Class 12 Biology Chapter 7 Human Health and Disease Solutions. Explore Class 12 Biology Chapter 7 Human Health and Disease Solutions with clear answers, important questions, and exam-focused explanations to understand key concepts, revise effectively, and prepare confidently for exams. Continue reading: Class 12 Biology Chapter 7 Human Health and Disease Solutions

Class 12 Biology Chapter 7 Human Health and Disease Solutions

A. Very Short-Answer Questions (1 mark each)

1. What is the basic meaning of health?

Ans: Health is a state of physical, mental and social well-being, rather than merely the absence of disease.

2. What is a disease?

Ans: A disease is an abnormal condition that disturbs the normal structure or functioning of the body.

3. Name a few communicable diseases.

Ans: Common cold, encephalitis, cholera, typhoid, malaria and amoebic dysentery are examples.

4. Which bacterium causes typhoid?

Ans: Salmonella Typhi.

5. Name the bacterium that causes pneumonia in humans.

Ans: Streptococcus pneumoniae.

6. What are the symptoms of amoebic dysentery?

Ans: Mucus and blood may be present in the stool. In more severe cases, stools may be frequent and accompanied by abdominal pain.

7. What is addiction?

Ans: Addiction is a condition involving compulsive use of a substance or engagement in a behaviour, often accompanied by physical or psychological dependence. Substances such as tobacco, alcohol and certain drugs can cause addiction.

8. Which drugs are sometimes misused by athletes to improve performance?

Ans: Anabolic steroids, diuretics and narcotic analgesics.

9. Which form of malaria is especially dangerous to humans?

Ans: Malignant malaria, usually caused by Plasmodium falciparum.

10. What is contact inhibition?

Ans: Contact inhibition is the phenomenon in which normal cells stop dividing when they come into contact with neighbouring cells.

11. What is the full form of ELISA?

Ans: Enzyme-Linked Immunosorbent Assay.

12. What are cannabinoids?

Ans: Cannabinoids are a group of chemical compounds that act on cannabinoid receptors, particularly those found in the brain and other parts of the body.

13. How can a healthy person become infected with typhoid?

Ans: A person may become infected by consuming food or water contaminated with Salmonella Typhi. The bacteria enter through the digestive tract and can spread through the bloodstream to different organs.

Fill in the blanks

14. The common cold is a __________ disease.

Ans: Viral.

15. Goitre is caused by a deficiency of __________.

Ans: Iodine.

16. Plasma cells are descendants of __________.

Ans: B lymphocytes.

17. Perforin is released by __________ T cells.

Ans: Cytotoxic.

18. Heroin can be obtained from morphine by __________.

Ans: Acetylation.

19. __________ is obtained from the unripe capsules of the opium poppy.

Ans: Opium.

20. Cocaine interferes with the transmission of the neurotransmitter called __________.

Ans: Dopamine.

21. Drugs that relieve pain are called __________.

Ans: Analgesics.

B. Short-Answer Questions (2 marks each)

22. What factors influence our health?

Ans: The main factors include: (i) genetic or hereditary abnormalities passed from parents to offspring; (ii) diseases caused by microorganisms or non-living factors; and (iii) lifestyle habits, including diet, drinking water, physical activity and rest.

23. State the measures used to control amoebic dysentery.

Ans: (i) Prevent faeces from contaminating water, milk and food. (ii) Drink boiled or otherwise safe water; wash raw vegetables and fruits thoroughly with clean water. (iii) Infected people should follow hygiene precautions to prevent transmission to others.

24. List the symptoms of typhoid.

Ans: Symptoms may include sustained high fever, abdominal pain, constipation, headache and loss of appetite.

25. What are the warning signs of cancer?

Ans: Possible warning signs include: (i) unexplained bleeding; (ii) a lump or swelling in the breast or another part of the body; (iii) a sore that does not heal; (iv) changes in bowel or bladder habits; (v) persistent cough or hoarseness; (vi) persistent indigestion or difficulty swallowing; and (vii) changes in the size, shape or colour of a mole or other skin mark. These signs do not by themselves prove that a person has cancer; medical assessment is needed.

26. What are the common symptoms of the common cold?

Ans: The common cold is caused by viruses, often rhinoviruses. Symptoms include irritation of the nose, a runny nose, sneezing, cough, headache and tiredness.

27. What problems may result from the misuse of drugs and intoxicating substances?

Ans: Possible problems include: (i) declining academic performance; (ii) irregular attendance at school or college; (iii) neglect of health and personal hygiene; (iv) withdrawal from friends and family; (v) aggressive or rebellious behaviour; (vi) loss of interest in activities; (vii) changes in sleep and eating habits; and (viii) frequent weight gain or loss.

