Revision: Biology and Human Welfare >> Human Health and Diseases Biology (Theory) ISC (Science) ISC Class 12 CISCE

It is to maintain a stable equilibrium of the body in accordance with the pressures and changes of the body environment.

Adverse functioning of one or more organs or systems of the body, characterised by specific signs and symptoms, is called disease.

A disease caused by a specific pathogenic organism and capable of being transmitted to another individual by direct or indirect contact is known as communicable (infectious) disease.

A disease not caused by pathogenic organisms and not transmitted from one person to another by direct or indirect contact is known as a non-communicable (non-infectious) disease.

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The diseases which don’t spread from infected person to a healthy person are known as non-communicable or non-infectious diseases.

Tumour is a mass of abnormally proliferating cells formed due to uncontrolled cell division.

Benign tumour is a non-cancerous tumour that remains confined to its original site and does not spread to other parts of the body.

Cancer is a disease characterised by uncontrolled and abnormal division of body cells due to loss of normal growth regulation.

Metastasis is the process by which cancer cells spread from the primary site to distant organs through blood or lymph.

Malignant tumour is a cancerous tumour that grows rapidly, invades surrounding tissues and spreads to distant organs.

A normal cellular gene involved in growth and development, which can become an oncogene after mutation or activation, is called a proto-oncogene.

Agents that cause cancer by disturbing the normal genetic and regulatory processes of cells are called carcinogens.

A cancer-causing gene that induces transformation of normal cells into cancerous cells is called an oncogene.

The organisms which produce disease must enter through a certain route called the portal of entry.

The antiviral substance secreted by virus-infected cells that inhibits viral multiplication is called interferon.

The antibody-mediated defence mechanism is called humoral immune response.

The system of defence mechanisms that protects the body against harmful agents is called immune system.

The hereditary, non-specific protection present from birth is called innate (natural) immunity.

The immunity developed during an individual’s lifetime after exposure to antigens is called acquired (specific) immunity.

The defence mechanism involving lymphocytes and macrophages without antibody production is called cell-mediated (cellular) immune response.

The ability of an antigen to stimulate the formation of specific antibodies or immune cells is called antigenicity.

A substance that induces an immune response and antibody formation when introduced into the body is called an antigen.

The antigens of proteinaceous nature are known as complete antigens.

A non-protein substance that becomes antigenic only after combining with a protein is called a hapten.

When disease-causing germs gain entry into the blood stream, they produce poisonous substances called toxins (meaning poisons). In response, the lymphocytes of the blood produce chemical substances called antibodies which circulate freely in the blood plasma.

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The B-lymphocytes produce an army of proteins in response to pathogens into our blood to fight with them. These proteins are called antibodies.

The processes by which antibodies label antigens for destruction by the immune system is called effector mechanisms.

The exaggerated response of the immune system to certain antigens present in the environment is called an allergy.

The substance that triggers an allergic immune response in a sensitive individual is called an allergen.

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes no adverse effects to most people. These diseases include hay fever, dermatitis, asthma, food allergies, etc.

The study of the immune system and immune responses is called immunology.

Health is defined as the state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.

The overall ability of the host to fight the disease-causing organisms conferred by the immune system is called immunity.

Innate immunity is the inborn, non-specific defence that protects the body from pathogens from birth.

The immunity obtained by the direct transfer of ready-made antibodies from another individual is called as passive immunity.

The immunity developed when the body produces its own antibodies in response to exposure to antigens through infection or vaccination is called as active immunity.

Acquired immunity is the specific defence developed after exposure to a pathogen, characterised by memory and a stronger response on re-exposure.

A group of small protein molecules produced in the body or by transgenic organisms and used in the treatment of viral diseases is called interferon.

Autoimmune disease is a pathological condition caused due to autoimmunity, where self-tissues are damaged or destroyed by the immune system.

Autoimmune response is an immune reaction in which antibodies or immune cells are produced against the body’s own antigens.

