Diversity of Organisms (DP IB Biology: HL): 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 than that of Genlisea margaretae.

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(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).

The size of the human genome, Homo sapiens, is 3000 mbp.

Using information from the question and your own knowledge, discuss the relationship between genome size and the complexity of organisms.

Many plants with very large genomes have a large proportion of non-coding DNA. 

State three roles of non-coding DNA. 

Define the term DNA barcode.

Researchers in France monitored the species richness of fish living in two rivers, the Marne and the Seine, over a period of several years. 

The researchers used a technique called electrofishing (EF) which involves stunning the fish with mild electric current and then recording the species of the stunned fish before releasing them back into the water.

In 2017 and 2018 the researchers trialled using eDNA samples in nine different sites to determine species richness in the area. They compared the results to the existing EF method. 

Describe the method that the researchers would have used to collect their eDNA data.

The results of this experiment are shown in the graph.

A student reading the research results concluded that eDNA is a better method than EF for determining fish species richness.

Use the data in the graph to evaluate the student's conclusion. 

Other than accuracy, suggest two reasons why the scientists might prefer to use eDNA sampling rather than electrofishing. 

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 by sharp spines.

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

State, with a reason, the type of variation that is represented by the graph.

Suggest the possible impact of grazing on the variation observed in the graph.

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

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

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

Suggest how 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 cultivars are kept separate from wild Opuntia ficus-indica populations. 

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

Explain why this 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 this in an organism.

Students 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).

Suggest why the genome size of a species does not always seem to correlate with 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.

Some species are divided into subspecies when there are distinct, consistent differences between populations. A subspecies is written by adding a third word—the subspecies epithet—to the usual binomial name.

A taxonomist suggested that the wolf and the domestic dog should be re-categorised as subspecies with the following names:

• Canis lupus familiaris

• Canis lupus lupus

Identify the genus name and the species name for the wolf 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.