Unit 4 Questions

Question 1

Suggest one abiotic factor that might have resulted in a population having longer leaves. Explain how this factor would give it longer leaves (2 marks)

Answer 1

Light - products of photosynthesis are linked to growth Temperature - increases rate of reaction Nitrate concentration - nitrates used for more protein sysnthesis

Question 2

Explain the meaning of these terms: Population Community (2)

Answer 2

Organisms of one species in an area Organisms of all species in an area at a time

Question 3

Give two conditions necessary for results from mark-release-recapture investigations to be valid (2)

Answer 3

No immigration/emigration No reproduction Idea of mixing Marking doesn’t influence behaviour Sample was large enough

Question 4

Explain how you would use a quadrat to estimate the number of dandelion in a field measuring 100m by 150m (3)

Answer 4

Randomly place quadrats Do this by using a random number generator to give co-ordinates Calculate mean per quadrat And Multiply to give an estimate for the total field

Question 5

What is an ecosystem? (1)

Answer 5

A self-supporting system in which all organisms interact with the physical environment

Question 6

New Zealand pygmy weed has been introduced into many garden ponds and has spread. Here it competes with naturally occurring plants. Suggest how the introduction of Pygmy weed may lead to a reduction in diversity of the community in the natural pond (3)

Answer 6

Pygmy weed competes for CO2, light etc which reduces the numbers of original plant Therefore there is a loss of habitat for fish Leading to their death or migration

Question 7

Give two advantages of collecting data about plant distribution as percentage cover (2)

Answer 7

Data can be collected rapidly It doesn’t require identifying individual plants

Question 8

Seals (or other animals) affect the vegetation in quadrats over a time period. Describe how (3)

Answer 8

There may be a change in the species composition So a greater area of bare ground Leading to lower diversity

Question 9

In china, the fern is cultivated and ploughed into fields to act as an organic fertiliser. Explain how ploughing the fern plants into the soil results in an improvement in the growth of the rice crop grown in these fields. (5)

Answer 9

Decomposed in the field Convert organic nitrogen into Ammonium ions These ions are converted into nitrite And nitrite is converted to nitrate Nitrate is used to form amino acids in rice

Question 10

A molecule of NBPT has a similar structure to a molecule of urea. Use this information to suggest how NBPT inhibits the entertainment urease. (2)

Answer 10

It is complementary so binds to the active site Preventing enzyme-substrate complex

Question 11

Explain how the decay of dead plants results in reduced oxygen concentration and increased nitrate production (6)

Answer 11

Sacrobiotic feeders feed on dead matter Oxygen reduces as bacteria respire They convert proteins to amino acids This then converts to ammonium compounds Nitrifying bacteria Convert ammonium compounds Via nitrates

Question 12

In the pr sense of oxygen, respiration yields more ATP per molecule of glucose than it does in he absence of oxygen. Explain why. (3)

Answer 12

Aerobic Oxygen is an electron acceptor Oxidative phosphorylation Fate of pyruvate Krebs cycle Glycolysis only produces 2 ATP compared to 36

Question 13

Nitrogenase also catalysed reactions involving other substances. Explain what this suggests about the shape of the molecules of these other substances. (2)

Answer 13

Will have similar tertiary structure Bind with the active site

Question 14

If scientists could transfer the gene that codes for nitrogen are to cereal plants, these cereal plants would be able to fix nitrogen. However, the scientists would expect these genetically engineered cereal plants to grow more slowly than cereal plants that get their nitrogen from fertiliser. Explain why they would grow more slowly (2)

Answer 14

ATP used for reeducation of nitrogen to form ammonia So less ATP available for growth and protein synthesis

Question 15

During an investigation on fish, the pH of the blood was monitored. It decreased in the group which had zinc in the water. Why? (3)

Answer 15

Less oxygen transported to cells in the blood There was anaerobic respiration Lactic acid was produced and less CO2 was removed

Question 16

Leaves had a concentration of 52 Woo slice had a concentration of 1130 Explain the difference in the copper ion concentration between the leaves and the woodlice. (2)

Answer 16

Woodlice eat large amount of leaves Copper accumulates in the body

Question 17

Explain two advantages and one disadvantage of an inorganic fertiliser such as sodium nitrate compared with an inorganic fertiliser such as manure (3)

Answer 17

+ve Easy to handle Releases ions quickly Can supply specific needs Easy to store and transport -ve Expensive Eutrophication Doesn’t add to soul structure

Question 18

Explain the advantage of having both algae and bacteria in a purification pond (4)

Answer 18

Breaks down organic matter Ammonia used by algae to make amino acids Algae photosynthesise Bacterial respiration uses O2 Respiration allows for reproduction

