Natural selection

A student wants to find how effective three antibiotics are for treating a range of bacterial infections.

This is their method:

• Spread bacteria across an agar plate.

• Soak discs with different antibiotics (A, B and C) and place them on the surface of the agar plate.

• Leave the plate to incubate for 5 days.

The student’s results are shown in the diagram.

Antibiotic discs

Which antibiotics are the most and least effective at inhibiting bacteria growth?

Most effective antibiotic A B C

Least effective antibiotic A B C

Explain your answers. Use the diagram.

Suggest two improvements to the method to increase validity of the investigation.

Bacteria are one cause of communicable disease.

Outline the role of the immune system of the human body in defence against disease.

Tuberculosis (TB) is caused by bacteria. The bacteria usually attack the lungs.

It is estimated that 8.7 million people develop TB worldwide each year.

1.1 million of these people are estimated to have HIV.

Calculate the percentage of people who develop TB worldwide each year who are estimated to have HIV.

Infection with HIV makes you more likely to develop TB.

State one reason why having HIV makes you more likely to develop TB.

Antibiotics are developed to kill bacteria.

Bacteria have appeared that antibiotics can not kill.

Explain how bacteria could have evolved to become antibiotic resistant.

Use ideas about natural selection.

Dodo

The dodo lived in the forests on the island of Mauritius.

They evolved from a much smaller pigeon that flew to the island.

Pigeons escape predators by flying away; they nest in trees so predators find it harder to eat their eggs.

There were originally no predators or humans on Mauritius.

Dodos nested on the ground and did not fly.

Humans arrived on the island in 1598. They brought with them animals that spread across the island destroying forests and eating eggs.

The dodo became extinct by 1700.

Pigeon similar to ancestor of dodo
Dodo

* Explain how the dodo evolved to become a flightless bird and how the arrival of humans resulted in its extinction.

Suggest one way scientists could find evidence that the pigeon and the dodo have a common ancestor.

The picture is of a sword-billed hummingbird feeding on a flower.

• The hummingbird feeds on nectar from the flower.

• The flower benefits because the hummingbird transfers pollen from one flower to the next.

• This helps the flower to reproduce and develop seeds.

Which word describes the interdependence between the hummingbird and the flower?

competition mutualism parasitism predation

The long beak of the hummingbird is an adaptation that helps the bird to feed. The bird’s ancestors had shorter beaks.

Complete the sentences about the long beak of the sword-billed hummingbird.

The ancestors of the sword-billed hummingbird showed........ in beak length.

Members of the species with longer beaks fed on more nectar.

This meant they were more likely to........

The allele for longer beaks was passed on to the next........

Over time, all the hummingbirds evolved to have longer beaks.

This process is called natural........

The picture is of a sword-billed hummingbird feeding on a flower.

• The hummingbird feeds on nectar from the flower.

• The flower benefits because the hummingbird transfers pollen from one flower to the next.

• This helps the flower to reproduce and develop seeds.

What word describes the interdependence between the hummingbird and the flower?

The long beak of the sword-billed hummingbird is an adaptation that helps the bird to feed. The bird’s ancestors had shorter beaks.

Explain how the sword-billed hummingbird may have evolved to have a long beak. Include ideas about natural selection.

When one species splits to become two new separate species it is called a speciation event. Phylogenetic trees represent speciation events from the past.

The diagram shows a phylogenetic tree.

How many speciation events are in this phylogenetic tree?

A 1

B 2

C 3

D 4

Complete Table 13.1 by choosing words from this list to identify the genetic term used to describe cell A and cell B.

diploid genotype haploid phenotype

Give an explanation for each choice of word in Table 13.1.

Huntington’s disease can cause death.

Fig. 13.3 shows the occurrence of HD by age when symptoms first appear.

What is the modal age range for the data shown in Fig. 13.3 ?

Early studies in the UK showed one in 15 000 have the HD allele. There are 66 000 000 people in the UK.

Calculate the number of people in the UK with the HD allele.

Read the information about HD in the box.

• The HD allele is a dominant allele that can lead to death.

• Alleles that cause death rarely persist in populations.

• About 10% of people with HD acquire the HD allele from a newly formed mutation and not through inheriting it from their parents.

