Extensive notes tailored to the specification points for OCR 2015 (new) Spec, needed for both the AS and A2 components.
My revision from then got me an A* equivalent raw mark last year, and I received an A* at A2.
They contain as much if not more information than your textbook, in a much more c...
(a) (i) Natural clones in plants and the production of natural clones for use in horticulture.
● To include examples of natural cloning and the methods used to produce clones (various
forms of vegetative propagation).
Plants can naturally clone themselves using vegetative propagations—reproduction from the
vegetative part of the plant, usually in an over-wintering organ, rather than specialized
reproductive structures. Totipotent meristematic cells in the tissues that grow allow vegetative
structures to develop into complete plants, genetically identical to the one from which it
propagated.
Bulbs are an overwintering mechanism for many perennial monocotyledonous plants, consisting
of an underground stem which grow a series of fleshy leaf bases and multiple apical buds, which
can grow into more than one separate plants. Stem tubers are a type of underground stem, found
on potatoes which are a storage organs, but also grow shoots. Many plants grow horizontal
stems, runners or stolons above ground or rhizomes below ground. They root and can grow new
plants.
Vegetative propagation is an advantage because if the conditions for growth are good for the
parent, then they will be good for the offspring; cloning is very rapid so the population can
increase quickly; reproduction can be carried out without two plants; and it helps plants to
survive non-growth seasons. However, the offspring may become overcrowded, there will be no
genetic variation and selection is not possible; if the environment changes, the whole population
may be susceptible.
Vegetative propagation is used in horticulture in order to cheaply produce new plants, which will
display desirable characteristics. Splitting up bulbs, removing plants from runner, and cutting up
rhizomes all increase plant number using vegetative propagation.
(ii) How to take plant cuttings as an example of a simple cloning technique.
● Dissection of a selection of plant material to produce cuttings.
In order to artificially propagate a plant, a section containing meristematic cells must be planted.
A stem can be cut at the nodes and placed in a favourable condition with a hormone rooting
powder containing auxins to promote rooting in good conditions. This is advantageous because
it is much faster to propagate plants than to plant from the seeds and also guarantees quality of
plants because they will be genetically identical from the stock the cuttings are taken from.
However, there will be a lack of genetic diversity which could make them susceptible to a
disease, pests or changes in abiotic factors.
(b) (i) The production of artificial clones of plants by micropropagation and tissue culture
Commercially, plants are often propagated through micropropagation—growing large numbers
of new plants from meristem tissue taken from a sample plant, using a tissue culture—growing
new tissues, organs, or plants from certain tissues cut from a sample plant. Micropropagation
involves taking a small piece of plant tissue, an explant, and using plant growth hormones to
stimulate growth, eventually into a complete new plant, genetically identical to the plant from
which the explant was cut.
Plant tissue containing meristematic cells are cut into explants. The explants are sterilised using
dilute bleach, alcohol or sodium dichloroisocyanurate. The explants are placed in a sterile
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