Question 19

Explain how the students could use the mark-release-recapture technique to estimate the number of insects (4)

Answer 19

Collect a sample of insects and mark them Release to allow time to re-integrate with rest of population Collect a second sample and count number unmarked S1 X S2 Number marked in second sample

Question 20

Purification ponds only work efficiently when they are shallow and warm. Explain why (4)

Answer 20

Sufficient light penetration for photosynthesis Warm water leads to faster enzyme activity Faster decomposition Faster photosynthesis Increased growth of bacteria

Question 21

Explain why the spotted knapweed plants (WEEDS) were never completely eliminated when using; Chemical control Biological control (4)

Answer 21

Chemical- Some plants are not sprayed Plant may be resistant to spray Biological- Because biological control never eats all plants As weeds diminish so discontent agents

Question 22

Other than spreading fertilisers, describe and explain how one farming practice results in addition of nitrogen-containing compounds to a field (2)

Answer 22

Growing legumes Means there are nitrogen fixing bacteria in nodules Allow cattle Add dung Spread manure Decompose to release nitrates

Question 23

Explain why the net primary production of an area does not represent the total amount of plant biomass formed per year by photosynthesis. (2)

Answer 23

Biomass respires Biomass lost as CO2

Question 24

Explain the role of bacteria in making carbon in dead plant remains available to plants. (4)

Answer 24

Decomposers Release enzymes and digest detritus Substances found in detritus Absorb products of digestion Respires and releases CO2 Used by plants in photosynthesis

Question 25

Substances found in fallen leaves contain the elements carbon and nitrogen. Explain how the activities of decomposes and nitrifying bacteria recycle the substances in fallen leaves for re-use by the trees. (7)

Answer 25

Decomposes: Release enzymes Hydrolyse (or digest) organic matter Absorb by active transport Respiration Release CO2 CO2 used in photosynthesis Release ammonia Nitrifying bacteria- Aerobic respiration Nitrates used in synthesis of amino acids

Question 26

Explain how the felling and burning of trees on a large scale could affect the concentration of CO2 in the atmosphere. (2)

Answer 26

Increase in CO2 because Burning releases CO2 Less CO2 is removed by trees

Question 27

Both tapidl-growing softwood trees and slow-growing hardwood trees grow in tropical rainforests. The seeds of both kinds of tree lie dormant on the floor of a mature forest and only germinate when exposed to light and warmth. However the seedlings of many hardwood species grow more successfully beneath the protective canopy of the softwood trees. When a small area of trees has been cut down it can return naturally to tropical rainforest. Suggest and explain how re-establishment of the rainforest ecosystem may occur in such areas. (6)

Answer 27

Free seeds germinate in light Light is used for photosynthesis Softwoods compete for light Hardwoods can grow in low light Less water evaporation from hardwood seedlings Less extremes of temperature Canopy reduces impacts of rainfall for hardwood Roots stabilise soil Litter will fall recycling ions Trees provide food for animals Trees provide habitat for animals

Question 28

A large lake is surrounded by fields. These fields are separated from each other by hedges. One hundred years ago the lake was a habitat for many plants, invertebrates and fish. Today thinkable has no fish and few plants or invertebrates. Explain how increased use of inorganic fertilisers on the fields may have led to these changes. (5)

Answer 28

Leaching of nutrients Leads to increased growth of algae Competition for light Death of plants Increased food for decomposers Respiration uses up O2 Fish and animals die due to lack of oxygen

Question 29

Explain how the removal of hedges near the lake would increase the impact of fertilisers on the aquatic ecosystem. (2)

Answer 29

Leads to soil erosion Increased run off carries more fertilisers Soil and fertilisers blown into lake Fewer nutrients taken upbeat the hedges

Question 30

It is estimates that, each year a total of 3X10+9 tonnes of ammonia are converted to nitrate. Only 2X10+8 tonnes of ammonia are produces from nitrogen gas. Explain the difference in these figures b(2)

Answer 30

Ammonia formed by decay On nitrogenous waste/compounds

Question 31

The conversion of ammonia to nitrate involves oxidation. What evidence in the diagram supports this? (1)

Answer 31

Oxygen is added

Question 32

Explain why the biomass of the primary consumers is less than the biomass of the producers in most communities. (3)

Answer 32

Loss of energy By respiration, movement

Question 33

Explain how large-scale deforestation for agriculture would lead to a decrease in the diversity of organisms in the area. (2)

Answer 33

Removal of forest removes many ecological niches Reduces number of species that can exist in the area

