Chapter 7: Human Health and Disease Long Questions | biology Class 12 CBSE

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Chapter 7: Human Health and Disease Long Questions | biology Class 12 CBSE | ByteNotes.in

Long Answer

Hard difficulty • Structured explanation

Hard

Question 1

Long Form

Trace the complete life cycle of Plasmodium in both its hosts, identifying the infectious form, sites of multiplication and the mechanism that produces malarial symptoms.

Plasmodium enters the human body as sporozoites (infectious form) through the bite of an infected female Anopheles mosquito; sporozoites travel to the liver where they initially multiply within liver cells.
After liver multiplication, Plasmodium attacks red blood cells (RBCs), replicates within them and causes their rupture; this release of haemozoin (a toxic substance) causes the recurring chills and high fever every three to four days.
When a female Anopheles mosquito bites an infected human, it ingests Plasmodium; the parasites undergo further development and multiply within the mosquito to form sporozoites stored in its salivary glands.
The female Anopheles mosquito acts as both the vector (transmitting agent) and the second host; transmission to a new human occurs when these sporozoite-carrying mosquitoes bite them.
Plasmodium falciparum causes malignant malaria—the most serious and potentially fatal type—while P. vivax and P. malariae cause milder forms; controlling the Anopheles mosquito vector is the cornerstone of malaria prevention.

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Long Answer

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Hard

Question 2

Long Form

Compare innate and acquired immunity under the headings: specificity, memory, types of response and examples of components involved.

Innate immunity is non-specific (acts against all foreign agents alike) and is present from birth; acquired immunity is pathogen-specific and develops during an individual's lifetime after exposure.
Innate immunity has no memory—its response is identical on each encounter; acquired immunity has immunological memory, producing a low-intensity primary response and a stronger, faster secondary (anamnestic) response on re-exposure.
Innate immunity includes four barriers: physical (skin, mucus), physiological (stomach acid, saliva, tears), cellular (neutrophils, macrophages, NK cells) and cytokine (interferons).
Acquired immunity operates through two arms: humoral immunity (B-lymphocytes producing antibodies IgA, IgM, IgE, IgG) and cell-mediated immunity (T-lymphocytes, responsible for graft rejection).
The memory property of acquired immunity underpins vaccination—memory B- and T-cells formed after vaccination rapidly overwhelm pathogens on actual infection, providing long-term protection.

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Long Answer

Hard difficulty • Structured explanation

Hard

Question 3

Long Form

Describe the mechanism of HIV infection from entry into the body to the development of AIDS symptoms, including the role of reverse transcriptase.

HIV, a retrovirus with an RNA genome, enters the body through sexual contact, blood transfusion, shared infected needles or mother-to-child transmission through the placenta.
After entry, HIV infects macrophages; inside the macrophage, the enzyme reverse transcriptase converts the viral RNA genome into viral DNA, which integrates into the host cell's DNA.
The infected macrophage is directed to produce virus particles continuously, acting as an HIV factory; simultaneously, HIV enters helper T-lymphocytes (TH cells), replicates and releases progeny viruses.
Released progeny viruses attack more TH cells, leading to a progressive and irreversible decrease in TH cell numbers; the patient experiences fever, diarrhoea and weight loss during this period.
As TH cell numbers decline, the immune system weakens, leaving the patient vulnerable to opportunistic infections by Mycobacterium, viruses, fungi and Toxoplasma; AIDS is diagnosed by ELISA and anti-retroviral drugs can only prolong life, not cure the disease.

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Long Answer

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Hard

Question 4

Long Form

Analyse the causes, detection methods and treatment strategies for cancer, highlighting how the property of contact inhibition is relevant.