Autoimmunity is the condition in which the immune system fails to recognise self and reacts against the body’s own cells and tissues.

Replacement of diseased tissues or organs by healthy ones is called transplantation.

Kidney transplantation is the surgical transfer of a healthy kidney into a patient with end-stage renal disease.

Adolescence is the period between the beginning of sexual maturation and entry into adult life.

Addiction is a condition of physical and psychological dependence on a substance or habit, leading to compulsive use despite harmful effects.

Any chemical substance which, when taken, alters the normal functioning of the body is called a drug.

Drugs that act on the central nervous system and produce marked changes in perception, thought and consciousness are called hallucinogens.

Drug abuse is the improper or excessive use of drugs that leads to harmful effects on physical, mental and social health.

• Communicable / Infectious diseases are caused by pathogens and spread from an infected to a healthy person via air, water, food, vectors, or contact.
• Common pathogens: bacteria (cholera, typhoid, TB), viruses (AIDS, hepatitis), protozoa (malaria), and helminths (ascariasis, filariasis).
• Incubation period: time between infection and symptoms — varies from hours (cholera) to years (HIV/AIDS, leprosy).
• TB (Mycobacterium tuberculosis) spreads through air; prevented by BCG vaccine, isolation, and DOTS.
• Hepatitis spreads through contaminated water, needles, or blood; prevented by boiled water and hygiene.
• Cholera, typhoid, and dysentery spread through contaminated food and water; prevented by hygiene, boiled water, ORS, and vaccination.

• Carcinogens disrupt normal cellular genetics, potentially transforming growth-regulating proto-oncogenes into cancer-causing oncogenes.
• Chemical factors such as nicotine, polycyclic aromatic hydrocarbons, and imbalanced sex hormones are known to induce various cancers.
• Radiation acts as a physical carcinogen, with ionising (e.g., X-rays) and non-ionising (e.g., UV rays) radiation damaging DNA and increasing cancer risk.
• Biological factors such as oncogenic viruses (e.g., HPV and EBV) carry viral oncogenes that can transform normal cells into cancerous ones.
• Lifestyle habits, particularly smoking, tobacco chewing, and alcohol abuse, significantly heighten the risk for multiple types of cancer.

• Cancer is detected through biopsy (tissue sample stained and examined under a microscope), histopathological studies, and blood/bone marrow tests (for leukaemia).
• CT scan uses X-rays to produce 3D images of internal organs; MRI uses strong magnetic fields and non-ionising radiation to detect tissue changes.
• Antibodies against cancer-specific antigens are also used for detecting certain cancers.
• Molecular biology techniques identify genes associated with inherited cancer susceptibility, helping in early prevention.
• Individuals with inherited cancer susceptibility are advised to avoid specific carcinogens, e.g., tobacco smoke in case of lung cancer.

• The immune system defends the body against infectious agents and consists of lymphoid organs, tissues, cells, and soluble molecules like antibodies.
• Primary lymphoid organs (bone marrow and thymus) are the sites where immature lymphocytes originate, develop, and differentiate into antigen-sensitive cells.
• Secondary lymphoid organs (spleen, lymph nodes, tonsils, and MALT) provide the specific sites where mature lymphocytes interact with antigens and proliferate.
• The spleen acts as a blood filter, trapping blood-borne microorganisms, while lymph nodes trap antigens in the lymphatic fluid, triggering localised immune responses.
• The humoral immune response is driven by specific lymphocytes that produce circulating antibodies to bind, neutralise, and eliminate foreign antigens.
• The cellular immune response does not involve circulating antibodies, but instead relies on the direct cooperation of lymphocytes and macrophages to destroy pathogenic organisms.

