Ecosystems

Question 1

The recorded number of elk legally shot by hunters provides accurate data.Suggest why these data are accurate, but the method used to obtain these data is not a valid way of estimating the number of elk in the population.

Answer 1

accurate because
idea that actual number of elk shot is recorded ;
method not valid because
idea that number of elk shot / hunting success ,
varies independently of population size ;

Question 2

Outline how the percentage efficiency of energy transfer between producers and herbivores can be estimated.

Answer 2

1
herbivore / primary consumer,energy x 100 ;
producer energy
Plus any 3 of the following:
2 (a sample of) producers collected ;
3 (a sample of) herbivores /primary consumers
collected;
4 (collected from) the same area ;
5 (measure) biomass / dry mass (of individual or
population) ;
6 energy content calculated of producer and
herbivore ;
7 use of calorimeter / described;

Question 3

Describe the differences between the following biological terms:
a pioneer community and a climax community

Answer 3

1 pioneers arrive , before climax / earlier ; ora
2 pioneer communities subject to , greater / more ,
change / succession / replacement ; ora
3 pioneer community (usually) has , less / lower ,
biodiversity ; ora
4 idea that pioneer community is (often) less ,
stable / self-sustaining ; ora
5 pioneer community has lower biomass ; ora

Question 4

Describe the differences between the following biological terms:
decomposition and denitrification

Answer 4

1 decomposition is break down ,
dead matter / waste
or
decomposition is conversion of
organic matter to inorganic ;
2 denitrification is conversion of nitrates to nitrogen (gas) ;
3 decomposition increases , mineral / nitrate , supply
and
denitrification reduces , mineral / nitrate , supply ;

Question 5

Describe the differences between the following biological terms:
conservation and preservation

Answer 5

1 conservation maintains , ecosystem / biodiversity /
species / habitats
or
conservation involves , active / sustainable ,
management of , ecosystem / resource / habitat ;
2 preservation leaves , ecosystems / habitats ,
undisturbed ;

Question 6

Suggest three ways that farmers can maximise the efficiency of the transfer of energy up food chains from primary consumers to humans.

Answer 6

animals = primary consumers
1 keep animals, warm / indoors ;
2 reduce animal movement ;
3 feed animals high, protein / energy, food ;
4 vaccination / (routine) antibiotics, for animals ;
5 selective breeding / genetic engineering,
for improved animals ;
6 slaughter just before, mature / full size ;

Question 7

Comment on what the different arrangements of plants in the Oxford Botanic Garden over time tell us about the nature of scientific knowledge.

Answer 7

idea of tentative / uncertain / developing / advancing /

improving / dynamic ;

Question 8

Suggest two purposes of a plant collection in a modern botanic garden.

Answer 8

1 conservation / keep rare plants / save endangered plants ;
2 gene bank OR genetic resource / store of alleles ;
3 teaching / education ;
4 leisure / amenity / visitor attraction / aesthetic value ;

Question 9

DNA sequence information is most useful when used with the phylogenetic (cladistic) approach to classification.How does the phylogenetic approach to classifying species differ from the biological species concept?

Answer 9

phylogenetic approach
no need to test for interbreeding ;
ref. common ancestor / monophyletic groups ;
can apply to organisms that reproduce asexually ;
can apply to, extinct organisms / fossils ;

Question 10

Dog fleas are small parasitic insects that live in the fur of dogs and feed on their blood. Dogs are routinely treated with sprays or powders to kill fleas.A vet believes that dog fleas may have become resistant to a popular flea-killer product.
He asks an A-level work experience student to plan an experiment to test this hypothesis. The student needs to sample fleas from dogs visiting the surgery and also fleas from long grass in fields visited by dog-walkers. The fleas then need to be tested for resistance to the flea-killer.Describe the methods the student could use to:
• collect both samples of fleas
• find out the proportion of fleas that are resistant
• process the data.

Answer 10

collection
1. named equipment for collecting from, dogs / fields ;
2. get, large number / over 100 (fleas) ;
3. use several, dogs / fields ;
4. idea of random sampling (dogs / field) ;
testing
5. (named) container ;
6. correct dose / range (of concentrations), tested ;
7. control without flea killer ;
8. delivery method described ;
processing
9. leave for set time ;
10. count number of, dead / live, fleas (after testing) ;
11. calculate percentage (frequency) of, alive / dead /
resistant / non-resistant ;

Question 11

Give two reasons why both plants and animals need to be able to respond to changes in their environment.

Answer 11

(both) to, avoid / counter, (abiotic) stress ;
(both) to avoid, being eaten / predation ;
(both) to access resources ;

Question 12

Outline the role of decomposers in the decomposition of leaves.

Answer 12

1 bacteria / fungi ;
2 idea of external digestion ; 
3 by , enzymes / named enzymes ; 
4 absorption of breakdown products ; 
5 release of carbon dioxide and water ; 
6 (breakdown of protein) makes , 
ammonium , ions / compounds 
or NH4 
\+ 
;

Question 13

Define the following terms:
producer
consumer
trophic level

Answer 13

producer
(leaves / plants) fix carbon / photosynthesise /
make food / autotroph(ic) /
convert light energy to chemical energy /
convert inorganic, C / CO2, to organic molecules ;
consumer
(bird) eat / derives energy from / feeds on ,
other organisms
or
heterotroph(ic) ;
trophic level
stage / position / place / level , in a food , chain / web ;

Question 14

In Ireland in 2002, two well-preserved Iron Age human bodies were found in peat bogs. Despite having been dead for over two thousand years, the bodies had not decomposed. They still had skin, hair and muscle.
Suggest why these bodies had not decomposed.

