Variation

Reproduction can be sexual or asexual.

What is an advantage of sexual reproduction?

A Advantageous features are preserved between generations.

B Genetic variation is increased.

C Offspring are genetically identical to parents.

D The risk of mutation is reduced.

Animals can undergo natural and artificial cloning.

Human identical twins are an example of natural animal clones.

Suggest why human identical twins do not look exactly identical.

Komodo dragons are large lizards.

Male Komodo dragons have two Z chromosomes. Female Komodo dragons have one Z chromosome and one W chromosome.

A reproductively isolated female Komodo dragon can reproduce without a male using a process called parthenogenesis. All of the offspring are males.

This process is outlined in the diagram.

The offspring are not the same sex as the parent.

Identify two other reasons why parthenogenesis in Komodo dragons is not an example of cloning.

Suggest why female mammals cannot produce male offspring by parthenogenesis.

Animals can be cloned artificially using embryo splitting.

This is the procedure for cloning by embryo splitting:

1. An egg from a female is fertilised by sperm from a male.

2. The zygote divides to form an embryo.

3. After a few days, the developing embryo is split into several smaller embryos.

4. After a few days, each smaller embryo is implanted into a surrogate mother.

5. Each embryo grows into a fetus and is born normally.

State the property of the cells in the embryo that allows cloning to be successful.

Embryos from stage 3 above are sometimes frozen for later use.

State one advantage to agriculture of freezing embryos from stage 3.

Animals can be cloned artificially using a technique called somatic cell nuclear transfer (SCNT).

SCNT can be used to increase the population of an endangered species.

Przewalski’s horse, Equus przewalskii, is a species of horse related to the domestic horse, Equus caballus. The common ancestor of both horse species is thought to have lived 45 000 years ago.

Przewalski’s horse became extinct in the wild in the 1960s. Captive breeding from 12 individuals has increased the population and some have since been reintroduced to the wild.

The genetic diversity of all modern Przewalski’s horses is very low.

In 2020 and 2022, SCNT using frozen cells from an individual that died 42 years previously has led to the birth of two cloned Przewalski’s horses which appear to be free of health problems.

Outline how genetic diversity in a species such as Przewalski’s horse can be measured.

State why SCNT is more useful than embryo splitting when increasing the population of endangered species.

Suggest one reason why the health of the cloned Przewalski’s horses is better than that of Dolly the sheep, the first mammal to be cloned by SCNT.

The Farne Islands are a group of small islands off the coast of Northern England.

The Farne Islands are a National Nature Reserve and Site of Special Scientific Interest. They are home to many species of bird, including arctic terns, guillemots, cormorants, shags, eider ducks, razorbills, and a variety of gulls. Particularly popular with the public are puffins. Considered by some to be a keystone species, puffins are small birds with large colourful beaks that fly very close to the surface of the sea. They come to the islands only to breed, nesting in underground burrows.

Local tour operators transport large numbers of visitors to the islands each year but no visitors are allowed on the islands during the winter to allow conservation work to be carried out. Such work includes repairing boardwalks and fences, tagging individual birds, and counting how many puffin burrows have been in use.

In 2023, an outbreak of bird flu caused a drop in the numbers of many species, including puffins, and visitors were banned from the islands. Local tour operators reported a drop in income.

Identify evidence from the information above that supports each of the following claims:

Puffins are important for aesthetic reasons........

Puffins are important for ecological reasons........

Puffins are important for economic reasons........

The Farne Islands can be seen as an environmental resource that is affected by human activities.

Identify one example of conservation that is necessary as a direct result of human activities.

There are no mammalian predators, such as rats and stoats, on the Farne Islands. Mammalian predators eat birds and their eggs.

Part of the conservation work involves ensuring that the islands remain free of these mammalian predators.

Suggest how human activity could be responsible for the arrival of these predators.

There are two types of conservation: in situ and ex situ.

State the type of conservation taking place on the Farne Islands and give a reason for your choice.

Puffins, like many species on the Farne Islands, eat small fish. Their main predators are large gulls. Puffins are on the IUCN Red List for threatened species.

The puffin population can be estimated from the number of burrows that are occupied.

After the bird flu outbreak in 2023 the number of occupied burrows declined.

It is important not to disturb the burrows and there is not enough money available to allow puffin burrows to be constantly monitored, either by humans or cameras.

Suggest one other type of evidence that could be used to infer that a burrow was being occupied by puffins.

Discuss the effect a decline in puffin population could have on other species in the area.