Normal cells show contact inhibition—their growth is inhibited when they come in contact with other cells; cancer cells lose this property and divide uncontrollably, forming tumors (benign or malignant).
Carcinogens—physical (ionising radiations like X-rays, UV), chemical (tobacco smoke) and biological (oncogenic viruses with viral oncogenes; cellular proto-oncogenes when activated)—induce neoplastic transformation of normal cells.
Detection relies on biopsy and histopathology, blood and bone marrow tests for leukemias, radiography, CT (3D X-ray imaging), MRI (magnetic fields) and antibodies against cancer-specific antigens.
Treatment involves surgery (removal of tumor mass), radiation therapy (lethal irradiation of tumor cells) and chemotherapy (drugs targeting rapidly dividing cancer cells, though with side effects like hair loss and anaemia).
Immunotherapy using biological response modifiers such as α-interferon activates the patient's immune system to detect and destroy tumor cells; early detection is critical as many cancers are curable in initial stages.

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Long Answer

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Hard

Question 5

Long Form

Explain the principles of vaccination and immunisation, including passive immunisation and the contribution of recombinant DNA technology to vaccine development.

Vaccination exploits the memory property of acquired immunity; a vaccine (antigenic proteins or inactivated/weakened pathogen) is introduced into the body to stimulate antibody production and memory cell formation.
On actual infection, memory B- and T-cells recognise the pathogen rapidly and mount a massive secondary immune response, neutralising the pathogen before disease develops.
Passive immunisation involves direct injection of preformed antibodies or antitoxin (e.g., in tetanus cases) or anti-venom (in snakebite cases) to provide immediate but temporary protection.
Recombinant DNA technology allows antigenic polypeptides of pathogens to be produced in bacteria or yeast, enabling large-scale, safer vaccine production; hepatitis B vaccine produced from yeast is a prime example.
Immunisation programmes using vaccines have enabled the complete eradication of smallpox and significant control of polio, diphtheria, pneumonia and tetanus.

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Long Answer

Medium difficulty • Structured explanation

Medium

Question 6

Long Form

Describe the harmful effects of drug and alcohol abuse on the individual's physical health, mental health and social life.

Physically, excessive drug/alcohol use causes reckless behaviour, vandalism; overdoses can lead to coma and death due to respiratory failure, heart failure or cerebral haemorrhage.
Chronic use damages the nervous system and liver (cirrhosis); use during pregnancy adversely affects foetal development; smoking increases incidence of lung, bladder and throat cancers.
Intravenous drug users who share needles risk serious infections like AIDS (HIV) and Hepatitis B—both chronic, ultimately fatal and transmissible through sexual contact or infected blood.
Mentally, drug/alcohol abuse causes drop in academic performance, depression, fatigue, aggressive behaviour, mood swings and deteriorating relationships with family and friends.
Socially, addicts may resort to stealing to fund their habit, creating financial and mental distress for their entire family; social adjustment problems and isolation compound the individual's decline.

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Long Answer

Medium difficulty • Structured explanation

Medium

Question 7

Long Form

Discuss the causes and prevention of adolescent drug and alcohol abuse, emphasising the role of parents, teachers and professional support systems.

Causes include curiosity and experimentation during the vulnerable adolescent period (12–18 years), peer pressure, stress from academic competition and the perception that substance use is 'cool' as reinforced by media.
Unstable family structures and unsupportive environments also increase the risk; the first use is often out of curiosity, but later escalates as adolescents use substances to escape problems.
Prevention requires that parents avoid undue pressure on children, combine high nurturance with consistent discipline, and educate and counsel children to handle failure and stress as part of life.
Teachers and parents should look for danger signs—unexplained absence, drop in performance, withdrawal, change in habits—and report or address these promptly to prevent deeper addiction.
Professional and medical help from psychologists, psychiatrists and de-addiction/rehabilitation programmes can fully restore the individual; energy should be channelled into sports, music, yoga and extracurricular activities.

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Long Answer

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Hard

Question 8

Long Form

Compare amoebiasis, ascariasis and filariasis in terms of causative organism, mode of transmission, main symptoms and preventive measures.

