South Tuen Mun Government Secondary School Biology Revision Note 8 Asexual reproduction – only one parent is required, do not involve gametes, the offspring is identical genetically as the parent and to each other Sexual reproduction – normally two sexes : always involve fusion of male gamete and female (fertilization), genetic variation in offspring is produced Vegetative propagation (asexual reproduction in flowering plant) - by perennating organ of flowering plant (annual plant) e.g. rhizome, corm, bulb, stem tuber Principle of vegetative propagation : In winter, parent plant dies leaving a food storage organ ↙ ↖ In spring, the storage organ supplies The leaves make food by photosynthesis, some food food for the growth of root and →→→→ are transported to make the new storage organ green leaves. Some examples of flowering plant Food storage organ Ginger, lotus rhizome - horizontal underground stem Gladiolus corm - vertical underground stem Onion, Daffodil bulb - fleshy scale leaf Potato stem tuber - underground branch of a stem Advantage of vegetative propagation: (1) A very fast way of reproduction – many offspring can be produced at a short period of time (2) Identical offspring - good characters of parents are certainly inherited by offspring (3) It allows the organisms to survive very bad condition e.g. cold winter (4) It does not need any external agent e.g. wind, insects Disadvantage of vegetative propagation: (1) Overcrowd – strong competition of space, water and light (2) No genetic variation – any change in the environment or disease can destroy the whole population (3) Inherited diseases of parents or unfavourable characters are transmitted to the offspring Sexual reproduction in flowering plants Structure and function of flower :

Anther – for the formation of pollen grains which carry the male gamete, male gametes are produced by meiotic cell division [Note : **pollen grains is not the same as male gametes] Ovary – for the formation of ovule which carry the female gamete / egg / ovum, the female gametes are produced by meiotic cell division [Note : ovule is not the same as female gamete / egg / ovum] The ovary develops into the fruit after fertilization Pollination – the transfer of pollen grains from anther to stigma Advantage of cross-pollination: more genetic variation, so the offspring can survive better in a changing environment. Insect-pollinated flowers Wind-pollinated flowers Petals large, colourful, scented to attract insects. Has of Petals small and white. insect guide. Anther and stigma are inside the petal. Anther and stigma are out of the petal, anther exposed so pollen grains can be blown away easier; stigma exposed to catch pollen grain easier. Stigma sticky to catch pollen grain. Stigma feathery with a large surface area to catch pollen grain. Has nectar as food for insect. No nectar. Pollen grains have rough coat - easily stick to the body Pollen grains are small and light - easily blown away, of insects. larger in number.

Fertilization When pollen grain falls on the stigma of the same species, the sugary solution produced by the stigma stimulates the pollen grain to germinate and develop a pollen tube.

The pollen tube carries the male gamete towards the ovary. The male gamete enters the ovule and fuses with the egg (female gamete) to form the zygote (fertilized egg).

*Significance of fertilization :  to restore original diploid number of chromosomes of the parent plant  due to independent assortment in meiotic cell division and random fertilization, the genetic materials of the offspring are genetically different, genetic variation increases the chance of survival of the species in a changing environment Fruit - developed from the flower after fertilization Stamen, style, stigma – wither and fall off Ovary wall - forms the juicy part of fruit Ovule - develops into seeds Integument of ovule - develops into protective seed coat Fertilized egg (zygote)  embryo and endosperm, Embryo  cotyledon (子葉), plumule (future shoot), radicle (future root); in some plants, cotyledon develops into a food storage part of the seed, the food is used for germination. The functions of fruit: (1) to protect the developing embryo and (2) to help seed dispersal Seed In germination, the radicle develops into root and plumule develops into shoot. The functions of seeds : (1) to protect the embryo before germination: to prevent excess loss of water; to prevent the entry of foreign particles; and it can remain alive under very bad condition (2) to develop into a new plant (3) to help dispersal of the species Dispersal - the distribution of offspring to other places (a) Wind dispersal: (1) Fruit is light so that it can easily blown away by wind. (2) Fruit is dry / non juicy. Juicy part is not needed. (3) Fruit has a large surface area so that it can be blown by wind easily. (4) Seeds are tiny and light so they can be easily blown away by wind. (5) Seeds have large surface area e.g. wings in pine (non-flowering plant), hair in dandelion so that it can be blown away by wind easily. (b) Animal dispersal (1) Some fruits are colourful to attract animals. (2) Some fruits are fleshy, juicy and sweet with good smell to attract animals as tasty food (3) Some plants have small, non tasty food. These seeds have hooks or sharp hair for attachment onto the body of animals. (4) For plants with juicy fruit, some seeds have thick coat to resist against the digestive juice. Some fruits develop stone with large seeds which is not eaten by animals. Importance of fruit and seed dispersal: prevents overcrowdedness and exploit more living area  less competition of space, water and light