Explain why the existence of a predator can improve the long-term survival of a species such as the puffin.

* The sea around the Farne Islands contains a large population of grey seals, Halichoerus grypus and a small population of common seals, Phoca vitulina.

The table contains some information about these two species of seal.

Use the information in the table to describe the different types of variation between organisms and the underlying causes of this variation.

Extra answer space if required.

Variation can be under genetic control.

Which statement about the genetic control of variation cannot be true for discontinuous variation?

A Variation is controlled by a single gene with multiple alleles.

B Variation is controlled by an epistatic interaction between two genes with multiple alleles.

C Variation is controlled by many genes on different chromosomes.

D Variation is controlled by two genes on the same chromosome.

Type 1 diabetes mellitus is characterised by a lack of insulin production. Type 2 diabetes mellitus can involve reduced production of insulin and a decreased response to insulin.

* Scientists analysed the occurrence of diabetes in identical and non-identical twins.

Identical twins have the same DNA. Non-identical twins share approximately 50% of each other’s DNA.

The scientists selected 614 pairs of twins in which at least one of the individuals had diabetes: 109 pairs had type 1 diabetes; 505 pairs had type 2 diabetes.

The scientists calculated the percentage probability of an individual having diabetes when their twin has the disease.

The table shows the percentage probability of both individuals in a pair of twins developing either type 1 or type 2 diabetes.

Explain what conclusions can be drawn from the data in the table about the influence of the environment and genetics on the probability of developing diabetes.

Extra answer space if required.

Insulin is secreted from cells in the pancreas.

This is a photomicrograph of pancreatic tissue.

Identify the structures labelled A, B and C.

The graph shows the changes in the rate of insulin secretion in a person with type 2 diabetes after consuming glucose.

The table shows the changes in the rate of insulin secretion in a person with normal glucose tolerance after consuming glucose.

Plot the data from the table on the graph and draw a line of best fit.

The table lists statements about a molecule of insulin.

Complete the table by stating the level of protein structure (primary, secondary, tertiary or quaternary) to which the statement relates.

Bacteria can be genetically modified to produce insulin.

State how a plasmid containing the gene coding for insulin can be transferred into a bacterial cell.

Suggest how bacterial cells can be screened to check if they have taken up a recombinant plasmid.

In the future, type 1 diabetes could be treated by giving patients new pancreatic -cells that have been produced in a laboratory from stem cells.

State a feature of stem cells that allows them to be used to produce pancreatic -cells.

Future treatments for type 1 diabetes may be able to use stem cells from a patient’s body to produce new -cells.

Explain why patients receiving these new -cells would still need to be given immunosuppressant drugs.

Many organisms undergo asexual reproduction by mitosis.

State two other roles of mitosis in organisms.

Plants reproduce asexually by mitosis.

Explain why mitosis, and not meiosis, is used for asexual reproduction in plants.

Bacteria reproduce asexually by a process called binary fission.

Suggest why bacteria are unable to reproduce asexually by mitosis.

During meiosis, the independent assortment of chromosomes leads to the formation of genetically different gametes.

Gametes of the western clawed frog contain 10 chromosomes.

Calculate the number of genetically different gametes resulting from the independent assortment of chromosomes that would be produced by an individual frog.

The Atlantic cod, Gadus morhua, is a large fish that is often eaten by humans.

In the space provided, plot the results from the table as a suitable graph.

Variation can be caused by genetic and environmental factors.

Explain why your graph shows that at least some of the variation in body length in Atlantic cod is caused by environmental factors.

It is important that commercial fishing is done in a sustainable way.

Fish farms are one potential solution to declining fish stocks.

List three other strategies that governments could use to increase the sustainability of commercial fishing.

International agreements are an important approach to sustainability.

Suggest why international agreements are particularly important in the case of sustainable fishing.

The adult wandering albatross, Diomedea exulans, has wingspans that range from 2.5 m to 3.5 m.

Which of the following describes the variation in wingspan of the wandering albatross?

A intraspecific and controlled only by genetic factors

B interspecific and controlled only by environmental factors

C intraspecific and controlled by both genetic and environmental factors

D interspecific and polygenic

Your answer

It is possible to manufacture antibodies to treat certain diseases. These are known as synthetic antibodies.

DNL-Fab3, shown in Fig. 4.2, is an example of a synthetic antibody.

State two conclusions that can be drawn from Fig. 4.2 about the differences between the way DNL-Fab3 functions and the functioning of normal antibodies.