AS & A Level Biology - 9700 Paper 4 2019 Summer Zone 2

(a) Fig. 1.1 is an electron micrograph showing a cross-section of a myelinated neurone.

[Image_1: Electron micrograph with labels A and B]

Fig. 1.1

Name A and B.

A .................................................................................................................

B ................................................................................................................. [2]

(b) Explain what is meant by saltatory conduction and describe its effect on the transmission of a nerve impulse.

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(c) A type of sea snail, Conus purpurascens, produces a toxin that blocks calcium ion channels in the presynaptic knob of a cholinergic synapse. The presence of this toxin results in no action potentials in the postsynaptic neurone.

Explain why the presence of this toxin results in no action potentials in the postsynaptic neurone.

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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.

(a) (i) Name the expected pattern of variation in wound-healing ability in a population of fish.
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(ii) Name the process that results in improved survival of captive fish in second, third and subsequent generations of captive-bred fish.
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(b) Suggest and explain three ways in which the tank environment may make the phenotype of a captive fish different from a wild fish.
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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.

(c) (i) Describe how microarray analysis can detect differences in the expression of many genes when comparing two samples, such as the offspring of wild and captive-bred fish.
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(ii) Explain how gene expression is controlled in eukaryotes such as fish.
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(d) Many of the differences in gene expression between the offspring of the wild and captive-bred fish were in genes coding for proteins involved in the immune response and in genes coding for proteins involved in wound healing. The fish from captive-bred parents expressed these genes to a greater degree.

The researchers concluded that the differences were inherited and adaptive.

Explain why the researchers concluded that the differences in gene expression between the two groups of fish were:

(i) inherited
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(ii) adaptive.
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Soybean, _Glycine max_, is an important food crop for human consumption and for feeding to animals.

Two varieties of soybean are _Vinton 81_ and _GTS 40-3-2_.

_Vinton 81_ has been developed in the traditional way by selective breeding (artificial selection) and _GTS 40-3-2_ is an example of a genetically modified (GM) organism.

(a) _GTS 40-3-2_ is described as herbicide-resistant, as it can withstand the application of glyphosate herbicide. Glyphosate is sprayed on the crop to kill weeds.

Outline how genetic engineering gave _GTS 40-3-2_ the trait of herbicide resistance.
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(b) Countries vary in the extent to which they grow GM varieties, such as _GTS 40-3-2_, instead of traditional varieties such as _Vinton 81_.

• In the USA, 94% of soybeans grown are GM.
• In Europe, 0% of soybeans grown are GM.

Scientists used computer models to predict the effect of two different changes in agricultural practice on soybean crop yields:

• a global ban that reduces the cultivation of GM soybeans to 0% everywhere
• all countries increasing the cultivation of GM soybeans to the 94% level of the USA.

Table 3.1 shows the results of this modelling for four countries.

[Table_1]

Explain what the data in Table 3.1 suggests about the social and ethical implications of growing GM soybeans.
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Oculocutaneous albinism (OCA) is a type of albinism. There are many different forms of OCA.

OCA1A is one form of OCA, caused by a recessive mutation in the autosomal gene, TYR, coding for the enzyme tyrosinase. This enzyme is involved in the biosynthetic pathway that results in the production of melanin, the pigment responsible for the colour of hair, skin and eyes.

A person with OCA1A has white hair, very pale skin and pink eye colour.

(a) Draw a genetic diagram to show the probability of a child having OCA1A, if both parents are carriers.

Use the symbols A and a for the alleles.

parental genotypes

gametes

offspring genotypes

offspring phenotypes

probability [4]

(b) Fig. 4.1 shows the biosynthetic pathway involving tyrosinase.

[Image_1: Fig. 4.1]

There are a number of different mutations of the TYR gene that can result in an absence of melanin and cause OCA1A. These include:

• a missense mutation, caused by a base substitution, is most common
• a nonsense mutation, caused by a base substitution, is less common
• an insertion mutation, which is extremely rare.

