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

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 twoways in which ex-situ conservation could maintain mint biodiversity. (2 marks)

Cell Structure (AS-1.1.1)

Cell Membranes (AS-1.1.2)

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 inµm. (2 marks)

State two advantages and two disadvantages of using electron microscopes compared to using light microscopes. (4 marks)

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)

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.

Mint plants occupy the first trophic level in a food chain.

(a) What term is used to describe organisms which occupy this tropic level? (1 mark)

(b) Name the type of nutrition used by organisms of this trophic level. (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)

Explain how each of the following farming practices helps to increase primary productivity:

Herbicides (2 marks)

Pesticides (2 marks)

Irrigation (2 marks)

Fungicides (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)

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? (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)

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)

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).

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: (2013)

Revising A-level biology – revision pack 5