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Ecology short-q 85-97
1.
List four biotic interactions which regulate the size of natural population. Briefly explain
how each works. (4 marks) 1985PIA3
Mutualism:互利共生 relationship between 2 organisms in which both derive benefits from the
association.
Commensalism:片利共生
Parasitism:寄生
Predation:捕食
Competition:競爭
2.
Define community, ecosystem, population and species.
With the aid of a diagram, explain the relationship between these terms. (6 marks) 1985PIA5
(i) Community: an assemblage of living organisms in a defined area or physical habitat. (1)
Ecosystem: a natural unit of living organisms/biotic components and non-living/abiotic
components interacting with each other to produce a stable and self-sustained system through
which interchanges of chemicals and energy occur.(1)Population: an assemblage of individuals
of the same species which occur together in a particular habitat.(1)
Species: is a group of similar individuals which share close similarity in genetic constituents,
functional and structural characteristics and can mate to produce fertile offspring
(ii) Diagram indicating populations (should be more than one) are subsets of the community
which in term is a subset of the ecosystem. (2)
(a) With reference to the nitrogen cycle, describe how the supply of nitrogen to green plants is
affected by the action of soil micro-organisms. (8 marks)
(b) Describe three ways in which man can enhance crop productivity by manipulating the nitrogen
cycle.
(6 marks)
(c) (i) Briefly illustrate how excess inorganic nitrogen applied to the soil may accumulate in
nearby water systems.
(ii) What are the biological consequences of the accumulation? (6 marks)85PII1
(3) Distinguish between
(a) a parasite and a saprophyte (2 marks) 86PIA1
(a) A parasite is an organism which lives in or on another living organism / the host, and
obtains food at the expense of the host.
A saprophyte is an organism who feeds on soluble organic compounds obtained from dead
animals and plants.
(b) nitrogen fixation and nitrification. (2 marks) 86PIA1
(b) Nitrogen fixation is the conversion (reduction) of nitrogen gas to ammonia.
Nitrification is the conversion (oxidation) of ammonia to nitrate.
(c) biodeterioration and biodegradation
(2 marks) 87PIA6
(c) Both processes involve the breakdown of organic material by micro-organisms. The
former results in unwanted decay of structures or substances e.g. wood rotting and food
spoilage. The latter is a beneficial breakdown e.g. sewage treatment, mineralisation by soil
micro-organisms.
(d) commensalism and mutualism
(2 marks)
87PIA6
(d) Both are associations whereby two organisms of different species either gain from being
together and are unable to survive separately (mutualism) or one is benefitted and the other
neither loses nor gains from the association (commensalism).
What is denitrification? Explain its effect on a natural ecosystem. Illustrate with an
example to show how this process could be utilized to the benefit of mankind. (5
marks)
88PIA2
Denitrification is part of the nitrogen cycle in which nitrate is converted to nitrous oxides and
to atmospheric nitrogen. (1) The process is carried out by a group of free living heterotrophic
bacteria under anaerobic or low oxygen conditions such as in a water-logged soil. (1). This
results in a loss of inorganic nitrogen from the soil. (1) In crop production, nitrogen is usually
the limiting nutrient
In a body of water rich in organic materials, the removal of nitrate effectively limits the
overgrowth of microscopic algae and in turn protozoa and reduce the pollution level.(1)
Denitrification is also one of the advanced wastewater treatment processes to reduce the
nitrogen level in sewage plant effluent. (1)
4.
Pyramids of biomass may sometimes be ‘inverted’. With the aid of an example, explain why
this is so. (4 marks) 1989PIA6
A pyramid of biomass is based on the total amount of living material at each trophic level at
any one time (1) OR it shows the standing crop/ biomass present at a given time.
Thus producers might be few or small, but at the same time they could be being produced at a
massive rate to feed the larger number of grazing consumers. (2)
Example: the food chain in a fertile, productive field which is being constantly grazed by cows.
(1)
5.
It is often found that certain toxic materials accumulate at a much higher concentration in the
tissues of the top carnivores than in other consumers in the food chain. Explain this
phenomenon with the aid of an example. (4 marks) 89PIA7
If the toxic chemical e.g. DDT/ heavy metals (1/2) cannot be metabolized and excreted (1), It
would be accumulated in the body of the organism and passes from one trophic level to another.
