Revising A-level Biology: Plants ‘r’ mint
Revision pack 5: Maintaining biodiversity and populations; cell
structure and cell membranes; diet, food production and
ecosystems; plant responses; animal behaviour; animal responses.
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 fifth 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.
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
Maintaining Biodiversity (AS-2.3.4)
Populations (A2-5.3.2)
Conservation of biological resources can be of economic benefit, both directly and
indirectly…there is potential to make a mint out of mint!
Suggest the potential economic benefits of conserving an area where:
(a) A new variety of an existing mint species is discovered.
(2 marks)
(b) A new mint species is discovered. (1 mark)
Outline two ways in which in-situ conservation could maintain mint biodiversity.
(2 marks)
Outline two ways in which ex-situ conservation could maintain mint biodiversity.
(2 marks)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
Cell Structure (AS-1.1.1)
Cell Membranes (AS-1.1.2)
Figure 4
Diagram of trichome on a mint leaf surface
www.plantphysiol.org/content/136/4/4215/F1.full
Figure 5
Electron micrograph of a mint trichome
www.sciencedirect.com/science/article/pii/S1369526602002
649
The essential oils produced by mint plants are secreted by specialised cells and stored in circular
structures called trichomes The natural role of mint oils is to inhibit the growth of other competitor
plant species (allelopathy), and to protect the mint plants from attack by insects and pathogens
such as bacteria and fungi. Many or the constituent ingredients of these oils are known to disrupt
cell membranes, thus making them more ‘leaky’.
Explain which type of electron microscope was used to take the picture in Figure 5. (2 marks)
Calculate the actual width of the storage cavity in Figure 5, given that the magnification of the
electron micrograph is X2000. Give your answer in µm. (2 marks)
State two advantages and two disadvantages of using electron microscopes compared to using
light microscopes. (4 marks)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
Suggest which components of cell membranes could be altered or damaged by mint oils.
(1 mark)
Suggest why the cell surface membranes of plants, insects, bacteria and fungi are all equally
susceptible to damage by mint oils. (1 mark)
Suggest how mint oils could interfere with biochemical reactions such as respiration and
photosynthesis. (3 marks)
Suggest why mint plants store the oils in specialised trichomes, rather than throughout the mint
plant. (2 marks)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
Diet & Food Production (AS-2.2.1)
Ecosystems (A2-5.3.1) & Populations (A2-5.3.2)
Peppermint, spearmint and cornmint are grown on a
vast agricultural scale in North America, China and
India. In recent years, farmers such as Sir Michael
Colman have re-established peppermint as a
commercial crop in the UK. Figure 6 shows one of
his peppermint fields.
Peppermint and spearmint thrive in sunny but moist
soil preferably in a temperate climate, whereas
cornmint prefers a subtropical climate. Mint plants
are susceptible to attack by a wide range of pests
(e.g. beetles, nematodes & weevils) and pathogens
(e.g. mildew), as well as competition from weeds
such as thistles and buttercups.
Figure 6
Peppermint field at Summerdown Farm
in Hampshire, UK
Image courtesy of Sir Michael Colman
Mint plants occupy the first trophic level in a food chain.
(a) What term is used to describe organisms which occupy this tropic level?
(b) Name the type of nutrition used by organisms of this trophic level.
(1 mark)
(1 mark)
Only a small percentage of the light energy in sunlight which hits the surface of mint plants is used
in photosynthesis. State three ways in which light energy is “lost” at this stage.
(3 marks)
Distinguish between gross primary productivity and net primary productivity. (2 marks)
When a farmer harvests the mint plants, which of these is he or she harvesting? (1 mark)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
Explain how each of the following farming practices helps to increase primary productivity:
Herbicides
(2 marks)
Pesticides
(2 marks)
Irrigation
Fungicides
*
(2 marks)
(2 marks)
Crop rotation with legumes (2 marks)
Many mint species grow in damp, marshy places alongside rivers, streams and ponds. A gardener
planted Mentha suaveolens and Mentha aquatica in a wet area of his garden. Initially, both
species thrived, but after five years, only one of the two species remained.
What type of competition has occurred here? Explain.
(2 marks)
What important population concept is illustrated by eventual loss of one species?
Why has it happened?
