Unit 7 Part 2

Question 1

Mutation is one cause of genetic variation in organisms.

Give two other causes of genetic variation

Answer 1

1. Crossing over between homologous chromosomes;
2. Independent segregation/assortment of homologous chromosomes;
3. Random fusion of gametes

Question 2

Variation in flower colour is considered one of the factors involved in the evolution of the following two species of monkeyflower.

*   Erythranthe lewisii (Great Purple Monkeyflower), which has pink flowers, is mostly found at higher altitudes (1600 to 3000 metres) and attracts bumblebees.

*   Erythranthe cardinalis (Scarlet Monkeyflower), which has red flowers, is mostly found at lower altitudes (up to 2000 metres) and attracts hummingbirds.

Bumblebees and hummingbirds are important in the pollination of flowers. Pollination involves the transfer of male gametes to female gametes.

Explain the different processes that may have been involved in the evolution of these two species of monkeyflower. Use the information provided to justify your answer.

Answer 2

1. Geographical isolation due to different altitudes;
2. Allopatric speciation due to isolation/separation;
3. Different selection pressures because of different environment(s);
4. However some overlap in distribution
5. So possibly sympatric speciation;
6. (Variation due to) mutation(s);

Reject mutation(s) if context incorrect e.g. ‘mutate to adapt’.

7. Reproductive isolation due to different pollinators so no gene flow
8. Change in allele frequency in each population;
9. Different species can no longer interbreed to produce fertile offspring;

Question 3

Lemurs are small mammals. Lemurs live in trees and feed on leaves and fruit.

Scientists used a computer program to predict the expected distribution of two species of lemur, Eulemur rufus and Eulemur rufifrons, on the island of Madagascar. These predictions were based on the environmental needs of each species.

Then, the scientists determined the actual distribution of these two species of lemur on the island of Madagascar.

The diagram below shows the scientists’ results.

Using all the information, suggest how speciation happened to produce two species of lemur.

Answer 3

1. Geographical isolation or Allopatric speciation;
2. No gene flow
3. Different selection pressures;
4. Variation due to mutation(s) in different populations;
5. Different/advantageous allele/s selected for;
6. Eventually different species as cannot interbreed to produce fertile offspring;

Question 4

In the mountains of North America, when winter changes into spring, the coat colour of snowshoe hares changes from white to brown. Climatic changes have caused the snow to melt earlier. This has reduced the survival rate of snowshoe hares in these habitats. The change in coat colour occurs when new fur replaces old fur. This is called moulting. Recent research has shown that snowshoe hares within a population moult at different times. Moulting at different times could be a major factor in ensuring the survival of snowshoe
hare populations.
Snowshoe hares within a population moult at different times.

Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats.

Answer 4

1. Hares which moult earlier are more likely to survive;
2. Hares which moult earlier more likely to reproduce;
3. Pass on advantageous allele;
4. Frequency of allele increases in future populations;

Question 5

Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase. Lactase is essential to newborn mammals as milk is their only source of food. Most mammals stop producing lactase when they start feeding on other food sources. Humans are an exception to this because some continue to produce lactase as adults. The ability to continue producing lactase is known as lactase persistence (LP) and is controlled by a dominant allele. A number of hypotheses based on different selection pressures have been put forward to explain LP in humans.

One hypothesis for LP in humans suggests that the selective pressure was related to some human populations farming cattle as a source of milk.

Describe how farming cattle as a source of milk could have led to an increase in LP.

Answer 5

1. LP due to mutation

Reject mutation caused by drinking milk.

Reject (LP) gene

2. Milk provides protein/ glucose;
3. Individuals with LP more likely to survive and reproduce

Reject (LP) gene

4. Directional selection;
5. Frequency of allele increases in the offspring/next generation;

Question 6

Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different.

Using this information, suggest how these two species of palm tree arose by sympatric speciation.

Answer 6

1. Occurs in the same habitat;
2. Mutation/s cause different flowering times;
3. Reproductive isolation so no gene flow;
4. Different allele/s selected for;
5. Disruptive natural selection;
6. Eventually different species cannot interbreed to produce fertile offspring;

Question 7

What is a gene pool?

Answer 7

All the alleles in a population;

Note: All or number of alleles in a species on its own is not enough on its own.

Question 8

To reduce the damage caused by insect pests, some farmers spray their fields of crop plants with pesticide. Many of these pesticides have been shown to cause environmental damage.

Bt plants have been genetically modified to produce a toxin that kills insect pests. The use of Bt crop plants has led to a reduction in the use of pesticides.

Scientists have found that some species of insect pest have become resistant to the toxin produced by the Bt crop plants. One farmer stated that the increase in the use of Bt crop plants had caused a mutation in one of the insect species and that this mutation had spread to other species of insect. Was he correct? Explain your answer.

Answer 8

(No – no mark)

1. Mutations are spontaneous / random;
2. Different species do not interbreed;
3. So mutation cannot be passed from one species to another.

Question 9

Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands. Describe how you could use the mark-release-recapture method to estimate the number of Anolis sagrei on one of these islands.

Answer 9

1. Capture sample, mark and release;
2. Method of marking does not harm lizard / make it more visible to predators;
3. Leave sufficient time for lizards to randomly distribute on island before collecting a second sample;
4. Population = number in first sample × number in second sample divided by number of marked lizards in second sample

Question 10

A weed is a plant growing where it is not wanted. Fat hen is a weed which grows in some crop fields.

Describe how you could estimate the number of fat hen plants in a field.

Answer 10

1. Use a grid to divide field into squares;
2. Obtaining random coordinates using a random number generator;
3. Count number in a quadrat;
4. Take a large sample and calculate mean number per quadrat;
5. Multiply mean number of plants per m2 by area of field

OR

Divide area of field by area of quadrat x mean number of plants per quadrat

Question 11

Define the biological term population

Answer 11

1. A group (of organisms) of the same species in a (particular) space at a particular time;
2. That can interbreed to produce fertile offspring

Question 12

In northern India, there is a conflict of interests between farmers of livestock (eg cows) and people trying to conserve ibex (a type of wild goat).

When livestock are given extra food, their populations can grow too large and compete with ibex.

Name the type of competition between livestock and ibex.

Answer 12

Interspecific

Question 13

Succession occurs in natural ecosystems. Describe and explain how succession occurs

Answer 13

1.   Colonisation by pioneer species;

2.   Pioneers species change the environment;

3.   Environment becomes less hostile for new species that out compete previous species;

4.  Increase in biodiversity;

5.  Until climax community is reached;

Question 14

The scientists concluded that the results shown in Figure 1 were due to succession taking place.

Use Figure 1 to explain why the scientists reached this conclusion.

Answer 14

1. Beach grass is the pioneer species;
2. Pioneer species change the abiotic environment/factors;
3. So less hostile for shrub-bunch grass
4. Conifer/hardwood trees represent climax community;

Question 15

Outline a method the ecologists could have used to determine the plant species richness at one habitat.

Answer 15

1. A method of selecting sampling sites at random;
2. Use of quadrat and use large sample;
3. Count number of different plant species at habitat;