NCERT Notes on Class 12 Biology Chapter 7 - Human Health and Disease

Last Updated : 21 Apr, 2025

NCERT Chapter 7 of Class 12 Notes on Human Health and Disease: According to the World Health Organisation, health can be defined as a state of complete physical, mental, and social well-being and not merely the absence of disease and infirmity. Good health has many benefits like it helps to keep us happy. Our skin, teeth, and eyes remain healthy, support muscles, enhance immunity, strengthen bones, and lower the risk of heart ailments, diabetes, and some cancers. It also supports healthy pregnancies and breastfeeding among women.

NCERT Notes on Chapter 7 Human Health and Disease: On the other hand, disease is any undesirable change in our body that may keep us disturbed whether it is physical, mental, or social. Our body can undergo a number of changes like any of the organs can stop functioning in a proper way which can also be associated with some other signs and symptoms. In plants and animals, the disease can also be occurred by pathogens, i.e. disease-causing organisms such as fungi, bacteria, viruses, protozoa, and certain types of invertebrates like tapeworms, wuchereria. Unhygienic surroundings, nutritional deficiencies, and unhealthy lifestyles also cause diseases.

Health

According to the World Health Organisation, health can be defined as a state of complete physical, mental, and social well-being and not merely the absence of disease and infirmity.

How Can We Achieve a Good Health?

The following factors are necessary to achieve good health:

Balanced diet
Personal hygiene
Regular exercise (yoga)
Awareness about diseases and their effects
Vaccination or immunization against diseases caused by pathogens
Proper disposal of wastes
Control of vectors, which carry diseases
Consumption of hygienic food and water

Disease

A disease can be defined as an illness or sickness that shows specific signs or symptoms.

Causes of Diseases

Heredity: It is the transmission of some deficiencies or defects which is inherited by a child from the parents by birth.
Infections: These can be caused by some pathogens, i.e. disease-causing organisms.
Unhealthy lifestyle: It includes a lack of exercise and consumption of tobacco and alcohol.

Diseases Can Be Classified Into

Infectious or Communicable Diseases: Infectious diseases are diseases that are caused by some disease-causing organisms or pathogens, e.g. bacteria, viruses, fungi, or protozoans. These diseases can be passed from an unhealthy person to a healthy person.
Non-infectious or Non-Communicable Diseases: Non-communicable diseases (NCDs) are diseases that are not transmitted by pathogens. They can be caused by unhealthy lifestyles, unbalanced diets, improper vaccination, etc. They are also known as chronic diseases as they remain for a long duration e.g. diabetes, heart ailments, cancer, etc.

Effect of Pathogens on Our Body

Diseases are caused by the pathogens in our bodies. The pathogens can take entry into our body in various modes and replicate. They also disturb the normal activities of the body which may lead to some undesirable changes and ultimately damage the organs in reference to their functions.

Adaptations of Pathogens in Our Body

Pathogens have to adapt in the host body for their survival e.g. if a pathogen takes entry in our gut, it must go to the way for survival against low pH and some digestive enzymes.

Some Examples of the Pathogens in Our Body

Following are the different examples of Diseases by various Pathogens.

Examples of Bacterial Diseases

Name of the Pathogen	Diseases Caused	Affected Body Part	Mode of Entry or Transmission	Symptoms	Diagnosis	Prevention and Control
Salmonella typhi	Typhoid fever	Small intestine	Contaminated food and water	high fever (39° to 40°C), weakness, stomach pain, constipation, headache, and loss of appetite	Widal test	Awareness, hygienic surroundings
Streptococcus pneumoniae and Haemophilus influenza	pneumonia	alveoli (air-filled sacs) of the lungs which possess grapes-like structures	fever, chills, cough and headache, severe problems in respiration	by inhaling droplets released by an infected or unhealthy person or by sharing personal belongings.		Isolation, hygienic surroundings

Some other diseases caused by bacteria are dysentery, plague, diphtheria, etc.

Example of a Viral Disease

Name of the Pathogen	Disease Caused	Affected Body Part	Mode of Entry or Transmission	Symptoms
Rhinoviruses	Common cold	Nose and respiratory pathway	By inhaling droplets released by an infected or unhealthy person or by sharing personal belongings	Nasal congestion and discharge, sore throat, wheezing, cough, headache, tiredness, etc.

Example of Diseases Caused by Protozoans

Name of the Pathogen	Diseases Caused	Affected Body Part	Mode of Entry or Transmission	Symptoms
Plasmodium (Plasmodium vivax, Plasmodium malaria and Plasmodium falciparum)	Malaria	Red blood cells and liver	Bite by an infected female mosquito, i.e. anopheles mosquito	High chills, vomiting, loose motions
Entamoeba histolytic	Amoebiasis (amoebic dysentery)	Large intestine		Constipation, cramps, abdominal pain, stool with mucus and blood clots

Note- Plasmodium falciparum is the most fatal species of plasmodium.

