A LOCAL ECOSYSTEM
TOPIC TEST - ANSWERS
Section a. MULTIPLE CHOICE
1) b; B has arrows pointing away from it only, so it must be a producer.
2) b
3) a; the percentage cover method does not actually count individual plants.
4) d
5) b; all of these involve living components of the ecosystem
6) a; we could expect the curve to decline if a predator was involved or if the species migrated from the ecosystem, and a sudden change in the abiotic factors would be unlikely to result in an equilibrium situation
7) a; the population of aquatic insects would probably increase because they would no longer be preyed on as much; b and d would probably occur, but not immediately
8) c; P = Ap/a
= 25 x 15/5
= 75
9) c; a small body size in fact increases the amount of surface area through which water can be lost (although this also allows the maximum amount of heat to be lost from the body in hot environments)
10) c; a and d would result in a decrease in algal numbers, and b would not affect the alga, as it is a producer organism
Section b.
11) a.
b. Species A and species B are competitors for the same resources; if this was a predator-prey relationship we would expect the population of species B to decrease after species A dies out, but it instead reaches an equilibrium situation (numbers at this stage are probably limited by available resources).
A LOCAL ECOSYSTEM
TOPIC TEST - ANSWERS (continued)
12) a. Temperature – Use either a data logger probe or a thermometer to measure air temperature at each site, and allow enough time for the instrument to equilibrate with the environment.
b. Moisture – The moisture content of the air or soil can be tested using either the probe of a data logger, or cobalt chloride paper. This paper must be stored over calcium chloride in an airtight container before use. When exposed to moisture, the paper will change from blue to a pink or white colour. The time taken for the paper to dry out again is a measure of the moisture present.
c. Acidity – Measure the acidity of any water or soil present at each site. Water can be collected in a test tube and tested with the appropriate probe on a data logger, or several drops of universal indicator solution can be added and the resulting colour checked against a pH colour chart. Soil can be mixed with water in a test tube and tested for pH in a similar manner to the above method, or wet universal indicator paper can be held against soil or rocks.
d. Wind speed/exposure – A wind meter or anemometer can be used to determine wind speed at each site, or a relative scale can be used in which + represents minimum wind exposure, and +++++ represents maximum wind exposure
13) a. No; energy is lost as heat or used in respiration. Only matter is recycled in an ecosystem.
b. water snails: 50,000 kg; small fish: 5000 kg; large fish: 500 kg; eels: 50 kg
14) a. i) The distribution and abundance of the prickly pear plant is affected by the presence of the cactoblastis moth, whose larvae eat all parts of the plant.
ii) Populations of the European rabbit are not present in northern Australia because of its extended periods of hot weather.
b. i) The distribution and abundance of native fish in Australia has been severely affected by the introduction of predatory fish such as the trout.
ii) Water temperature affects the larval growth, adult size and number of eggs produced in adult mayflies.
15) i) Land clearing – Clearing land for agricultural purposes can cause erosion, as the soil can no longer be held in place.
ii) Reduction in diversity of species – Many native species in Australia have become extinct or reduced in numbers because their natural habitats have been cleared to make way for agricultural or urban ecosystems.
iii)Pollution –Urban wastes containing sewage and detergents and agricultural run-off containing insecticides and fertilisers, for instance, often find their way into waterways. This can result in eutrophication - the overgrowth of water plants and algae at the expense of other aquatic life, which is starved of oxygen.
iv) Introduced species -The water hyacinth is an example of an introduced plant that has adversely affected ecosystems by choking up waterways and restricting the growth of other vegetation.
16) Example of working:
Number of random quadrats counted: 10; Average number of plants per m2 quadrat: 0.9; Estimate of total number of plants per 100m2: 90
A LOCAL ECOSYSTEM
TOPIC TEST - ANSWERS (continued)
17)
18) a. Decomposers act to break down dead or decaying organic matter, so releasing important minerals back to the soil.
b.
19) a. This helps to reduce heat and water loss, as the kangaroo rat is sheltered from the sun during the hottest part of the day.
b. This reduces heat loss from the blood by convection, as the blood vessels are no longer exposed to the lower temperatures at the skin's surface.
c. Freshwater fish are constantly subjected to water moving into their bodies by osmosis (because the solute concentration inside their bodies is higher than in the surrounding water). The production of dilute urine helps to get rid of some of this water.
d. Rainforest trees compete with each other for light, so having leaves with a large surface area allows the plant to use as much available light as possible for photosynthesis.
20)
alleopathy / A detrimental relationship in which one plant reduces the growth of another one in its vicinity by secreting inhibitory chemicals; e.g. eucalypts produce chemicals that inhibit the growth of other plants under them.parasitism / A relationship in which one organism uses another organism (the host) as its food source. The host is adversely affected, but does not usually die; e.g. tapeworm in the human gut.
mutualism / A necessary beneficial relationship between two organisms; both need each other for survival; e.g. the alga (provides food) and the fungus (provides moisture and support) in lichens.
commensalism / A relationship between two organisms in which one or both benefit and neither are harmed; e.g. an epiphytic plant using a rainforest tree as support.