(a) Contraception is an artificial methods or other techniques mainly used to prevent pregnancy as a consequence of sexual intercourse.
Methods of Contraception can be :
(i) Barrier Method : This method involves putting up a barrier between the male and the female sex cells (sperms and ova). It blocks the sperms from reaching the ovary, thus preventing fertilisation. The barrier method can be used by both men and women.
Women could use items like the contraceptive sponge, diaphragm, cervical shield or cervical cap to prevent the sperm from reaching the egg. The barrier method in males involves the use of male condoms.
(ii) Hormonal Method : The hormonal method of birth control interferes with the hormonal balance in a woman's body in order to hamper fertilisation, ovulation or fertilised egg implantation. It could be done with the help of contraceptive pills, estrogen and progestin-releasing patches or vaginal rings. Birth control injections are also available now-adays.
(b) Bacterial infections such as gonorrhoea and syphilis, and viral infections such as warts and HIV-AIDS can be sexually transmitted.
(c) Two advantages of using condom are :
(i) Condom for the penis during sex helps to prevent transmission of many infections to some extent and it is highly effective against the most dangerous of sexually transmitted infections-HIV, the virus that causes AIDS.
(ii) The sexual act always has the potential to lead to pregnancy. Condoms provide a mechanical barrier so that sperm does not reach the egg and are also effective against unintended pregnancy.
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(b) Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals. This process is known as budding. Bud formation is a result of cell division. Then this bud enlarges and receives a nucleus from the parent. While attached to the parent, this bud becomes matured. Later it detaches from the parent cell and becomes a new individual which is genetically identical to its parent. In some organisms, these buds can remain attached to the parent cell for a long time until a chain of buds develops. This resulting chain of buds is known as pseudomycelium.In multi-cellular organisms with relatively simple body organisation for example Spirogyra, simple reproductive methods can work. The body simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals. This process is known as fragmentation Fragmentation is a type of asexual reproduction which occurs in multicellular organisms. These individuals are genetically identical to each other and to parent.Fragmentation is commonly seen in flatworms, marine worms, algae, jellyfish, starfish, fungi and other echinodermata. Fragmentation is the simplest method of reproduction in fungi. Small fragments of the fungal thallus can be separated from the mother thallus and grow into new fungal thalli. Fragmentation produces clones of the original organism. Hence, it is a common type of vegetative propagation method in plants
(c) There are many plants in which parts like the root, stem and leaves develop into new plants under appropriate conditions. Vegetative propagation is used in methods such as layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes. Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds. Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds. Another advantage of vegetative propagation is that all plants produced are genetically similar enough to the parent plant to have all its characteristics.