(1) Reproduction is defined as a biological process in which every living organism give rise to new organisms similar to themselves.
(iii) Formation of reproductive bodies or units.
Difference between Asexual and Sexual Reproduction
Asexual Reproduction
Asexual reproduction in plants
In flowering plants there are two main types of asexual reproduction:
(a) Agamospermy – The formation of embryo without fertilization and meiotic division. There are three different types of agamospermy:
(i) Diplospory
(ii) Adventive embryony
(iii) Apospory
(b) Vegetative propagation –
(i) Plants belonging to this category propagates by a part of their body other than a seed. The structural unit that is employed in place of seed for the propagation of new plants is called propagule.
(ii) In angiosperms any parts of the plants – roots, stemsand leaves can be used for vegetative propagation.
(5) Following are the asexual reproductive structures:
(a) Zoospores: aquatic fungi, Chlamydomonas
(b) Conidia: Penicillium
(c) Bud: Hydra
(d) Gemmules: sponges
(6) Below given are the vegetative propagation units in plant: (Vegetative propagules)
Runner, rhizome, sucker, tuber, offset, bulb
Sexual reproduction:
Sexual reproduction involves fusion of male and female gametes by the process of fertilization.
Features of sexual reproduction:
(a) The period between birth and sexual maturity is called juvenile phase.
(b) Juvenile phase is also known as vegetative phase in plant.
(c) Oestrus cycle: The cyclical changes during reproduction in non-primate mammals like cows,sheep, rats, deers, dogs, tiger etc.
(d) Menstrual cycle: The cyclical changes during reproduction in primate mammals like monkeys,ape, and humans.
(e) Seasonal breeders: The reproductive cycle takes place only in favorable seasons as in wild animals.
(f) Continuous breeders: They are reproductively active throughout their reproductive phase.
(g) Gametogenesis is the process of gamete formation.
(h) Isogametes are one of a pair of conjugating gametes, exhibiting no differences in form, size, structure, or sex.
(i) Gametes produced of two morphologically distinct types are called heterogametes.
(j) Male gamete is called antherozoid or sperm and the female gamete is called ovum or egg.
Sexuality in organism:
(a) Plants having only one sex organ is called heterothallic or dioecious.
(b) Plants having both male and female sex organ called homothallic or monoecious.
(c) In flowering plants, the unisexual male flower is staminate (bearing stamens), while the female is pistillate (bearing pistils).
(d) Animals having one type of reproductive system are called unisexual.
(e) Animals having both male and female reproductive system are called hermaphrodite or bisexual.
Cell division during gamete formation:
(a) Gametes in all heterogametic species are of two types namely male and female.
(b) Gametes are always haploid irrespective of parent’s ploidy.
(c) Gametes are produced by a haploid parent by mitotic division.
(d) Gametes are produced by a deploid parent by meiotic division.
(e) In diploid organisms specialized cells called meiocytes undergo meiosis to produce haploid gametes.
Gamete transfer:
(a) Male and female gamete must be physically brought together to facilitate fusion called fertilization.
(b) In most cases female gametes are non-motile , male gametes are motile.
(c) In case of few fungi and algae, both male and female gametes are motile.
(d) In most cases the medium for gamete transfer is water.
(e) Number of male gametes are produced is several thousand times the number of female gametes produced to compensate the loss during transfer.
Fertilization:
The process of fusion of male and female gamete is called fertilization or syngamy.
Sexual Reproduction in Flowering Plants
Flower
Flower is a modified stem which functions as a reproductive organ and produces ova and/or pollen
(1) Structure of the flower:
The flower is commonly borne on short or long stalk called the pedicel. It has an upper swollen region known as receptacle (thalamus or torus).
(2) Parts of a flower:
A typical angiospermic flower consists of four whorls of floral appendages attached on the receptacle: calyx, corolla, androecium and gynoecium.
(i) Calyx: It is the outermost whorl of the flower. It is composed of leaf like green sepals. The sepals are essentially green in colour but in some cases they are coloured like petals. Such a condition of calyx is called petaloid.
(ii) Corolla: This is the second whorl of the flower and consists of a number of petals. Petals are generally brightly coloured and sometimes fragrant which make the flower to become attractive.
(iii) Androecium: It is the third whorl of flower and is the male reproductive organ consisting of stamens. Each stamen is made of filament and anther. The filament supports anther at its tip.
(iv) Gynoecium: This is the last and the fourth whorl of flower and is the female reproductive organ of the flower. It occupies the central position on the receptacle and composed of ovary, style and stigma and the component parts are called carpels.
(3) Functions of a flower
(i) Flowers are modifications of shoot to perform the function of sexual reproduction.
(ii) Flowers of most of the angiosperms are shaped variously to help diverse modes of pollination.
(iii) Flowers provide seat for germination of pollen, development of pollen tube, formation of gametes and fertilization.
(iv) The ovary part of the carpel gets transformed into fruit and the ovules are transformed into seeds after fertilization.
(v) Some floral parts like calyx and various modifications in ovaries help in the dispersal of fruits and seeds.
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