• Origin of lymphocytes: In embryos, lymphocytes arise from mesenchymal cells of the yolk sac, liver and spleen, while in adults they originate from stem cells in the bone marrow.
• T-lymphocytes: Some lymphocytes migrate from bone marrow to the thymus, where they mature into T-lymphocytes responsible for cellular immunity.
• B-lymphocytes: Lymphocytes that do not pass through the thymus mature in other lymphoid tissues and are called B-lymphocytes, which produce antibodies.
• Circulation and function: Both T- and B-lymphocytes circulate between blood and lymphoid organs, responding to antigens to provide cellular and humoral immunity respectively.

• An allergy is an exaggerated immune response to environmental antigens.
• IgE is the antibody involved in allergic reactions.
• Histamine and serotonin released from mast cells are responsible for allergic symptoms.
• H1 receptors are related to allergic manifestations, whereas H2 receptors are related to gastric acid secretion.
• Severe systemic allergy is called anaphylactic shock.
• Diagnosis is done by testing with small doses of allergens.
• Antihistamines, adrenaline, steroids, and sodium cromoglycate are used in treatment.

• Immunology studies the immune system, while immunity is the host's ability to fight disease-causing organisms.
• Body defence works at two levels: external local barriers that prevent entry, and the internal immune system that fights invading germs.
• The immune system can accurately distinguish between the body's own cells (self) and foreign invaders (non-self).
• Foreign substances that trigger an immune response are antigens, and the protective chemicals produced against them are antibodies.
• Stimulated lymphocytes divide into active effector cells (to fight the immediate infection) and dormant memory cells.
• Memory cells stay in the lymph nodes to mount a much faster and stronger immune response upon subsequent encounters with the same antigen.

• Innate immunity is a non-specific, natural defence present at birth that prevents the entry of and destroys foreign agents.
• Physical barriers, such as the skin and mucous membranes, physically block and trap invading microorganisms.
• Physiological barriers utilise bodily secretions - like stomach acid, saliva, and lysozyme in tears - to inhibit or destroy microbial growth.
• Cellular barriers rely on phagocytic cells (neutrophils, macrophages) and Natural Killer cells to actively ingest and destroy pathogens.
• Cytokine barriers consist of interferons, which are secreted by virus-infected cells to protect surrounding healthy cells from further viral infection.
• Additional systemic defences include fever, the complement protein system, and acute-phase proteins that enhance host resistance and eliminate pathogens.

• Acquired immunity is a pathogen-specific defence system developed over a lifetime that remembers infections and forms the basis of vaccination.
• Its main features include specificity against distinct pathogens, diversity in recognising various antigens, self/non-self recognition, and immunological memory.
• Initial pathogen exposure causes a low-intensity primary response, while later exposures trigger a much faster and stronger secondary response due to memory cells.
• B-lymphocytes produce protective proteins called antibodies (structured as H₂L₂), and T-lymphocytes help B-cells while mediating cellular responses.
• The immune response is classified as either humoral (antibody-mediated in the blood) or cell-mediated (T-cell mediated, responsible for graft rejection).
• Immunity can be active (the body produces its own antibodies, providing long-term protection) or passive (the body receives ready-made antibodies for immediate, short-term protection).

• A vaccine is a biological preparation introduced into the body to stimulate active immunity.
• Vaccines contain weakened, killed pathogens or their antigenic proteins that induce antibody production.
• Vaccination also produces memory B-cells and T-cells, providing long-term protection against future infections.
• Modern vaccines include genetically engineered second- and third-generation vaccines developed using biotechnology.

• Monoclonal antibodies are homogeneous antibodies of single, specific type produced against one antigen.
• They are produced by hybridoma technology using fused antibody-producing lymphocytes and myeloma cells.
• Hybridoma cells combine continuous growth with the ability to secrete specific antibodies.
• Monoclonal antibodies are highly specific and therefore useful for accurate diagnosis and screening.
• They are widely used in immunoassays, pregnancy tests, drug detection, and diagnosis of diseases like AIDS.