Answer 14

decomposers / named decomposers, not, present / active ;
waterlogging reduces, air / oxygen ;
acidity / low pH , stops (decay) enzymes working ;

Question 15

Explain why two areas of the same size were monitored.

Answer 15

two areas
as a control / for comparison / to see the effect of removal of
starfish ; 
same size 
to make test, valid / fair / unbiased ;

Question 16

the nature of scientific knowledge and the role of the scientific community in validating new knowledge.

Answer 16

knowledge , tentative / uncertain / subject to change ;

to re-test / check, hypotheses / results ;

Question 17

the study of the interactions between organisms and their environment

Answer 17

ecology

Question 18

the physical (non-living) factors in the environment

Answer 18

abiotic factors

Question 19

a physical area that includes all the organisms present and their interactions with each other and with the physical environment.

Answer 19

ecosystem

Question 20

The distribution and abundance of plants in a habitat can show how a physical factor varies across the habitat.
Describe how you would measure the distribution and abundance of plants over a distance of 100 metres.

Answer 20

1 tape measure / rope, laid ;
2 line / belt, transect ;
3 continuous / interrupted / AW ;
4 (use quadrat to) record percentage cover of plants ;
5 (use quadrat with) ACFOR scale ;
6 point quadrat use described ;
7 use of key to identify species ;
8 data recording sheets prepared in advance ;

Question 21

Briefly describe the steps that must occur for plant protein to be converted to animal protein

Answer 21

1 (sheep / animals) ingest / consume / eat / feed on
(grass / plants) ;
2 digest / hydrolyse , (protein) to amino acids ;
3 amino acids move into , blood / cells ;
4 synthesis of proteins / translation ;

Question 22

Name the bacteria that carry out processes nitrification and explain the significance of these bacteria for the growth of plants.

Answer 22

1 C is Nitrosomonas ;
2 D is Nitrobacter ;
3 C and D are nitrifying bacteria ;
for mps 1 , 2 and 3 internal max 2
4 plants need nitrates to make ,
amino acids / protein(s) / enzymes / DNA / RNA /
nucleic acids / chlorophyll / cytoplasm / new cells ;

Question 23

Suggest a crop she could plant that would allow process nitrogen fixation to occur and explain how this would add nitrate to the soil.

Answer 23

1 legume / any named leguminous plant ;
2 Rhizobium / nitrogen-fixing bacteria (in root nodules) ;
3 idea of converting nitrogen gas / N2 , into ,
compounds / ammonium / ammonia /
amino acids / protein (in plants) ;
4 plants ploughed in / plants left to decay /
ref B / ref C / ref D ;

Question 24

Three suggested methods to reduce the effect of hedgehogs on the numbers of waders in area 2 were considered. These were:• trapping and moving hedgehogs to the mainland• trapping hedgehogs and keeping them in captivity indefinitely• trapping of hedgehogs followed by humane killing.The third method was judged to be the most effective and likely to succeed in reducing hedgehog numbers.Comment on the ethical issues involved in making this decision.

Answer 24

idea that the following may be ethically wrong
1 killing hedgehogs ;
2 letting hedgehogs , kill / decrease number of , waders ;
3 introducing hedgehogs to island (upset the ecosystem) ;
4 catching / moving , hedgehogs might cause suffering ;
5 doing nothing ;

Question 25

Suggest a suitable technique by which the student might have collected his samples of ladybirds along this transect.

Answer 25

1 sweep netting / sweep vegetation with a net ;
2 beating / beat trees and bushes ;
3 pooter / pooting / described ;

Question 26

The student’s teacher suggested he should make several transects up the hill rather than just one transect. Explain why this is good experimental design.

Answer 26

idea of ladybirds not evenly distributed /
some parts of hill different /
more representative ;
lets reliability be assessed / anomalies identified ;

Question 27

Suggest a method of processing this data to make comparisons between the frequency of the red form and black form of ladybird at the different altitudes more valid.

Answer 27

M1 (calculate) % / proportion / ratio ;
E1 as different total numbers at each site ;
or
M2 (draw) bar chart / kite diagram ;
E2 pictorial data easier to understand ;

Question 28

Discuss possible reasons for the differences in net primary production in these ecosystems.

Answer 28

climate - tropical versus temperate
tropical has …
1. higher temperature / hotter 
2.more (sun)light / days longer ;
3 photosynthesis faster ;
4 idea that
more storage of , organic molecules / biomass / energy
or
more formation of , organic molecules / biomass ;

vegetation - woodland or rainforest versus grassland(s)
woodland or forest has …
6. idea of greater complexity / greater biodiversity /
more niches ;
7. competition for space less limiting ;

Question 29

Outline how the energy content, in kJ, of a primary producer such as grass can be measured in the laboratory.

Answer 29

(bomb) calorimeter ;

detail of technique ;
● known / dry , mass of (organic material)
● (material) burnt in oxygen

detail of , measurement / analysis ;
eg ● temperature rise of water measured
● known volume of water
● calculation described / converted to kJ