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Flowering plants: 5. (a) Asexual reproduction in flowering plants and (b) The implications to a species of self-pollination & cross-pollination

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(5a) Asexual reproduction in flowering plants

What is the difference between asexual and sexual reproduction in flowering plants?

Sexual reproduction in flowering plants involves the fusion of a male nucleus with a female egg cell.

See (3) Sexual reproduction - fertilisation and the formation of seeds and fruits

In principle, asexual reproduction is simpler than sexual reproduction e.g. a bacteria nucleus splits in two and two new identical bacteria are formed, an example of cloning (genetically identical) from a single parent. This an example of cell division by mitosis.

In the case of plants, a good example is the potato, an important crop for farmers. From a single potato plant, stems grow out into the soil and swell with stored food forming tubers. If the tubers are left in the ground, they will grow into new potato plants, so all the new potatoes are identical and derived from a single parent plant.

The cloning effect can be both positive and negative, e.g. all the plants of the crop might give consistent high yield, but, all the same plants might susceptible to a particular pathogen disease.

(5b) The implications to a species of self-pollination and cross-pollination

Implications of the two modes of pollination

(i) Advantages of self-pollination

The species purity is maintained and seed creation is guaranteed.

Far less pollen grain is wasted because less needs to be created.

Pollination is not dependent on external conditions like wind or pollinators like insects.

No need for elaborate flowers to attract pollinators.

(ii) Disadvantages of self-pollination

Fewer seeds are produced.

New plant varities cannot be produced, much less chance of adaptations developing.

With reduced potential variation in new characteristics, the genetic stock can be weakened, so the species offspring are weakened in the face of changing conditions e.g. climate change or pathogens.

(iii) Advantages of cross-pollination

New varities can be created.

Larger number of viable seeds are created.

The genetic recombination produces a greater variation increasing the more probable survival of offspring i.e. greater resistance to changes e.g. climate change or pathogen attack.

(iv) Disadvantages of cross-pollination

Significant numbers of pollen grains are wasted, only a small fraction complete fertilisation.

Plants widely scattered so pollination must occur over greater distances.

Undesirable genetic traits can be introduced or useful traits eliminated.

Its inefficient to produce large, scented, nectar producing flowers to attract insects.

Keywords, phrases and learning objectives for this part on flowering plants

Be able to describe asexual reproduction in flowering plants including cell division by mitosis. mitosis

Be able to describe, understand and discuss the implications to a flowering plant species of self-pollination and cross-pollination, noting the advantages and disadvantages of these two modes of pollination.



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