1. Reproduction in Human Beings

2. 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.

3. Sexual reproduction
Sexual reproduction involves two organisms of a species – a male and a female.
The male produces reproductive cells or gametes called sperms.
The female produces reproductive cells called eggs or ova (singular ovum).
In sexual reproduction, a sperm fuses with an egg to give rise to an offspring.
The male and female individuals are known as the parents.
Only sexually mature male and female organisms can produce reproductive cells.

4. 27.2 Puberty
Puberty is the period of rapid growth and development during which a person becomes sexually mature and become capable of reproducing.
Increased secretions of certain hormones in the body bring about puberty.
Puberty occurs in girls at about 10 to 12 years, and about 2 years later in boys.
During puberty, the reproductive organs grow and develop to produce sperms or mature eggs.
Dramatic physical, emotional and social changes also occur.

5. 27.2 Puberty Some physical changes during puberty includes: Boys Girls
Facial hair starts to grow and hair starts to grow in the pubic region and armpits.
Hair starts to grow in the pubic region and armpits.
Voice-box enlarges and voice deepens. -
The penis and testes increase in size.
Breasts and uterus enlarge, and hips broaden
Production of sperms begins and ejaculation occurs.
Menstruation and ovulation begin.

6. 27.3 The Male Reproductive System
Male sex glands
They secrete an alkaline fluid containing nutrients and enzymes. The nutrients provide the sperms with the energy they need to move rapidly.
Sperm duct
There are two sperm ducts, one leaving each testis. Each sperm duct is a muscular tube which rises up the body and joins the urethra. It carries sperms from the testis to the urethra.
Scrotum
Each testis is found in a scrotum. The scrotum is a sac that hangs outside the body, where the temperature is slightly lower than body temperature. This lower temperature is important for the production of healthy sperms.
Testis (plural: testes)
The testis produces sperms and male sex hormones (testosterone). These hormones are responsible for the development of male characteristics during puberty.
kidney
urinary bladder
urethra
penis

7. 27.3 The Male Reproductive System
Sperms and fluid from the sex glands make up semen.
Semen is deposited in the female passage during sexual intercourse.

8. 27.3 The Male Reproductive System
Penis The penis is the male reproductive organ which becomes erect when sexually excited. This make sexual intercourse possible. It is through the penis that sperms are ejaculated into the female passage during sexual intercourse. In a healthy male, each ejaculation contains about 100,000,000 sperms.
Urethra The urethra is a tube which leads to the outside of the body through an organ called the penis. During sexual intercourse, sperms pass from the testes into the sperm ducts and then into the urethra. From the urethra, the sperms pass to the outside of the body and into the female.

9. 27.3 The Male Reproductive System
The urethra joins the base of the bladder where urine is stored.
When a person urinates, the urine passes through the urethra to the outside.
During sexual intercourse, the opening between the urethra and the bladder is closed so that urine and semen never mix.

10. Sperm
The human sperm is the male reproductive cell and is about 0.06 mm long.
The sperm has a head containing a nucleus where chromosomes from the male parent are found.
The sperm has a long tail which helps the sperm to swim towards the egg.

11. 27.4 The Female Reproductive System
Oviduct (or fallopian tube)
The egg released from the ovary is pushed along the oviduct towards the uterus by the muscular contractions of the wall of the oviduct. It is in the oviduct that the sperms meet the egg.
Uterus
The uterus is a pear-shaped organ with thick muscular walls. Its inner surface is covered by a soft and smooth layer called the uterine lining. This lining breaks down and is shed with some blood every month from puberty onwards. The uterus is the place where the foetus develops.
kidney
Ovary
It produces eggs and female sex hormones. These hormones are responsible for the development of the female characteristics during puberty.
uterine lining
cervix
vagina
urinary bladder

12. 27.4 The Female Reproductive System
Each ovary produces about 250 mature eggs in the life of the female.
From puberty onwards, an egg is released from one of the ovaries every month.
When a woman is about 45 to 55 years old, the egg production slows down and finally stops.
The woman is said to have reached the stage of menopause.

13. 27.4 The Female Reproductive System
Cervix
The cervix is a ring of muscle at the lower end of the uterus. It enlarges to allow the foetus to pass through during birth.
Vagina (or birth canal)
The vagina is a muscular tube. It joins the cervix to the outside of the body.

