Previous year questions: Human Health and Disease

The questions below come from official CBSE board papers and official Sample Question Papers. The year label in each heading is printed on the source, and the marks are the marks printed for that question or part. Try the question before reading the answer.

Q1 (CBSE Board 2025, 1 mark)

Assertion (A): A person infected with malaria suffers from chill and high fever, recurring every three or four days. Reason (R): The parasite attacks the RBC resulting in their rupture and release of haemozoin.

Answer: Both the assertion and the reason are true, and the reason correctly explains the assertion, so the answer is option (A). The Plasmodium parasite multiplies inside the red blood cells and bursts them in a synchronous cycle, and the haemozoin pigment released at the rupture causes the chill and the high fever that returns every few days. The periodicity of the fever therefore follows directly from the cycle of rupture of the red blood cells.

Q2 (CBSE Board 2025, 2 marks)

Explain how the immunity of a person is affected if there is atrophy (degeneration) of the thymus gland at an early stage of life.

Answer: The thymus is the primary lymphoid organ in which the T lymphocytes mature, so the production of mature, antigen-sensitive T cells depends on it. If the thymus atrophies early in life, the number of mature T lymphocytes falls and the cell-mediated immune response becomes weak. The person becomes more susceptible to infections, and the immune response to pathogens that hide inside cells is especially affected.

Q3 (CBSE Board 2025, 2 marks)

What are interferons? Explain their role in providing immunity to a person. Which category of innate immunity defence barrier can interferons be classified into?

Answer: Interferons are proteins released by cells that have been infected by a virus. They do not protect the infected cell itself, but they stimulate the neighbouring uninfected cells to become resistant to the virus, so the spread of the infection is limited. They belong to the cytokine barriers of innate immunity, which act by chemical means rather than by the physical, physiological or cellular barriers.

Q4 (CBSE Board 2025, 2 marks)

What is the scientific name of the plant from which the opioids are derived and from which part of the plant is it extracted?

Answer: The plant is Papaver somniferum, the opium poppy. The opioids are extracted from the latex of its unripe or green capsules. Morphine is one of the opioids obtained from this latex, and heroin, or smack, is made from morphine by acetylation.

Q5 (CBSE Board 2024, 1 mark)

In which of the following conditions or diseases is there a substantial increase in the activity of mast cells observed in the human body? (A) Typhoid (B) Allergy (C) Ascariasis (D) AIDS

Answer: Option (B), Allergy. In an allergic reaction the body produces IgE antibodies against the allergen, and these antibodies attach to the mast cells. When the allergen is met again it binds to the antibodies and the mast cells then release histamine along with other chemicals, producing sneezing, watery eyes, a runny nose and trouble in breathing. Typhoid, ascariasis and AIDS do not involve mast cell activity in this way.

Q6 (CBSE Board 2024, 2 marks)

A farmer while working on his farm was bitten by a poisonous snake. He was rushed to a nearby health centre where the doctor gave him an injection to save his life. (i) What did the doctor inject and why? (ii) Name the kind of immunity provided by this injection.

Answer: (i) The doctor injected antivenom, which contains antibodies raised against the snake venom. The antibodies bind and neutralise the venom before it can act on the nervous system and the tissues, which is why the injection has to be given quickly. (ii) This is passive immunity, because the antibodies were made outside the body, in another animal, and are given ready-made; it acts immediately but the protection lasts only for a short time.

Q7 (CBSE Board 2022, 3 marks)

When Plasmodium enters the human body it reproduces asexually and increases its number, and the affected person suffers from malaria. After a number of asexual cycles the parasite enters the sexual phase of its life cycle. Trace the sexual stages in the life cycle of Plasmodium in a female Anopheles mosquito, when it bites an infected person, up to the formation of mature infective stages of the parasite.

Answer: The female Anopheles mosquito picks up the gametocytes of the parasite along with the blood of the infected person. In the gut of the mosquito the gametocytes mature into gametes, the male and the female gametes fuse and form a zygote, and the zygote develops into a motile ookinete. The ookinete moves through the gut wall and forms an oocyst, and inside the oocyst the parasite divides and produces many sporozoites. These sporozoites are the mature infective stages; they travel to the salivary glands of the mosquito and are passed into the blood of a healthy person at the next bite, beginning the asexual cycle again. The sexual phase therefore happens only inside the mosquito, which is why the mosquito is called the definitive host and the human the intermediate host.

Q8 (CBSE SQP 2022-23, 1 mark)

Interferons are most effective in making non-infected cells resistant against the spread of which of the following diseases in humans? (a) ascariasis (b) ringworm (c) amoebiasis (d) AIDS

Answer: Option (d), AIDS. Interferons are the cytokine barrier of innate immunity and they act against viral infections, because a virus-infected cell releases interferons that make the neighbouring cells resistant to the virus. AIDS is caused by HIV, a virus, while ascariasis and amoebiasis are caused by worms and protozoans and ringworm by fungi, so interferons are not their main defence.

Q9 (CBSE SQP 2022-23, 3 marks)

Highlight the structural importance of an antibody molecule with a diagram. Name the four types of antibodies found to give a humoral immune response, mentioning the functions of two of them you have studied.

Answer: The antibody molecule has four peptide chains, two light chains and two heavy chains, represented as H2L2, and they are held together by disulphide bonds in a Y shape. The two arms of the Y carry identical antigen binding sites, so one antibody can bind two antigen molecules and clump them; this is the structural feature that gives the antibody its specificity for the antigen. The four types are IgA, IgM, IgE and IgG. IgA is present in the colostrum and in the mucosal secretions and protects the newborn, while IgG is the most abundant antibody in the blood and can cross the placenta to protect the foetus.

Q10 (CBSE SQP 2023-24, 2 marks)

The graph given below indicates the administration of the first (L) and second (M) dose of a vaccine, and the corresponding response of the body is indicated by X and Y. Interpret the graph and explain the reason for such a response shown by the body.

Answer: The first dose at L produces a small, slow response, X, which is the primary immune response, because the immune system is meeting the antigen for the first time. The second dose at M produces a much larger and faster response, Y, which is the secondary or anamnestic response. The reason is that the first dose produced memory B and T cells, and when the antigen enters again these cells recognise it at once and multiply rapidly to make a large amount of antibody. That is why two doses give far better protection than one, and this is the principle of the standard vaccination schedule.