(a) Fig. 5.1 is a photomicrograph of part of the cortex of a kidney.



Fig. 5.1

(i) On Fig. 5.1, use label lines and letters to label:
G – the glomerulus
L – the lumen of the Bowman’s (renal) capsule. [2]

(ii) During ultrafiltration, components of blood in the glomerulus with a relative molecular mass greater than 68 000 are prevented from passing into the Bowman’s capsule.

Name the structure that acts as this filtration barrier.
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(b) The glomerular filtration rate (GFR) is the rate of flow of filtered fluid through the kidneys per unit time.

The afferent arterioles supply blood to the glomerulus of each nephron within the kidney and the efferent arterioles take blood away from each glomerulus. The lumen diameters of the afferent and efferent arterioles have a large effect on the GFR. Normally the lumen diameters of the afferent and efferent arterioles are different, but they can change to increase or decrease the normal GFR in response to changing conditions.

Complete Table 5.1 to indicate whether the GFR is normal, increased, or decreased for each combination of arteriole diameters shown.

The first row has been completed for you.

[Table_1]

Table 5.1

afferent arteriole lumen | efferent arteriole lumen | GFR
diameter | diameter |
normal | normal | normal
decreased | normal | .............................
normal | increased | ............................. [2]

(c) After leaving the Bowman’s capsule, the glomerular filtrate passes through the proximal convoluted tubule, where selective reabsorption occurs.

Describe and explain how all of the glucose in the glomerular filtrate is reabsorbed back into the blood.
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(d) State and explain three features of a proximal convoluted tubule cell that adapt it to its function.
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(a) State the general theory of evolution.
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[1]

(b) Different types of organism have evolved different structures containing light receptors. Eyes are organs containing light receptors.

Fig. 6.1 describes the light receptors of several types of organism.



Using the information in Fig. 6.1, suggest how a complex eye such as that of mammals could have evolved in successive stages.
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(c) Octopuses are molluscs that have eyes very similar to those of mammals.

Octopuses and mammals are not closely related.

Octopuses and mammals have lenses that can change shape to focus on objects at different distances.

Suggest reasons why octopuses and mammals have evolved similar eye structures.
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(d) Molecular evidence is used to investigate evolution. One study involved a marine worm, Platynereis dumerilii, that still has characteristics similar to its ancestors from 600 million years ago.

Researchers sequenced all the proteins in light receptor cells of P. dumerilii and humans. The results showed that there are many similarities between the protein sequences of P. dumerilii and humans, particularly in the light-detecting protein opsin.

(i) State what this molecular evidence indicates about the evolutionary origins of P. dumerilii and humans.
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(ii) Explain how amino acid sequences indicate how close the relationship is between two species.
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(a) Define the term ecosystem.
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(b) State the term used to describe:
the functional role of a species within an ecosystem
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a reproductively isolated group of organisms that interbreed to produce fertile offspring
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physical factors in the environment such as temperature and soil pH.
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(a) Oxidative phosphorylation takes place in the mitochondrion.

Table 8.1 shows the different stages of oxidative phosphorylation.
The stages are not listed in the correct order.

[Table_1]

Complete Table 8.2 to show the correct order of the stages.
Two of the stages have been completed for you.

[Table_2]

(b) State the precise location in a mitochondrion of each of the following.

ATP synthase ..............................................

Krebs cycle ...............................................

electron transport chain ........................................

coenzyme A ................................................

pyruvate ..................................................

(a) Describe how you would carry out an investigation into the effect of temperature on the rate of photosynthesis of an aquatic plant. [8]
(b) Outline how degraded habitats may be restored, with reference to named examples. [7]

(a) Outline the biological basis of contraceptive pills containing oestrogen and progesterone. [8]
(b) Explain how speciation may occur as a result of geographical separation. [7]