Deck 45: Ecosystems

Question 1

Choose the term for which a definition requires reference to both biotic and abiotic interactions.

A) Population.
B) Ecosystem.
C) Symbiosis.
D) Habitat.
E) Community.

Answer 1

Ecosystem.

Question 2

All organisms are either

A) autotrophs or heterotrophs.
B) photosynthetic or chemosynthetic.
C) heterotrophs or chemosynthetic.
D) photosynthetic or autotrophic.
E) herbivores or carnivores.

Answer 2

autotrophs or heterotrophs.

Question 3

Fungi can be classified as

A) omnivores.
B) detritivores.
C) autotrophs.
D) decomposers.
E) parasites.

Answer 3

decomposers.

Question 4

Eucalypt leaves are eaten by beetles, which are eaten by birds, which are preyed upon by quolls. This is an example of a

A) trophic pyramid.
B) food web.
C) food chain.
D) forest ecosystem.
E) a trophic relationship.

Question 5

Which of the following statements about food chains is true? Typically

A) food chains rarely involve more than four trophic levels.
B) omnivores are scarce.
C) one species can occur in many food chains.
D) green plants are at the base of food chains.
E) All of the answers are true.

Question 6

When ecosystems are considered in terms of trophic interactions, which of the following is NOT found at the base of a food chain?

A) Algae
B) Decomposer bacteria
C) Cyanobacteria
D) Green plants
E) All of these could be found at the base.

Question 7

The small number of trophic levels uniformly found in food chains

A) can be explained by energy reduction up the trophic scale.
B) is due to the uniformly low energy base (primary productivity) of all ecosystems.
C) is a phenomenon for which ecologists do not yet have a satisfactory explanation.
D) is because there are few predatory organisms in the chain.
E) is a result of the greenhouse effect.

Question 8

Under some conditions, trophic diagrams may be inverted (i.e. broader at the top). Under which of the following conditions would you expect a biomass pyramid to be inverted?

A) When primary producers are slow growing and long lived.
B) When grazers are rare.
C) When primary producers are heavily grazed.
D) When predators are slow and hunt inefficiently.
E) When the ecosystem is dominated by large herbivores.

Question 9

In an ecosystem, the total amount of living material present at a given time

A) is a measure of the community structure of the system.
B) is a measure of primary productivity.
C) is the biomass of the system.
D) is a measure of the rate of turnover of organisms.
E) contributes to the base of the ecological pyramid.

Question 10

What is the productivity of an ecosystem?

A) The rate at which the main primary producers of an ecosystem synthesise energy.
B) The rate at which primary consumers use energy.
C) The rate at which energy is synthesised by primary producers plus the rate at which it is recycled by degraders.
D) The total amount of material present at any time.
E) The difference between the energy produced by primary producers and that consumed by consumers.

Question 11

Experiments using 'potted webs' showed that the number of trophic levels in a food chain was limited by the

A) amount of energy at the bottom of the chain only if energy levels were kept far below natural levels.
B) amount of energy at the top of the chain in all cases.
C) amount of energy at the bottom of the chain in all cases.
D) size of the experimental pot.
E) amount of energy at the bottom is dependent on the number of relationships in which any species is involved.

Question 12

In an ecosystem consisting of phytoplankton being grazed by zooplankton, you would expect to find

A) a higher biomass of consumers than producers.
B) a large biomass of producers but fewer consumers.
C) no consumers.
D) an equilibrium between the producers and consumers.
E) no producers.

Question 13

Which type of food web do models predict would enable the persistence of an ecosystem in a variable environment? One with

A) many linkages.
B) a low level of complexity.
C) many omnivores.
D) many complex interactions.
E) long food chains.

Question 14

Which of the following is thought by some to govern the stability of a food chain?

A) The number of links
B) Energy limitations in the ecosystem
C) The number of autotrophs
D) The number of carnivores
E) The number of omnivores

Question 15

In general, marine ecosystems

A) have a low net primary productivity.
B) are more productive than terrestrial ecosystems.
C) have productivity similar to terrestrial ecosystems.
D) contain adequate phosphate levels but are limited by nitrogen.
E) are limited by light more than by nutrients.

Question 16

Which of the following ecosystems would you expect to have the highest primary productivity?

A) A savanna grassland
B) A coral reef
C) A tropical rainforest
D) A deciduous forest
E) Oceans

Question 17

The world's major oceanic fisheries are in upwelling zones because

A) this is where the warmest and thus most productive waters are found.
B) deep water is forced up in these zones bringing fish to depths where they are more economically fished.
C) deep water is forced up in these zones bringing nutrients to phytoplankton near the surface.
D) the deep water forced up in these zones contains high levels of phosphorous.
E) deep water is forced up in these zones bringing phytoplankton to fish near the surface.

Question 18

Compared to a similar but undisturbed reef, a coral reef recovering after severe storm damage would generally have

A) higher productivity and lower biomass.
B) lower productivity and lower biomass
C) higher productivity and higher biomass
D) lower productivity and lower biomass.
E) about the same productivity but lower biomass.

