Notes of ch how the organism reproduce science 0
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There are two main types of reproduction in living organisms. Asexual reproduction and sexual reproduction. Asexual reproduction :- is reproduction in which new individuals are produced from a single parent. Sexual reproduction :- is reproduction in which two individuals are involved to produce a new individual. Asexual reproduction is of different types. They are:- fission, budding, regeneration, fragmentation, spore formation, vegetative propagation etc.
i) Fission :- Fission is an asexual reproduction by which a unicellular organism divides and forms two or more new individuals. It is of two types. Binary fission and Multiple fission. i) Binary fission :- An organism divides and forms two individuals. First the nucleus divides and forms two nuclei. Then the cytoplasm divides and forms two daughter cells. Eg:- Amoeba, Paramaecium etc. ii) Multiple fission :- One organism divides into many daughter cells. Eg.Plasmodium.
ii) Budding :- A bud like projection is formed on the body of the organism. The bud then develops into a new individual.Eg:- Hydra, Yeast etc.
iii) Regeneration :- In this method a part of the body if the organism if cut or broken can develop into a new individual. Eg :- Hydra, Planaria, Star fish etc.
iv) Fragmentation :- The body of a simple multicellular organism breaks up into smaller pieces on maturation and each fragment develops into new individuals. Eg :- Spirogyra.
v) Spore formation :- Structures called sporangia produce tiny cells called spores. When the spores come in contact with a moist surface, it develops into new individuals. Eg :- Rhizopus , Mucor, Penicillium etc.
vi) Vegetative propagation :- New plants are produced from the vegetative parts of the plant like root, stem or leaf.
a) Sexual reproduction in flowering plants :- a) Reproductive parts of a flower :- The stamen and pistil are the reproductive parts of the flower. Stamen is the male reproductive part. It produces pollen grains in the anther which contains the male germ cell (male gamete). Pistil is the female reproductive part. It produces ovules in the ovary which contain the female germ cell (female gamete).
b) Pollination :- The transfer of pollen grains from the anther to the stigma of a flower is called pollination. Pollination takes place by insects, wind, water etc. Self pollination Cross pollination
c) Fertilisation :- After the pollen grain is transferred to the stigma it produces a pollen tube which passes through the style and enters the ovary and ovule. In the ovule the male germ cell (male gamete) fuses with the female germ cell (female gamete) to form a zygote. This process is called fertilisation.
vii) Reproduction in human beings :- a) Male reproductive system :- The male reproductive system consists of a pair of testes which produces the male reproductive cells called sperms and the hormone testosterone. It is contained in sac like structures called scrotum. From each testis arises a tube called vas deferens. It joins into the urethra. The urethra is enclosed in a muscular organ called penis. It has an opening called genital pore. The seminal vesicles and prostate glands produce fluids which provide nutrition and help in the movement of the sperms.
viii) Female reproductive system :- The female reproductive system consists of a pair of ovaries which produces the female reproductive cells called ova or eggs and the hormone oestrogen. Above the ovaries are tubes called oviducts or fallopian tubes. The two oviducts unite into a bag like structure called uterus. The uterus has opening called vagina. Human ovum (egg)
ix) Fertilisation in human beings :- During sexual intercourse the sperms from the male enters into the vagina of the female. The sperms reaches the oviduct. One sperm fuses with an egg and forms a zygote. The zygote then gets implanted in the uterus. The zygote then starts dividing to form an embryo. The embryo gets nutrition from the mother’s blood through the placenta. The development of the child takes nine months and then the child is born.