web view(a)insecticides are pesticides which kill insects. a low concentration of insecticide was...

1. (a) Insecticides are pesticides which kill insects. A low concentration of insecticide was sprayed on the leaves of rose plants to kill greenfly which were feeding on the plants. Ladybirds eat greenfly. One month after spraying, the concentration of insecticide in the tissues of ladybirds was found to be higher than the concentration sprayed on the rose plants. Explain why.

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(b) Spotted knapweed is a common weed in the USA. Two methods, chemical control and biological control, have been used to reduce the numbers of spotted knapweed plants.The table shows the results of an investigation comparing the effectiveness of these two methods.

Month Mean number of spotted knapweed plants per m2

Chemical control Biological control

February 2 2

March 15 3

April 3 3

May 20 5

June 3 4

July 16 3

August 2 2

(i) Describe the pattern of plant numbers resulting from the use of

chemical control; ........................................................................................................

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biological control. .......................................................................................................

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Woodford High School 1

(ii) Explain how chemical control leads to the changes in the number of spotted knapweed plants from March to June.

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(c) Explain why the spotted knapweed plants were never completely eliminated when using

(i) chemical control;

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(ii) biological control.

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(Total 10 marks)

2. One of the most valuable crops planted by the Forestry Commission is spruce because use its yield of timber is high. Early trial plantings showed that spruce trees grew very slowly when planted on land on which heather was also growing.

(a) Name the type of competition shown between spruce and heather.

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(b) Give two resources for which spruce and heather are likely to be competing.

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(c) Further trial plantings on land dominated by heather showed that the growth of spruce was greatly assisted by planting another tree species at the same time. This use of a ‘nurse’ crop is now standard practice. The table shows the results of some of these trial plantings.

Height of spruce after15 years / metres

spruce, heather and Japanese larch 4.5

spruce, heather and Scots pine 3.1

spruce, heather and Corsican pine 3.5

spruce and heather 2.0

(i) Young spruce trees were 50cm high when planted. Calculate the difference in the rate of growth when these trees were grown with Japanese larch compared to the control. Show your working.

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(ii) Suggest one way in which a ‘nurse’ crop may aid the growth of spruce trees.

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(Total 5 marks)

3. Carbon dioxide is an essential raw material required by plants, but its concentration in the air is only about 0.03%. In a closed glasshouse carbon dioxide concentrations are often enriched. Carbon dioxide enrichment is normally carried out in the light and when vents are closed. Enrichment is only worthwhile for most crops during winter or early spring.

(a) Give two methods for enriching the carbon dioxide content of the air in glasshouses.

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(b) Explain why the concentration of carbon dioxide is not normally enriched to more than 0.1%.

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(c) Suggest why carbon dioxide enrichment is normally carried out only in winter or early spring.

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(Total 6 marks)

4. The expanding human population places increasing demands on limited resources to satisfy food production. Farmers employ a variety of methods to eliminate crop-destroying pests in order to increase food production. In the short term, chemical sprays have proved an effective method. However, the use of chemicals, particularly ‘broad spectrum’ compounds, has caused problems. For this and other reasons alternative methods of controlling pests are now being used. Integrated pest management utilises chemical and biological control methods, together with a number of agricultural practices, e.g. crop rotation and planting pest-resistant varieties. Pest-resistant varieties have been produced by many years of selective breeding and more recently by genetic engineering.

(a) Explain what is meant by ‘biological control’, and describe one example of how biological control has been used to control a specific pest.

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(b) Explain the advantages and disadvantages of using biological methods, rather than chemicals, to control pests.

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(c) Briefly describe the process of genetic engineering and suggest one advantage it has compared to selective breeding.

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(Total 12 marks)


5. The rhinoceros beetle is a pest which damages coconut palms growing on South Pacific islands. One method of control is to introduce a virus which kills the beetles. The virus was first used on the island of Tonga in 1971. The table shows the results of surveys of rhinoceros beetle damage to palm trees carried out at two sites in 1971 and 1978.

Site 1971 1978Number of palmtrees examined

Number of palmtrees damaged

by beetles

Number of palmtrees examined

Number of palmtrees damaged

by beetlesA 289 48 302 23

B 226 34 278 28

(a) The virus was introduced at sites A and B. At site A the virus was introduced as part of an integrated pest management scheme.Was the introduction of the virus more successful at site A or at site B?Support your answer with suitable calculations from the data in the table.

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(b) (i) Suggest two techniques which could be combined with the introduction ofthe virus to produce effective pest management schemes.

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(ii) Explain the benefits of an integrated pest management scheme.

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(c) Introduction of the virus is an example of biological control.

Explain two possible limitations of biological control methods.

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(Total 9 marks)

6. The energy value of the biomass synthesised by the producers in an ecosystem is a measure of the productivity of the ecosystem. The table shows the estimated annual mean energy value of the biomass synthesised in ecosystems in a country and the sea beside it.

Ecosystem Estimated mean energy value of biomasssynthesised by producers/kJ m–2y–1

Deep oceanShallow seaAlluvial plain – farmlandAlluvial plain – woodlandMountain grasslandDesert

3 00010 20029 00035 000 3 500 2 200


(a) Explain how energy is transferred into biomass by producers.

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(b) (i) Suggest why the deep ocean has a lower productivity than the shallow sea.

