Sexual Reproduction Sexual reproduction is the reproduction that involves the fusion of two gametes or sex cells. The male gametes are called sperms and are produced in the testes. The female gamete is called ova and are produced in the ovaries.
Formation of Zygote Normal body cells have a diploid number of 46 chromosomes. Gametes have the haploid number of 23 chromosomes. When the gametes fuse together, they form a zygote. It will then have the diploid number of 46 chromosomes. The zygote will divide further by cell division or mitosis.
The Male and Female Gametes or Sex cells
The Sperm – components HEAD Acrosome of digestive enzymes for breaking down of cell membrane of ovum. Haploid nucleus of 23 chromosomes. MIDDLE-PIECE Mitochondria to produce energy for movement. TAIL Beating movement or flagellum for propulsion
The Sperm – other adaptations STREAM-LINED BODY SHAPE Enables efficient swimming LIGHT AND SMALL Enables fast movement
The Ovum – components CYTOPLASM Storage of food to enable ovum to survive while awaiting fertilisation NUCLEUS Haploid nucleus of 23 chromosomes OUTER VITALLENE MEMBRANE Hardens after one sperm has penetrated to prevent multiple fertilisation
The Ovum – other adaptations LARGE SIZE Enables sufficient food storage PLASMA CELL MEMBRANE Enables certain materials into the cell
Parts of the Reproductive System
Male Reproductive System
Penis and Erectile tissue An erectile organ and contains erectile tissue. The tissue inside contains spaces to be filled with blood, turning it erect and hard. This enables it to enter the vagina during sex to deposit semen containing sperms.
Urethra and Semen A tube which passes from the bladder to the outside of the body. Semen and urine passes through it to go out of the body at different times. During ejaculation or release of semen, urine does not come out due to the sphincter muscle controlling it.
Testis and Epididymis Is egg-shaped which produces sperms and male sex hormones called the testosterone. Receives blood from blood vessels in a spermatic cord. Beside each testis lies the epididymis which stores inactive sperms from the testis before entering the sperm duct.
Sperm duct and Seminal vesicle Loops over a ureter and opens up to a uretra. Sperms travel through it after being released from the testes. The seminal vesicle is a gland that opens into each sperm duct. It stores sperms before they are released through the urethra.
Cowper’s , Prostate & other glands Prostate gland is at the base of the urinary bladder where two sperm ducts join the urethra. Cowper’s gland is located beneath. Secrete a slippery fluid which mixes with the sperms. It nourishes the sperms and stimulate them to swim actively.
Female Reproductive System
Ovary and Oviduct They produce eggs and female sex hormones, which are responsible for development of secondary sexual characteristics. When the eggs become mature, they are released from the ovaries. The egg is usually fertilised in the oviduct.
Uterus Also known as the womb, it is where the fetus or embryo develops during pregnancy. The uterus has elastic muscular walls with smooth muscular tissues to push the embryo out during birth. The inner lining of the uterus is the uterus lining that is used for implantation.
Cervix and Vagina The circular ring of muscle at the narrow end of the uterus is the cervix. It enlarges to allow passage of the fetus during birth. Semen is deposited in the vagina during mating through through the opening called the vulva.
Puberty and The Menstrual Cycle
Puberty Puberty is the stage of human growth and development in which a person becomes physical mature. The body begins to change from a child to adult. It begins at 11 for girls and 14 for boys. The reproductive system begins to function. The sex organs mature and start producing gametes.
Changes at Puberty In boys Facial hair, pubic hair, and armpit hair starts growing The penis and testicles increase in size. Production of sperms starts. Voice box enlarges and voice deepens IN GIRLS Pubic hair and armpit hair starts growing. Breasts and uterus enlarge, hips broaden. Menstruation and ovulation start.
Menstruation Menstruation refers to the monthly discharge of blood from the uterus via the vagina. The menstrual period lasts for about 5 days. Menstruation is part of a cycle of events in the female reproductive organ called the menstrual cycle. The average menstrual cycle from an adult woman is 28 days.
The Menstrual Cycle Menstruation in which uterine lining is discharged or broken down. (Day 1 – 5) Growth, thickening and repair of uterine lining. (Day 6 – 10) Fertile period, sperms likely to cause fertilisation (Day 11 – 17) Ovulation in which an ovum is released into the fallopian tube from the ovary. (Day 13 – 15)
Fertilisation to Implantation of embryo
Sexual intercourse in fertile period Ovulation occurs and mature eggs are released from the ovaries. One of the ovum fuses with a sperm to form a zygote through fertilisation. Formation of an embryo, hollow ball of cells. Implantation of embryo in the uterine lining. Placenta, amniotic fluid in amniotic sac and the umbilical cord form after implantation during the embryo development.
Development of embryo Amniotic fluids in amniotic sac supports and protects the embryo, allowing it to move freely. Placenta allows diffusion of oxygen, food substances, antibodies and excretory products to and from the embryo’s and mother’s blood. Umbilical cord transports deoxygenated blood from the embryo to placenta and food substances from the placenta to embryo.
When Fertilisation does not occur The ovum breaks down together with uterine lining on the 28th day. The ovum is discharged with the blood in menstruation through the vagina. This marks the start of menstruation and the whole cycle is repeated.