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.

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.

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

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

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

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

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

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

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

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

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

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

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

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

The antigens of proteinaceous nature are known as complete antigens.

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

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 allergy.

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

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

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

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

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.

• 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.

• 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.

• 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.