Please refer to Human Health and Diseases Class 12 Biology Notes and important questions below. The Class 12 Biology Chapter wise notes have been prepared based on the latest syllabus issued for the current academic year by CBSE. Students should revise these notes and go through important Class 12 Biology examination questions given below to obtain better marks in exams
Human Health and Diseases Class 12 Biology Notes and Questions
The below Class 12 Human Health and Diseases notes have been designed by expert Biology teachers. These will help you a lot to understand all the important topics given in your NCERT Class 12 Biology textbook. Refer to Chapter 8 Human Health and Diseases Notes below which have been designed as per the latest syllabus issued by CBSE and will be very useful for upcoming examinations to help clear your concepts and get better marks in examinations.
The state of complete physical, mental and social well beings is called health. Health simply does not simply means disease free condition or physical fitness. Health is affected bya.
a. Genetic disorders – the defect which child inherits from it parents.
b. Infection from microbes or other organisms.
c. Life style- includes food and water we take, exercise and rest.
Good health can be maintained by
• Balanced diet.
• Personal hygiene
• Regular exercise
• Awareness about the disease and their effect
• Immunization against the infectious disease
• Proper disposal of wastage
• Control of vectors
• Maintenance of hygienic food and water.
Disease – Diseases can be broadly grouped into infectious and non-infectious.
a) Infectious disease -Diseases which are easily transmitted from one person to another, are called infectious diseases e.g AIDS, common cold, malaria, tuberculosis etc
b) Non-infectious disease – Diseases which cannot transmitted from one person to another, are called non- infectious diseases e.g cancer, hypertension, diabetes etc.
Common Diseases in Humans:
• The disease causing microorganisms like bacteria, virus, fungus, protozoa, helminthes are called pathogen.
• The pathogen can enter the body by various means and multiply and interfere with normal vital activities resulting in morphological and functional damage.
Life cycle of plasmodium : Plasmodium enters the human body as small sporozoites through the bite of infected female anopheles mosquito and multiplies within the lever cells. Later attacks the RBCs resulting the rapture with release of toxic substance, haemozoin, which is responsible for high fever and chill recurring every three to four days.
Malarial parasite requires two hosts, human and anopheles mosquito to complete their life cycle. Female anopheles is vector of this disease to human beings.
Flowchart to show lifecycle of Plasmodium
Immunity – the ability of host cells to fight the disease causing microorganism due to immune system is called immunity. There are two types of immunity-
Innate immunity – non-specific types of defence presents at the time of birth and provide different kinds of barriers to the entry of foreign agents into the body. it consists of four types of barrier-
a. Physical barrier- skin, mucus coating of epithelium lining the respiratory, gastrointestinal and urogenital tract.
b. Physiological barrier- acid in stomach and saliva in mouth.
c. Cellular barrier- leucocytes, neutrophils, monocytes.
d. Cytokine barriers- virus infected cells secretes protein called interferon.
Acquired Immunity- pathogen specific defence characterised by memory. When our body encounters a pathogen first time produces a response called primary response of low intensity. Subsequent encounter by same pathogen produce highly intensified response called secondary response or anamnestic response due to memory of first encounter.
Primary and secondary responses are carried out with the help of B-lymphocytes and Tlymphocytes. B-lymphocytes produce army of protein called antibodies each having two light and two heavy chains.
It involves two types of lymphocytes –
• B lymphocytes: Show humoral immune response (HI)
• T lymphocytes: Show cell mediated immunity (CMI)
Structure of an Antibody:
• The antibodies are protein molecules called immunoglobulins and are of various types like IgA, IgM, IgE, IgG.
• Each antibody molecule consists of four polypeptide chains, two are long called heavy chains and other two are short called light chains. Both are arranged in the shape of ‘Y’, hence an antibody is represented as H2L2.
On the basis of production of antibodies, immunity can be further categorised as –
• Active immunity: Body produces its own antibodies against antigens
• Passive immunity: Readymade antibody is transferred from one individual to another
• Colostrum (contains antibodies IgA) is an example of passive immunity provided by the mother to her child.
Different types of antibodies produce in blood include IgA, IgM, IgEete. They are called humoral immune response due to presence in blood.
Human immune system can distinguish between self and foreign molecules or foreign bodies. Sometimes, due to genetic or unknown reasons, the body attack self-cells. This results in damage to the body and called auto-immune disease. Rheumatoid arthritis is due to this effect
Allergies – the exaggerated response of immune system to certain antigens present in the environment is called allergy. The substance to which such immune response is produced is called allergens. The antibodies produced due to these are IgE types. Allergy is due to secretion of chemicals like histamine and serotonin from the mast cells.
