Natural selection

Katydids are insects that are green and look like the leaves that they feed on. The photograph shows a katydid.

Explain how katydids affect the growth of the plants that they feed on.

Explain how katydids have evolved to look like leaves.

(a) Charles Darwin observed finches (birds) in the Galapagos, a group of islands off the coast of South America. Darwin’s observations helped develop his theory of evolution by means of natural selection. The diagram shows the common ancestor and some of the finch species now living in the Galapagos.

The large ground finch has a large beak and feeds on big seeds with hard seed coats. The cactus finch feeds on nectar from cactus flowers.

Explain how the beak of the cactus finch could have evolved by natural selection.

One of the Galapagos islands is called Fernandina. Suggest why the large ground finch is found on Fernandina but the cactus finch is not.

A student uses 400 clay models of mice to investigate natural selection. He paints 200 of the clay models white and 200 brown. He places the model mice in woodland in the morning. He checks the models in the evening for damage by predators. The graph shows his results.

Calculate the difference between the number of damaged white model mice and the number of damaged brown model mice.

Suggest why the results would differ if the student used live white mice and live brown mice rather than clay models.

Galactosaemia is an inherited condition. It is caused by a mutation to a gene on chromosome 9. This gene codes for an enzyme that removes the sugar galactose from the body. The normal allele, G, can produce the enzyme and is dominant to the recessive allele, g. The pedigree shows the inheritance of galactosaemia in a family.

How many individuals in the family pedigree have an X and a Y chromosome in each of their body cells?

How many individuals in the family pedigree are homozygous recessive?

Give the genotype of individual 1.

Individuals 8 and 9 are going to have another child. Give the probability of this child having galactosaemia.

What is meant by the term mutation ?

The mutation for galactosaemia is harmful but some mutations can be beneficial. Describe one example of a beneficial mutation.

Some inherited conditions can be fatal but medical treatment is often available. Explain what would happen to the frequency of alleles for these inherited conditions if medical treatment was not available.

Name the producer in this food web.

Gazelles try to avoid being caught by lions by running away quickly. They can run at a top speed of 96 km per hour.

Calculate the distance in metres a gazelle runs in one minute at a speed of 96 km per hour. Show your working.

distance =_........ metres

Gazelles cannot maintain their top speed for a long time because a change in the type of respiration takes place in their muscle cells. Explain how this change in respiration stops gazelles from running at a top speed for a long time.

Zebras also try to avoid being caught by lions. It was thought that the striped coat of zebras helps to camouflage them. A new theory suggests the striped coat evolved because it reduces the number of biting flies that feed on zebra blood. Use your knowledge of natural selection to explain how a striped coat that reduces the number of flies feeding on zebra blood may have evolved.

Lions’ eyes are adapted to help them see in dim light.

Their eyes have a layer of cells behind the retina that reflects light which has passed through the retina. Suggest how this would help a lion see in low light intensities.

Suggest one other adaptation in the structure of a lion’s eye that helps the lion to see in low light intensities.

When a lion catches its prey it tears the meat into smaller pieces in its mouth before swallowing.

Suggest why the saliva released into the lion’s mouth does not contain amylase.

Explain how tearing the meat into smaller pieces helps digestion in the stomach.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Many humans are frightened of being attacked and eaten by alligators. However, alligators may have a role as potential lifesavers. Scientists have discovered proteins in alligator blood called alligacins. They hope these proteins may provide a source of new antibiotics to help fight infections, particularly those associated with diabetic ulcers and severe skin burns. The scientists collected blood samples from alligators. They extracted the antibiotic proteins from the white blood cells involved in destroying pathogens. In laboratory tests the protein extracts killed a wide range of bacteria, including MRSA (methicillin-resistant Staphylococcus aureus). These ‘superbugs’ are increasingly resistant to many antibiotics and cause thousands of deaths each year. The investigation by the scientists of the antibiotic properties of alligacins discovered a range of other uses for these proteins. For example, they help to cure infection caused by the yeast Candida albicans in AIDS patients. The antibiotic proteins killed six out of eight different strains of Candida albicans. They also discovered that the blood proteins may help destroy HIV, the virus that causes AIDS. Alligators have an immune system that is different from the immune system of humans. Humans need a vaccination to be able to respond quickly to infection by pathogens. However, the alligator immune system can quickly destroy pathogens without having had prior exposure to them. Scientists believe that natural selection has created this evolutionary adaptation as it promotes quick wound healing. These wounds are caused by alligators fighting to defend their territory from other alligators. The scientists are hoping to identify the exact chemical structures of the antibiotic proteins. They can then begin to develop antibacterial or antifungal drugs.

What is meant by the term pathogens (line 8)?

Describe how a non-resistant Staphylococcus aureus bacterium can produce a bacterium that is resistant to methicillin (lines 8 and 9).

A pathogen named in the passage is Staphylococcus aureus. Name one other pathogen named in the passage.

What term is used in the passage to describe pathogens that are resistant to antibiotics?

Suggest why an MRSA infection may have to be treated with many different antibiotics (line 10).

Explain how a vaccination will protect a human from having an infection.

Describe how natural selection increases the number of alligators with alligacin in their blood.

Suggest two reasons why an alligator defends its territory (line 24).

Flies lay their eggs in the urine and faeces that sticks to the wool on sheep. The eggs hatch and the larvae damage the skin of the sheep leading to infection. To reduce this problem, farmers in New Zealand have been developing sheep that have no wool growth on their legs, their backside or on the underside of their abdomen.

Suggest why flies are attracted to urine and faeces.

Farmers have crossed different breeds of sheep to produce offspring with desired characteristics. The characteristics of different breeds of sheep are shown in the

Describe how farmers could use selective breeding to develop sheep with bare legs and bare backsides.

Describe two differences between selective breeding and natural selection.

Farmers sometimes use pesticides to prevent flies attacking sheep. Give two problems with the use of chemical pesticides.

The use of a pesticide may result in an increase in the number of pest organisms that are resistant to the pesticide. Use your knowledge of natural selection to explain the increase in the number of pest organisms that are resistant to the pesticide.