Question 19

A major difference between energy cycles and the cycling of inorganic materials through ecosystems is that

A) energy is continuously added to the cycle while materials are drawn from geologic stores.
B) energy cycling occurs on a global scale while materials are cycled on a local scale.
C) energy cycles are short while material cycles are long.
D) energy cycling is global while inorganic materials change with the location.
E) All of the answers are true.

Question 20

Which of the following statements is NOT correct?

A) 97 per cent of the world's water is in the oceans.
B) Some of the world's water is in inaccessible storage pools.
C) Transpiration removes water from circulation.
D) Soil moisture and ground water provide substantial pools of water.
E) Water circulates in the atmosphere by convection.

Question 21

Compared to most of the world, Australia has

A) areas of very high rainfall.
B) extremely variable rainfall.
C) a majority of ecosystems limited by water.
D) a large proportion of dry area.
E) All of the answers are true.

Question 22

Most of the world's carbon stores are in

A) the enormous biomass of the world's tropical rain forests.
B) krill populations in the cold oceans of the world.
C) rocks.
D) trees.
E) fossil fuels.

Question 23

In the global carbon cycle, the smallest pool of carbon is found in

A) rocks.
B) the atmosphere.
C) fossils fuels.
D) marine organic matter.
E) the oceans.

Question 24

Which of the following chemical conversions does NOT directly occur in the nitrogen cycle?

A) Nitrate ions to atmospheric nitrogen gas
B) Nitrite ions to nitrate ions
C) Nitrate ions to ammonium ions
D) Ammonium ions to nitrite ions
E) Atmospheric nitrogen gas to nitrite ions

Question 25

Most animals obtain nitrogen by

A) fixing it.
B) ingesting amino acids.
C) ingesting nitrites.
D) ingesting ammonia.
E) ingesting nitrates.

Question 26

All of the following processes add nitrogen to ecosystems EXCEPT

A) oxidation of nitrogen by lightning.
B) fixation by symbiotic bacteria.
C) volatilisation of organic wastes.
D) industrial high temperature conversion of atmospheric nitrogen.
E) fixation by cyanobacteria.

Question 27

Which of the following statements about termites is true?

A) Termites are an exclusively wood-eating family.
B) Termites can digest cellulose directly.
C) Termites maintain a high biomass in dry environments.
D) Termites build mounds that are low in nutrients but high in organic carbon.
E) Termites recycle about 80% of the ecosystem's carbon.

Question 28

All of the following have a significant gaseous atmospheric pool EXCEPT

A) carbon.
B) nitrogen.
C) oxygen.
D) phosphorus.
E) All of the answers have a significant atmospheric pool.

Question 29

Plants inhabiting ecosystems with low levels of phosphorous are able to achieve high rates of productivity by

A) recycling phosphorous stores contained within the living biomass.
B) having a low absolute requirement for phosphorus.
C) efficiently utilising phosphorus extracted from soil and litter by mycorrhizal associations.
D) mycorrhizal recycling of phosphorous to make it readily available.
E) All of the answers are correct.

Question 30

A farmer with a stand of eucalyptus trees that appear to be suffering from rural dieback wants to arrest the problem. His best course of action would be to

A) spray the trees to poison the flying insects that defoliate the trees and monitor them carefully in case they return.
B) decrease stocking rates around trees, reduce fertiliser application and plant more trees and shrubs.
C) fertilise the soil with superphosphate to enable better growth.
D) increase stocking rates to reduce weeds and grasses that compete with the trees for soil moisture.
E) reduce the density of other, less-desirable native trees in the area to reduce the available feed for the defoliating insects.

Question 31

Termites play a crucial role as decomposer organisms in dry soils. Termites have which of the following advantages in arid regions?

A) Insulating properties of their nests
B) Co-operative social structure
C) Ability to store food for long periods
D) Concentrate moist nutrients in their nests
E) All of these answers contribute to the success of termites in arid regions.

Question 32

Ecosystems

A) are explained by analysing the flow of energy up the tropic scale.
B) consist of a simple sequence of organisms eating and being eaten. Generally the reasons are unknown.
C) realistically consist of food webs which are a series of interlocking food chains.
D) require scavengers and degraders.
E) All of the answers are correct about ecosystems.

Question 33

Food chains are usually short. Reasons for this are thought to be

A) the energy available at each level.
B) populations of organisms in a food web are in stable equilibrium, which is maintained by short chains.
C) there is a hierarchy in which species fed on those below and are eaten by those in levels above it, and so is limited by the tropic levels.
D) the relatively few organisms in any ecosystem.
E) Generally the reasons are unknown.

Question 34

The limited number of tropic levels is most likely due to

A) reduction in energy up the tropic scale.
B) the large proportion of energy that is transferred from one tropic level to the next.
C) the high level of energy available at the top of the ecological pyramid.
D) the constant level of energy available at the base of different ecosystems.
E) The constant energy flowing from one energy level to the next.

Question 35

Primary productivity of an ecosystem

A) is relatively constant.
B) is similar between different ecosystems.
C) is determined by the activity of plants and algae.
D) is highest in marine ecosystems.
E) depends on its state of regeneration since regenerating ecosystems are more productive than mature ecosystems.