Question 34

Suggest how increased growth of algae could lead to the death of the submerged plants. (2)

Answer 34

Reduced light Less photo synthesis

Question 34

Changes in ecosystems can lead to speciation. In south California 10000 years ago a number of interconnecting lakes contained a single species of pupfish Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a number of different species of pupfish. Explain how these different species evolved. (5)

Answer 34

Geographical isolation Separate gene pools/no interbreeding Variation due to mutation Different environmental/abiotic/biotic contortions/selection pressures Selection for different characteristics Different reproductive success Leads to change in allele frequency Occurs over a long period of time

Question 34

Glaciers are masses of moving ice. When glaciers shrink, the thick covering of ice gradually disappears to leave behind bare land. Land exposed by a shrinking glacier in Alaska became covered by sense forest in 150 years Explain how succession resulted in the formation of the forest. (4)

Answer 34

Pioneers colonise land They change the environment Enable a change in species Conditions change further to favour tree growth

Question 34

The water and soil in sphagnum bogs are usually acidic. Suggest why sphagnum is not fully decomposed after it dies. (3)

Answer 34

Action I bacteria/decomposers inhibited Acidic conk rooms inhibits enzymes/changes the active site/enzymes are denatured H+ ions affect active site Anaerobic conditions

Question 34

Stage 5 illustrates the final stage of succession which is known as the climax community. During this stage the number of different species in the habitat and the size of each population remain fairly constant. Explain what limits the size of populations in a climax community. (5)

Answer 34

Named nutrient availability Number of producers providing energy Light intensity affecting the rate oh photosynthesis Disease killing members of species Space for best building Reproductive rate balancing death rate Competition for a named limited resource Intra and interspecific competition explained

Question 34

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 (3)

Answer 34

Green flies take in a small mass of insecticide from roses Ladybirds eat a larger number of greenflies Bio accumulation is the concept that the insecticide cannot be excreted and remains in the body

Question 34

Describe how the reduced oxygen concentration of the water will change the composition of the communities in the river. (2)

Answer 34

Lower species diversity Of species that can tolerate a low oxygen level/those requiring high oxygen die out

Question 34

NBPT is an inhibitor of urease and can be added to urea fertiliser to reduce the loss of ammonia to the atmosphere. Suggest how the addition of NBPT to urea fertiliser could result in increased growth of crop plants. (3)

Answer 34

Bacteria/fungi feed on dead matter sacrobiotically Bacteria/fungi multiply Respiration uses up oxygen Converts proteins to amino acids Then to ammonium compounds Nitrifying bacteria Convert ammonium compounds via nitrates Nitrification uses oxygen

Question 35

Clearing the forests and burning the begetation affects the carbon dioxide concentration in the atmosphere. Describes how and explain why (4)

Answer 35

CO2 concentration increases Clearing–> less vegetation so less photosynthesis Less CO2 removed Burning –> burning produces CO2

Question 36

Explain how large-scale deforestation could: increase the concentration of CO2 in the atmosphere in the area Decrease the concentration of CO2 in the atmosphere in the area (3)

Answer 36

Reduce the amount of CO2 used in photosynthesis Increase the amount of CO2 produced in combustion Less respiration By plants and animals

Question 37

Give the equation that links gross productivity and net productivity (1)

Answer 37

Gross productivity=net productivity + respiratory losses

Question 38

The net productivity of plants in a field was higher in August than in July. Use the gross productivity = net productivity + respiratory losses equation and knowledge of photosynthesis and respiration to suggest why. (2)

Answer 38

Less respiration Light-dependant reaction less affected by temperature increase Lower energy loss

Question 39

A horse was kept in a field from March to October. During the summer months, the horse was able to eat more than it needed to meet its minimum daily requirements. Suggest how the horse used the extra nutrients absorbed (1)

Answer 39

stored as fat/glycogen Used for growth/movement/reproduction

Question 40

A horse was kept in a field from March to October. During the summer months, the horse was able to eat more than it needed to meet its minimum daily requirements. The horse’s mean energy expenditure was higher in March than it was in August. Use the information in the table to suggest why (2)

Answer 40

More heat energy lost in March Maintaining body temperature By respiration

Question 41

Explain why the biomass of phytoplankton in a lake should be less than that of zooplankton (1)

Answer 41

Phytoplankton reproduce at a rate greater than the rate of their consumption

Question 42

Suggest why inorganic fertiliser improves the yield of mangold crop more than the sugar beet crop (1)

Answer 42

Contains nutrients important for mangolds/inhibits beet growth

Question 43

Give three explanations for the difference between the amount of solar energy reaching the primary producers and the energy in the biomass of the primary producers (3)