• Autoimmunity is a condition where the immune system loses its ability to distinguish between "self" and "non-self" cells, mistakenly targeting the body's own tissues.
• An autoimmune response is a specific abnormal reaction in which the body actively produces antibodies or immune cells directed against its own self-antigens.
• Autoimmune disease is the resulting pathological condition where this misdirected immune response causes actual physical damage and destruction to self-tissues.
• Common examples include Rheumatoid arthritis, Hashimoto’s disease (targeting the thyroid), myasthenia gravis (targeting muscles), Addison’s disease, and chronic anaemia (targeting red blood cells).

• AIDS is a fatal, non-congenital condition caused by HIV, leading to severe immune system deficiency.
• HIV is a spherical retrovirus featuring two single-stranded RNA molecules, the enzyme reverse transcriptase, and a lipid envelope with specific glycoproteins.
• The virus targets and destroys CD4 (T4) helper T-cells and uses macrophages as replication factories, progressively weakening the host's immune response.
• Transmission occurs through contact with infected body fluids, specifically via sexual intercourse, contaminated blood transfusions, shared needles, or from mother to child.
• Individuals at high risk include those with multiple sexual partners, intravenous drug users, recipients of repeated blood transfusions, and children born to infected mothers.
• Diagnosis involves a primary screening test called ELISA, followed by a highly specific confirmatory test known as Western Blot.
• While there is no cure, antiretroviral drugs like AZT can partially reduce viral load and extend patients' lifespans.
• Prevention - including education, safe sexual practices, blood screening, and the use of disposable needles - is critical, supported by social sympathy for those living with HIV.

• Kidney transplantation is the replacement of a non-functional kidney with a healthy kidney in end-stage renal disease.
• The donor kidney can be obtained from a deceased (cadaveric) donor or a living donor.
• Living donors can be genetically related or non-related to the patient.
• Immunosuppressant drugs are given after a transplant to prevent rejection of the new kidney.

• Stem cells are undifferentiated cells capable of self-renewal and differentiation into various specialised cell types.
• They are used in medical treatment to replace or repair damaged tissues and organs through controlled differentiation.
• Stem cell therapy has been successfully used in the treatment of blood cancers such as leukaemia and lymphoma using bone marrow and umbilical cord blood.
• Stem cells hold great potential for future treatment of degenerative diseases, injuries, and genetic disorders with minimal risk of rejection.

• Adolescence is the stage between childhood and adulthood (ages 10–19), marked by fast physical and emotional changes.
• It has three stages: Early (10–14), Middle (15–17), and Late (18–19), each with different body and thinking developments.
• Puberty brings sexual and physical changes due to hormones—testosterone in boys and oestrogen in girls.
• Physical changes include growth in height, changes in body shape, changes in voice, and increased sweat/oil production.
• Emotional and social changes include mood swings, seeking independence, peer pressure, and identity formation.

• Meaning: Physical, mental, and physiological dependence on habits (gambling) or substances (nicotine, alcohol, drugs) despite harmful consequences.
• Brain Mechanism: Involves the brain's reward & reinforcement pathways using the neurotransmitter dopamine, affecting motivation.
• Reversibility: Neurological changes are reversible once substance use or behaviour is stopped.
• Effects: Impairs physical, physiological, and psychological functions of the body.
• Causes in Adolescents: Insufficient parental supervision, lack of communication, family conflicts, risk-taking behaviour, and favourable parental attitudes towards drugs/alcohol.

• Opioids: Source - Papaver somniferum (poppy). Effect - depressant, pain killer. Example - Heroin (diacetyl morphine).
• Cannabinoids: Source - Cannabis sativa (hemp). Effect - daydreaming affects the cardiovascular system. Examples - Marijuana, hashish, charas, ganja.
• Cocaine: Source - Erythroxylum coca. Effect - stimulates the CNS, causes euphoria, irritability, paranoia. Example - Cocaine.
• Hallucinogens: Source - Atropa belladonna, Datura. Effect - unreal perceptions of unreal objects. Examples - LSD, cannabis.
• General Effect: All abused drugs cause addiction, dependence, and impair physical, physiological, and psychological functions.