Reproduction in Humans

P5/6 science

Reproduction In Humans

Sexual reproduction does not only occur in plants. It also occurs in humans where the female reproductive cell and the male reproductive cell unite to form a new individual.

Female Sex Organs

The ovary is part of the female sex organ. There are two ovaries in each woman’s body.

Ova (singular ovum) or eggs are the female sex cells. The ova are stored in the ovaries of a female. A female is born with all the unripe eggs (or ova) she will ever have in her lifetime. When she reaches puberty, an egg will start to mature in the ovary. Every month, an egg will be released by the ovary into one of the Fallopian tubes. This is called ovulation.

On average, a female is born with approximately one million eggs but they decline in number and quality as she grows older. In fact, a girl is only left with about 400,000 eggs by the time she reaches puberty. Only a few hundred are released during ovulation.

Fallopian tubes

ovary uterus (womb) cervix

vagina

Female reproductive system

Male Sex Organs

A male has two sex organs. They are the testis and the penis. Sperms are the male sex cells. They are produced in the testes. When a boy reaches puberty, his testes will start to produce sperms. It takes about 72 days for a sperm to grow.

urinary bladder (stores urine, not part of the reproductive system) sperm ducts

testes penis Male reproductive system

Taken from Science Partner: A Complete Guide To Upper Block Science © Singapore Asia Publishers Pte Ltd SAPSCSP5&6_W04 Website: www.sapgrp.com | Facebook: Singapore-Asia-Publishers Page 1/8 P5/6 science

Reproduction In Humans

A sperm cell consists of a head (where the nucleus lies), the midpiece (which is the motor of the sperm) and a tail which helps it to swim. tail body head

nucleus

A sperm cell (magnified)

From the testes, sperms swim in a liquid known as semen. The sperms travel through the sperm ducts (which are the tubes that carry the sperms) to the penis.

How A Human Life Begins

During sexual intercourse between an adult male and female, the male deposits the sperms into the vagina of the female. The millions of sperms then travel up the vaginal canal through the cervix and into the uterus until they reach the Fallopian tubes. If an egg has just been released by an ovary and is travelling through the Fallopian tube, the sperms will surround it and try to enter it.

Sperms trying to enter an egg

Once one sperm enters the ovum, no other sperms can enter it any more. The other sperms will die very quickly. The joining together or fusion of a sperm and an ovum is called fertilization. The fertilized egg then travels through the Fallopian tube until it reaches the uterus. It implants itself in the wall of the uterus. The wall of the uterus contains nutrients and is richly supplied with blood vessels so that the fertilized egg can grow and develop well. The fertilized egg in the uterus is called an embryo.

Reproduction In Humans

uterus Fallopian tube fertilized egg

Fertilization takes place.

egg ovary

Implantation of the fertilized egg in the wall of the uterus. The passage taken by a fertilized egg

The fertilized egg cell divides very rapidly as the embryo develops. At 3 months (12 weeks), the embryo has developed arms, legs and most of the internal organs. It is now called a foetus. The time the foetus takes to develop inside its mother’s uterus (or womb) is known as pregnancy or gestation. In humans, the gestation period is about 40 weeks. Sometimes, babies may be born earlier. A baby who is born after 28 weeks of gestation is able to survive, but it has to spend some time in an incubator to develop and grow more fully before it can leave the hospital to begin its new life. Babies born earlier than they are supposed to are called premature babies. In the uterus, the foetus is attached to the placenta by an umbilical cord. The placenta is attached to the uterus. The foetus receives oxygen and nutrients from its mother and gives out its waste products through the placenta. The foetus remains in a watery environment inside the uterus. The fluid is known as amniotic fluid. It protects the foetus from shock or sudden movements which may be made by the mother.

placenta uterine wall villi umbilical cord

amniotic sac

amniotic fluid

The foetus is attached to the placenta by the umbilical cord.

Reproduction In Humans

When the foetus is ready to be born, it comes out of the mother’s body through the vagina.

Eight-month-old foetus

The umbilical cord will be tied and cut. The newborn baby can now breathe on its own, take in milk and water from its mouth and pass out waste from its excretory organs. As such, it no longer needs the umbilical cord in the outside world. The place where the umbilical cord was now exists as the belly button. The placenta is also delivered out through the vagina after the baby is born. Sometimes, the baby may not be able to be delivered through the vagina. A surgery will then be performed to extract the baby from the mother’s uterus. This is known as a caesarean section. A mother may deliver two or more babies at a time. Identical twins are two babies who look alike. They develop from a single fertilized egg which later divides into two embryos. Fraternal or non-identical twins develop when two eggs are released into the Fallopian tube and these two eggs are fertilized by two different sperms. Apart from humans, all mammals (except the platypus and spiny anteater) undergo sexual reproduction in a similar manner and give birth to their young alive, although the period of gestation varies.

