Question 1

Paper 2Medium16 marks

Figure 1 presents diploid chromosome numbers for six organisms. Humans and chimpanzees are the named examples in the IB Biology guide. Plant P, Plant Q, Animal R and Animal S are hypothetical species; no prior knowledge of their chromosome numbers is required. For each of these four hypothetical species, the plotted count was obtained from one diploid cell.

HumanChimpanzeePlant PPlant QAnimal RAnimal S46481428123001020304050Chromosomes in one diploid cell
(a)

Calculate the difference between the diploid chromosome numbers of chimpanzees and humans.

[2]
(b)

State the highest and lowest diploid chromosome numbers shown in Figure 1, and calculate the range of the values.

[3]
(c)

Explain why diploid cells have an even number of chromosomes.

[2]
(d)

Plant Q has a diploid chromosome number of 28. Determine the number of chromosomes in a gamete produced by meiosis and in the zygote formed when two such gametes fuse. Explain how the chromosome number changes between these stages.

[3]
(e)

A student proposes that an animal species always has a higher diploid chromosome number than a plant species. Evaluate this proposal using the data for Plant P, Plant Q, Animal R and Animal S in Figure 1.

[4]
(f)

Suggest an improvement to the sampling method that would make the chromosome number recorded for each hypothetical species more reliable.

[2]

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