Unit 4 questions

Question 1

Describe how the mark-release-recapture method could be used to estimate the population of mice in the area being studied.

Answer 1

Method of trapping, trap a large sample to be representative, Method of marking; (in an unobtrusive way, does not make them more vulnerable to predation or less likely to reintegrate, shave a little piece of fur form underneath), Release and wait a period of time to allow reintegration into population, Number marked are counted then released, Number recaptured are counted, Number of marked animals/in second sample are recorded

Question 2

Ground beetles are large black insects. The mark-release-recapture method can be used to estimate the ground beetle population on a roundabout. Describe how.

Answer 2

Sample of ground beetles captured and counted; Released and second sample captured; Count total number of beetles and number marked; Detail of method e.g. pitfall trap/marking with tippex; Refinement to ensure greater accuracy e.g. large number/marking in position such that does not affect survival

Question 3

Give two conditions necessary for results from mark-release-recapture investigations to be valid.

Answer 3

No immigration/migration (Ignore references to emigration); No reproduction (Ignore references to death); Idea of mixing; Marking does not influence behaviour / increase vulnerability to predation; Sample/population large enough

Question 4

Describe the techniques you would use to obtain reliable data in order to compare the sizes of the populations of the snail in a muddy area and in a area covered by vegetation.

Answer 4

Use of large numbers of quadrats in each area (if number stated then 10+); random sampling method (e.g. grid + random numbers)/systematic sampling method (allow regular sampling along a transect); counting.

Question 5

Describe how you would use quadrats in an investigation to determine whether or not there is a difference in the number of clover plants in two large areas of equal size

Answer 5

Large (and equal) number of quadrats in each area; (reject several), random sampling method, described; (accept described ?systematic? method) percentage cover/point hits per quadrat/count plants; mean/average value for each area; statistics test to see if differences significant

Question 6

Describe how you would use a half meter by half meter quadrat frame and a 30-metre tape measure to produce a transect along a stream to investigate the distribution of species growing there

Answer 6

Use of tape measure to produce transect, placing of quadrats, transect placed across stream, score presence of each plant species, use quadrat at regular, intervals along tape, Repeat transect several times along stream, at random or regular intervals

Question 7

Explain what limits the size of populations in a climax community.

Answer 7

1. Named nutrient availability; 2. Numbers of producers providing energy (for a food chain); 3. Light intensity affecting the rate of photosynthesis; 4. Disease killing (weaker) members of species; 5. Space for nest building / niches;6. Reproductive rate balancing death rate; 7. Competition for a named limited resource; 8. (Intra and interspecific) competition explained; 9. Predation described

Question 8

Using one example of each to illustrate your answer, explain the difference between density dependent and density independent factors

Answer 8

Example of density dependent factor (factors whose effect change as population size changes), e.g. food, space, disease; Example of density independent factor, e.g. light, temperature (reject: weather, climate); Density dependent factors depend on / affected by size of population; Density independent factors affect organisms whatever the population size, or, examples used to explain, e.g. increasing competition for food

Question 9

Suggest how predation by weasels acts as a density-dependent factor controlling great tit population size.

Answer 9

At low densities / high distance between nests few are killed by weasels; so more great tits survive; Great tit population increases; so greater percentage taken by weasels; or At high densities / low distance between nests more are killed by weasels; so fewer great tits survive; Great tit population decreases; so smaller percentage taken by weasels

Question 10

Give three uses of energy from ATP in a liver cell.

Answer 10

Active transport; Phagocytosis; Synthesis of glycogen; Protein / enzyme; DNA / RNA; Lipid / cholesterol; Urea in glycolysis; Bile production; Cell division

Question 11

ATP is sometimes described as an immediate source of energy. Explain why

Answer 11

Energy release) only involves a single reaction/one-step/(energy released) in ATP ? ADP (+Pi)/ energy transfer direct to reaction requiring energy

Question 12

Explain why humans make more than their body mass of ATP each day

Answer 12

1. ATP is unstable; 2. ATP cannot be stored / is an immediate source of energy; 3. Named process uses ATP ; 4. ATP only releases a small amount of energy at a time;

Question 13

Describe how the leaf is adapted to allow photosynthesis to occur effectively

Answer 13

Large surface area to collect solar energy; transparent nature of cuticle to allow light penetration; position of chlorophyll to trap light; stomata to allow exchange of gases; thin / max. Surface area to volume ratio for diffusion of gases; spongy mesophyll / air spaces for carbon dioxide store; xylem for input of water; phloem for removal of end products

Question 14

Describe how the structure of a chloroplast is adapted to its function in photosynthesis.