Reproduction In Humans

1. Which one of the following traits is not passed on from parents to their child? (1) Colour of the eyes (2) Eating habits (3) Rolling of tongue (4) Type of ear lobe ( )

2. Look at the pictures shown below.

peahen egg toad eggs

Which of the following statements is/are true? A. Both eggs are fertilized internally. B. Both eggs are laid by the female parents. C. Both eggs have a hard covering. (1) A only (3) A and B only (2) B only (4) A, B and C ( )

3. Which pair of animals undergoes external fertilization? (1) ape and tiger (3) frog and platypus (2) fox and starfish (4) salmon and toad ( )

Study the family tree below. Then answer questions 4 and 5.

Legend: Male

Female A C D

B Monique

4. Which of the following letters, A, B, C or D, represents Monique’s father’s sister? (1) A (3) C (2) B (4) D ( )

Taken from Nail Those MCQs! Primary Science upper Block 5/6 © Singapore Asia Publishers Pte Ltd SAPSCSP5&6_W04 Website: www.sapgrp.com | Facebook: Singapore-Asia-Publishers Page 5/8 P5/6 science

Reproduction In Humans

5. Which one of the following statements is true? (1) Monique has an aunt and three uncles. (2) There are four members in Monique’s family. (3) Monique has a niece. (4) There are four generations in Monique’s family tree. ( )

6. Which of the following statements about reproduction in humans are wrong? A. A female egg is fertilized by more than a sperm. B. Fertilization can take place in the fallopian tube of the female’s body. C. The fertilized egg implants itself into the abdomen of the female’s body. D. The male always releases the sperms inside the female’s body. (1) A and B only (2) A and C only (3) B and C only

(4) A, C and D only ( )

6. 2 6. 4 5. 3 4. 4 3. 2 2. 2 1. Answers:

Taken from Nail Those MCQs! Primary Science upper Block 5/6 © Singapore Asia Publishers Pte Ltd SAPSCSP5&6_W04 Website: www.sapgrp.com | Facebook: Singapore-Asia-Publishers Page 6/8 P5/6 science

Reproduction In Humans

1. The table below shows some children within a town who inherit the hair colour from their parents.

Hair colour Hair colour Family (parents) (children) Legend:

1 female

male 2 brown hair

3 blonde hair

black hair

4 brunette hair

Based on what you observe in the table, which is the correct statement about the passing on of hair colour from the parents to the children, assuming no one has dyed the hair at all? (1) When both parents have the same hair colour, all their children will inherit the same colour. (2) If the mother has brown hair, all the daughters will have brown hair. (3) If the father has brown hair, 75% of the children will have brunette hair. (4) When both parents have blonde hair, all their children will have the same hair colour as them. ( )

2. Which of the following statements about reproduction in both flowering plants and most animals is/are correct? A. The female reproductive cells are stored in the ovaries. B. For fertilization to occur, both male and female organisms must be present. C. The male reproductive cells are also known as sperms. D. The fertilization process takes place in the female reproductive system. (1) B only (2) A and D only (3) B and C only (4) A, B, C and D ( )

Taken from Nail Those MCQs! Primary Science upper Block 5/6 © Singapore Asia Publishers Pte Ltd SAPSCSP5&6_W04 Website: www.sapgrp.com | Facebook: Singapore-Asia-Publishers Page 7/8 P5/6 science

Reproduction In Humans

3. A group of monsters is classified according to their physical traits as shown in the classification table below.

Name of monster Physical traits

Creepy 4 eyes, 8 legs, 2 feelers

Scary 6 eyes, 8 legs, 4 feelers

Wimpy 6 eyes, 20 legs, 4 feelers

Grumpie 4 eyes, 20 legs, 2 feelers

Based on the information given, which two possible monsters have reproduced the offspring shown below?

offspring (1) Creepy and Scary (2) Creepy and Grumpie (3) Scary and Grumpie (4) Wimpy and Scary ( )

4. The diagram below shows the female reproductive system.

B C

A D

Which of the following statements is correct? (1) The zygote implants itself in B after fertilization. (2) The female reproductive cells travel from C to A. (3) A fertilized egg is released from A monthly.

(4) The sperm fuses with the egg in A during fertilization. ( )

4. 1 4. 2 3. 2 2. 4 1. Answers:

Taken from Nail Those MCQs! Primary Science upper Block 5/6 © Singapore Asia Publishers Pte Ltd SAPSCSP5&6_W04 Website: www.sapgrp.com | Facebook: Singapore-Asia-Publishers Page 8/8