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

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

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Question 1

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Define health as per modern biological understanding and list the three main factors that affect it.

Health is a state of complete physical, mental and social well-being, not merely the absence of disease or physical fitness.
Genetic disorders—inherited or congenital deficiencies—are one major factor affecting health.
Infections by pathogens and lifestyle choices (diet, rest, exercise, habits) are the other two factors that affect health.

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Question 2

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What is a pathogen? Give two examples of pathogenic bacteria and the diseases they cause.

A pathogen is a disease-causing organism that lives in or on a host, multiplies and interferes with its normal vital activities causing morphological and functional damage.
Salmonella typhi is a pathogenic bacterium that causes typhoid fever, entering the body through contaminated food and water.
Streptococcus pneumoniae causes pneumonia by infecting the alveoli of the lungs, which become filled with fluid causing respiratory problems.

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Question 3

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How is typhoid fever diagnosed, and what are its two potentially fatal complications?

Typhoid fever is confirmed by the Widal test, which detects specific antibodies against Salmonella typhi in the patient's blood serum.
Intestinal perforation is a serious complication where the intestinal wall ruptures due to ulceration caused by the bacteria.
Death may occur in severe cases, especially if intestinal perforation is not treated promptly.

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Question 4

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Name the causative organism of malignant malaria and explain why it is considered the most dangerous form.

Plasmodium falciparum causes malignant malaria, the most serious type among the three species (P. vivax, P. malariae, P. falciparum).
P. falciparum causes massive and rapid destruction of red blood cells, leading to severe anaemia and organ damage.
Malignant malaria can even be fatal if not treated promptly, making it the most dangerous form of malaria.

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Question 5

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What is haemozoin and what role does it play in malaria?

Haemozoin is a toxic substance released when Plasmodium-infected red blood cells (RBCs) rupture inside the human body.
This toxin is responsible for the characteristic recurring chills and high fever that occur every three to four days in malaria patients.
The periodic nature of fever in malaria is directly linked to the synchronized rupture of infected RBCs and subsequent haemozoin release.

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Question 6

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Distinguish between filariasis and ascariasis in terms of causative organism and main symptom.

Ascariasis is caused by Ascaris (roundworm), an intestinal parasite; symptoms include internal bleeding, muscular pain, fever, anaemia and blockage of intestinal passage.
Filariasis (elephantiasis) is caused by Wuchereria bancrofti and W. malayi (filarial worms) that live in lymphatic vessels causing chronic inflammation and gross deformities.
While Ascaris affects the intestinal tract, Wuchereria primarily affects the lymphatic vessels of lower limbs and sometimes the genital organs.

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Question 7

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Name the fungi responsible for ringworm and describe the characteristic symptoms of this infection.

Ringworm is caused by fungi belonging to the genera Microsporum, Trichophyton and Epidermophyton.
The main symptoms are dry, scaly lesions on various parts of the body such as skin, nails and scalp, accompanied by intense itching.
The fungi thrive in warm, moist conditions such as skin folds in the groin or between the toes, and are generally acquired from soil or infected individuals' belongings.

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Question 8

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What are the four types of barriers that constitute innate immunity?

Physical barriers include the skin and mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts, which trap microbes.
Physiological barriers include acid in the stomach, saliva in the mouth and tears from the eyes—all of which prevent microbial growth.
Cellular barriers (neutrophils, monocytes, macrophages, natural killer cells) and cytokine barriers (interferons secreted by virus-infected cells) make up the remaining two types.

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Question 9

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What is an antibody? Describe its structural composition.

An antibody is a protein produced by B-lymphocytes in response to antigens (pathogens or foreign molecules) to fight infections.
Each antibody molecule consists of four peptide chains: two shorter light (L) chains and two longer heavy (H) chains, represented as H2L2.
Different classes of antibodies are produced including IgA, IgM, IgE and IgG, each serving different immunological functions.

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Question 10

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Differentiate between active immunity and passive immunity.

Active immunity is produced when a host is exposed to antigens (via natural infection or vaccination); antibodies are produced by the host's own immune system and the response is slow but long-lasting.
Passive immunity involves direct transfer of ready-made antibodies into the host; it provides immediate protection but is short-lived as the host does not produce its own antibodies.
Examples of passive immunity include colostrum (IgA) providing protection to newborns and antibodies transferred from mother to foetus through the placenta.

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Question 11

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Why is colostrum considered essential for a newborn infant?

Colostrum is the yellowish fluid secreted by the mother during the initial days of lactation after childbirth.
It contains abundant antibodies of the IgA class, which provide passive immunity to protect the newborn infant against infections.
Since the newborn's own immune system is not yet fully functional, these maternal antibodies act as the first line of immunological defence.

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Question 12

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What is an allergy? Name the chemicals responsible for allergic symptoms.

Allergy is the exaggerated response of the immune system to certain antigens (allergens) present in the environment, such as pollen, dust mites and animal dander.
The antibodies produced against allergens are of the IgE type; these trigger mast cells to release chemicals that cause symptoms.
Histamine and serotonin, released from mast cells, are responsible for allergic symptoms like sneezing, watery eyes, running nose and difficulty in breathing.

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Question 13

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Name the primary and secondary lymphoid organs and state the function of each.

Primary lymphoid organs are bone marrow and thymus; they are sites where immature lymphocytes differentiate into antigen-sensitive mature lymphocytes.
Secondary lymphoid organs include spleen, lymph nodes, tonsils, Peyer's patches of the small intestine and appendix; they provide sites for lymphocyte–antigen interaction and subsequent immune response.
After maturation in primary organs, lymphocytes migrate to secondary lymphoid organs to encounter antigens and proliferate into effector cells.

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Chapter 7: Human Health and Disease | Short Questions

Define health as per modern biological understanding and list the three main factors that affect it.

What is a pathogen? Give two examples of pathogenic bacteria and the diseases they cause.

How is typhoid fever diagnosed, and what are its two potentially fatal complications?

Name the causative organism of malignant malaria and explain why it is considered the most dangerous form.

What is haemozoin and what role does it play in malaria?

Distinguish between filariasis and ascariasis in terms of causative organism and main symptom.

Name the fungi responsible for ringworm and describe the characteristic symptoms of this infection.

What are the four types of barriers that constitute innate immunity?

What is an antibody? Describe its structural composition.

Differentiate between active immunity and passive immunity.

Why is colostrum considered essential for a newborn infant?

What is an allergy? Name the chemicals responsible for allergic symptoms.

Name the primary and secondary lymphoid organs and state the function of each.

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