Practice Paper 1B (SL IB Biology)

The graph below shows the impact of environmental factors on biome development.

Describe the conditions under which the following biome types will develop, according to the graph:

Temperate rainforest

[1]

(ii)

Tropical forest

[1]

The transition between one biome and another is usually gradual, and there are some situations where variables other than those indicated on the graph may influence biome development (indicated on the graph by dashed line).

Suggest a variable, other than those shown on the graph axes, that may influence biome development in these transition zones.

Plant species found in desert biomes often share similar features.

Explain two features common to desert biome plants.

[2]

(ii)

Explain why desert biome species share these features despite living in different parts of the world.

[2]

Sickle cell anemia is a genetic disorder with symptoms such as dizziness, a rapid heart rate and fatigue. It is caused by an allele that leads to altered haemoglobin proteins. These altered proteins undergo aggregation (sticking together), an event which changes the shape of red blood cells.  This can be seen in the image below.

Suggest how sickled red blood cells may result in the symptoms noted above.

Suggest why the shape of white blood cells is not affected by sickle cell anaemia.        

Mutations such as the one seen in sickle cell patients are usually caused by an error during DNA replication. 

Identify the enzyme that is responsible for catalysing the process of DNA replication.

Serotonin is a neurotransmitter found in the brain. Low serotonin levels are thought to contribute to symptoms of clinical depression. One commonly used treatment for depression involves a group of drugs called SSRIs.

The diagram below shows a serotonin synapse in the brain both before (left) and after (right) treatment with SSRIs.

Suggest how SSRIs might be effective at treating the symptoms of depression.

The image below shows the chemical structures of serotonin and an SSRI called Citalopram. Citalopram is commonly prescribed for depression due to its limited side effects, but it does sometimes cause some nausea and sleep disturbance during the first few weeks.

Use the image to suggest how Citalopram can have the effect shown in part a) while also having some side effects.

Although the use of SSRIs has increased significantly in recent years there is still controversy over their effectiveness in the treatment of depression, along with some concern surrounding withdrawal symptoms at the end of treatment. One group of researchers analysed the results of around 300 studies involving treatment for depression; some of their results are shown in the graph below.

The placebo in this case was a pill identical in appearance to an SSRI but containing no active chemical ingredients.

Suggest the role of a placebo in a study of this type.

State what can be concluded about the effectiveness of SSRIs in the treatment of depression from the information provided in part c). Note that the error bars in the graph represent standard deviation.