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C19.1 Populations and ecosystems AQA A2 Biology B19 Population And Ecosystem Kerboodle Answers
In the following passage, state the word that best replaces each of the numbers in brackets. The study of the interrelationships between organisms and their environment is called ecology (1). An ecosystem is a more or less self-contained functional unit made up of all the living or biotic (2) features and non-living or abiotic (3) features in a specific area. Within each ecosystem are groups of different organisms, called community (4) which live and interact in a particular place at the same time. A group of organisms occupying the same place at the same time is called population (5) and the place where they live is known as habitat (6). The population size of a species that an ecosystem can support is known as the carrying capacity (7).
19.2 Variation in population size AQA A2 Biology B19 Population And Ecosystem Kerboodle Answers Page No. 207
1 Certain factors limit growth, e.g. availability of food, accumulation of waste, disease.
2 Biotic factors involve the ac1ivi1ics of living organisms. Abiotic factors involve the non-living part of the environment.
3 a Low light intensity
b Lack of water
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Low temperature
4 a Using a standard scale, most of the points plotted for the population of the world would be so dose together as to be indistinguishable from each other on the graph. A logarithmic scale separates these points.
b c. 19.3 Competition AQA A2 Biology B19 Population And Ecosystem Kerboodle Answers Page No. 211
1 Intraspecific competition occurs when individuals of the same species compete with one another for resources. lnterspecific competition occurs when individuals of different species compete for resources.
2 Food /water /breeding sites (or any other relevant factor, e.g. light, minerals).
19.4 Predation AQA A2 Biology B19 Population And Ecosystem Kerboodle Answers Page No. 215
1 The range and variety or laboratory habitats is much smaller than in natural ones. This means that in nature there is a greater range of hiding places and so the prey has more space and places to escape the predator and survive.
2 With fewer predators, fewer prey arc taken as food. The death rate of prey is reduced. Assuming the birth rate remain unchanged the population size increases.
3 Graph showing population fluctuations (peaks and troughs) of A. Species B mirrors these changes after a time lag. The population size of B is, for the most part, smaller than A. Beats A–+ population of A rails –+ fewer A for B to eat –+ population of B falls –+ fewer B means fewer A are eaten–+ population of A rises–+ more A means more food for B –+ population or B rises.
19.5 Investigating populations AQA A2 Biology B19 Population And Ecosystem Kerboodle Answers Page No. 219
1 100 x 80/5= 1600
2 a Population over-estimated (appears larger) as there will be proportionally fewer marked individuals in the second sample.
b Population over-estimated I appears larger as there will be proportionally fewer marked individuals in the second sample because all the ‘new’ individuals will be unmarked.
c No difference because the proportion of marked and unmarked individuals killed should be the same.
c (120 x 120) / 960 = 15 Banner 2
19.6 Succession AQA A2 Biology B19 Population And Ecosystem Kerboodle Answers Page No. 222
1 Pioneer species
2 Primary colonisers (pioneer species) photosynthesise and fix nitrogen –+ these die and form a soil with nutrients–+ further colonisers can survive in this soil –+ environment is a little less hostile–+ more habitats and food sources available –+ other species arc able to survive–+ increased biodiversity.
3. Climax community.
19.7 Conservation of habitats AQA A2 Biology B19 Population And Ecosystem Kerboodle Answers Page No. 224
1 The species within the habitat possess unique genes that at some point in the future may be useful. Conserving habitats maintains biodiversity. The greater the variety of’ habitats, the greater their potential to enrich our lives and provide enjoyment.
2 Cut back reeds to prevent them becoming dominant. Remove dead vegetation to prevent build-up and thus stop fens drying out. Pump water into fens to keep them waterlogged. Cut back grasses and shrubs to prevent succession. Banner 3
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Practice questions: Page No. 226-227
1 (a) (i) Decrease in spadefoot toad. Decrease in southern toad up to 4 newts per pond, then increase (at 8 newts per pond).
(ii) Predators/newts eat/feed/prey on toad (tadpoles). Less competition more food/resources / fewer toads feeding on frogs.
(b) Fewer toads/tadpoles (as number of predators increases in Figure 1). More food, so are larger / grow more / increase in mass.
2 (a) Ulva lactuca.
(b) (i) Difficult/too many/too many to count /individual organisms not identifiable /too small to identify / grows in clumps.
(ii) Texture / flat / composition chemicals / nutrients etc.
(c) - Pioneer species/Ulva increases then decreases.
- Principle of a species hanging the conditions / a species makes the conditionsless hostile.
- New/named species better competitor /previous/named/pioneer species outcompeted.
- G. coulteri/Gelidium increases and other/named species decreases.
3 (a) Crabgrass.
(b) 1. Species/plants/animals change the environment/conditions/add humus/nutrients etc.
- Less hostile (habitat).
- Species/plants better competitors.
(c) (Only) plants which can photosynthesise with less light (remain). Banner 5
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