Practice Paper 2 (SL IB Biology)

The Pyrenean desman (Galemys pyrenaicus) is a small, semi-aquatic, globally threatened mammal related to moles and shrews. It lives in the Pyrenees, a mountain range between France and Spain, and can be seen in the image below.

Suggest one adaptive feature of the Pyrenean desman.

The scientists found that there were two populations of desman living in the Pyrenees; a northern and southern population. Analysis showed that there was variation between the two populations. Some of the variation could be accounted for by environmental factors such as food availability, but some could not.

Outline a source of variation other than environmental factors.

During a study that lasted many years, scientists found that the number of desman travelling from the northern population to the southern side of the mountain range was extremely low. The scientists suspect that the original desman species may have split into two different species.

Explain how the original desman species may have split into two separate species.

Following partial hydrolysis of a naturally-occurring protein, samples of the polypeptides that were produced were identified.

Select from the table below the two molecular formulas that could be one of the naturally-occurring polypeptides.

Give reasons for your answer.

A protein found in leaves is thought to be the most abundant protein in nature.

State its name and describe its basic function. 

Holly is a common type of evergreen plant that can be found in British gardens. The leaves of holly bushes possess particularly thick waxy cuticles. A student investigated the rate of transpiration in holly leaves. They cut 10 leaves for set X and 10 leaves for set Y. The student then covered the leaves in set Y in petroleum jelly. After weighing each set of leaves, they attached the leaves in each set to a separate wire.The student then weighed each set of leaves at 30-minute intervals for a duration of 3 hours.

Their results are seen in the graph below.

Environmental conditions can affect the rate of transpiration in plants. State one environmental variable that should be controlled in this investigation.

As seen in the graph in part b), between 90 minutes and 120 minutes the rate of transpiration begins to slow in both sets of leaves.

Explain why this happens.

The results for the leaves in set X are different from the leaves in set Y.

Suggest an explanation for this.

A study was carried out into the impact of a node of Ranvier length on nerve transmission. The graph below shows the relationship between the node of Ranvier length and the number of sodium ion channels at each node.

A student concluded from the graph that there will be more sodium ion channels at longer nodes of Ranvier.

Evaluate the student's conclusion.

The study also looked at the impact of node of Ranvier length on the speed of impulse conduction in axons. The graph below shows some of the results.

Calculate the percentage change in impulse conduction speed when the node of Ranvier length increases from 0.5 μm to 1.5 μm. 

Suggest an explanation for the change in conduction speed for nodes of Ranvier lengths between 0.25 and 1.75 μm.

Tundra soils are mainly composed of peat that forms in the extreme cold conditions found within this ecosystem. Peat contains large amounts of carbon which is released when the tundra soils thaw during warmer seasons. Scientists investigated the amount of carbon released from tundra soils at one location, that were thawed to different extents over the course of three years. The results from this investigation can be seen in the graph below.

Explain why tundra soils act as a carbon store.

Calculate the difference in the mean carbon loss that occurred in tundra soils that were thawed considerably and those that were thawed slightly. Show your working.

Compare the rate of carbon release in moderately thawed soils with those in soils that were considerably thawed.

One additional mark is available for the construction of your answer. 

The diagram below shows the processes involved in the amplification of a sample of viral RNA.

Compare and contrast the process in the image with the process used in the amplification of a fragment of DNA.

The addition of RNAase enzyme occurs between stages 3 and 4 shown in the diagram from part a).

Suggest why this is a necessary part of the process.

Seven skeletons were discovered in a house in Pompeii, three of which were children. It is believed they were inhabitants and workers within the house when Mount Vesuvius erupted in 79 AD.

Researchers were able to isolate very small amounts of DNA from these skeletons. The DNA obtained was used in the polymerase chain reaction (PCR). Genetic fingerprinting was then carried out on this DNA to identify the skeletons.

The image below shows some of the results of the genetic fingerprinting of the three children and four adults.

Explain why the researchers used PCR in their investigation.

It was determined that the three children were siblings and shared the same biological parents. Their mother is Adult B.

Identify, with a reason, which of the other adults was the children’s father.