Use this information and the data in Fig. 13.3 to suggest why the HD allele still persists in the human population.

White clover plants have two variants.

Cyanogenic variants produce a toxin when their cells are damaged. Acyanogenic variants do not produce a toxin.

The cells of clover plants can be damaged by freezing temperatures or by snails eating the leaves. The toxin kills snails but also damages the plant.

Table 15.1 shows growing regions of the two variants.

Complete the hypothesis to link each variant to the region it is most often found.

Acyanogenic variants are found in colder climates because........

Cyanogenic variants are found in warmer climates because........

To investigate a hypothesis a field study is needed.

Sampling techniques are used to estimate the population size of each variant in different areas.

Why are sampling techniques used instead of counting the total number of individual plants in each area?

Two students investigate the variant plants living at altitudes of 0–250 metres.

The students use random sampling as a starting point of their investigation. They then go on to complete a transect.

Explain how random sampling differs from a transect.

Explain why using a transect would develop and improve their investigation.

Fig. 15.1 shows the number of cyanogenic variant plants found in a total clover population of 200 at different altitudes.

What conclusion can be made about the effect of altitude on the distribution of cyanogenic clover?

Predict the altitude where you would expect to find mostly acyanogenic clover plants. Explain why most clover plants are acyanogenic at that altitude.

Altitude........

Explanation........

Use the theory of natural selection to explain how the cyanogenic variant of white clover plant could have developed.

White clover plants have two variants.

Cyanogenic variants produce a toxin when their cells are damaged. Acyanogenic variants do not produce a toxin.

The cells of clover plants can be damaged by freezing temperatures or by snails eating the leaves. The toxin kills snails but also damages the plant.

Table 11.1 shows growing regions of the two variants.

Complete the hypothesis to link each variant to the region it is most often found.

Acyanogenic variants are found in colder climates because........

Cyanogenic variants are found in warmer climates because........

To investigate a hypothesis a field study is needed.

Sampling techniques are used to estimate the population size of each variant in different areas.

Why are sampling techniques used instead of counting the total number of individual plants in each area?

Two students investigate the variant plants living at altitudes of 0–250 metres.

The students use random sampling as a starting point of their investigation. They then go on to complete a transect.

Explain how random sampling differs from a transect.

Explain why using a transect would develop and improve their investigation.

Fig. 11.1 shows the number of cyanogenic variant plants found in a total clover population of 200 at different altitudes.

What conclusion can be made about the effect of altitude on the distribution of cyanogenic clover?

Predict the altitude where you would expect to find mostly acyanogenic clover plants. Explain why most clover plants are acyanogenic at that altitude.

Use the theory of natural selection to explain how the cyanogenic variant of white clover plant could have developed.

The diagrams show two Blue Moon butterflies.

The two butterflies are the same species. However, there are differences between the colour and wing shape of the two butterflies.

What controls the colour and wing shape within the species?

Evolution can take thousands of years, but occasionally change happens very quickly.

Read the information.

Male embryos of the Blue Moon butterfly were attacked by a parasite.

Only 1% of the male butterfly population survived.

Within ten generations (1 year) males had returned to 40% of the butterfly population.

The parasite had not disappeared.

Use ideas about natural selection to describe how the male Blue Moon butterfly population may have returned to 40% within a year.

Classification of living organisms has changed over time.

Describe how scientific methods and theories develop over time.

MRSA is a type of bacteria that cannot be treated with most antibiotics.

How has MRSA developed?

A Genetic engineering

B Natural selection

C Protein synthesis

D Selective breeding

12* (a) Look at the diagram, it shows how humans, Homo sapien s, evolved.

It also shows that humans are closely related to other apes, like chimpanzees.

Describe how humans, Homo sapiens, evolved from Australopithecus afarensis and the evidence for this shown in the diagram.

Describe how the use of DNA in phylogenetics has changed classification systems.

How does the structure of DNA support its use in phylogenetics?

Some bacteria have evolved to become resistant to antibiotics.

Which statement is true about the evolution of these bacteria?

A Antibiotics killed the resistant bacteria.

B Bacteria reproduce slowly allowing the resistance to have affect.

C Mutations in some bacteria were an advantage.

D Mutations occurred within the nucleus of the bacteria.