Heredity & Reproduction

Question 1

Fertilisation

Answer 1

The process in which the nucleus of a female gamete and male gamete fuses / The fusion of the nuclei of a spent and egg to form a zygote

• male gametes are sperm cells
• female gametes are egg cells

Each contain 23 chromosomes, fertilised cell is called the zygote. It has 46 chromosomes in 23 pairs.

Question 2

Sexual reproduction

Answer 2

• Involves a female and male parent
• Each parent passes on half of its genetic material to its offspring
• Gametes are produced by organisms
• Off spring are genetically dissimilar to parent
• Involves the fusion of gametes during fertilisation

Question 3

Heredity

Answer 3

Passing down of genetic material from one generation to the next.

Question 4

Biological traits

Answer 4

Physical or behavioural characteristics of an organism. May be determined by genetic and/or environmental factors.

Question 5

Male reproductive system

(Refer to notes for pictures)

Answer 5

Testis/Testes: Produced sperms and male sex hormone; each tetanus is connected to epididymis

Epididymis: Narrow, coiled tube that stores inactive sperms before they enter the sperm duct

Sperm duct: Transports sperms released from tested and subsequently epididymis into the urethra

Male sex glands: Contain nutrients and enzymes that help sperms move actively

Penis: Erectile organ that deposits sperms into vagina of female during sexual intercourse; Blood vessels in erectile tissue found in penis fill with blood during sexual arousal

Urethra: A tube which passes through the centre of the penis to the exterior; Transports urine and semen at different times

Question 6

Female reproductive system

(Refer to notes for pictures)

Answer 6

Ovaries/Ovary: Produces eggs (ova) during foetal stage; Only 500 eggs will mature between puberty and menopause; One egg (ovum) is generally released each month (the ovaries take turns to release the egg; not necessarily alternate); Produces female hormones oestrogen and progesterone

Oviduct/Fallopian tube: Muscular tube leading from ovaries to uterus and transports the mature ovum released from the ovary once every month; site of fertilisation, where the sperm meets and fuses with the mature ovum

Uterus: Has thick, muscular, elastic walls; Site of foetus development during pregnancy; Inner lining is spongy and filled with blood capillaries — prepare for embryo implantation

Cervix: Circular passage of muscle that dilates to allow passage of baby during birth

Vagina: Site where semen is deposited in vagina during sexual intercourse; Also known as the birth canal

Question 7

The Menstrual cycle
- Menstruation
- Repair of uterine lining
- Ovulation
- Maintain thickness of uterine lining

Answer 7

Menstruation (1-5 days):
Takes place when there is no fertilisation in the previous cycle
- Thick uterine wall supplied with blood capillaries will break down together with unfertilised ovum
- Discharged out of female’s body through the vagina

Question 8

Repair of uterine lining

Answer 8

(Days 6-13)
Repair of uterine lining
- Uterine lining starts to thicken and blood vessels form inside the thick lining

Question 9

Ovulation

Answer 9

(Day 14)
Ovulation takes place about 14 days after menstruation starts
- One of the ovaries releases a mature ovum
- ‘Fertile Period’ is usually 3 days before and after ovulation (Days 11-17). Ovum can usually survive for about 12-24 hours after ovulation while sperms can survive within the female for about 3 days

• No fertilisation: Ovum dies and disintegrates

Question 10

Maintain thickness of uterine lining

Answer 10

(Days 15-28)
Preparation for fertilisation
- The lining of the uterus is at its thickness
- If there was no fusion between sperm and ovum, the thick uterine lining begins to break down
- If fertilisation occurs, thickness of uterine lining is maintained to support foetus development

Question 11

Fertilisation and Implantation

Answer 11

Fertilisation
- 2 haploid gametes fuse to form a zygote, resulting in a diploid
- Zygote divides by normal cell division, resulting in all the cells in the child to have diploid number of chromosomes
- After zygote continually divide, a ball of cells known as the embryo is formed and will implant in the uterine lining of the uterus

Question 12

Birth control methods

Answer 12

Temporary and permanent

Question 13

Temporary

Answer 13

Couple is able to have children when they wish to and when they stop using the birth control

Question 14

Rhythm

Answer 14

This method involves avoiding sexual intercourse during the fertile period of the woman’s menstrual cycle.

Question 15

Spermicide

Answer 15

A chemical that kills or block sperms from entering the uterus. This reduces the chances of fertilisation. It is inserted into the vagina.

