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A-Level CAIE Biology 17 1 Variation Question Bank

Practice A-Level CAIE Biology 17 1 Variation questions by syllabus topic with past-paper context, marks, difficulty and question previews on Eduninja.

10 matching questions ยท Open interactive library

Question 1

1

0 marks

Question 1(b)

1(b)

The dominant allele of the huntingtin gene contains many repeats of a triplet sequence of nucleotides, CAG. The age at which symptoms of HD first appear is linked with the number of CAG repeats. This is shown in Fig. 1.1. Describe the pattern shown in Fig. 1.1.

Mediumstructured2 marks

Answer

the greater the number of (CAG) repeats the earlier the symptoms first appear / inversely proportional / negative correlation ; paired figures ;

Question 1

1

Fig. 1.1 shows a snow leopard, Panthera uncia. The habitat of the snow leopard is the high mountains of Central Asia. Snow leopards usually live and hunt alone. Their main prey is grazing herbivores, such as wild sheep and wild goats. They will also hunt domesticated animals and livestock. The number of snow leopards has decreased dramatically in the last 40 years.

structured0 marks

Question 1(c)

1(c)

State how a decrease in the number of snow leopards will affect the genetic diversity of the species. Outline the possible future consequences of this change in genetic diversity.

Mediumstructured2 marks

Answer

two from: 1 genetic diversity decreases / AW ; 2 increased chance of two harmful recessive alleles coming together / increase in inbreeding depression / decrease in hybrid vigour ; 3 (some) less likely to survive ; 4 (because) less likely to adapt to change in, environmental conditions / selection pressure ;

Question 1

1

The St. Lawrence river in Canada has been identified as an area with very high biodiversity.

structured0 marks

Question 1(b)

1(b)

The St. Lawrence river is rich in species of aquatic mammals, especially whales. In spring, thousands of whales swim from the Atlantic ocean up the St. Lawrence river. Thirteen different species of whale have been recorded. One of these is the blue whale, Balaenoptera musculus. Fig. 1.1 is a diagram of a blue whale. Photographs of blue whales are analysed by computer so that individual whales can be identified and population abundance can be estimated. Each blue whale is different in colour and in the shape of dorsal fin. Different whales also have different patterns of scarring.

structured0 marks

Question 1(b)(i)

1(b)(i)

State the two sources of phenotypic variation in the blue whale population.

Easystructured1 marks

Answer

genes and environment ;

Question 1

1

The Bali starling, Leucopsar rothschildi, is found on the island of Bali, Indonesia. Fig. 1.1 shows a Bali starling.

structured0 marks

Question 1(b)

1(b)

Explain the consequences on genetic biodiversity of having a wild population of just six birds.

Mediumstructured4 marks

Answer

any four from 1 low / little / less / decreased (genetic) (bio)diversity / variation ; 2 low / little / less / decreased, heterozygosity ; 3 harmful recessive alleles may come together ; 4 inbreeding depression ; 5 no / less / decreased, hybrid vigour ; 6 not / less, able to adapt to, new / changed, selection pressure / disease / environment ;

Question 2

2

Steelhead trout, Oncorhynchus mykiss, are fish that live in streams in North America. To increase the number of steelhead trout, captive breeding has occurred since 1992. Fish eggs and sperm are mixed and the young fish grow in large tanks of aerated water for the first year of their lives. Most are then released into the wild, however a few male and female fish are kept to become the parents of the next generation of captive-bred fish. Each tank may hold up to 50000 fish. The young captive fish are fed processed food. Some young fish are unable to survive these conditions and a proportion die. Death is usually the result of poor wound-healing after accidents due to overcrowding and due to the spread of diseases.

structured16 marks

Question 2(a)

2(a)

0 marks

Question 2(a)(i)

2(a)(i)

Name the expected pattern of variation in wound-healing ability in a population of fish.

Easystructured1 marks

Answer

continuous; A normal distribution

Question 2(b)

2(b)

Suggest and explain three ways in which the tank environment may make the phenotype of a captive fish different from a wild fish. Two groups of fish were bred and grown in the same environment and were then compared to see if they showed differences in gene expression. The two groups of fish came from: - eggs and sperm from parent fish that had always lived in the wild - eggs and sperm from parent fish that had been bred in captivity. Results from microarray analysis showed that the offspring of the wild and captive-bred fish differed in the expression of over 700 genes.

