Q1. What are the various public health measures, which you would suggest as safeguard against infectious diseases?
Answer: Public health measures are crucial for preventing and controlling many infectious diseases. Measures to safeguard against infectious diseases are:

1. Waste and Excreta Disposal: Proper disposal of waste and excreta.
2. Water and Hygiene: Periodic cleaning and disinfection of water reservoirs, pools, cesspools, and tanks; maintenance of hygiene in food and water resources.
3. Vector Control: Control or eliminate insect vectors and their breeding places by avoiding water stagnation and using mosquito nets.
4. Immunisation: Vaccination (immunisation) against infectious diseases.
5. Public Hygiene Practices: Observing standard hygiene practices in public catering.
6. Infected Contact Avoidance: Avoiding close contact with infected persons or their belongings, especially for airborne diseases.

Q2. In which way has the study of biology helped us to control infectious diseases?
Answer: The study of biology has armed us to effectively deal with many infectious diseases through the followings:

1. Vaccination and Immunisation: Biological knowledge enabled the use of vaccines and immunisation programs, which controlled or eradicated diseases like smallpox, polio, diphtheria, pneumonia, and tetanus.
2. Antibiotics and Drugs: Discovery of antibiotics and various other drugs allows effective treatment of infectious diseases.
3. Biotechnology: Advances like recombinant DNA technology permit production of newer and safer vaccines (e.g., Hepatitis B vaccine from yeast).
4. Understanding Immunity: Study of the immune system helps develop strategies based on the body’s ability to differentiate self and non-self.

Q3. How does the transmission of each of the following diseases take place?
(a) Amoebiasis (b) Malaria (c) Ascariasis (d) Pneumonia
Answer:

(a) Amoebiasis: It spreads through food and water contaminated with faeces. Houseflies can carry the parasite from infected faeces to food, causing infection.

(b) Malaria: It is transmitted through the bite of an infected female Anopheles mosquito, which injects the Plasmodium parasite (sporozoites) into the human bloodstream.

(c) Ascariasis: Infection occurs when a person consumes food, vegetables, or water contaminated with the eggs of Ascaris present in soil or faeces.

(d) Pneumonia: It spreads through inhaling droplets released by an infected person while coughing or sneezing, or by sharing contaminated objects like utensils and glasses.

Q4. What measure would you take to prevent water-borne diseases?
Answer: Measures to prevent water-borne diseases focus on ensuring the cleanliness and safety of water and food consumed:

1. Maintain personal hygiene.
2. Consume clean drinking water, food, vegetables, and fruits.
3. Implement public hygiene measures including proper disposal of excreta and periodic disinfection of water reservoirs.

Q5. Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.
Answer: In DNA vaccines, a ‘suitable gene’ refers to a gene that codes for an antigenic polypeptide or protein of a pathogen. This gene is cloned into a vector (like a plasmid) and introduced into the host body. The host cells transcribe and translate the foreign gene to produce the pathogenic protein, which acts as an antigen and induces a primary immune response without causing disease. A gene is suitable if its protein product effectively generates a protective immune response.

Q6. Name the primary and secondary lymphoid organs.
Answer:

• Primary Lymphoid Organs: Bone marrow (where all blood cells and lymphocytes are produced) and thymus (site for T-lymphocyte maturation).
• Secondary Lymphoid Organs: Spleen, lymph nodes, tonsils, Peyer’s patches of small intestine, and appendix.

Q7. The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form:
(a) MALT (b) CMI (c) AIDS (d) NACO
(e) HIV
Answer:

(a) MALT – Mucosa-Associated Lymphoid Tissue
(b) CMI – Cell-Mediated Immunity
(c) AIDS – Acquired Immuno Deficiency Syndrome
(d) NACO – National AIDS Control Organisation
(e) HIV – Human Immuno Deficiency Virus

Q8. Differentiate the following and give examples of each:
(a) Innate and acquired immunity (b) Active and passive immunity 
Answer:

(a) Innate and Acquired Immunity: Innate immunity is the natural, non-specific defense present from birth. It provides immediate protection against all kinds of pathogens through barriers like skin, mucus, and secretions. It does not have memory.
On the other hand, acquired immunity is specific to particular pathogens and develops during a person’s lifetime after infection or vaccination. It has memory, meaning it responds faster and stronger upon a second exposure to the same pathogen.

(b) Active and Passive Immunity: In active immunity, the body produces its own antibodies in response to infection or vaccination. It develops slowly but provides long-lasting protection.
In passive immunity, ready-made antibodies are transferred from another source, such as from mother to child through colostrum or through injections like anti-toxins. It gives immediate but short-term protection.

Q9. Draw a well-labelled diagram of an antibody molecule.
Answer:  

Q10. What are the various routes by which transmission of human immuno-deficiency virus takes place?
Answer: The various routes by which transmission of human immuno-deficiency virus takes place are-

1. Sexual Contact: Sexual contact with an infected person.
2. Contaminated Blood: Transfusion of contaminated blood or blood products.
3. Infected Needles: Sharing infected needles (e.g., intravenous drug abuse).
4. Mother to Child: Transmission through the placenta.

Q11. What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
Answer: The HIV virus attacks macrophages and helper T-lymphocytes (Tₕ). Inside, viral RNA replicates to form DNA using reverse transcriptase. This viral DNA integrates into the host genome and directs production of new virus particles. Macrophages act as HIV factories. The progeny viruses destroy more Tₕ cells, leading to a progressive fall in their count, making the person severely immuno-deficient and vulnerable to infections.

Q12. How is a cancerous cell different from a normal cell?
Answer: Normal cells grow and divide in a controlled and orderly manner. They stop dividing when they come in contact with neighbouring cells (contact inhibition) and have normal nutrient needs. In contrast, cancerous cells divide uncontrollably and lose contact inhibition, forming masses or tumors. They require more nutrients, depriving nearby healthy cells, and can spread to other body parts through a process called metastasis.

Q13. Explain what is meant by metastasis.
Answer: Metastasis is the most feared property of malignant tumors. Cells from the original tumor travel through blood or lymph to distant body parts and form secondary tumors there.

Q14. List the harmful effects caused by alcohol/drug abuse.
Answer: The harmful effects caused by alcohol/drug abuse are-

1. Immediate Effects: Reckless behavior, violence, coma, or death.
2. Behavioral Effects: Poor academic performance, withdrawal, depression.
3. Health Effects: Damage to liver and nervous system, fetal harm, AIDS risk.
4. Social Effects: Theft, financial distress, and family problems.

Q15. Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
Answer: Yes, peer pressure can influence drug and alcohol abuse. Protection measures include avoiding peer pressure, seeking counseling, engaging in healthy activities, and seeking help from parents or trusted friends.

Q16. Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit?
Answer: Once a person starts taking alcohol or drugs, it becomes difficult to quit because the body and mind develop addiction (a strong psychological craving) and dependence (physical need for the substance). Over time, the person develops tolerance, needing larger doses to feel the same effect. When they try to stop, withdrawal symptoms such as anxiety, nausea, and sweating make it hard to give up the habit.

Q17. In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
Answer: Youngsters often take to alcohol or drugs out of curiosity, peer pressure, stress, frustration, or lack of guidance. This can be prevented by proper family support, open communication, moral education, counseling, awareness programs, and encouraging youth to engage in sports, hobbies, and positive social activities.