(3 marks)
Describe a method that could be used to study the abundance of Mentha suaveolens in the wild,
in an area where the plant is uniformly distributed.
(4 marks)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
Plant Responses (A2-5.4.1)
When you took your original mint cuttings from the parent plant, you were instructed to remove the
apical bud and to dip the base of the shoot in a rooting powder containing auxins.
With reference to the effects of auxins, suggest why:
(a) the apical bud was removed. (3 marks)
(b) the shoots were dipped in rooting powder. (1 mark)
Over the coming months, you will have to make sure your mint plants get an adequate supply of
light.
With reference to auxins and tropisms, explain what would happen to your mint plants if they were
illuminated only from one side and why.
(3 marks)
How does this tropic response help the plant to avoid abiotic stress?
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
(2 marks)
Animal Behaviour (A2-5.4.3)
Many of the phytochemicals produced by mint plants have a direct toxic effect on insects and
other primary consumers which eat mint plants, and so are classed as natural pesticides.
However, peppermint plants (Mentha x piperita) have evolved an additional and more indirect
means of protection. They secrete a pheromone which is given off by the peppermint plant leaves,
which both repels aphids and attracts natural predators of aphids such as ladybirds and parasitic
wasps.
The pheromone 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. Note
that natural predators have evolved to respond to this pheromone, so that although it acts as a
warning to other aphids to keep away from predators, it actually attracts predators too!
The pheromone produced by peppermint is released in minute quantities. It deters aphids when
there is no real danger, and attracts aphid predators so that any aphids which are present are
more likely to get eaten. In short, it protects the plant.
Production of the aphid pheromone by peppermint plants is finely tuned. With reference to
habituation, suggest whether or not increased production of the pheromone would lead to
increased or decreased damage by aphids. Remember, the pheromone is not actually toxic to
aphids. (5 marks)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
Animal Responses (A2-5.4.2)
Peppermint oil is said to relieve a wide range of human ailments. The oil is extracted from Mentha
x piperita by steam distillation. It is comprised mainly of L-menthol, a volatile organic compound
which has a cooling effect the skin. Peppermint oil helps clear the nasal passages in people
suffering from respiratory tract infections; it has antibacterial properties which help to freshen
breath and it even helps remove head lice.
There is some evidence that peppermint oil eases stomach and bowel spasms by relaxing
muscles in the alimentary (digestive) tract and so may be effective in treating of IBS (irritable
bowel syndrome).
If the claimed effects of peppermint oil on the human digestive system are true, suggest which
type of muscle peppermint helps relax. (1 mark)
Some researchers hypothesise that peppermint helps relax muscles by inhibiting the release of
calcium ions in muscle cells. With reference to the sliding filament theory, explain why inhibition of
calcium ion release would prevent muscle contraction.
(3 marks)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5
Animal Responses (A2-5.4.2)
Carvone is an organic compound which exists in
two forms called R-carvone and S-carvone.
As shown in figure 7, the two forms of carvone
are mirror images of each other (they are called
enantiomers).
R-carvone is produced by spearmint plants
(Mentha spicata) whereas S-carvone is produced
by caraway plants (Carum carvi).
Figure 7
Structures of R-carvone and S-carvone
R-carvone and S-carvone are thought to bind to different olfactory receptors in the nose. The brain
interprets R-carvone as a minty smell whereas S-carvone is interpreted as a more spicy smell.
Some people cannot differentiate between these two smells!
Suggest why R-carvone cannot bind to an S-carvone olfactory receptor, and why S-carvone
cannot bind to an R-carvone olfactory receptor (think about hands fitting into gloves!).
(2 marks)
20% of people cannot differentiate between the smells of R-carvone and S-carvone (these people
perceive both as smelling like spearmint). Suggest whether these people:
(a) Lack R-carvone receptors
(b) Lack S-carvone receptors
(c) Possess S-carvone receptors with an altered shape which bind to both R-carvone & S-carvone.
(d) Possess R-carvone receptors with an altered shape which bind to both R-carvone & S-carvone.
(e) A combination of (a) and (c)
(f) A combination (b) and (d)
Briefly, explain your choice.(2 marks)
Science & Plants for Schools: www.saps.org.uk (2013)
Revising A-level biology – revision pack 5