Summative Practice 11 – Question 5 & 6 (Form 4 Biology Textbook Exercise and Answer)

Question 5:
Two individuals acquired immunity against chickenpox in different situations. Individual X recovered from chickenpox. Individual Y was injected with a type of suspension and received immunity against chickenpox after a few months.
Explain the immunity acquired by
(a) individual X
(b) individual Y

In individual X, lymphocytes are stimulated to produce antibodies that destroy antigens. Memory cells remain in the body. Individual X acquires natural active immunity and is able to fight against the disease in the future.

The suspension that is injected into individual Y is a vaccine. Vaccine is weakened pathogens used to induce lymphocytes to produce antibodies. Individual Y acquires artificial active immunity and obtains immunity against measles.

Question 6:
(a) A newborn baby needs to receive immunisation based on the Immunisation Plan recommended by the World Health Organisation (WHO).
Explain why the immunisation programme is required.

(b) (i) Some vaccine injections require only one dose throughout the lifetime of an individual. Explain why.
(ii) Sinti’s mother forgot to bring Sinti to the clinic for the third dosage of the hepatitis vaccination. Explain the effects on Sinti’s immunity.
(iii) Aziman accidentally stepped on a rusty nail during a mountain climbing expedition.
Describe the type of injection that is suitable to be administered by the doctor.
Explain your answer.

(c) Explain how HIV can paralyse the immune system of a person infected by the virus.

• A newborn needs to acquire immunisation based on the Immunisation Plan because, the baby does not acquire immunity against certain diseases from the mother (natural passive immunity) during the foetal stage.

• Also, after the baby reaches the age of 6 months, his/her natural passive immunity will recede.

• Furthermore, the baby maybe exposed to various infectious diseases, for example measles. Babies are unable to fight infections because they do not have the immunity against the disease.

• Therefore, babies must be given immunisation for him/her to acquire immunity against diseases.

One dose is sufficient to induce the body’s immune system to produce an antibody concentration that exceeds the immunity level and permanent throughout life to prevent infections.

Sinti may contract hepatitis B if she is exposed to the hepatitis B virus because the antibody level in her body has not reached the required concentration to offer complete protection from the disease.

• For an immediate treatment, Aziman needs to be given an antitetanus injection. Antitetanus contains antibodies that will act against tetanus. The rusty nail stepped on by Aziman may contain Clostridium tetani that can cause tetanus (lockjaw).

• As the antibodies for tetanus is already available in the antitetanus, the antibodies can act immediately against the bacteria.

• The body immune system does not need to be stimulated to produce antibodies against the disease.

• Thus the immunity acquired by Aziman is known as artificial passive immunity.

• The antiserum injection can save Aziman immediately compared to immunisation that will take a long time to stimulate the body’s immune system to produce the required quantity of antibodies.

• The HIV virus attacks and cripples the immune system (lymphocytes), rendering the body incapable of fighting diseases.

• Bacteria, yeasts, parasites and viruses that normally do not cause any serious diseases in individuals with healthy immune systems can now endanger and become fatal to those with AID

• This is because the HIV virus attacks and destroys cells that carry the CD4 molecule on their surface, for example, T lymphocyte. The function of the T lymphocyte is to destroy pathogenic
microorganisms. In an infection, the T lymphocyte becomes a host for the HIV virus. The HIV virus will attach itself to the plasma membrane of the T lymphocyte and start building its DNA’s genetic materials.

• The viral DNA then enters the nucleus of the T lymphocyte, combines with and becomes a part of the T lymphocyte’s DNA.
• In the T lymphocyte, the HIV virus can replicate to produce new HIV populations that will attack other T lymphocytes. In this way, the HIV virus will cripple the immune system of the infected individual.

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