Short Answer Questions (DP IB Biology: HL): Exam Questions

Testosterone is a steroid hormone that affects muscle development. Steroid hormones are lipid-soluble molecules, which means they can pass through the cell membrane easily.

Identify the main component of the cell membrane.

Once inside a cell, testosterone binds to a receptor protein in the nucleus, which leads to the production of mRNA.

State two differences between RNA and DNA.

mRNA, produced in the nucleus, moves to the ribosomes in the cytoplasm of the cell.

Describe the process that occurs at the ribosome of eukaryotic cells.

High levels of testosterone can increase cell division in some tissues.

Explain how this could stimulate the growth of cancerous tumours.

The graph shows the changes in membrane potential of a motor neurone during one action potential.

(i) Identify the phase of the action potential represented by the upward slope labelled P.

[1 ]

(ii) Explain the cause of the change in membrane potential during this phase.

[2]

Describe how the membrane potential returns to resting potential after 1.0 ms.

Describe how ATP is used in synaptic transmission.

Outline how the brain and spinal cord integrate sensory input and produce motor responses.

State the function of memory cells in the immune response.

Explain the impact of mutations in genes controlling the cell cycle.

Pathogens evolve rapidly, changing their surface proteins in a process called antigenic variation.

Suggest how gene expression in pathogens can influence antigenic variation.

Antigenic variation produces a new antigen, enabling the pathogens to evade host immune responses and persist within the population.

Identify the type of natural selection represented by this persisting bacterial population.

The spruce bark beetle (Ips typographus) is an insect that feeds and reproduces beneath the bark of conifer trees.

In recent years, foresters have reported outbreaks of beetle infestations across parts of Europe and North America.

Ecologists collected data from three different forest regions.

(i) Describe the trend shown in the table.

[1]

(ii) Explain how the environmental conditions shown could lead to the changes in beetle population density.

[1]

Discuss how an increase in beetle population size could affect carbon cycling in conifer forest ecosystems.

In a population of spruce bark beetles, tolerance to high temperature is controlled by a single gene with two alleles:

• T = heat-tolerance allele (dominant)

• t = non-tolerant allele

In one population, 16% of beetles are homozygous recessive (tt).

(i) Assuming the population is in Hardy–Weinberg equilibrium, calculate the frequency of the T allele.

[2]

(ii) State why it is unlikely that the population would be in Hardy-Weinberg equilibrium.

[1]

Over time, environmental conditions in southern forests cause beetles in these areas to develop almost complete heat tolerance, while northern populations remain cold-adapted.

Explain how these environmental differences could lead to speciation in spruce bark beetles.

Forests periodically experience disturbances such as storms, fires or tree falls that remove vegetation and expose patches of bare ground. These areas are recolonised by fast-growing herbaceous plants, followed by the gradual re-establishment of shrubs and trees as the forest regenerates.

A group of ecology students investigated the growth responses of sunflower (Helianthus annuus) seedlings in three different forest clearings with varying light conditions.

The data collected from their investigation is shown in the table below.

Describe the trend shown in the table.

Explain the effect of the light conditions on the growth of sunflower seedlings.

In a temperate woodland, an outbreak of ash dieback disease (Hymenoscyphus fraxineus) has caused the death of many mature ash trees. Over time, increased light reaching the forest floor allows ash saplings and other young trees to establish and eventually replace the lost canopy.

Identify the ecological process described and explain why it occurs.

Explain how the death of mature ash trees would lead to a reduction in secondary production.

A team of biochemists investigated the role of reduced NAD in cellular respiration using isolated mitochondria from cardiac muscle cells. They prepared experimental solutions containing mitochondria, ADP and inorganic phosphate. The researchers then added pyruvate and malate to ensure that reduced NAD would be the primary coenzyme produced during the Krebs cycle.

State the role of reduced NAD in mitochondria.

The biochemists wanted to investigate how reduced NAD interacts with the electron transport chain, as shown below.

Rotenone is a compound known to inhibit complex I, the first protein carrier of the electron transport chain. The biochemists added rotenone to the experimental solution.

Predict and explain the likely effect of rotenone on oxygen consumption and ATP synthesis.

The diagram in part (b) shows the location of a protein known as cytochrome C, or cyt C, which forms part of the electron transport chain. The DNA sequence of the gene that codes for cytochrome c is very similar in many different organisms, although small differences do occur.

Suggest why the DNA sequence of the gene that codes for cytochrome c is so similar across many different organisms.

Cytochrome c oxidase is an integral protein of the inner mitochondrial membrane.

Describe how chemical bonds form between R-groups to maintain the tertiary structure of cytochrome C.

A gene for fungal disease resistance (denoted R) was studied in a crop plant species. The dominant allele R confers resistance, while the recessive allele r results in susceptibility.

Scientists crossed two heterozygous plants (Rr × Rr) and tested offspring for the presence of the resistance allele and for actual disease symptoms.

Using the data, calculate the phenotypic ratio for resistant : susceptible offspring.

Explain how the results in part (a) provide evidence that resistance is controlled by a single gene with complete dominance rather than through incomplete dominance or codominance.

Fungal infection rates were also recorded in a population growing in two fields: one treated with fungicide, one untreated.

Use this data to describe the relationship between genotype and environmental conditions.

Discuss how this genetic variation could influence evolution in the crop population if the use of fungicide were stopped.