Answer 14

Membranes / (disc) shape provides large surface for light absorption; layering of membrane allows a lot of pigment; (permeable) membrane allows diffusion of gases / carbon dioxide; membranes provide surface for attachment of electron / hydrogenacceptors; stroma / matrix containing enzymes for Calvin cycle /light?independent reactions; Contains chlorophyll / pigments for light absorption; Different pigments to absorb different wavelengths; Stacking / arrangement of grana/thylakoids maximises light catchment; Stroma contains enzymes for photosynthesis; Outer membrane keeps enzymes in chloroplast; Starch grains / lipid droplets store products of photosynthesis; Ribosomes / DNA for enzyme/protein synthesis; Shape of chloroplast gives large surface area for CO2, absorption

Question 15

Describe how plants absorb light energy from the sun and use this energy to produce useful substances in the light-dependent stage of photosynthesis

Answer 15

Light absorbed by/strikes,chlorophyll/photosystem/PSI/PSII; electrons excited; pass down chain of carriers; energy released/transferred; producing ATP from ADP and phosphate; reduced NADP/formed with electrons; photolysis of water /allow light splits water; (water) supplies protons/H+ ions to reduce NADP

Question 16

Describe the light-independent reactions of photosynthesis and explain how they allow the continued synthesis of hexose sugars

Answer 16

1. 5C/RuBP combines with CO2; 2. to form 3C compound / TP / GP; 3. using ATP; 4. and reduced NADP / eq; 5. 2 molecules of 3C compound/ TP / GP form hexose; 6. all RuBP is regenerated; 7. 10 molecules of 3C/TP/GP form 6 molecules of 5C/RuBP

Question 17

Explain the roles of water, light and ribulose bisphosphate in the process of photosynthesis

Answer 17

provides hydrogen; to reduce NADP; provides electron; to stabilise / reduce chlorophyll; LIGHT : excites / oxidises / removes an electron from chlorophyll / photosystem; photophosphorylation / ATP produced; electron used in reduction of NADP; RIBULOSE BISPHOSPHATE: carbon dioxide acceptor; forms GP;

Question 18

Explain why an increase in temperature will increase the rate of photosynthesis

Answer 18

Enzymes are involved; extra kinetic energy / molecules move faster; molecules collide more often / more enzyme substrate complexes formed; increased rate of diffusion of raw materials

Question 19

The carbon dioxide concentration was monitored at ground level in the centre of a small roundabout. The measurements were made on a summer day. Describe and explain how you would expect the concentration of carbon dioxide to fluctuate over the period of 24 hours

Answer 19

1 Higher carbon dioxide concentration at night/during darkness; 2 Photosynthesis only takes place during light; 3 Photosynthesis removes carbon dioxide and respiration adds carbon dioxide; 4 Respiration taking place throughout 24 hours; 5 Quantitative considerations such as that in plants overall photosynthetic rate greater than respiration rate; 6 Human effects such as additional carbon dioxide from heavy daytime traffic/street lighting could prolong photosynthesis

Question 20

Describe how ATP is made in mitochondria

Answer 20

1. Substrate level phosphorylation / ATP produced in Krebs cycle; 2. Krebs cycle/link reaction produces reduced coenzyme/reduced NAD/reduced FAD; 3. Electrons released from reduced /coenzymes/ NAD/FAD; 4. (Electrons) pass along carriers/through electron transport chain/through series of redox reactions; 5. Energy released; 6. ADP/ADP + Pi 7. Protons move into intermembrane space; 8. ATP synthase

Question 21

Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion

Answer 21

ATP formed as electrons pass along transport chain; oxygen is terminal electron acceptor / accepts electrons from electron transport chain; electrons cannot be passed along electron transport chain if no O2 to accept them; forms H2O / accepts H+ from reduced NAD/FAD / oxidises reduced NAD/FAD

Question 22

Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the advantage of mitochondria in muscle cells having more cristae

Answer 22

(more cristae / larger surface area) for electron transport chain / more enzymes for ATP production/oxidative phosphorylation; muscle cells use more ATP (than skin cells)(not just more respiration)

Question 23

Describe the effect of lactate production on muscles.

