Reason: fertilisation can only occur if the ovum and sperms are carried simultaneously.

(a) polythene packets
(b) vegetable peels
(c) Dry cells, blades
(d) aluminium foils
(e) Pieces of glass etc. Polythene packets can be avoided by using cotton bags, jute bags etc.(or any other waste with reason)

For explanation refer text book.
a. Micro-injection
b. Biolistics

Zygote is formed by fusion of male gamete (n) and egg cell (n), hence diploid (2n).
Primary endosperm nucleus is formed by the fusion of two polar nuclei or secondary nucleus (n + n) and male gemete (n), hence triploid (3n).

The secretion of the acrosome help the sperm enter into the cytoplasm of ovum through zona pellucida and the plasma membrane, this induces the completion of second meiotic division of the secondary oocyte, forming second polar body and a haploid ovum, soon the haploid nucleusof the sperm and that of the ovum fuse tdgether to form a diploid zygote.

Sarcoma. Cancer of the tissues derived from mesoderm such as connective tissue  (bones, cartilages and tendons), lymphoid tissue and muscles is termed sarcoma 

1. SO₂ is released into atmosphere from various factories which use ores of Cu, Zn, Pb, Ni and Fe. The sulphur present in these ores is oxidised and SO₂ is given out. Besides this vehicle exhaust, coming of coal and oil refineries also given out SO₂.
2. SO₂ have harmful effects on man and plants. High concentation of SO₂ destroys chlorophyll in plants (Chlorosis disease), lysis of the cell occurs, parts of the plant are destroyed and it may result in the death of the whole plant (Necrosis). Even if death does not occur, It results in prevention of growth and production, plasmolysis and various metabolic diseases.

Virulence depends upon:
1.The ability of an organism to invade the host and grow in its tissues.
2.Its ability to produce toxins or poisons.

Ornithophily. Pollination carried out by small birds is called ornithophily. e.g. Australian plants.
Chiropterophily. It is pollination by bats. e.g. Sausage tree.​​​​​​​
Marcophily.  Snails also bring pollination, it is termed malacophily.

MEthanogens are found in
(i) the anaerobic sludge
(ii) rumen of cattle
(iii) marshy places
(iv) flooded rice fields.

Gause's competitive exclusion principle states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated, e.g.
On the rocky sea coasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal area and excludes the smaller barnacle, Chathamalus from that zone

(i) Productivity
(ii) Decomposition
(iii) Energy flow
(iv) Nutrient cycling

1. The RNA will resemple the coding strand.
2. The RNA transcribed on the template strand will be complementary to that.
3. The coding strand is also complementary to the template strand and hence RNA will resemple the coding strand of DNA
4.The coding strand will have deoxyribose sugar and thymine but the RNA will have ribose sugar and uracil.

1. Since DNA helix runs continuously for one end to the other in a chromatid in a highly coiled manner, any deletion or duplication / insertion of a segment of DNA can alter the chromosome.
2. Since genes are present in the chromosomes, such alteration(s) in the chromosomes lead(s) to abnormalities or aberrations.

In male partner the process is called vasectomy in which a small part of the fallopian tube is removed or tied up through a small incision in the abdomen.
In female partner, the process is called tubectomy in which a small part of the fallopian tube is removed or tied up through a small incision in the abdomen.
However, their possible ill effects like nausea,abdominal pain, breakthrough bleeding, irregular menstrual bleeding or even breast cancer, should not be totally ignored. Still on the counterpart, these methods have significant role in checking growth of population.

In the absence of fertilisation, the corpus luteum degenerates.
It causes dis integration of the endometrium of uterus, leading to menstruation

1. In haploid organisms, showing haplontic life cycle, gamete formation involves only mitosis; the diploid zygote formed by the fusion of two haploid gametes, undergoes meiosis (zygotic meiosis).
2. In diploid organisms, showing diplontic or haplodiplontic life cycle, gamete formation involues meiosis (gametic meiosis) and haploid gametes are formedl; the diploid zygote undergoes mitosis to form diploid individuals.

1. Since geitonogamy involves two different flowers of the same plant, it is genetically similar to autogamy; both autogamy and geitonogamy do not result in genetic variation in the progeny.
2. Geitonogamy and cross-pollination involve different flowers and a pollinating agent.