(1). As energy is lost from one trophic level to another by respiration, reproduction and so on,
(1/2) the conumers at the higher trophic level have to feed on a large number/ biomass of
smaller consumers which in turn feed on a larger number/ biomass of producers, thus the
concentration of the toxic chemical will be the highest at the top consumer level. (1)
1.
Define the terms community, succession and climax community. (6 marks) 86PII3(a)
A community is a group of interacting populations living in a given area, representing the
living part of an ecosytem.
Succession is the replacement of some species/ populations by others through time.
Climax community is the final stable and self-perpetuating/ self-sustaining community which
is in equilibrium with its environment. It is brought about by continued ecological
succession.
2.
Distinguish between:
(a) niche and habitat (2 marks) 1990PIA7
(b) production and biomass
(2 marks) 1990PIA7
(c) succession and zonation
(2 marks) 1990PIA7
(d) biome and habitat (2 marks) 93PIA6(b)
(e) the cause of greenhouse effect and the causes of ozone depletion (2 marks) 95PIA4(c)
(a) Niche is the functional role of the species i.e. what it does in the community (including
the habitat, food, nest sites, its place in the community in relation to other species and so on,
that it needs in order to survive).
Habitat is the place in nature where the species lives (or where you can find the species)
(b) Biomass is the amount of living / organic material (e.g. in terms of weight or carbon) of a
biological unit at any given time.
Production is the difference in biomass within a certain time interval (Biomass T1 - Biomass
T0).
(c) Zonation refers to the spatial distribution pattern of various species within a community at
any one time according to the environmental gradient (gradient of physical factors).
Succession refers to the replacement of some species within a community by other species
through time.
(d) A biome is an ecological term used to describe a major terrestrial community unit which
results from an interaction between regional climate and biota.
A habitat is an ecological concept of a space which is characterised by a set of physical
conditions or limiting factors that influence the presence, distribution and survival of
organisms within it.
(e) Causes of green house effect - accumulation of excessive carbon dioxide and methane/
hydrocarbon gases (1/2) in the atmosphere which traps heat reflected from the earth‘s surface
(1/2). Causes of ozone depletion - gases such as CFC/ halons enter into the stratosphere (1/2)
irreversibly react with ozone (1/2) molecules breaking them to oxygen gas.
3.
Explain what you understand by the following concepts:
(a) non-renewable resources
(b) eutrophication
(4 marks) 1994PIA6
(a) Resources of which their abundance is limited / finite (1/2) and which cannot be replaced
/ recycled (1/2). Their continued use will result in exhaustion (1/2), with harmful (social and
economic) consequences (1/2).
(b) Eutrophication is a process whereby a water body (1/2) (sea, lake) becomes enriched with
nutrients / inorganic and organic material (1/2) at rates which cannot be assimilated. This
causes an increase in the growth of aquatic plants (1/2) which then results in unfavourable
changes to water quality. (1/2)
4.
(a) What is meant by biodeterioration?
(a) Biodeterioration is any undesirable change (1/2) in the properties of a material caused by
the activities of organisms (1/2).
(b) Describe an example of a biodeteriorative effect caused by a microorganism. (3 marks)
94PIA7
(b) Bacterial spoilage of milk (1/2) caused by the fermentation of lactose / milk (1/2) sugar to
lactic acid (1/2) which causes souring of milk. (1/2)
Describe the ways in which living organisms obtain energy from the environment through
different kinds of nutrition. How do the differences in energy acquisition amongst living
organisms determine their ecological roles? (20 marks) 95PII5
Nitrogen in the air enters and leaves living systems by way of the nitrogen cycle. Describe
the events which take place when atmospheric nitrogen molecules move along a food chain
(involving legumes and herbivorous mammals) and eventually return to the atmosphere. In
your answer, describe the uptake, processing and utilization of nitrogen in the bodies of these
organisms. (20 marks) 97PII 5
5.
Why is the pyramid of energy always upright whereas the pyramid of biomass can sometimes
be inverted? (4 marks) 97PIA3
In the pyramid of energy, there is a progressive decrease in energy flowing through successive
trophic levels up a food chain (1/2). This is due to a net loss of energy to the environment
(1/2) as a result of processes such as respiration/ heat loss/ dead body/ incomplete eating/
excreta (1). Inverted pyramids of biomass can result when the turn-over rate of producers is
fast compared to the consumers (1), thus at any time the standing biomass of the producer can
be smaller (1/2) to sustain a larger biomass of consumers (1/2) (4 marks)