Answer 23

Decrease pH/Increase in acidity; Muscle fatigue; Denaturation / alteration of proteins / enzymes

Question 24

Suggest two reasons why not all of the solar energy can be used in photosynthesis

Answer 24

Light missed plant / leaf/ chloroplast / reflected; wrong wavelength of light / inefficiency of photosynthesis /other limiting factors; Some light reflected/ not absorbed/refracted (if qualified) back into?atmosphere; some light misses chloroplasts/chlorophyll; only certain wavelengths of light used (in photosynthesis). 2 Energy lost as heat/by respiration/metabolic processes; qualified comment on the inefficiency of photosynthesis e.g. 25% efficient/energy lost as electrons passed on; carbon dioxide/temperature limiting

Question 25

Explain why a food chain rarely contains more than four trophic levels

Answer 25

Energy losses (at each trophic level) / energy use; In named process ? e.g. excretion / egestion / movement / respiration / ? / as heat; (NOT ?growth? ? CANCEL, ignore ?waste?) Not available / (too) little left to sustain higher trophic levels /to be passed on

Question 26

Explain how the intensive rearing of domestic livestock increases net productivity

Answer 26

1 Slaughtered when still growing/before maturity/while young so more energy transferred to biomass/tissue/production; 2 Fed on concentrate /controlled diet /controlled conditions/so higher proportion of (digested) food absorbed/lower proportion lost in faeces / valid reason for addition; 3 Movement restricted so less respiratory loss / less energy used; 4 Kept inside/heating/shelter / confined so less heat loss / no predators; 5 Genetically selected for high productivity

Question 27

Explain how farming practices increase the productivity of agricultural crops

Answer 27

1. Fertilisers/minerals/named ion (added to soil); 2. Role of named nutrient or element e.g. nitrate/nitrogen for proteins / phosphate/phosphorus for ATP/DNA; 3. Pesticides/biological control prevents damage/consumption of crop; 4. Pesticides/weed killers /herbicides/weeding remove competition; 5. Selective breeding / genetic modification (of crops); 6. Glass/greenhouses enhance temp/CO2/ light; 7. Ploughing aerates soil/improves drainage; 8. Ploughing/aeration allows nitrification/decreases denitrification; 9. Benefit of crop rotation in terms of soil nutrients/fertility/pest reduction; 10. Irrigation/watering to remove limiting factor; 11. Protection of crops from birds/pests/frost by covers/netting etc

Question 28

Explain why plants may fail to grow if high concentrations of nitrate are applied to the soil

Answer 28

Water potential of soil reduced/more negative/ reduced water potential gradient; less water moves into roots/water moves out of roots by osmosis

Question 29

Fertilisers are added to soils to replace the nutrients lost when crops are harvested. Give two advantages of using an organic fertiliser such as farmyard manure

Answer 29

More micronutrients / greater range of nutrients; Nutrients released slowly; Improves soil quality / adds humus / adds microbes / improves soil structure; Improves water-holding capacity of soil / reduces leaching/eutrophication; Improves soil aeration; Already available

Question 30

Describe why phosphates are needed by a growing plant

Answer 30

Production of phospholipids; in cell membranes; synthesis of ATP; production of DNA; production of RNA; production of NADP

Question 31

Describe and explain the effects of monoculture on the environment

Answer 31

Loss of hedgerows; since small fields impracticable for large machines; soil more exposed to wind; resultant increase in soil erosion (once); reduction in diversity; since smaller variety of niches/habitats; since smaller variety of producers/plants deeper rooted plants removed; resultant increased soil erosion (once); increased risk of large-scale crop failure/increased disease/increased number of pest; since large numbers of same crop species grown close to each other; increased use of fertilisers result in eutrophication/damage to soil structure; reduction of gene pool

Question 32

Describe two features that a predator must have if it is to be a successful biological control agent

Answer 32

Only feeds on pest species/does not affect non-target population; can live in environment of the host/ establish/maintain its population/ can reproduce under conditions of use/active during the season; (ignore references to effect on crop)

Question 33

Explain the benefits of an integrated pest management scheme

Answer 33

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; Chemical controls initial surges in pest numbers / less chemicals used; biological gives longer term control of pests

Question 34

Explain how the use of pesticides can result in resistant strains of insect pests

Answer 34

1. Variation/variety in pest population; 2. Due to mutation; 3. Allele for resistance; 4. Reference to selection; 5. Pests with resistance (survive and) breed / differential reproductive success; 6. Increase in frequency of allele

Question 35

What is the difference between the ways in which microbial decomposers and detritivores obtain their nutrients?