Answer 43

Light reflected Light misses the chlorophyll Wrong wavelength Respiration Inefficiency of photosynthesis

Question 44

Explain why there is an increase in the mass of a crop produced when the mass of fertiliser increases (2)

Answer 44

Replaces nutrients removed Fertiliser provides nitrate needed for protein production More fertiliser Added means more growth

Question 45

Explain why the spotted knapweed plants were never completely eliminated when using: Chemical control (2) Biological control (2)

Answer 45

Chemical Some plants/part of plants are not sprayed Plant may be resistant to spray Biological They never eat all plants As weeds diminish so do control agents

Question 46

Application o very high concentrations of fertiliser to the soil causes plants to wilt. Explain why (2)

Answer 46

Lower water potential in soil Prevents roots from taking up water By osmosis

Question 47

Describe and explain how one farming practice results in the removal of nitrogen containing compounds from a field (2)

Answer 47

Farm animals eat plants in field Animal then removed Uptake of nitrates by crop Crop is harvested

Question 48

Because the forest soil is often nutrient-poor, nitrogen containing fertilisers may be applied to ensure good crop yields. Use your knowledge of the nitrogen cycle to explain the potential benefit of applying a fertiliser containing ammonium nitrate rather than one containing potassium nitrate. (3)

Answer 48

Carbon dioxide combines with RuBP To produce two molecules of GP Reduced to TP Requires reduced to NADP Energy from ATP

Question 49

Human skeletal muscle can respite both aerobically and anaerobically. Describe what happens to pyruvate in anaerobic conditions and explain why anaerobic respiration is advantageous to human skeletal muscle. (4)

Answer 49

Forms lactate Use of Nadh Nad can be re-used to oxidise more respiratory substrate Can still release energy When oxygen is in short supply

Question 50

The respiratory quotent for yeast respiring aerobically and using glucose as a substrate is 1.0. However some students found the rq of yeast respiring glucose to be 1.6. Assuming that their technique was correct, explain how this is possible. (2)

Answer 50

Rq = amount co2 produced Amount O2 used Anaerobic respiration occurring Produces CO2 but not O2

Question 51

The rate of carbon dioxide production was higher when the apple slices were in nitrogen than when they were in the air. Explain why. (3)

Answer 51

Respiring anaerobically Less ATP produced More anaerobic respiration to produce same amount of ATP so more co2 produced

Question 52

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 24 hours. (5)

Answer 52

Higher co2 at night Photosynthesis only takes place during light Photosynthesis removes co2 and respiration adds co2 Respiration taking place throughout 24 hours Quantitative consideration such as that in plants overall photosynthetic rate greater than respiration rate Human effect of additional co2 from heavy daytime traffic

Question 53

How do multiple alleles of a gene arise? (2)

Answer 53

mutations; which are different/at different positions in the gene

Question 54

Colour blindness is controlled by a gene on the X chromosome. The allele for colour blindness, Xb, is recessive to the allele for normal colour vision, XB . The gene controlling the presence of a white streak in the hair is not sex linked, with the allele for the presence of a white streak, H, being dominant to the allele for the absence of a white streak, h. (a) Explain why colour blindness is more common in men than in women. (2)

Answer 54

males are XY and females XX / males have one X chromosome and females two X chromosomes; males only have one allele (of the gene) present / recessive allele always expressed; colour blindness is masked in heterozygote / female needs 2 recessive alleles to be colour blind;

Question 55

What is meant by a sex-linked gene? (1)

Answer 55

gene located on X/Y/one sex chromosome

Question 56

A sex-linked gene controls fur colour in cats. Ginger-coloured fur is controlled by the allele G, and black-coloured fur is controlled by the allele g. Some female cats have ginger and black patches of fur. They are described as tortoiseshell. Male cats cannot be tortoiseshell. A male cat with the genotype Xg Y mates with a tortoiseshell female. Give the phenotype of the male. (1) Give the genotype of the tortoiseshell female. (1)

Answer 56

black XG Xg

Question 57

In a species of fruitfly, females have two X chromosomes, and males have an X and a Y chromosome.

A gene controlling eye shape in fruitflies is sex-linked, and found only on the X chromosome.
This gene has two alleles, R for round eyes and B for bar eyes.

A homozygous, round-eyed female (X^R X^R) was crossed with a bar-eyed male. In the offspring (Offspring 1), all the female offspring had wide bar eyes (intermediate in size) and all the males had round eyes.

