JWSS Biology Chapter 13 Reproduction in Humans

4G3 Sci(Bio) Reproduction in Human Notes Name:_______________________ ( ) Class: _________ Date: __________________ JURONG WEST SECONDARY SCHOOL SECONDARY FOUR – SCIENCE (BIOLOGY) (5088) Chapter 12: Reproduction in Human Learning Outcomes: (a) define sexual reproduction as the process involving the fusion of nuclei of male and female gametes to form a zygote and the production of genetically dissimilar offspring (b) identify the male reproductive system and state the functions of: testes, scrotum, sperm ducts, prostate gland, urethra and penis (c) identify the female reproductive system and state the functions of: ovaries, oviducts, uterus, cervix and vagina (d) outline the menstrual cycle with reference to the alternation of menstruation and ovulation, the natural variation in its length, and the fertile and infertile phases of the cycle with reference to the effects of progesterone and oestrogen only (e) describe fertilisation and early development of the zygote simply in terms of the formation of a ball of cells which becomes implanted in the wall of the uterus (f) discuss the transmission of human immunodeficiency virus (HIV) and methods to reduce transmission (a) define sexual reproduction as the process involving the fusion of nuclei of male and female gametes to form a zygote and the production of genetically dissimilar offspring Sexual reproduction is a process involving the fusion of nuclei of male and female gametes (sex cells) to form a zygote and the production of genetically dissimilar offspring. Gametes in Humans • Male gametes – Sperm • Female gametes – Egg (ovum) • Produced in the respective reproductive organs o Testes in male, o Ovaries in female • Gametes contain half the number of chromosomes (haploid) as compared to the normal body cell (diploid) Examples o 46 chromosomes in normal human cell, gametes contain 23 chromosomes o 78 chromosomes in normal chicken cell, gametes contain 39 chromosomes o 18 chromosomes in normal radish cell, gametes contain 9 chromosomes

4G3 Sci(Bio) Reproduction in Human Notes 2 Fertilisation of gametes • Nucleus of sperm (23 chromosomes) fuses with nucleus of ovum (23 chromosomes) to form a zygote (46 chromosomes) • The zygote undergoes normal cell division (mitosis) to form embryo then the foetus and finally a baby • All cells in the baby contain 46 chromosomes (b) identify the male reproductive system and state the functions of: testes, scrotum, sperm ducts, prostate gland, urethra and penis 1. Male Reproductive System Why should gametes be haploid? So that after each fertilisation event, the number of chromosomes does not double, and the diploid number of chromosomes is restored.

4G3 Sci(Bio) Reproduction in Human Notes 3 I. Parts and Functions of the Male Reproductive Parts Parts Functions Testis (plural: testes) • There are 2 testes • Produces sperm • Produces male hormones such as testosterone, which maintain development and maintenance of secondary sexual characteristics in males. Scrotum • The testes lies between the thighs in a pouch-like sac called scrotum • Scrotum lies outside the human body. Epididymis • Stores inactive sperms from the testes for several days • During ejaculation, sperms are forcefully expelled from epididymis to the sperm duct which travels behind the bladder and is joined by the seminal vesicle, and then exits the penis through the urethra. Sperm Duct • Also known as vas deferens • During ejaculation, the sperm cells from the epididymis are propelled through the sperm duct (see epididymis) Glands: 1. Prostate gland 2. Cowper’s gland 3. Seminal vesicle • The glands secrete a fluid which mixes with the sperms → form semen • Fluid contains nutrients and enzymes: nourish the sperms and stimulates them to swim actively Why does the testes need to be outside the body? They are outside the abdominal cavity to maintain a lower temperature, crucial for sperm development

4G3 Sci(Bio) Reproduction in Human Notes 4 Urethra • A tube that passes from the bladder through the center of the penis to the outside of the body • Both semen and urine pass out of the body through the urethra Penis • An erectile organ • Deposits sperms into vagina of the female during sexual intercourse II. Parts and Function of the Male Gametes • Also called spermatozoa • Numerous sperms are produced throughout the life of a matured male human Structure of sperm • Made up of three parts: Head, Middle piece and the Tail o Head ▪ Contains nucleus which carries haploid set of chromosomes (23 chromosomes in human sperm cell) ▪ Acrosome in head is a vesicle containing enzymes that breaks down part of egg membrane during fertilization so that the sperm can penetrate the egg o Middle piece ▪ Contains numerous mitochondria to release energy for sperm to swim towards egg o Tail (flagellum) ▪ Enables the sperm to swim towards the egg ▪ Sperm is motile (can move on its own) Can you describe the pathway taken by a sperm?

4G3 Sci(Bio) Reproduction in Human Notes 5 (c) identify the female reproductive system and state the functions of: ovaries, oviducts, uterus, cervix and vagina Parts Functions Ovary • There are two ovaries • Produces Eggs • Contains many follicles (immature eggs) which contain oocytes which mature into ova (singular: ovum = egg) • The process of releasing ova is called ovulation • When the eggs become mature, they are released from the ovaries. • Produce hormones (e.g. progesterone and estrogen) Fallopian tubes • Matured egg is released into the fallopian tube • Narrow, muscular tube leading from the ovary to the uterus • It has a funnel like opening lying close to the ovary o Makes it easier for the egg to enter the fallopian tube • Egg is usually fertilised in the fallopian tube o The fertilised egg is known as the zygote Uterus • The place where the development of the fetus occur • Elastic muscular walls contract to push the fetus during birth • The soft, smooth inner lining of the uterus is called uterine lining or endometrium. o This is where the embryo implants and develops (See section on menstruation) Cervix • Lower portion of the uterus that joins the vagina • Opening of the cervix allows menstrual blood to flow out and into the vagina during menstruation Vagina • Also known as the birth canal • Semen is deposited at the vagina during sexual intercourse

4G3 Sci(Bio) Reproduction in Human Notes 6 II. Parts and Function of the Female Gametes • Large nucleus containing haploid set of chromosomes (haploid: half the no. of normal chromosomes) • Has a outer jelly coat which needs to be broken down by the sperm • A woman is born with all the potential eggs she will ever have. • Usually one mature egg is released every month until menopause

4G3 Sci(Bio) Reproduction in Human Notes 7 EXTENSION: Twins • Identical twins o Produced from one fertilised egg (zygote) o Zygote divides into two cells and each cell develops to form a baby o Both babies have the same genes and they are identical • Fraternal twins or non-identical twins o Two eggs are released into the fallopian tube at about the same time o Two eggs are fertilized by two different sperms o Two zygotes formed DO NOT contain the same genetic materials o They may be of different gender o They do not look alike 3. Differences between male and female gametes Feature Male gamete (Sperm) Female gamete (Egg) Structure • Head, middle piece and tail • Nucleus contains either X or Y chromosome • 60 𝝻m long • Spherical • Nucleus has one X chromosome • Diameter between 120 𝝻m to 150 𝝻m Motility • Motile • Beating movement of the tail enables it to swim • Non-motile • Cilia and peristalsis of the fallopian tube moves the egg along the tube in