Immune system in the body- the human immune system includes lymphoid organs, tissue, cells and soluble molecules like antibodies.
Lymphoid organs are the organs where origin and maturation and proliferation of lymphocytes occur. Primary lymphoid organs include bone marrow and thymus.
After maturation lymphocytes migrate to secondary lymphoid organ like spleen, lymph nodes, tonsils, peyer’s patches of small intestine and appendix. They provide the sites for interaction lymphocyte with antigens.
There is lymphoid tissue also located within the lining of respiratory, digestive and urogenital tract called mucosal associated lymphoid tissue ( MALT). It constitute 50% of lymphoid tissues in human body.
AIDS (Acquired Immuno Deficiency Syndrome) was first reported in 1981. It is caused by HIV (human Immuno deficiency virus), a retrovirus. Transmission of HIV virus occurs bya.
a. Sexual contact with infected person
b. Transfusion of contaminated blood and blood products
c. Sharing infected needles as in intravenous drug abusers
d. Infected mother to her child through placenta.
Replication of retrovirus in Macropahges
AIDS/HIV does not spread by physical contact. It spread only through body fluids. There is always time lag between infection and appearance of symptoms that may vary from 5-10 years.
Diagnostic test for AIDS is ELISA (enzyme-linked Immuno-sorbent assay). The treatment of this disease with anti-retroviral drug is partially effective and just prolonged the life but not prevents the death
Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the world. Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibit their uncontrolled growth. Cancer cells lost this property.
Cancerous cells continue to divide giving rise to masses of cells called tumors. There are two kind so tumors-
(a) Benign tumors
(b) Malignant tumors
Causes of cancer – cancerous neoplastic cell may be induced by physical, chemical and biological agents called carcinogens. Cancer causing viruses called oncogenic virus have
gene called viral oncogenes. Several genes called cellular oncogenes (c-onc) or proto oncogenes have been identified in normal cells which, when activated under certain conditions, could lead to oncogenic transformation of the cells.
Cancer detection and diagnosis-cancer detection is based on biopsy and histopathological study of the tissues, blood and bone marrow test for increased cell counts. Radiography, CT (computed tomography), MRI (magnetic resonance imaging) are very useful to cancers of internal organs.
Treatment of Cancer-
1. Surgical – cancerous tissues are surgically removed.
2. Radiotherapy – tumor cells are irradiated lethally by radiation.
3. Chemotherapy – drugs are used to kill cancerous cells, but shows side effects like hair loss, anemia, etc.
4. Immunotherapy – patients are given with alpha-interferon which activate their immune system and help in destroying the tumor
Drugs and Alcohol Abuse
Commonly abused drugs include opioids, cannabinoids and coca alkaloids obtained from flowering plants and a few from fungi.
Opioids are the drugs which bind to specific opioids receptors present in our central nervous system and gastrointestinal tract. Heroin commonly called smack is chemically diacetylmorphine which is a white, odourless, bitter crystalline compound. It is extracted from the latex of poppy plant (Papaversomniferum).Generally taken by snorting and injection, heroin is a depressant and slows down body functions.
Cannabinoids are a group of chemicals which interact with cannabinoid receptors present in the brain. Natural cannabinoids are obtained from the inflorescence of the plant cannabis sativa. They include marijuana, hashish, charas and gangja. They generally taken by inhalation and oral ingestion, these are known for their effects on cardiovascular system of the body.
Coca alkaloid or cocaine is obtained from coca plant Erythroxylum coca, native to South America. It interferes with the transport of the neuro-transmitter dopamine. Cocaine, commonly called coke or crack is usually snorted. It has a potent stimulating action on central nervous system, producing a sense of euphoria and increased energy.
Adolescence and Drug abuse
• Adolescence is the period during which the child becomes matured.
• It is between 12 – 18 years of age.
Causes of drug abuse –
• Stress or pressure to excel in examination
Effects of drug/alcohol abuse –
• Reckless behaviour
• Malicious mischief
• Drop in academic performance
• Depression, isolation, aggressiveness, etc.
Dependence is the tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome if regular dose of drug/alcohol is abruptly discontinued that includes anxiety, shakiness, nausea and sweating.
Prevention avoid undue peer pressure, education & counselling, seeking helps from parents and peers, seeking professional and medical help etc.