Amoebiasis is caused by Entamoeba histolytica (protozoan), transmitted through food and water contaminated by faecal matter via houseflies; symptoms include constipation, abdominal pain, cramps and blood-streaked mucous stools.
Ascariasis is caused by Ascaris (roundworm helminth), transmitted through contaminated water, vegetables or fruits ingested by a healthy person; symptoms include internal bleeding, muscular pain, fever, anaemia and intestinal blockage.
Filariasis (elephantiasis) is caused by Wuchereria bancrofti/W. malayi (filarial helminth), transmitted through bites of female mosquito vectors; symptoms include chronic lymphatic inflammation causing gross deformities of lower limbs and genital organs.
Prevention of amoebiasis and ascariasis centres on safe drinking water, proper food hygiene, sanitation and disposal of excreta to break the faecal-oral transmission route.
Prevention of filariasis requires elimination of mosquito breeding sites, use of mosquito nets, insecticide spraying and introduction of larvivorous fish like Gambusia in water bodies.

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Long Answer

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Hard

Question 9

Long Form

Explain the concept of auto-immune disease and its relationship to the immune system's ability to distinguish self from non-self, giving a relevant example.

The immune system of higher vertebrates evolved the ability to distinguish self-cells from foreign organisms (non-self), which is the molecular basis of acquired immunity.
Normally, immune cells that react against self-antigens are eliminated during maturation; when this tolerance breaks down due to genetic or unknown factors, the immune system attacks the body's own cells.
This self-attack results in tissue damage and is defined as auto-immune disease; it represents a failure of the self/non-self discrimination mechanism of the immune system.
Rheumatoid arthritis is a well-known auto-immune disease that affects many people; the immune system targets joint tissues, causing chronic inflammation, pain and progressive joint damage.
Cell-mediated immunity (T-lymphocytes) is also responsible for graft/organ transplant rejection—it recognises transplanted tissue as 'non-self', necessitating tissue matching and life-long immuno-suppressant therapy.

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Long Answer

Medium difficulty • Structured explanation

Medium

Question 10

Long Form

Describe the structure and function of lymph nodes, thymus and bone marrow, explaining how they collectively maintain the immune system.

Bone marrow is the primary lymphoid organ and the main site of haematopoiesis—all blood cells including lymphocytes originate here; it provides the micro-environment for early lymphocyte development.
The thymus is a lobed primary lymphoid organ located near the heart beneath the breastbone; it is large at birth, reduces with age, and provides the micro-environment for T-lymphocyte maturation; both bone marrow and thymus produce antigen-sensitive lymphocytes.
Lymph nodes are small solid secondary lymphoid structures distributed along the lymphatic system; they trap micro-organisms and antigens from lymph and tissue fluid, activating lymphocytes present there.
The activation of lymphocytes in lymph nodes triggers clonal expansion and differentiation into effector cells that produce antibodies or attack infected cells, mounting the specific immune response.
Together, bone marrow produces lymphocytes, the thymus matures T-cells, and lymph nodes serve as battlegrounds where mature lymphocytes encounter antigens—collectively ensuring a coordinated, multi-layered immune defence.

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Chapter 7: Human Health and Disease | Long Questions

Trace the complete life cycle of Plasmodium in both its hosts, identifying the infectious form, sites of multiplication and the mechanism that produces malarial symptoms.

Compare innate and acquired immunity under the headings: specificity, memory, types of response and examples of components involved.

Describe the mechanism of HIV infection from entry into the body to the development of AIDS symptoms, including the role of reverse transcriptase.

Analyse the causes, detection methods and treatment strategies for cancer, highlighting how the property of contact inhibition is relevant.

Explain the principles of vaccination and immunisation, including passive immunisation and the contribution of recombinant DNA technology to vaccine development.

Describe the harmful effects of drug and alcohol abuse on the individual's physical health, mental health and social life.

Discuss the causes and prevention of adolescent drug and alcohol abuse, emphasising the role of parents, teachers and professional support systems.

Compare amoebiasis, ascariasis and filariasis in terms of causative organism, mode of transmission, main symptoms and preventive measures.

Explain the concept of auto-immune disease and its relationship to the immune system's ability to distinguish self from non-self, giving a relevant example.

Describe the structure and function of lymph nodes, thymus and bone marrow, explaining how they collectively maintain the immune system.

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