B8 reproduction 3 Sexual reproduction in humans



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B8 - REPRODUCTION

8.3 - Sexual reproduction in humans
1. Identify on diagrams of the male reproductive system, the testes, scrotum, and sperm ducts, prostate gland, urethra and penis, and state the functions of these parts.



Part

Function

Epididymis

A mass of tubes in which sperm are stored

Penis

Can become firm, to insert into the vagina of the female during sexual intercourse, to transfer sperm

Prostate gland

Adds fluid and nutrients to sperm, to form semen

Scrotum

A sac that holds the testes outside the body, keeping them cooler than body temperature

Seminal vesicle

Adds fluid and nutrients to sperm, to form semen

Sperm duct

Muscular tube which links the testis to the urethra to allow the passage of semen containing sperm

Testis (pl. testes)

Male gonads that produce sperm

Urethra


To pass semen containing sperm through the penis, also carries urine from the bladder at different times

3. Identify on diagrams of the female reproductive system, the ovaries, oviducts, uterus, cervix and vagina, and state the functions of these parts.



Part

Function

Cervix

A ring of muscle that separates the vagina from the uterus

Funnel of oviduct

Directs an ovum (egg) from the ovary into the oviduct

Ovary

Contains follicles in which ova (eggs) are produced

Oviduct

Carries an ovum to the uterus, with propulsion provided by tiny cilia in the wall; also the site of fertilization

Urethra

Carries urine from the bladder

Uterus

Where the fetus develops

Vagina

Receives the male penis during sexual intercourse; sperm are deposited here


2. Compare male and female gametes in terms of size, numbers and mobility.


Types of gamete

Structure

Egg

  1. Is large in size 0.1mm because it has all cell components that is needed for the cell to grow and multiply; has yolk to nourish the embryo.

  2. During ovulation, only one egg is released every month.

  3. Ovum is immobile as the sperm moves towards it to fertilise it.

Sperm



  1. Size is very small 0.05mm.

  2. During ejaculation millions of sperms are produced into the women’s vagina.

  3. Sperms are highly mobile and can swim towards the oviduct with he help of its tail.




  1. Describe the menstrual cycle in terms of changes in the uterus and ovaries.







    1. During sexual intercourse, erect penis is inserted into vagina;

    2. Semen is ejaculated into the neck of vagina;

    3. Many sperms cluster around ovum but only one penetrates;

    4. A fertilization membrane is secreted around the egg once one sperm enters;

    5. The sperm nucleus fuses with egg nucleus to form zygote, this process is called fertilization.
    5. Describe the fertilization in terms of the joining of the nuclei of male gamete (sperm) and the female gamete (egg).


6. Outline early development of the zygote simply in terms of the formation of a ball of cells that becomes implanted in the wall of the uterus.



7. Indicate the functions of the amniotic sac and amniotic fluid.

Structure

Function

Amniotic sac

A thin membrane, formed from cells of embryo, contains the amniotic fluid;

It encloses the fetus and prevents entry of bacteria.



Amniotic fluid

Supports the fetus, protecting it from physical damage;

It absorbs excretory materials (urine) released by the fetus.




8. Describe the function of the placenta and umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products (no structural details are required).



  • The placenta brings the blood supply of the fetus close to that of the mother, but prevents mixing;

  • This is important because the fetus and mother may have different blood groups and any mixing can result in blood clotting;

  • Also the mother’s blood pressure is higher compared to the fetus which might damage the fetal organs;

  • Blood from fetus passes through the umbilical cord in the umbilical artery to the placenta.

  • Substances that diffuse across the placenta are as follows:

Type of substance

To fetus from mother

To mother from fetus

Respiratory gases

Oxygen

Carbon dioxide

Soluble nutrients

Amino acids, glucose, fatty acids, glycerol, vitamins, minerals, water




Disease-preventing substances

Antibodies, antibiotics




Nitrogenous excretory substances




Urea

Potentially harmful substances

Alcohol, nicotine and other drugs, viruses, bacteria





9. Describe the advantages and disadvantages of breast-feeding compared with bottle-feeding using formula milk.

Advantages of breast-feeding over bottle-feeding:

  • There are antibodies present in the breast milk, giving the baby protection against infection;

  • Foodstuffs are present in breast milk in the correct proportions;

  • There are no additives and preservatives in breast milk;

  • Breast feeding builds a bond between mother and baby;

  • Breast milk does not require sterilization as there are no bacteria present that could cause intestinal disease;

  • Breastfeeding triggers a reduction in the size of the mother’s uterus.

  • Formula milk is much more expensive than breast milk, which is free.

Advantages of bottle-feeding over breast-feeding:

  • Someone else can feed the mother’s baby;

  • This can also help the father to bond with the baby, if he is involved in feeding.


10. Describe the method of transmission of human immunodeficiency virus (HIV), and the ways in which HIV/AIDS can be prevented from spreading.

HIV may result in AIDS




Methods of transmission

Ways of preventing its spread

Unprotected sexual intercourse with an infected person

Use of condom for sexual intercourse

Drug use involving sharing a needle used by an infected person

Abstinence from sexual intercourse

Transfusions of unscreened blood

Screening of blood used for transfusions

Infected mother to fetus

Use of sterilized needles for drug injections

Feeding a baby with milk from an infected mother

Feeding a baby with bottled milk when the mother has HIV

Use of unsterilized surgical instruments

Use of sterilized surgical instruments


11. Outline how HIV affects the immune system in a person with HIV/AIDS.

  • HIV virus attacks some types of lymphocyte (white blood cells) in the bloodstream;

  • Lymphocytes produce antibodies, which attack the antigens present on invading microbes;

  • So HIV stops this happening - thus the person develops symptoms of AIDS;

  • So they become vulnerable to infections (like pneumonia, tuberculosis and cancer);

  • A person with AIDS usually dies of a collection of several illnesses.


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