28. Differentiate between B lymphocytes and T lymphocytes.

Ans: B lymphocytes: (i) are responsible for humoral immunity; (ii) in humans, mature in the bone marrow; (iii) can differentiate into plasma cells that produce antibodies; and (iv) help defend the body against pathogens through antibody-mediated responses.T lymphocytes: (i) are responsible for cell-mediated immunity; (ii) mature in the thymus; (iii) include cells that attack infected or abnormal cells and cells that regulate immune responses; and (iv) do not themselves secrete antibodies.

29. Briefly describe T lymphocytes and cell-mediated immunity.

Ans: T lymphocytes have receptors that recognise specific antigens. When activated, they can multiply and differentiate into specialised cells. They do not produce antibodies; instead, different T-cell types directly attack infected or abnormal cells or coordinate immune responses. This is called cell-mediated immunity.

30. How is HIV transmitted?

Ans: HIV may be transmitted through: (i) unprotected sexual contact with an infected person; (ii) transfusion of HIV-contaminated blood; (iii) sharing contaminated needles or other injecting equipment; and (iv) transmission from an infected mother to her child during pregnancy, childbirth or breastfeeding.

31. Describe the harmful effects of cigarette smoking.

Ans: Nicotine stimulates the adrenal glands to release adrenaline and noradrenaline, which can increase heart rate and blood pressure. Smoking also increases the risk of cancers, especially of the lungs and respiratory tract, and can cause breathing difficulties and other cardiovascular and respiratory diseases.

32. Differentiate between active and passive immunity.

Ans: Active immunity: (i) develops when the body produces its own immune response after infection or vaccination; (ii) usually lasts longer; (iii) takes time to develop; and (iv) produces memory cells, helping the body respond more quickly to later exposure.

Passive immunity: (i) results when ready-made antibodies are received from another source; (ii) is temporary; (iii) provides immediate protection; and (iv) does not usually produce memory cells.

33. What is immunodeficiency? Describe it briefly.

Ans: Immunodeficiency occurs when one or more parts of the immune system function poorly or are absent. Primary immunodeficiency results from inherited or intrinsic defects in immune-system components.

Secondary immunodeficiency develops because of external factors, such as certain infections, medicines, malnutrition or other conditions. Both B-cell and T-cell functions may be affected. AIDS, caused by HIV, severely weakens the immune system.

C. Descriptive Questions (3–5 marks each)

34. Describe the life cycle of Plasmodium in humans.

Ans: The infective stage of Plasmodium injected into humans by an infected female Anopheles mosquito is the sporozoite. Sporozoites enter the bloodstream and reach the liver, where they multiply. The resulting parasites enter red blood cells and multiply further. Infected red blood cells rupture and release parasites and substances that contribute to recurrent fever and chills. When another female Anopheles mosquito feeds on an infected person, it ingests the parasite stages present in the blood. Sexual reproduction and further development occur in the mosquito, ultimately producing sporozoites that migrate to its salivary glands. The mosquito can then transmit malaria to another person.

35. How is cancer diagnosed? Describe its treatment.

Ans: Cancer involves uncontrolled growth of abnormal cells, sometimes forming a tumour. Diagnosis may involve clinical examination, imaging, laboratory tests and examination of a tissue sample (biopsy) under a microscope. Treatment depends on the type and stage of cancer and may include: (i) surgery; (ii) radiotherapy using ionising radiation; (iii) chemotherapy using anticancer drugs; and (iv) immunotherapy or targeted therapy in suitable cases. The source also mentions radiation treatment; gold, cobalt and iodine are not interchangeable general treatments, and treatment must be selected by medical specialists.

36. What are lymphocytes? Briefly describe them.

Ans: Lymphocytes are white blood cells important in adaptive immunity. The two major types are B lymphocytes and T lymphocytes. They originate from precursor cells in the bone marrow. In humans, T lymphocytes mature in the thymus, while B lymphocytes mature in the bone marrow. B cells can differentiate into plasma cells that secrete antibodies and into memory B cells. T cells contribute to cell-mediated immunity and include helper, cytotoxic and regulatory types. Lymphocytes are found in blood, lymph and lymphoid organs such as the spleen and lymph nodes.

37. What is ringworm? Explain.

Ans: Ringworm is a fungal infection of the skin, hair or nails; it is not caused by a worm. It can produce itchy, scaly, sometimes ring-shaped patches. Warm and humid conditions favour fungal growth, including in skin folds and between the toes. It can spread through direct contact with an infected person or animal, contaminated clothing, towels or combs, and sometimes contaminated surfaces or soil.

