Difference between pollination and fertilization: Transfer of pollen grains from anther to stigma is called pollination. On the other hand, fusion of male and female gametes is called fertilization. Pollination is a physical process in which movement of pollen grains are attained by certain physical factors. Fertilization is a biological process. Ovary is the site of fertilization and embryo is the product of fertilization.

The following figure shows fertilization in plant:

Gamete is formed as a result of meiosis in gametogenetic cells. Zygote is formed after fusion two different kinds of gametes. Different types of gametes are formed by different parents. Zygote is formed in the female reproductive part only.

Role of gamete in sexual reproduction: Gamete formation results in halving of number of chromosomes which is necessary to maintain the number of chromosomes in an organism which reproduces sexually.

Role of zygote in sexual reproduction: Zygote formation makes the number of chromosome equal to the somatic cells. Further, it is the zygote which undergoes mitosis to develop into an embryo and subsequently into a new individual.

• Ovary: Produces female gametes

• Anther: Produces male gametes

Placenta is a disc-like structure embedded in the uterine wall. It contains villi on the embryonal side. Blood spaces are present on the mother’s side. Following are the functions of placenta:
• Supplying nutrients to the foetus.
• Supplying oxygen to the foetus.
• Taking away carbon dioxide from the foetus.
• Taking away excretory products from the foetus. 

Various ways to avoid pregnancy are as follows:
 (a) Physical barrier
 (b) Copper -T
 (c) Hormone pills
 (d) Surgical procedure
Hormone Pills: Many hormones pills are available in the market. These pills stop ovulation and thus prevent conception. Many new pills are available which need to be taken in fewer number of doses. These are more convenient and have least side effects. 

In human beings, one egg is released from either of the ovaries once in a month. The egg is transferred to the fallopian tube. Sperms swim up to the fallopian tube. Only one sperm is able to penetrate the egg. That is how fertilization takes place. A menstrual cycle is composed of about 28 days. This means only one egg is available for fertilization in one menstrual cycle. Hence, it can be said that fertilization can occur only once in a month.

Survival of an individual depends on many factors. An individual can survive if he/she gets food and shelter. An individual can survive if he/she is not killed by a predator. An individual can survive if he/ she is not killed by a competitor. In biological sense, an individual can survive if all the life processes continue in the body. But reproduction creates a new individual and the new individual carries the lineage of the species even after the death of parents. Moreover, a good rate of reproduction ensures a large population which counterbalances mortality in the population. We know that a higher birth rate and lower mortality rate helps in growth of population. If mortality rate becomes more than birth rate, then a population can be wiped out. Thus, reproduction helps in maintaining the stability of a species.

Sexualy Transmitted Diseases: Diseases which spread from one person to another through sexual act are called sexually transmitted diseases. HIV, Gonorrhoea, Herpes, etc. are examples of STDs. Ways to prevents STDs: • Use of condoms or other physical barriers. • Avoiding sexual contacts with unknown partners.