Name the relationship between the two alleles that control eye shape. (1)

Give the genotype of the male parent. (1)

Offspring 1 were allowed to interbreed. Complete a genetic diagram to show the phenotypic ratio you would expect in the resulting Offspring 2. (3)

Parental phenotypes

Parental genotypes

Offspring 1 phenotypes

Offspring 1 genotypes

Gametes

Offspring 2 genotypes

Offspring 2 phenotypes and ratio

Answer 57

Condominance 1

X^BYOR B(-) 1

Parental genotypes are given: X^R X^R (X^B Y)

Offspring 1 genotypes: X^R X^B X^R Y

Offspring 2 genotypes: X^R X^R X^R X^B X^RY X^B Y

Offspring 2 phenotypes: round eyed wide-bar round eye bar-eye
female female male male;

Ratio: 1 : 1 : 1 : 1

Question 58

A species of flowering plant can have white, red or purple flowers. The colour of the flowers is controlled by two genes. Each gene is found on a different chromosome, and is responsible for one step in a biosynthetic pathway. The biosynthetic pathway is (PIC)

Gene 1 has the dominant allele A and the recessive allele a. Gene 2 has the dominant allele B and the recessive allele b. In both cases, the dominant allele needs to be present for the production of the associated enzyme.

Explain how the two genes are involved in producing white, red or purple flowers. (6)

Answer 58

(Gene 1) allele A makes enzyme converting J to K / colourless to red;
Allele a produces no / non-functional enzyme;
(Gene 2) allele B makes enzyme converting K to L / red to purple;
Allele b produces no / non-functional enzyme;
(“Recessive alleles produce no / non-functional enzyme” = 2)
White flowers result from genotype aa;
… regardless if B or b / even if aaB_ ;
Colourless (substance) / J produces white;
Red flowers when A_bb / enzyme 1 only;
Purple flowers when A_B_ / enzymes 1 and 2

Question 59

Nail-patella syndrome is an inherited condition caused by a single gene. Sufferers have abnormal nail growth and underdeveloped kneecaps. The pedigree shows how members of one family were affected by the syndrome.

Explain one piece of evidence from the pedigree which indicates that

• the allele for the nail-patella syndrome is dominant (2)
• the gene is not sex-linked (2)

Answer 59

3 and 4 produce unaffected male/8 / female/10, so must
carry recessive;
but both affected by nail-patella which must be dominant

3 inherits X from mother, who is not affected;
if sex-linked, 3 would have nail-patella on X chr and
would pass on to all female offspring;
10 is recessive female, so gene not sex-linked.

Question 60

Serious diseases caused by dominant alleles are relatively uncommon compared with diseases caused by recessive alleles.
Suggest an explanation for this (2)

Answer 60

all individuals with allele develop / aware of disease;
therefore might choose not to have children;
OR carriers may be unaware that they have allele/are unaffected;
and therefore have children

Question 61

The fruit fly is a useful animal for studying genetic crosses. The diagram shows the life cycle of the fruit fly.

Using information from the diagram explain three ways in which the fruit fly is a useful animal for studying genetic crosses (3)

Answer 61

lays many eggs or large number of offspring - more information /
low sampling error;
short life cycle - short generation time / results obtained quickly;
male and female easily distinguished - for mating / sex linkage;
small size - easy to handle / large numbers can be kept /
small space required;

Question 62

In a village with a population of 500, there were 8 people who were homozygous for the sickle–cell allele and 96 who were heterozygous. Calculate the frequency of the HbS allele in the village. Show your working. (2)

Answer 62

0.0112/11.2%

Question 63

Chloroquine is a drug which has been used very successfully to treat malaria. The use of chloroquine to treat malaria has produced changes in the frequency of the HbS allele. Explain how. (2)

Answer 63

Effective treatment for malaria linked to advantage
If more HbA HbA individuals survive, frequency of HbS allele would fall

Question 64

It was important that ladybirds in the samples were collected at random. Explain why. (1)

Answer 64

Avoid bias/can only apply statistical test/Hardy-Weinberg
expression to randomly collected data;

Question 65

Year

Season

Frequency of b allele

1933

Autumn

0.70

1934

Spring

0.82

1934

Autumn

0.59

1935

Spring

0.76

1935

Autumn

0.57

1936

Spring

0.78

Use the Hardy-Weinberg expression to estimate the percentages of red ladybirds and black lady birds in the Autumn 1933 ladybird population.
Show your working.

red ladybirds

black ladybirds

(2)

Answer 65

49% red and 51% black

Question 66

The scientists found that black ladybirds heated up more quickly and became active at lower temperatures than red ladybirds. How might this explain the poorer survival of black ladybirds over winter? (2)

Answer 66

Black ladybirds would become more active so respiration rate
increases;
Deplete food reserves;