Infectious agents spread through contaminated food, water, air, contact or vectors. Therefore, public measures should include clean water supply, sewage and waste management, regular cleaning and disinfection of tanks and pools, hygienic food handling, avoiding close contact during airborne infections, eliminating mosquito breeding sites, using insecticides and mosquito nets, and vaccination programmes.
Public health safeguards include sanitation, safe drinking water, proper disposal of wastes and excreta, disinfection of water reservoirs, hygiene in public catering, vector control and immunisation.
Knowing the causative organisms and their modes of spread allows targeted prevention. For example, understanding Plasmodium and mosquito vectors helps malaria control, while immunology has enabled vaccination. Microbiology and biotechnology have also contributed antibiotics, safer vaccines and better diagnostic methods.
Biology has helped by identifying pathogens, understanding their life cycles and transmission, developing vaccines, antibiotics, diagnostics and vector-control strategies.
Entamoeba histolytica reaches food and water through faecal contamination. Plasmodium requires a female Anopheles mosquito vector, which injects sporozoites. Ascaris eggs are passed in faeces and contaminate soil, water and plants. Pneumonia-causing bacteria spread through respiratory droplets and contaminated articles such as glasses or utensils.
(a) Amoebiasis spreads through food and water contaminated with faecal matter; houseflies can act as carriers. (b) Malaria spreads through the bite of infected female Anopheles mosquito. (c) Ascariasis spreads through ingestion of food, water, fruits or vegetables contaminated with eggs from infected faeces. (d) Pneumonia spreads by inhaling droplets or aerosols from an infected person or by sharing contaminated utensils.
Water-borne diseases spread when pathogens contaminate drinking water or food. Prevention requires safe water supply, proper disposal of excreta, protection and disinfection of reservoirs and tanks, hygienic handling of food and vegetables, and personal cleanliness such as handwashing.
Use clean drinking water, boil or filter water when needed, prevent faecal contamination, dispose of sewage properly, wash food, and maintain personal and public hygiene.
The selected gene should express an antigen that the host immune system can recognise. When introduced into host cells, it produces the antigenic polypeptide, leading to antibody and memory-cell formation. It should be specific, safe and immunogenic.
In DNA vaccines, a suitable gene is a gene from the pathogen that codes for an antigenic protein capable of inducing a protective immune response without causing disease.
Primary lymphoid organs are where immature lymphocytes differentiate into antigen-sensitive lymphocytes. Secondary lymphoid organs provide sites where lymphocytes interact with antigens and proliferate into effector cells.
Primary lymphoid organs are bone marrow and thymus. Secondary lymphoid organs include spleen, lymph nodes, tonsils, Peyer's patches of the small intestine and appendix.
MALT occurs in the lining of respiratory, digestive and urogenital tracts. CMI is mediated by T-lymphocytes. AIDS is caused by HIV. NACO is the national organisation involved in AIDS control.
(a) Mucosa-associated lymphoid tissue. (b) Cell-mediated immunity. (c) Acquired Immuno Deficiency Syndrome. (d) National AIDS Control Organisation. (e) Human Immunodeficiency Virus.
Innate immunity includes physical barriers such as skin, physiological barriers such as stomach acid, cellular barriers such as phagocytes and cytokine barriers such as interferons. Acquired immunity involves B- and T-lymphocytes and produces primary and secondary responses. Active immunity occurs after vaccination or natural infection. Passive immunity occurs when preformed antibodies are given, as in antitoxin injection, or naturally received through colostrum or placenta.
(a) Innate immunity is non-specific and present from birth; acquired immunity is pathogen-specific and has memory. (b) Active immunity is produced by the host after antigen exposure; passive immunity is protection by ready-made antibodies.
Label the two longer heavy chains forming the inner arms and stem of the Y, the two shorter light chains on the outer arms, disulphide bonds joining the chains, and the antigen-binding sites at the two upper tips. NCERT represents an antibody molecule as H2L2.
A correct diagram should show a Y-shaped antibody with two heavy chains and two light chains, usually represented as H2L2, with antigen-binding sites at the tips.
The chapter lists the major HIV transmission routes as sexual contact, infected blood, contaminated needles and mother-to-child transmission. HIV does not spread by ordinary physical contact such as touch or sharing food.
HIV is transmitted by sexual contact with an infected person, transfusion of contaminated blood or blood products, sharing infected needles, and from an infected mother to her child through placenta.
After entering the body, HIV enters macrophages and helper T-cells. Viral RNA is reverse-transcribed into DNA, which integrates into host-cell DNA and produces more viruses. As HIV multiplies, the number of helper T-cells progressively decreases. Since helper T-cells are essential for immune coordination, the person becomes vulnerable to opportunistic infections.
HIV infects and destroys helper T-lymphocytes, reducing cell-mediated and antibody-mediated immune responses and causing immunodeficiency.
Normal cells show controlled growth and contact inhibition. Cancer cells lose this regulation and continue dividing to form tumours. Malignant cells can invade nearby tissues and enter blood or lymph to spread to other body parts.
A cancerous cell divides uncontrollably, ignores normal growth regulation, can invade surrounding tissues and may spread to distant sites, unlike a normal cell.
Cells sloughed from malignant tumours can reach distant tissues through circulation. They lodge in new locations, proliferate and form new tumours. This property makes malignant cancers especially dangerous.
Metastasis is the spread of cancer cells from the original tumour to distant body sites through blood or lymph, where they form secondary tumours.
NCERT lists immediate effects such as vandalism, violence and risky behaviour. Excessive doses may cause respiratory failure, heart failure, cerebral haemorrhage, coma or death. Sharing needles can transmit AIDS and hepatitis B. Long-term use damages the nervous system and liver, disrupts family and social life, and use during pregnancy can adversely affect the foetus.
Alcohol and drug abuse can cause reckless behaviour, violence, overdose, coma, death, poor academic and social functioning, addiction, dependence, infections such as AIDS and hepatitis B, nervous system damage, liver cirrhosis and harm to the foetus during pregnancy.
The chapter identifies peer pressure and the idea that substance use is 'cool' as causes of abuse among adolescents. A student can protect themselves by respecting personal limits, discussing stress and pressure with trusted adults, avoiding risky company and channelising energy into sports, reading, music, yoga or other constructive activities.
Yes. Peer pressure can influence a person to try alcohol or drugs. Protection comes from resisting undue pressure, choosing supportive friends, seeking help from parents, teachers or trusted peers, and engaging in healthy activities.
Repeated use produces psychological attachment to effects such as euphoria and temporary well-being. Receptors develop tolerance, so higher doses are needed. If use is stopped abruptly, withdrawal symptoms such as anxiety, shakiness, nausea and sweating may occur, making quitting difficult without guidance and medical help.
It is difficult because alcohol and drugs are addictive and can cause dependence, tolerance and withdrawal symptoms.
Adolescence is a vulnerable stage. Pressure to excel, desire to escape problems, unstable family support and peer influence can push adolescents toward alcohol or drugs. Prevention requires avoiding undue pressure, counselling young people to face stress and failure, seeking help from parents, teachers and trusted peers, recognising danger signs early, and using professional de-addiction or rehabilitation support where needed.
Youngsters may be motivated by curiosity, adventure, experimentation, stress, peer pressure, family instability, media influence and the false idea that substance use is fashionable. This can be avoided through education, counselling, supportive parenting, resisting peer pressure, healthy activities and timely professional help.