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(ii) Suggest one reason why the productivity of the farmland on the alluvial plain is lower than that of the woodland. Explain your answer.

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(c) In which ecosystem would you expect there to be the smallest number of animal species? Explain your answer.

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(Total 9 marks)

7. (a) The graph shows the yield of a crop when different amounts of a nitrogen-containing

fertiliser are applied.

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4

3

2

1

00 5 0 1 0 0 1 50 2 0 0

A m o u nt o f fe rtilise r a pp lied /k g n itro g en pe r he c tare

Y ie ld /to n n esp e r h e c ta re

A

BC

(i) Explain the effect of the amount of fertiliser applied on the yield of the crop for each of the labelled sections of the curve.

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(ii) A fertiliser costs 120p per kg nitrogen and the crop sells for £200 per tonne. Use the graph to calculate whether applying 125 or 150 kg nitrogen per hectare would be more profitable. Show your working.

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(b) Give one advantage and one disadvantage of using inorganic fertilisers instead of manure.

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(Total 7 marks)

Mark Scheme

1. (a) (a) greenflies take in (small mass of) insecticide from roses/leaves;ladybirds eat large numbers of/more/many greenflies;bioaccumulation idea / insecticide cannot be excreted/remains in body/stored in fat/not broken down; 3

(b) (i) chemical: numbers fluctuate throughout year;biological: numbers fairly constant throughout year / accurate description; 2

(ii) number of plants drops because of spraying/reapplication, then rises because insecticide washed away/new plants grow; 1

(c) (i) chemical: some plants/parts of plants are not sprayed / spray washes off before it has effect;plant may be resistant to spray; (Reject ‘ immune’) 2

(ii) biological: because biological control never eats all plants;as weeds diminish so do control agents and/or vice versa / is balance between food and consumer; 2

10]

2. (a) interspecific; 1

(b) one mark for two resources e.g. light; named nutrient, water; 1

(c) (i) one mark for working showing spruce and heather as control;0.16/0.17 metres per year; 2

(ii) produces substance/ nutrient which stimulatesgrowth of spruce / inhibits growth of spruce /provides nitrogen-fixing bacteria; 1

[5]


3. (a) dry ice;combustion;manure / compost; max 2

(b) not cost effective;since some other factor limiting rate of photosynthesis; 2

(c) cost of provision covered by extra cash from sale;as crops fetch higher price in winter; 2

[6]

4. (a) using a predator / parasite / pathogen to control (the numbers of) apest organism;name of control organism and pest;explanation of control method; 3

(b) advantages (max 3)(if well-screened) a biological control agent only attacks the pest;forms self-perpetuating population (only one application required);cheaper (qualified) e.g. saves cost of repeatedly using chemicals;safer because does not leave chemical residue;organisms do not become resistant to biological control;

disadvantages (max 3)doesn’t completely eradicate pest;cost of researching / setting up a biological control system;biological control agent may become a nuisance itself/must be wellscreened;slower to get rid of pest than chemicals;more subject to environmental factors; any 4

(c) use of restriction / endonuclease enzyme;cuts DNA at specific base sequence / recognition site;reference to vector / method of inserting DNA;same endonuclease to cut vector/host DNA;use of ligase enzyme (to join DNA strands);(allow equivalent mark points for use of reverse transcript) max. 4

one mark for advantage of genetic engineeringe.g. much quicker / more efficient / several genes can be inserted at once;

[12]

5. (a) correct % reduction for A; (16.6 7.6 OR 9%)correct % reduction for B; (15.04 10.07 OR 5%)greater percentage reduction in A 3

(b) (i) destruction of affected trees;use of insecticides;release sterile males / femalesselective breeding of beetle resistant palms max 2

(ii) if one method fails, other still partially effective;reduced amounts of pesticides needed;increased yield / less chance of resistant species developing /less effect on food webs; max 2

(c) possible effects on non-target species;possibility of population explosion due to lack of natural predators;not all pests killed;difficulty in maintaining population of control organism max 2

[9]


6. (a) Light / solar energy used for photosynthesis;Synthesis of materials used in growth / storage;Chemical energy stored / energy in biomass; 3

(b) (i) Fewer nutrients available;Limited light penetration;No organic matter from terrestrial sources;Other limiting factor explained; max 2

(ii) Reason for difference, e.g. plants smaller / less vegetation / cropsharvested / grazing;Explanation linked to difference, e.g. less area for photosynthesis / notstructured into layers / nutrients removed in harvesting; 2

(c) Desert, because lowest productivity;few plant species so few animal species able to feed on them;or, desert because abiotic conditions extreme / named factor;few species adapted to extreme conditions / less stable food web; 2

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7. (a) (i) A = nitrogen is limiting so crop increases with nitrogen added;

B = nitrogen is no longer limiting crop growth restricted byother factors/ shading / carbon dioxide;

C = nitrogen apparently inhibiting growth/high nitrate causesplants to lose water; 3

(ii) fertiliser costs yield sales net profit

125 x 120 = £150 4.8 x 200 = £960 £810

150 x 120 = £180 5.0 x 200 = £1,000 £820 2

(b) Advantage:ions in readily available form;

effects relatively rapid;

easy to apply;

quantities applied can be controlled/measured; max 1

Disadvantage:quickly leached;

more likely to cause pollution;

relatively expensive; max 1[7]


web view(a)insecticides are pesticides which kill insects. a low concentration of insecticide was...

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