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Biochemistry is a field within Biology Topics that explores the chemical processes in living organisms.
Describe the Process of Fertilization in Human Beings
The sperms made in the testes of man are introduced by penis into the woman’s body through vagina. The sperms enter into vagina, pass through the uterus and then go into the oviducts (see Figure). The tail of sperms helps them in moving and reach the oviducts. If at the same time, the ovary of woman releases
an egg (or ovum), then this egg also goes into the oviduct. One of the sperms enters the egg (see Figure). The fusion of sperm with egg is called fertilisation. During fertilisation, the nucleus of sperm fuses with the nucleus of egg cell to form a single nucleus. This results in the formation ola fertilised egg called zygote. Thus, a sperm combines with the egg in the oviduct and fertilises it to form a zygote. The zygote (or fertilised egg) is the beginning of the formation of a new baby (or a new individual).
Development of Embryo
The zygote (or fertilised egg) divides repeatedly to make a ball of hundreds of cells. This is called an embryo. The embryo moves down the oviduct into the uterus. The embryo gets embedded in the soft and thick lining/of the uterus (see Figure). This is called implantation. When the embryo settles down in the uterus, the woman is said to have become pregnant (or said to have conceived). The embryo starts growing
into a baby. The embryo gets food and oxygen from the blood vessels in the lining of the uterus. The cells of embryo begin to form specialised groups that develop into different tissues and organs of the baby. Embryo is an early stage in a developing baby. Thus, an unborn baby at an early stage of development in the uterus is called an embryo. The body features of the unborn baby are not much developed at the embryo stage. The unborn baby remains an embryo in the first eight weeks of pregnancy. A human embryo at 4 to 5 week’s development is shown in Figure. We cannot identify any body features (hands, legs, head, eyes and ears, etc.) of the developing baby in this embryo.
The embryo continues to grow and develop in the uterus to form a baby. The embryo gradually develops body parts such as hands, legs, head, eyes and ears, etc. An unborn baby in the uterus at the stage when all the body parts can be identified, is called a foetus (The word ‘foetus’ is pronounced as ‘fetus’). A human embryo becomes a foetus after about eight weeks of pregnancy. From about eight weeks until birth, the unborn baby is called foetus (see Figure).
It takes about 38 weeks (about nine months) from the fertilisation of egg to the formation of fully developed baby. When the development of the foetus into a baby is complete, the mother gives birth to the baby. The fully formed baby comes out of the mother’s body through vagina. And we say that a baby is born. This is how humans reproduce by giving birth to babies. All of us were born in this way.
Differences Between Zygote, Embryo and Foetus
A zygote forms after fertilisation. A zygote becomes an embryo. And finally, an embryo becomes a foetus. The main differences between zygote, embryo and foetus are given below.
| Zygote | Embryo | Foetus | |||
| 1. | A zygote is formed by the fusion of male and female gametes (sperm and egg) | 1. | An embryo is formed by the repeated cell division of a zygote. | 1. | A foetus is formed by the growth and development of an embryo. |
| 2. | A zygote is the beginning of the formation of a baby. | 2. | An embryo is an unborn baby in the uterus in the early stages of development (up to 8 weeks) | 2. | A foetus is an unborn baby in the uterus in the later stages of development (after 8 weeks till birth). |
| 3. | A zygote is a single cell. It is smaller than a full stop (.) | 3. | An embryo is multicellular. The body features of growing baby in the embryo are not much developed. | 3. | A foetus is also multicellular. The body features of developing baby (like hands, legs, head, eyes and ears, etc.) can be identified. |