Question 16

Diaphragm

Answer 16

A dome-shaped rubber cap with an elastic rim. It is inserted into the vagina and placed over the cervix. The diaphragm is impermeable and does not allow sperms to pass though. This prevents sperms from entering the uterus and prevents fertilisation.

Question 17

Condom

Answer 17

A thin rubber tube used to cover the erect penis before sexual intercourse. It is impermeable to sperms. Hence, sperms cannot enter the uterus and no fertilisation occurs. The condom is also impermeable to bacteria and virus. It can protect the user from getting sexually transmitted infections.

Question 18

Intra-uterine device

Answer 18

The IUD is a piece of plastic or metal inserted into the uterus by a doctor. It disrupts the function of the uterus. It prevents the embryo from being implanted onto the uterine lining

Question 19

Contraceptive pills

Answer 19

Contain certain female sex hormones that prevent ovulation. The pills disrupt the function of the ovary and prevents it from releasing a mature egg every month.

Question 20

Permanent

Answer 20

Couple will not be able to have any more children as the effects of such methods are usually irreversible

Question 21

Vasectomy

Answer 21

Involves the cutting and tying of sperm ducts during surgery. As a result, no sperms will be deposited during sexual intercourse and the male is unable to make his partner pregnant. This helps to prevent fertilisation.

Question 22

Tubal ligation

Answer 22

Involves the cutting and tying of both fallopian tubes during surgery. As a result, the egg is prevented from meeting the sperm and no fertilisation occurs.

Question 23

Sexually transmitted infections (STI)

Answer 23

Spread primarily by close sexual contact and sexual intercourse .

Question 24

Viral STI

Answer 24

If the virus causes a disease, it is possible for it to remain “asymptomatic” for a period of time. It is also possible to have the virus and not know it, as the virus remains dormant. Moreover, it is also possible to pass it to another person without either person knowing it. Viral STIs generally cannot be cured. Treatment generally manage the symptoms only. An example of such STIs includes HIV.

Question 25

Bacterial STI

Answer 25

If bacteria causes a disease, it needs to be treated with antibiotics and antimicrobial medication. STIs that are bacterial include gonorrhoea and syphilis.

Question 26

AIDS

Answer 26

Blood borne disease that can be spread by close sexual contact and sexual intercourse, as well as other means of blood transfusions, sharing needles, or body piercing or tattoo equipment. It is caused by HIV, human immunodeficiency virus. HIV usually develops into AIDS.

Question 27

Transmission of HIV

Answer 27

1. Sexual intercourse with an infected person
2. Sharing hypodermic needles with an infected person e.g. when drug addicts share needles. Needles used for tattooing, acupuncture or ear-piercing may transmit the disease if they are not cleaned properly or stained with contaminated blood
3. Blood transfusion with blood from an infected person that contains HIV
4. During pregnancy, virus may be passed from the infected mother to the foetus across the placenta through the umbilical cord
5. Through breast-feeding

Question 28

Protection from HIV

Answer 28

1. Keep to one unaffected sex partner or do not have sex
2. Males should wear a condom to reduce HIV transmission and prevent the transfer of semen
3. Do not abuse drugs. Drug addicts tend to share needles that prick the skin
4. Do not share instruments that are likely to break the skin and be contaminated with blood, e.g. razors and toothbrushes
5. Go to reliable operators if you require acupuncture treatment or ear-piercing. Make sure that the needles used are sterile or insist on using single-use, sterile, disposable instruments

Question 29

Gonorrhea; Bacteria

Answer 29

Transmission
- By having unprotected sex with a person who has gonorrhea
- Childbirth from an infected mother to an unborn baby
- Infected fluid contact
Treatment
- Antibiotics may help if detected early

Question 30

Syphilis; Bacteria

Answer 30

Transmission
- By having direct contact with a syphilis sore
- Sex with infected partner
- Mother to fetus
Treatment
- Antibiotics may help if detected early

Question 31

HIV and AIDS; Virus

Answer 31

Transmission
- Contact with blood, semen
- Vaginal secretions or breast milk
- Unprotected sex
- Pregnancy — from an infected mother to unborn baby, breastfeeding, childbirth
- Sharing needles, syringes or other drug supplies with traces of blood of an infected person (e.g. tattooing, sharing needles, piercing) or other blood exposure to infected blood/blood products
Treatment
- No cure at present