)
predator-prey relationship / X preys on Y
(b)
(i)
(b)
(ii)
Y and X out of phase (½) + at least 2 oscillation cycles are shown(½), peak,
for Y higher than that of X (½), 2 curves correctly labelled as X and Y (½)
(axes without labels - ½)
Both X and Y would not die out completely / X and Y would show oscillating
cycle pattern.
In the natural environment, as the population density of Y falls, it would be
difficult for X to locate Y / less food is available for X / X may prey on other
available food source other than Y.
When X falls in population, Y will take chance to reproduce (½) and this is
1
2
1
1
1
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followed by an increase in X population as more food is available (½).
(6)
7.
(a)




No replicate is carried out and so the results may not be representative.
Quadrat sampling is not accurate for determining the number of mobile
animals like crabs.
Burrowing bivalves will be missed if only animals on the surface are
collected.
Sampling is not random and hence a biased sample may be taken.
)
)
) any 3
)
)
)
(b) The population size of the crabs remains constant (1)
as the crabs will eat more snails when the abundance of clams is reduced. (1)
3
2
OR
The population size of the crabs may be reduced (1)
as more snails are consumed when the number of clams is reduced. The number of
snails may not be enough to maintain the population size of the crab. (1)
(5)
8.
(a) (Primary / ecological) succession
1
(b) (i)
1
nitrogen fixing bacteria*
(ii) The bacteria fixed atmospheric nitrogen into ammonium compounds
and supplied the nitrogenous compounds for plant species A and B to synthesize
proteins.
The decay / decomposition of the plant species A and B after their death released
the fixed nitrogen to the soil.
This increased the soil nitrogen content in Stages 1 and 2.
1
1
1
(5)
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9.
(a) (10 000 000 – 1 000 000) / 10 000 000 x 100%
= 90%
1
1
(b) 
some energy is not obtained by the organisms of higher trophic level as part of the
body of prey is not consumed (1) / part of the food is not digestible or is egested
(1)
some energy is lost by the organisms at the higher trophic level through excretion
(1) / respiration (1) / in the form of heat (1)
1
the percentage decrease in energy content is greater (1)
as caterpillars mainly feed on leaves of trees, leaving most of the part of the
biomass of trees unconsumed (1) / lignin is not consumed
1
1

(c) 

1
(6)
10. (a) nitrification* (1)
(1)
(b) 

nitrifying bacteria (1)
which convert nitrite to nitrate (1) and help lower the nitrite level
(2)
(c) 

adding aquatic plants to the aquarium (1)
the plants will assimilate / absorb / convert nitrate into their biomass (1)
(2)
5
11.
(a) 



correct title (1)
- concept: distribution of species, defined location, e.g.
 The distribution and abundance of animal species A and B on a rocky
shore
 Abundance of species A and B from the back of a shore to the water front
correct choice of axes (1)
axes with labels and units (1)
- X: distance from the back of the shore (m); Y: abundance (number of
(5)
individuals m-2 of m-2)
correct plotting and joining of line showing the distribution of species A and B (1,
1)
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11.
(b) 



(c) 


species A is found to be more abundant at the back of the shore than species B (1)
the back of the shore has a lower chance / shorter period of time to be convered by
seawater (1)
thus, organisms found at this region is more likely to face the problem of
desiccation (1)
therefore, it can be deduced that species A has a higher tolerance of desiccation
(1)
place a transect line from the back of the shore to the waterfront (1)
place a quadrat along the transact line at regular intervals (1)
count the number of species A and B in the quadrate (1) and record the results
(4)
(3)
12
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