Mediumstructured3 marks

Answer

any three from: captive fish: 1 controlled conditions so phenotype less varied ; 2 more oxygen so larger ; 3 less space / overcrowding, so smaller ; 4 less space / overcrowding, so (signs of) disease / wounds ; 5 food qualified linked to, size / muscle / fat ; 6 AVP ; e.g. named tank condition linked to skin colour / no predators linked to increase in size / temperature linked to size

Question 2

2

Phenotypic variation exists in many forms.

structured7 marks

Question 2(a)

2(a)

Some examples of phenotypic variation in plants and animals are described in Table 2.1. Complete Table 2.1 by stating whether the cause of variation for each described example is likely to be due to: - genetic factors, \(\mathrm{V}_{\mathrm{G}}\) - environmental factors, \(\mathrm{V}_{\mathrm{E}}\) - a combination of genetic and environmental factors, \(\mathrm{V}_{\mathrm{G}}+\mathrm{V}_{\mathrm{E}}\).

Easystructured3 marks

Answer

![](question-bank/25728/images/answer_page8_fig1.png) five correct = 3 marks ;;; four or three correct = 2 marks two or one correct = 1 mark

Question 2(b)

2(b)

Name a spontaneous, random event occurring in cells that can be a source of phenotypic variation.

Mediumstructured1 marks

Question 2

2

The IUCN Red List provides information about the conservation status of species throughout the world, including the American badger, Taxidea taxus, and the black-footed ferret, Mustela nigripes. Fig. 2.1 shows an American badger and Fig. 2.2 shows a black-footed ferret. Fig. 2.3 shows the IUCN conservation status of the American badger and the black-footed ferret in 1987 and in 2013.

structured16 marks

Question 2(c)

2(c)

Black-footed ferrets were released at three different locations in the wild at different times. Each population was established from captive-bred animals.

structured8 marks

Question 2(c)(ii)

2(c)(ii)

Use Table 2.1 to describe how the gene pools and leg sizes of the Wyoming and Arizona black-footed ferret populations have changed, compared to the original captive population.

Mediumstructured2 marks

Answer

1 Wyoming ferret bone lengths smaller ; 2 Wyoming has lost, alleles/genetic variability/polymorphism or gene pool decreased ; 3 Arizona has gained, alleles/genetic variability/polymorphism or gene pool increased ; [max 2]

Question 2

2

The interpupillary distance (IPD) is the distance in millimetres between the centres of the pupils of the eyes. Fig. 2.1 shows how IPD is measured. IPD is one example of a characteristic of human facial structure that shows variation. Fig. 2.2 shows the pattern of variation in IPD in a large sample of adults.

structured0 marks

Question 2(a)

2(a)

0 marks

Question 2(a)(i)

2(a)(i)

Name the type of variation shown in Fig. 2.2.

Easystructured1 marks

Answer

1 continuous ;

Question 2(a)(ii)

2(a)(ii)

Suggest and explain how genes and the environment contribute to variation in IPD in humans.

Mediumstructured3 marks

Answer

any three from: 1 several / many, genes ; 2 additive effect / gene(s) (products) interact ; 3 environment has, big / significant, effect ; 4 (named) environment(al factors) affects gene expression ; 5 e.g. age / diet / disease / parasites / chemicals / mutagens / alcohol in utero, can affect, development / growth / IPD / phenotype ;

Question 2

2

The stickleback fish, Gasterosteus aculeatus, has two distinct forms, the saltwater form and the freshwater form. The larger, freshwater form is thought to have evolved from the smaller, saltwater form. Both forms have armour plating on each side of the body. The plates are made of bone and contain a high proportion of calcium. The ectodysplasin gene, EDA, codes for a protein involved in the development of armour plates. The EDA gene has two alleles, low armour and high armour. Three main morphs of armour plating have been described. Complete morph armour plating: - is found mainly in the saltwater form - has many plates from head to tail to cover most of the body - provides defence against large, predatory fish - limits the growth of the fish. Partial morph armour plating: - is found mainly in the freshwater form - has a reduced number of plates to cover only part of the body. Low morph armour plating: - is found mainly in the freshwater form - has very few, undeveloped plates and no body cover.

structured8 marks

Question 2(a)

2(a)

Explain why the variation in armour plating in stickleback fish can be described as discontinuous.

Mediumstructured2 marks

Answer

any two from: 1 discrete / distinct, categories / phenotypes / morphs / groups ; A (only) 3 groups 2 no range of phenotypes / no intermediates / no normal distribution ; 3 (only) one gene / only EDA, involved ; 4 not affected by environment ;

Question 2

2

Variation exists in populations of a species and this may provide the opportunity for evolution to occur.

structured0 marks

Question 2(a)

2(a)

Phenotypic variation exists in many forms and has a number of possible causes. Describe the main factors that are the cause of phenotypic variation.

Mediumstructured3 marks

Answer

1 genetic / genotype / alleles or example ; mutation / crossing over / independent assortment / random fertilisation / random mating 2 environmental or example ; climate / disease / food availability / soil pH / selection pressure 3 combination / interaction, of genes and environment or example ; gene (expression) is modified by environment