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.
Aims
1.
To develop your breadth of knowledge (including AS topics) and your ability to apply
both AS and A2 knowledge in new contexts.
2.
To help you make links between different topics and modules to encourage
synoptic thinking.
2
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)
Eukaryotae
Kingdom
Plantae
Magnoliophyta
Table 5
Taxonomic classification of
Mentha spicata
Magnoliopsida
Lamiales
Lamiaceae
Genus
Species
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 4
3
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)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 4
4
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)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 4
5
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?
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 4
6
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)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 4
7
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)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 4
8
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)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 4
9
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 http://www.rothamsted.ac.uk/Content-Section=AphidWheat.html
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)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 4