ecology (food web)

8/9/2019 Ecology (Food Web)

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ECOLOGY Biology Concepts

Prepared by: Ahmed Kaleem Khan Niazi 1

Name of Candidate: .... Date: ..

Subject: Biology Total Marks: [ ]

1. Fig. 5.1 shows a food web.

(a) (i) Complete the food chain from this food web.

[1]

(ii) Complete each column of Table 5.1 by naming two appropriate organisms from the food web. Someorganisms could occur in more than one column.

[3]

Name of Candidate: .. Date:

Subject: Biology / 5090 Total Marks: [23]


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(b) The overuse of some pesticides can make the eggs of birds of prey, such as the kestrel, infertile. Thismay cause a large decrease in the population of kestrels.Predict and explain the possible effects this could have on populations of stoats and rabbits in the foodweb, Fig. 5.1.

stoats ..

..

..

rabbits

..

[4]

(c) About 20 years ago a failure at a nuclear plant resulted in the release of radioactive material into theatmosphere. The radioactive material was deposited on grasslands over parts of Europe. Some of the

radioactive chemicals got into organisms in the food web, Fig. 5.1. Not all of these radioactive chemicalstaken in by organisms are excreted.

(i) Suggest which organism would have accumulated the highest concentration of radioactive chemicalsand explain why this would happen.

organism ...

explanation ...

..

[3]

(ii) One of the radioactive chemicals present was strontium, which behaves very much like calcium in ananimals body. Suggest where this strontium would be found in high levels in an animals body.

..

[1]

[Total: 12]


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2.

Lake Victoria is the largest tropical lake in the world. Until the 1960s it provided an ecosystem with habitatsfor 500 species of small cichlid fish. They feed on algae (aquatic plants). Prawns also feed on algae.Nile perch were introduced into the lake. These fish are excellent food for humans, as well as providingsport for tourists. The Nile perch eat cichlids.Deforestation of the lake shore and pollution by humans caused eutrophication and resulted in a hugereduction in cichlid numbers. However, the Nile perch are able to survive in poor quality water, even whenthe oxygen level is low. As the cichlid population dropped, prawn numbers increased and Nile perch noweat them.(a) Define the term ecosystem.

.. [2]

(b) Using information in the text above, state two reasons why Nile perch were introduced into LakeVictoria.

1.

..

1.

. [2]

Complete the table to identify at which trophic level each of the organisms named in the text are feeding.

algae-------cichlid------fish-------human------Nile perch-----prawn

[3]

(d) Explain how eutrophication could have resulted in a reduction in the numbers of cichlid fish.

.

.

.

.[4][Total: 11]


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EXAMINER REPORT

Question no 1:

In (a)(i) two errors arose that have been identified elsewhere in this report, in that candidates did neitherread the question clearly enough nor gave attention to the positioning of labels A and B. In the former casea number identified the type of vessel, artery and vein, but did not name them and in the latter case therewere a significant number of responses with the correct names but linked to the wrong letter label. Thefunction of the valve was regularly correctly identified but it was misnamed as either tricuspid or semilunarvalve. Unfortunately there were candidates who expanded their responses about preventing backflow thenincorrectly qualified this with phrases such as to the ventricles. In Section (b)(i) many candidates quotedthe maximum output of the heart, 14 dm3

per minute, rather than the requested response, namely the maximum increase in heart output, 7 dm3

per minute. Perhaps this is another example of lack of attention in reading the question. Far too many

responses in (b)(ii) are worded as if the events mentioned do not occur before exercise rather than

increasing during exercise, for example now blood carries oxygen to the muscles because they start

respiring. In (c) most candidates were well versed in the ways in which the risk of a blockage of the

coronary artery could be reduced, although some discussed medical intervention which is curative rather

than preventative. Far fewer appreciated that the blockage would lead to no flow of blood with oxygen and

glucose to the tissue beyond X and thus the death of the tissue. Many responses simply identified the

events as a heart attack or cardiac arrest and some used even more technical medical terms. Candidates

should appreciate that a heart attack and a stroke are not synonymous.

Question no 2:

(a) The candidates were asked for another definition here this time of ecosystem. Some candidatesdefined a habitat instead because they referred to an organism instead of a community of organisms.Some candidates gave definitions of ecology rather than ecosystem. However, most candidates gave asatisfactory definition of this widely used term that implied that an ecosystem consists of organisms thatinteract with each other and/or with the physical environment in a defined place. The Examiners found

quite a few non living organisms.(b) Most candidates found the appropriate answers to this question from the text and referred to foodfor humans and sport for tourists. Candidates lost marks if they did not qualify food and sport in theiranswers. Some thought that Nile perch were introduced to balance the ecology of Lake Victoria.(c) As in June 2007, some candidates did not realise that this table should include more than onespecies. They often wrote one species in each row and this gained a maximum of one mark for givingalgae as the producer.(d) Knowledge of eutrophication seemed somewhat patchy. Some candidates gave very detailedanswers gaining the four marks available very easily. These were splendid answers. Other candidates did

not realise that eutrophication leads to the death and decomposition of plants so that the oxygen

concentration of the water decreases. Instead they wrote about the loss of algae as food for cichlid fish or

predation by the Nile perch.


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MARK SCHEME

Question no 1:

(a) (i)

[1](ii) consumer Any two animals in web; carnivore Any two from carnivorous insect, spider, fox, toad,lizard, stoat, kestrel; herbivore Any two from herbivorous insect, vole, rabbit; Each correct column 1mark [3](b) * 1 stoat population could rise;2 as kestrels eat less voles;3 more food/voles for stoats; *4 (if more stoats then) population of rabbits fall;5 as stoats eat more of them;

6 more voles would eat more grass;7 less food for rabbits (population falls); Any four 1 mark each [4](c) (i) 1 foxes/kestrel/top carnivore; [1]2 plants absorb radioactive minerals/ions/chemicals;3 taken in by herbivores within plants/on plants;4 passed to carnivore;5 at each stage predator eats lots of prey individuals;6 (bio)accumulation occurs; Any two 1 mark each [2](ii) bones and teeth/where there are high levels of calcium; [1]

[Total: 12]

Question no 2:

ecology (food web)

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