Answer 35

Decomposers secrete enzymes / onto organic matter/ food/ extracellular breakdown; Detritivores ingest / eat/ take in organic matter/food first

Question 36

Explain how the carbon in dead insects is made available to a plant

Answer 36

Hydrolysis/breakdown/digestion of carbon compounds; respiration (by bacteria); releasing carbon dioxide; taken up by the plant during photosynthesis

Question 37

Explain how a reduction in the amount of ploughing would lead to more carbon being stored in the soil

Answer 37

Less oxygen can enter the soil (from the air); For saprobionts / soil microorganisms / bacteria / fungi /decomposers correctly named soil organisms; For use in aerobic respiration; Less breakdown of organic matter / humus / dead plants /dead animals / other e.g.;Less carbon dioxide released / formed

Question 38

Describe the part played by soil bacteria in making the nitrogen in compounds in the dead spruce seeds available to pine seedlings

Answer 38

Release ammonia / ammonium / ammonification; BY Decomposers / putrefying / saprotrophic / ammonifying bacteria; Ammonia ? nitrite ? nitrate / nitrification; BY Nitrifying bacteria / named bacteria

Question 39

Fertilisers may leach out of farmland into freshwater streams and lakes. Explain how this can be harmful to the environment

Answer 39

1. More growth of algae/ surface plants; 2. Blocks light; 3. Plants lower down unable to photosynthesise; 4. Less oxygen produced 5. Dead (plant) material present; 6. Broken down by bacteria/decomposers; 7. Respiration; 8. Depletes oxygen in water; 9. Other organisms unable to live/grow;

Question 40

Explain succession and climax community

Answer 40

Change in community over time; either due to change environmental/abiotic factors / change is due to species present; Stable community/no further succession/final community

Question 41

Describe why ecological succession occurs

Answer 41

1. Colonisation/pioneering; 2. Microscopic plants at start; 3. Death / decomposition; 4. Named change in environment e.g. increase in organic matter/ stabilisation; 5. New species colonise once there is a change; 6. Increase in number of species/diversity; 7. Increase in total amount of living material/biomass/ more niches; 8. Increase in nutrient availability; 9. Change from more extreme conditions / more stability

Question 42

Under natural and suitable conditions, bare soil would eventually become covered by a woodland community. Explain how farming practices prevent this from happening

Answer 42

e.g. crops are planted (not native plants); these compete with native plants; Ploughing returns to bare soil; destroys herbaceous plants/tree/shrub seedlings; Grazing by farm animals; destroys herbaceous/shrub seedlings/communities

Question 43

What is meant by conservation

Answer 43

Concept of preservation/maintenance ? e.g. sustainable management/sustainable use of resources/management to maintain diversity/maintain forest; (Allow ref. To ?keeping? / ?saving? / ?non-destruction?)

Question 44

Give three reasons why tropical rainforests should be conserved

Answer 44

To avoid: Any three from: Loss of species / decrease in diversity / loss of habitat / loss of niche / disruption of food chain; Loss of pharmaceuticals / ?medicines? / timber / ?wood?; CO2 build-up in atmosphere / global warming / trees take in CO2 / trees = carbon sink (described) / to maintain CO2 in air; (NOT just ?carbon? in air) Leaching of ions / mud slides / flooding / desertification; [ALLOW converse of above ? e.g. ?Rainforest is a habitat for (various) species?]

Question 45

Explain how natural selection produces changes within a species

Answer 45

variation between members of population/species; predation/disease/competition results in differential survival; some have adaptations that favour survival; survive to reproduce/have more offspring/ pass on their alleles/genes; produces changes in frequency of allele /gene pool/genotypes/phenotypes

Question 46

Describe how stabilising selection will affect the mean and standard deviation. Give the reason for your answer

Answer 46

Mean ? no change; Standard deviation ? decreases; Reason ? selects against/removes (both) extremes/extremes die/better survival of middle nos

Question 47

Explain what is meant by stabilising selection and describe the circumstances under which it takes place

Answer 47

1. Occurs in an unchanging environment; 2. (Initial range of values in which) mean is best adapted; 3. Selection against extremes / selection for the mean; 4. Mean/median/mode unaltered 5. Range/S.D is reduced; 6. Repeated over many generations; 7. Increasing proportion of populations becomes well adapted to environment

Question 48

What is meant by reproductive isolation

Answer 48

Organisms cannot interbreed/ breed or mate or reproduce with another group/ incompatible gametes/ wrong courtship behaviour/ other valid

Question 49

Explain how geographical isolation can lead to the formation of new species

Answer 49

1 Populations separated by physical barrier/ example; 2 No mixing of gene pools; 3 Different selection pressures; 4 Become adapted to local environment; 5 Survive and reproduce; 6 Mutation in one group (different from other group); 7 Change in allele frequencies; [Reject: Gene] 8 Isolated populations/ new species cannot interbreed