Reproduction in Human Beings

27.1 Why Must We Reproduce? In order for all species to survive, organisms, including human beings, must produce new organisms like themselves. The process by which organisms produce new organisms like themselves is called reproduction.

Fertilisation Sexual reproduction involves the fusion of the sperm and the egg. This process is known as fertilisation.

penis oviduct vagina testis Fertilisation 1. During sexual intercourse, the penis is inserted into the vagina. 2. Semen (containing sperms) ejaculated from the penis is deposited into the upper end of the vagina. The sperms will begin to swim into the uterus and enter the oviducts. 3. If an egg is present in an oviduct, fertilisation may take place.

Fertilisation 4. Sperms deposited in the vagina during sexual intercourse travel up the uterus to the oviduct to fertilise the egg released by the ovary. vagina sperm ovary egg uterus ovary oviduct vagina uterus uterine lining ready to receive fertilised egg embryo implanted in uterine lining 5. The fertilised egg (zygote) divides repeatedly to form the embryo, which moves into the uterus and becomes embedded in the uterine lining.

Fertilisation After fertilisation, the fertilised egg or zygote divides to form a ball of cell called the embryo. The embryo travels along the oviduct into the uterus where it embeds itself in the uterine lining. This is called implantation.

uterine wall cavity of uterus foetus oviduct umbilical cord cervix Fertilisation The embryo develops into a foetus. In humans, pregnancy lasts about nine months. At the end of this period, the muscles of the uterus contract to push out the baby in a process called birth.

Fertilisation Week Arms and legs begin to form. The embryo also has a little tail.

Fertilisation After Week 7, the nose, ears and fingers can be seen.

Fertilisation After Week 11, the embryo now looks like a baby. We call this embryo a foetus.

Fertilisation After Week 20, the foetus looks more and more like a human baby.

Fertilisation After about 9 months the baby is ready to be born.

Heredity Sexual reproduction involves the fusion of gametes. The male gamete (sperm) fuses with the female gamete (egg) to form a zygote. Gametes contain chromosomes and chromosomes contain genes. The sperm contains genes from the father, and egg from the mother. During fertilisation, the zygote will get genes from both the parents. As a result, the baby that develops will inherit characteristics from both parents.

What is heredity? Some characteristics that may be passed down to you by your parents: hair type (e.g. straight or wavy) skin type (e.g. fair or dark) ear shape (e.g. lobed or attached) tongue (e.g. roller or non-roller) chin (with or without cleft) face shape (e.g. squarish or oval) nose bridge (e.g. low or high) eyebrow (e.g. bushy or thin)

What is heredity? Children within a family usually share their parents’ characteristics. The study of our characteristics and how they are passed down to us from our parents is called heredity. When characteristics are passed down to us from our parents, we say that we inherit these characteristics from them. Such characteristics are known as hereditary characteristics. Where can we find the materials that carry information on hereditary characteristics?

What is heredity? Chromosomes contain DNA (deoxyribonucleic acid) molecules. Each sequence of DNA containing genetic information is known as a gene. Genes in a human cell contain instructions for making a human being. This genetic information determines what we look like, how intelligent we are, etc.

What is heredity? nucleus nucleus containing chromatin material or chromosomes chromatin (chromosomes) cell containing a nucleus There are 46 chromosomes in the nucleus of a human cell.

What is heredity? The nuclei of eggs and sperms carry genes. During sexual reproduction, these genes are passed down from the parents to the offspring. Hence, genes are known as hereditary materials. Genes are passed down from one generation to the next.

How are genes passed down? The sperm and egg each has a nucleus, which contains chromosomes that carry genes. The sperm contains a set of genes from the father, while the egg carries a set of genes from the mother. When the sperm fuses with the egg, the fertilised egg or zygote is formed. The zygote contains genes from both parents.

How are genes passed down? An egg A sperm Fertilisation A zygote An embryo A foetus

Miscellaneous OBK/BioBookREPROD.html#Human%20Reprod uction%20and%20Developmhttp:// OBK/BioBookREPROD.html#Human%20Reprod uction%20and%20Developm scloning/ scloning/