CBSE Class 10 Answered

A grown individual cannot be obtained directly. First the production of haploid gametes takes place, followed by the union of male and female gametes to produce the one-celled diploid zygote. This union restores the chromosome number of the species. The zygote divides again and again to form a ball of cells called an embryo, which then gets attached to the lining of the uterus. As time proceeds, the embryo will develop into a stage with noticeable human features called foetus. So it is only gradually that the human features begin appearing in the embryo and not as soon as it is formed, since there is a great deal of specialisation involved to form the shape of a multi-cellular organism. This cannot be shown by a single celled zygote.