Question 36

The ecosystem which occupies the largest area of the earth is

A) tropical rainforest.
B) savanna.
C) semiarid desert.
D) woodlands.
E) continental shelf.

Question 37

A prokaryotic cyanobacteria has no chloroplasts but does contain chlorophyll as well as having the ability to fix atmospheric nitrogen. Its chlorophyll content gives it the ability to convert atmospheric CO₂ into photosynthates, meaning that it must be a

A) heterotroph.
B) decomposer.
C) detritivore.
D) chemotroph.
E) autotroph.

Question 38

Which of the following is NOT a basic pattern exhibited by all food webs?

A) Omnivores typically feed on organisms in adjacent trophic levels.
B) Food chains typically have only three or four levels.
C) Food webs typically have two to three omnivores per top predator.
D) Omnivores are usually scarce in number.
E) Although a small number of subgroups may exist, trophic interactions occur only within a particular habitat.

Question 39

According the first law of thermodynamics, energy is conserved. That is, the internal energy of a system changes as energy flows in or out of it. In biological terms, this can be interpreted as meaning that whenever energy is transformed from one form to another, some is lost (typically as thermal energy). What does this tell us in relation to the structure of an ecological pyramid?

A) Whenever an organism eats another, not all of the energy consumed is converted into usable energy.
B) There will always be fewer top predators than those that are consumed at the base.
C) The number of mid-range organisms in a pyramid will be fewer than those at the top.
D) All of the options listed are correct.
E) The number of mid-range organisms in a pyramid will be more than those at the bottom.

Question 40

Behind tropical rainforests, what is the second most productive ecosystem on earth in relation to their annual cumulative biomass?

A) Estuaries and reefs
B) Tropical seasonal forest
C) Cultivated, agricultural areas
D) Temperate deciduous forest
E) Woodland

Question 41

Which of the following raw materials is required for life and is NOT cycled through a global cycle?

A) Oxygen
B) Silicon
C) Carbon
D) Hydrogen
E) Manganese

Question 42

Approximately what fraction of the world's water is stored in biologically inaccessible forms such as glaciers and ice-caps?

A) <1%
B) 2%
C) 5%
D) 3%
E) 8%

Question 43

A photosynthetically active plant in moist soil and full sun is respiring rapidly. What would be the NET carbon cycle status of this plant at this point in time?

A) It is a net exporter of carbon, returning large amounts of carbon to the atmosphere via respiration.
B) There is no net gain or loss of carbon; the plant both accumulates and returns carbon to the carbon cycle at roughly equal rates.
C) It is a net accumulator of carbon, converting atmospheric carbon primarily into ATP, NADPH and FADH₂.
D) It is a net exporter of carbon, returning large amounts of carbon to the atmosphere via the decomposition of dead and decaying plant matter.
E) It is a net accumulator of carbon, converting atmospheric carbon primarily into carbohydrates.

Question 44

A farmer has a large field that she uses to grow wheat with minimal agricultural inputs. The wheat grown in this field originally gave a reasonable yield but over time the yield has steadily declined until it becomes economically unviable. Frustrated, the farmer abandons growing wheat in the field and the following year instead plants lentils and produces a good harvest. The farmer grows lentils again the following year and produces another good yield, but the following year she in unable to source lentil seed stock in time to sow the field. Rather than leave the field fallow, she decides to cut her losses and sow wheat again. To her surprise, despite identical climatic conditions and uniform disease conditions, the wheat harvest noticeably improved. What could explain this observation?

A) Thunderstorms have converted atmospheric nitrogen into oxides which have been deposited in the soil by rain and accumulated.
B) Lentils secrete an exotoxin which has killed soil bacteria, resulting in less competition for nutrition.
C) Wheat stubble had built up in the soil of the field, inhibiting the growth and development of future wheat plants. Two years of lentils gave enough time for decomposing microorganisms to break down the build-up of stubble.
D) Lentils are a leguminous plant, therefore they have increased the available nitrogen levels in the field.
E) Lentils use fewer nutrients than wheat, meaning there was more available for the wheat when it was grown after two years of growing lentils.

Question 45

Plant growth is found to be particularly vigorous in a rural area of Australia, until the opening of a bauxite mine for Al production. After the opening of the mine, the growth rate of plants declines in a manner proportional to the plants' proximity to the mine. Rainfall is good, the soil is neutral and there is no change in pathogen levels or soil nutrient content. Why might plant growth be limited around the mine?

A) The mine is leeching nutrients from the surrounding soil via its tailings dam.
B) Mine construction has disturbed a reservoir of previously bound toxins in the soil.
C) The activities of the mine have increased Al³⁺ levels in the soil, which is toxic to root growth and development.
D) Dust and run-off from the mine has increased the Al content of surrounding soils. The Al has bound to phosphorous causing it to become immobile and unavailable to plants.
E) Dust and run-off from the mine has increased the Al content of surrounding soils. The Al has bound to nitrogen causing it to become immobile and unavailable to plants.