Because many of these parts of plants sometimes contain stored food in a concentrated form, they may have another function in the plant's life-cycle: perennation, i.e. survival through the unfavourable months of the year. It also explains why we find it easy to use some plants ("vegetables") for food.
What chemical form will the stored food be in?
What is the name of the process of nuclear division which takes place during the growth of these parts which then function independently?
List at least 5 types of structure which are used in asexual reproduction.
> runners > tubers > rhizomes
> corms > bulbs > plantlets etc
Which example of vegetative reproduction does not involve storage of food as well?
Which examples of vegetative reproduction do not contribute to Man's food supply?
> iris, gladioli
The same principle can also be used by Man in order to grow more plants, perhaps starting from only one plant, a process called artificial propagation. This is especially useful if you want to produce many copies of a plant which has some desirable characteristics, such as flowers of a different colour, or fruits with a particular taste or quality.
One fairly easy way of doing this is to take cuttings of a plant, by removing part of a plant, which then eventually grows into a whole plant on its own.
Which parts of a plant can be used for cuttings?
> shoot (tip) > root > leaf
> It is vigorous, probably with no virus or other infection
What is the importance of selecting a "non-flowering" shoot?
> All resources go into growth, they are not diverted into seeds, etc
Why are the lower leaves stripped off?
> They will eventually be under the soil, and may rot in water
> This will reduce water loss by transpiration
What is the reason for trimming below a leaf node?
> This is where roots will (most likely) grow out from.
Cuttings may be placed in water until roots have formed, or directly into a pot of soil, when they are usually covered with a polythene bag and kept out of direct sunlight.
What is the purpose of the polythene bag?
> To reduce water loss by evaporation/transpiration (also warmer, and protects against pests)
Why is it unnecessary if a cutting is put directly into water?
> Cut surface give xylem direct access to water
Why not keep them in complete darkness?
> The plant needs light to photosynthesise, make organic food for growth)
Grafting is a somewhat similar process used by gardeners to propagate plants, especially fruit trees. A piece of one plant (it could be as small as a bud) is joined onto the top of another plant, and it continues to grow and eventually produce flowers and fruit. Sometimes more than one variety of apple, for instance, may be grafted onto one tree.
The part onto which the graft is attached is called the rootstock, and it may have some desirable feature, such as strong roots, or resistance to disease, and some apple trees are specially "dwarfed" in this way to make them easier to harvest! The rootstock is not expected to produce flowers or fruits, so its own buds are removed.
"Suckers" are long thin shoots forming as outgrowths from the root regions of fruit trees, especially if damaged during mowing of grass in orchards.
Why do you think these are looked on as undesirable?
> They divert the effort of plant growth, taking nutrients etc away from fruit formation
> The rootstock may be a different (unsightly/unproductive?) variety
Why do you think damage to the roots causes suckers to form?
> It is like taking root cuttings! Dormant side buds may be stimulated.
Suppose that you have two varieties of the same species of plant: one with brightly coloured flowers but no scent, and the other with poorly coloured flowers but a good scent.
How would you go about the process of combining the bright colour with the scent in one plant? Give some details of the practicalities of the method. (Not necessarily in this unit)
> Cross-pollinate variety A with B (and B with A?). Prevent self-pollination, or access by other pollen (remove stamens/ shield flowers with paper bags?). Collect seeds, germinate them and grow on seedlings. Screen the resulting plants. Some will probably have neither of the desired characteristics! THIS IS SEXUAL REPRODUCTION.
When you are successful, how would you make more plants of your new variety, so as to sell for a vast profit?
> Take cuttings or propagate using some other form of ASEXUAL REPRODUCTION.
List some characteristics that would be useful, in combination with others, in a crop plant, i.e. one which is used in the production of food for Man.
> Heavy yield > High in protein > Good flavour
Others: pest/disease resistance, easy to harvest, withstands weather, e.g. drought resistance/ short so not easily blown over, enhanced vitamin/mineral content etc.