38. What measures can be adopted to prevent communicable diseases?

Ans: Prevention includes personal hygiene and public-health measures: (i) wash hands and maintain cleanliness; (ii) consume safe drinking water and clean, properly prepared food; (iii) dispose of waste and sewage safely and keep drains clean; (iv) disinfect or treat contaminated water where appropriate; (v) isolate or limit close contact with people with certain infections when advised; (vi) use recommended vaccines; and (vii) control vectors by preventing stagnant water, keeping surroundings clean and using mosquito nets or other recommended protection. Respiratory infections may also be reduced by ventilation, respiratory hygiene and avoiding close contact when ill.

39. Explain how HIV acts in the human body.

Ans: HIV enters certain immune cells, especially CD4 T lymphocytes. Using the enzyme reverse transcriptase, it makes DNA from its RNA. Viral DNA integrates into the host cell’s DNA, allowing the virus to replicate. Newly formed viruses infect additional cells, gradually reducing the number and function of CD4 T cells. As immunity weakens, the person becomes more vulnerable to opportunistic infections and some cancers. Possible symptoms include fever, diarrhoea and weight loss, but symptoms alone cannot diagnose HIV.

40. Describe the prevention and control of drug abuse.

Ans: (i) Reduce harmful pressure and support young people in their studies, sports and other interests while respecting their abilities and choices. (ii) Provide accurate education and counselling so they can cope with stress, disappointment and personal problems. Encourage constructive activities such as sports, music, drama, yoga and exercise. (iii) Encourage supportive communication with parents, guardians, teachers and friends. (iv) Be alert to warning signs and seek help early rather than respond with blame or stigma. (v) When needed, seek assistance from qualified health professionals, counsellors, psychologists or addiction-treatment services.

D. Additional Questions and Answers (Human Health and Disease Solutions)

1. How do pathogens cause harm?

Ans: Pathogens enter the body, multiply and interfere with normal body functions. They may damage tissues directly or cause harm through toxins and the body’s inflammatory response.

2. Which organ acts as a reservoir for erythrocytes?

Ans: The spleen stores and filters blood cells, although it is not simply a reservoir of all erythrocytes.

3. Name the two hosts of the malaria parasite.

Ans: Humans and the female Anopheles mosquito.

4. Which organ filters blood by trapping microorganisms?

Ans: The spleen helps filter the blood and trap microorganisms.

5. How can pathogens adapt to the host environment?

Ans: Pathogens may possess adaptations that help them survive host conditions, evade immune defences and resist some digestive or other protective mechanisms. The exact adaptation depends on the pathogen; the source’s broad claim about all pathogens surviving stomach acid and digestive enzymes is not universally true.

6. Name three factors that can harm health.

Ans: (i) Genetic abnormalities; (ii) infections; and (iii) lifestyle-related factors.

7. What is the role of immunoglobulin A (IgA) in humans?

Ans: IgA helps protect mucosal surfaces by neutralising pathogens and toxins and by limiting their attachment to and entry through mucous membranes.

8. What is the principle of immunotherapy?

Ans: Immunotherapy treats disease by stimulating, restoring or directing the immune system to recognise and attack diseased cells, including cancer cells, in appropriate cases.

9. How does nicotine act as a stimulant?

Ans: Nicotine stimulates the nervous system and can promote the release of adrenaline and noradrenaline. This can increase heart rate and blood pressure.

10. What is a vaccine? How does it help develop immunity?

Ans: A vaccine presents the immune system with an antigen, or instructions for making an antigen, without causing the disease in the usual way. It stimulates an immune response and the formation of memory B and T cells. If the person later encounters the pathogen, these memory cells help produce a faster and stronger response.

11. What are the functions of the spleen?

Ans: (i) It contains lymphocytes and phagocytic cells. (ii) It filters blood and helps remove microorganisms and worn-out blood cells. (iii) It can store a portion of the body’s platelets and blood cells.

12. How is a biopsy performed?

Ans: A small sample of tissue is taken from the area under investigation. The sample is prepared and examined under a microscope by a trained specialist to look for abnormal cells or disease.

13. What is metastasis?

Ans: Metastasis is the spread of cancer cells from the original tumour to other parts of the body. Cells may enter blood vessels or lymphatic vessels, travel to another site and establish secondary tumours.

14. Discuss measures for maintaining public health. What would you recommend to prevent communicable diseases? (H S ‘24)

Ans: Public-health measures aim to prevent disease and reduce its spread. These include personal and community hygiene, nutritious food, safe drinking water, proper sewage and waste disposal, and cleaning or treating contaminated water sources. Isolation or other infection-control measures may be used for selected airborne diseases, according to public-health advice. Vaccination protects against diseases for which vaccines are available, such as polio, tetanus, diphtheria and measles. Vector-borne diseases such as malaria, filariasis, dengue and chikungunya can be reduced by eliminating stagnant water, controlling mosquito breeding sites and using mosquito nets or other protective measures.

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