Science Write notes.

(i) Excessive growth of population within shortduration is called as population explosion.
(ii) Due to population explosion we have to face problems like unemployment, decreasing per capita income and increasing loan, stress on natural resources etc.
(iii) There is only one solution for all such problems and it is population control.
(iv) Population control can be achieved by family planning.

(i) There are various problems in sperm production in case of many men like absence of sperms, slow movement of sperms etc.
(ii) So as to have children in case of such couples, new concept of sperm bank has been introduced. This concept is similar to blood bank.
(iii) Semen ejaculated by the desired men is collected after their thorough physical and medical check- up and stored in the sperm bank.
(iv) As per the wish of the needful couple, oocyte of woman of the concerned couple is fertilized by IVF technique using the semen from the sperm bank.
(v) Resultant embryo is implanted in the uterus of the same woman.
(vi) Name of the semen donor is strictly kept secret as per the law.

(i) Some women have problems in implantation of embryo in uterus.
(ii) Such women can take the help of the modern remedial technique called as surrogacy.
(iii) In this technique, oocyte is collected from the ovary of the woman having problem in implantation in uterus.
(iv) That oocyte is fertilized in test-tube with the help of sperms collected from her husband.
(v) The embryo formed from such fertilization is implanted in the uterus of some other woman having normal uterus.
(vi) Such a woman, in whose uterus the embryo is implanted is called as surrogate mother.

(i) Transfer of pollen grains from the anther to the stigma is called as pollination.
(ii) Pollination occurs with the help of abiotic agents (wind, water) and biotic agents (insects and animals).
(iii) When pollination involves only one flower or two flowers of the same plant, it is called as self- pollination
(iv) If it is involves two flowers borne on two plants of the same species, it is called cross-pollination.

(i) Wall lizard breaks up and discards some part of its tail in emergency.
(ii) Discarded part is regenerated after a period. This is an example of limited regeneration.
(iii) However, under certain situation, an animal- planaria breaks up its body into parts and thereafter each part regenerates remaining part of the body and thus new planaria are formed.
(iv) This is called regeneration.

(i) This type of asexual reproduction occurs in multicellular organisms.
(ii) In this type of reproduction, the body of parent organism breaks up into many fragments and each fragment starts to live as an independent new organism.
(iii) It is seen in algae like spirogyra and sponges like sycon.
(iv) When plenty of water and nutrients are available to spirogyra, its filaments grow up very fast and break up into small fragments.
(v) Each fragment starts to live independently as a new spirogyra fiber.
(vi) Similarly if the body of Sycon breaks up accidentally into many fragments, each fragment develops into a new sycon.

(i) Asexual reproduction by multiple fission is performed by amoeba and other similar protists.
(ii) Amoeba stops the formation of pseudopodia and thereby its movements whenever there is lack of food or any other adverse condition.
(iii) It becomes rounded and forms a protective covering around plasma membrane. Such encysted amoeba or any other protist is called as cyst.
(iv) Many nuclei are formed by repeated nuclear division in the cyst, followed by cytoplasmic division and thus many amoebulae are formed.
(v) They remain encysted till there are adverse conditions.
(vi) Cyst breaks open on arrival of favourable conditions and many amoebulae are released.