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Revising a-level Biology: Plants ‘r’ mint Revision pack 4: Classification; meiosis and variation; diet and food production; classification; cloning; biotechnology; gene technology

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Revising A-level Biology: Plants ‘r’ mint

Revision pack 4: Classification; meiosis and variation; diet and food production; classification; cloning; biotechnology; gene technology.

In this revision pack, you will revise information you’ve studied at AS and A2. You’ll look at one particular living organism, and see how this can be linked to the topics that you’ve already studied.

This is the fourth of five revision packs, covering the A2 syllabus.


  1. To develop your breadth of knowledge (including AS topics) and your ability to apply both AS and A2 knowledge in new contexts.

  1. To help you make links between different topics and modules to encourage synoptic thinking.

Classification (AS-2.3.2)

In the binomial system of naming organisms, spearmint is called Mentha spicata.

What is the “binomial system of classification”? (2 marks)

What are the benefits of this system? (2 marks)

Organisms can be classified into 8 major taxon levels. Mentha spicata is in the kingdom Plantae. State three key features of all the organisms found in this kingdom. (3 marks)

Table 5 shows the full taxonomic classification of Mentha spicata. Fill in all the gaps.

(7 marks)




Table 5

Taxonomic classification of Mentha spicata







Meiosis & Variation (A2-5.1.2)

There are 18 different species of mint, and 11 hybrids. Peppermint (Mentha x piperita) is the best known hybrid. In the plant world, peppermint is the equivalent of a mule, since it is a cross between two distinct species (Mentha aquatica X Mentha spicata) and thus is infertile. It can only be reproduced by taking cuttings.

Chromosome analysis of peppermint has shown that it is polyploid. The plant is triploid (3n), being the product of fertilisation of a diploid gamete (2n) from one parent species and a haploid gamete (n) from the other parent species.
With reference to the “Biological species concept” explain why Mentha x piperita cannot be classified as a true species. (1 mark)

With reference to the events which normally take place in meiosis, explain why Mentha x piperita plants are sterile. (3 marks)

Mentha x piperita plants could be made fertile by chromosome doubling to create a hexaploid plant. Explain how chromosome doubling would make peppermint plants fertile. (2 marks)
Suggest why hexaploid Mentha x piperita plants would produce a higher yield of peppermint oil than triploid plants. (3 marks)

Meiosis & Variation (A2-5.1.2)

Diet & Food Production (AS-2.2.1)

Amongst the 18 mint species and 11 mint hybrids, there are many cultivars of the various mint species and hybrids. Here’s just one example: Mentha sauveolens (apple mint) has a cultivar called pineapple mint. The leaves of apple mint are green; whereas the leaves of pineapple mint are variegated (i.e. they are green with bands of white). As the common names suggest, apple mint leaves smell like apples whereas pineapple mint leaves smell like pineapples.

Suggest how plant breeders used selective breeding/artificial selection to establish a variety of apple mint which smelt like pineapple. (3 marks)

Suggest why, in selecting for a pineapple aroma, plant breeders may have inadvertently selected for variegated leaves. (2 marks)

Some of the novelty mint varieties, such as Mentha avensis (cultivar banana mint) suffer from “lack of vigour”. Suggest why, in selecting for a banana aroma through inbreeding, plant breeders have produced a weakened plant variety. (2 marks)

Meiosis & Variation (A2-5.1.2)

Classification (AS-2.2.1)
Figure 9 shows a cladistic tree showing the phylogenetic relationships of the 18 different Mentha (mint) species. The tree is based on morphology, phytochemicals (such as ingredients of the oils the mint plants produce) and DNA analysis.

Figure 9

Cladistic tree for

Mentha species

Image courtesy of Dr Brian Lawrence

Which species of mint is most closely related to spearmint (Mentha spicata)? (1 mark)

Which two species of mint are the “oldest” species in evolutionary terms? (2 marks)

Is Mentha pulegium more closely related to Mentha cervina or Mentha diemenica? (2 marks)

How do you know?

Cloning (A2-5.2.1)

Mentha species can reproduce sexually (by producing seeds) or asexually (by vegetative propagation). They produce flowers, but also spread themselves by producing horizontal stems called rhizomes or stolons, which form roots to help the plant spread.
State two advantages and two disadvantages of reproducing asexually. (4 marks)

State two advantages and two disadvantages of reproducing sexually. (4 marks)

Write a concluding statement to explain why the survival of any mint species is enhanced by its ability to reproduce both sexually and asexually. (2 marks)

Cloning (A2-5.2.1)

To propagate your mint plants at the beginning of this project, you took cuttings and rooted them. Outline how you could micropropagate your mint plants using tissue culture. (7 marks)

State three advantages micropropagation for large scale plant production. (3 marks)

State three disadvantages micropropagation for large scale plant production. (3 marks)

Biotechnology (A2-5.2.2)

Think about the commercial uses of mint plants, e.g. food and drink, fragrances, etc.

With reference to the definition of “biotechnology”, explain how mint oil production is an example of biotechnology. (3 marks)

The ingredients of the essential oils of mint plants are known to have antibacterial properties. Outline how you would to compare the effectiveness of peppermint oil versus spearmint oil in inhibiting bacterial growth. (5 marks)

Describe three aseptic techniques used. (3 marks)

Gene Technology (A2-5.2.3)

Recently, scientists from Rothamsted Research Station in Hertfordshire have genetically engineered a new variety of wheat which contains a gene isolated from peppermint. The gene codes for a pheromone which both repels aphids and attracts natural predators of aphids such as ladybirds and parasitic wasps. The pheromone produced naturally by peppermint plants mimics the action of a pheromone which aphids produce themselves when they are under threat of predation, and which warns other aphids to stay away to avoid danger.
Aphids are a major pest of cereal crops, causing an estimated £120m worth of damage to cereal crops per year in the UK alone. The Rothamsted scientists say that the new wheat variety could lead to increased crop yield and reduced use of insecticides, which are costly to apply and environmentally damaging.
Anti-GM campaigners disagree. They say that manipulation of plant genomes, such as introducing genes from other plants, could have unpredictable consequences, and there are safety concerns about eating wheat which produces new phytochemicals. They say that, in the long term, aphids could become habituated to the pheromone, and could learn not to respond to it. They also say the peppermint gene might spread into wild grasses by hybridisation.
Scientists from Rothamstead, however, argue that benefits far outweigh the risks. Further information on the project is at
Pick out two suggested benefits and two suggested risks of introducing the pheromone gene from peppermint into wheat by genetic engineering. (4 marks)

Outline the role of Ti plasmid, Agrobacterium tumefaciens and micropropagation in the creation of GM crops such as wheat containing a gene from peppermint. (4 marks)

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