Diversity of Organisms (DP IB Biology: SL): Exam Questions

The table below shows the genome sizes of several different plant species.

(i) Calculate how many times bigger the genome of Paris japonica is in comparison with Genlisea margaretae.

[1]

(ii) Mistletoe is a diploid plant with 10 pairs of homologous chromosomes. 

Calculate the average size of one of these chromosomes.

[1]

State the best method that can be used to compile the information found in the table in part (a).

Prickly pear cacti are plants that are adapted to live in arid conditions. They store water in thick stems which are protected from grazing by herbivores through the presence of multiple spines. The number of spines that are present on the prickly pear cacti may vary greatly, depending on the frequency of grazing that they experience.

The graph shows the number of spines present in a species of prickly pear cacti, Opuntia ficus-indica.

State the type of variation that is represented by the graph and provide two reasons for your answer.

Suggest the possible impact of environmental factors on the variation observed in the graph, with regards to the number of spines on prickly pear cacti.

The prickly pear, Opuntia ficus-indica, is native to Mexico in Central America. 

(i) State the genus and the species of the prickly pear. 

[2]

(ii) The prickly pear can be grown on an agricultural scale for use in food types all over the world.

Suggest why the binomial name assists with the international trade of this cactus. 

[1]

Since the 19th Century there have been cultivars of Opuntia ficus-indica that have been artificially selected to have no spines. 

These species have been used for agricultural uses by humans and are kept separately from the wild Opuntia ficus-indica populations. 

Scientists studying these plants want to determine if these two groups are still the same species. 

Explain why this process can present a challenge to these scientists. 

The table below shows the genome size and haploid chromosome number of different organisms.

Calculate the percentage difference in the chromosome number found in the zygotes of chickens compared to those of humans.

Show your working and give your answer to three significant figures.

The diploid number in an organism is always an even number.

Using your knowledge on the behaviour of chromosomes during meiosis, explain the importance of the diploid number in an organism.

Scientists hypothesised that a high chromosome number leads to the development of a more complex organism.

Discuss this hypothesis using the data provided in part a).

Based on your knowledge of chromosomes, suggest a reason why the genome size of a species does not always seem to correlate with the chromosome number.

The images show two organisms from the genus Canis.

Grey wolves, Canis lupus, are wild animals native to Eurasia and North America.

Domestic dogs, Canis familiaris, descended from wolves and became domesticated over many years.

A wolfdog is a hybrid produced when a domesticated dog (Canis familiaris) breeds with a wolf (Canis lupus). Genetically, dogs and wolves are very similar and the resulting offspring are fertile. Wolfdog hybrids are rare as natural habitats and territorial behaviours isolate wolves from domestic dogs.

Using the information provided, discuss the validity of the claim that wolves and dogs are the same species.

A taxonomist suggested that the wolf and the domestic dog should be re-categorised as follows:

• Canis lupus familiaris

• Canis lupus lupus

Identify the genus name and the species name for the wolf and the domestic dog under this re-categorisation.

Cri du chat syndrome is a rare genetic condition caused by a chromosomal mutation. Babies born with Cri du chat syndrome experience a variety of symptoms and have a characteristic cry that clinicians have described as cat-like.

The karyograms below compare the karyotype of a child who does not have Cri du chat syndrome (A) with that of a child who has the syndrome (B).

Karyotype A

Karyotype B

Use the karyotypes to describe the chromosome mutation that causes Cri du chat syndrome.

Some individuals with Cri du chat syndrome do not experience significant symptoms.

Suggest an explanation for this observation.

Most people affected by Cri du chat syndrome do not have a family history of the condition.

Suggest what this indicates about the heritability of the condition.