Both frogs and goats reproduce by sexual methods. Planaria can reproduce both sexually and asexually. Amoeba reproduces through binary fission, which is an asexual mode of reproduction.

Binary fission is a type of asexual reproduction seen in unicellular organisms. In this method, first the nucleus divides followed by cytoplasmic division. This forms two daughter cells from one parent cell. Therefore, Paramecium dividing itself to form two daughter cells represents binary fission.

The part of a sperm cell which contains the male nucleus is called the 'head' (A). The middle portion (B) is known as the 'middle piece'. It contains mitochondria which provide energy for sperm movement. The last portion (C) is known as the 'tail' and is responsible for sperm motility.

In internal fertilisation, the survival chances of the zygote are more than external fertilisation. In external fertilisation, the male and female gametes are released into the environment (mostly in water) and fertilisation takes place outside the body of both the parents. Thus, there is a higher chance of the gametes and the zygote getting destroyed by agents like water, wind, heat and predators.  

Haploid cells have only one set of chromosomes, unlike diploid cells, which have two sets of chromosomes. Haploid cells are formed by meiotic cell division. Both sperm and ovum are haploid cells and are also called gametes.

Fusion of the male and the female gamete, i.e., the sperm and the ovum, is called fertilisation. This results in the formation of a single-celled zygote. After fertilisation, the zygote divides repeatedly to give rise to a ball of cells. This ball of cells eventually develops into the various types of cells and tissues in an organism.