14. Egg The human egg (or ovum) is the female reproductive cell.
It is spherical in shape and has a diameter of about 1.20 mm.
The egg contains a nucleus where chromosomes from the female parent are found.

15. 27.5 Menstrual Cycle
Menstruation is the monthly discharge of blood and tissues out of the body through the vagina.
Menstruation lasts for about 5 days. However, the length of the menstrual period and the amount of blood lost varies from person to person.
Menstruation is the start of a cycle of events that occurs in the female reproductive organs.
We call this cycle the menstrual cycle.

16. Menstrual Cycle The average menstrual cycle lasts about 28 days.
This is the length of time from the first day of one menstrual period to the day before the next one begins.
The main function of the menstrual cycle is to prepare the uterus to receive a fertilised egg (an egg that has fused with a sperm).
The events in this cycle are controlled by hormones including the female sex hormones.

17. Stages in the Menstrual Cycle
Menstruation
Menstruation occurs if the egg released by the ovary is not fertilised.
The uterine lining, prepared for receiving the fertilised egg, breaks down.
Together with blood, it is shed through the vagina to the outside of the body as menstrual flow or discharge.
Considering the day when menstruation starts as the first day of the cycle, it will last for an average of about 5 days and usually ends on the 5th day.
uterus
uterine lining (thin)
vagina
menstrual discharge

18. Stages in the Menstrual Cycle
Repair and growth of the uterine lining
When menstruation stops, the uterine lining is very thin.
A female sex hormone called oestrogen causes the uterine lining to repair itself and grow in thickness.
This repair and growth continues for about nine days.
The lining becomes vasularised (very rich in blood capillaries.
ovary
developing egg
uterine lining (vascularised)

19. Stages in the Menstrual Cycle
Ovulation
Ovulation is the release of a mature egg from the ovary into the oviduct.
This usually occurs on the 14th day from the start of menstruation.
Having sexual intercourse during this period just before or after ovulation is likely to result in a pregnancy.
This period is called the fertile period.
mature egg (discharge)
uterine lining (thick)

20. Stages in the Menstrual Cycle
Further thickening of the uterine lining
After ovulation, the ovary begins to secrete another female sex hormone called progesterone into the bloodstream.
Progesterone maintains the thickness of the uterine lining which is ready for the embryo to be implanted.
After the implantation, the embryo gets nutrients and oxygen for growth from the uterine lining.
uterine lining (ready for implantation of embryo)

21. Stages in the Menstrual Cycle
If a sperm does not fertilise an egg, the ovary stops producing a lot of progesterone.
As a result, the uterine lining breaks down gain, bringing on an onset of menstruation.
This usually occurs on the 28th day of the cycle.

22. Stages in the Menstrual Cycle
Repair of uterine lining
Uterine lining thickens further and becomes more vascular, preparing for implantation.
Menstruation

23. Stages in the Menstrual Cycle
Thickness of uterine lining
Menstruation
Ovulation
Menstruation

24. 27.6 Fertilisation
Sexual reproduction involves the fusion of the sperm and the egg.
This process is known as fertilisation.

25. 27.6 Fertilisation
penis
oviduct
vagina
testis
3. If an egg is present in an oviduct, fertilisation may take place.
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.
1. During sexual intercourse, the penis is inserted into the vagina.

26. 27.6 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.
egg
uterine lining ready to receive fertilised egg
uterus
ovary
vagina
sperm
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.
oviduct
uterus
ovary
vagina

27. 27.6 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.

28. 27.6 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.
uterine wall
cavity of uterus
foetus
oviduct
umbilical cord
cervix

29. 27.6 Fertilisation
Week 1 - 4
Arms and legs begin to form. The embryo also has a little tail.

30. 27.6 Fertilisation
After Week 7, the nose, ears and fingers can be seen.

31. 27.6 Fertilisation
After Week 11, the embryo now looks like a baby. We call this embryo a foetus.

32. 27.6 Fertilisation
After Week 20, the foetus looks more and more like a human baby.

33. 27.6 Fertilisation
After about 9 months the baby is ready to be born.

34. 27.7 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.

35. 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)
eyebrow (e.g. bushy or thin)
nose bridge (e.g. low or high)
ear shape (e.g. lobed or attached)
face shape (e.g. squarish or oval)
tongue (e.g. roller or non-roller)
chin (with or without cleft)

36. 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?

37. 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.

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

39. 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.

40. 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.

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

42. Miscellaneous