Life Cycle of Plasmodium

Stages Involved

Exoerythrocytic stage- It occurs in the liver of the infected person.
Erythrocytic stage- It occurs in the RBCs of the infected person.
Sporogonic stage- It occurs in the female mosquito, i.e. Anopheles

Steps Involved

Infected plasmodium enters the human body by a bite of an infected female anopheles mosquito (transmitting agent or vector)
The plasmodium multiplies in the liver cells or hepatocytes and affect the RBCs which rupture later as a result, hemozoin (toxic) is released which causes a high fever and chills for three to four days.
Multiplied plasmodium enters the body of a mosquito when Anopheles bites the infected person and starts multiplying within the body and forms sporozoites (stored in salivary glands).
When these mosquitoes bite a human, those sporozoites enter the human body and the cycle repeats.

Diseases Caused by Helminthes

Name of the Pathogens	Diseases Caused	Affected Body Part	Symptoms	Modes of Transmission
Ascaris (roundworm) and Wuchereria (filarial worm)	Ascariasis	Intestine in the human body and contaminate soil, water, and plants	Internal bleeding, muscular pain, fever, anemia, and blockage of the intestinal pathway.	Contaminated water, vegetables, and fruits.
Wucheria bancrofti and Wucheria malayi	Chronic inflammation in the organsElephantiasis or filariasis	Lymphatic vessels of the lower limbs, genital organs	Swelling in the pelvic region	By the bite of a female mosquito vectors

Diseases Caused by Fungi

Name of the Pathogens	Disease Caused	Affected Body Part	Symptoms	Modes of Transmission
Microsporum, Trichophyton, and Epidermophyton	Ringworms	Skin, nails, and scalp	Itching because of the dry and scaly lesions on the skin, nails, and scalp	Contaminated soil, wet and moist towels or fabrics, or comb

Prevention and Control

Maintenance of public and personal hygiene
Isolation of the suffering person from healthy persons
To destroy vectors and their breeding areas to control their growth
Vaccination
Course of antibiotics

Immunity

Immunity is the body's ability to sense germs to inhibit them from causing any illness. The immune system identifies and destroys germs that enter the body before they can start causing disease.

Types of Immunity

Innate immunity
Acquired immunity

Innate Immunity (inborn)	Acquired Immunity
It is also known as natural or inborn immunity.	It is also known as adaptive immunity.
It is present by birth.	It is not present by birth. Instead, acquired during the lifetime of the person.
It is not dependent on previous exposure to pathogens or disease-causing organisms.	It depends on the previous exposure to the pathogens or disease-causing organisms.
It is genetic and transmits from parents to their offspring.	It is not genetic.
Its effects can be seen immediately in the body.	It can take a few days to show the effects or to be activated.
It consists of various types of barriers to provide defense against pathogens.	It consists of some special cells which produce antibodies.

Some Examples of Barriers to Innate Immunity

Physical Barriers: Skin, gastrointestinal mucus, and the lining of the respiratory and urogenital tract.
Physiological Barriers: HCL production in the stomach, tear gland in the eyes, secretion of saliva in the mouth.
Cellular Barriers: Leukocytes (WBCs) of our body destroy various microbes. They are known as the soldiers of our body.
Cytokine Barriers: The virus-infected cells produce some special proteins, known as interferons which help to protect the other non-infected cells.

Special Cells Provide Acquired Immunity by Producing Antibodies

The lymphocytes, B-lymphocytes, and T-lymphocytes are the special cells that help in the production of antibodies to provide acquired immunity.

B-lymphocytes	T-lymphocytes
They form humoral or Antibody-Mediated Immune Systems (AMIS)	They form Cell-Mediated Immune System (CMIS)
They provide protection against bacteria and viruses that enter the blood and lymph.	They provide protection against fungi and protists that enter the cell.
They form memory cells or mast cells and plasma cells.	They form killer, helper, and suppressor cells.

Antibody-Mediated Immune System	Cell-Mediated Immune System
It is mediated by the antibodies present in the blood and lymph.	It is mediated by T-lymphocytes to produce antibodies.
It does not react against organ transplantation.	It shows reactions against organ transplantation

Antibody Structure

Antibodies are the 'Y' shaped structures, made up of four polypeptide chains, i.e. two heavy polypeptide chains and two light polypeptide chains. It is represented as H2 L2. Disulfide bonds are present between the chain which keep their position fixed. The different types of antibodies found in our bodies are IgA, IgG, IgE, and IgM.

Active Immunity and Passive Immunity

Active Immunity	Passive Immunity
It is developed by contact with pathogens or antigens.	It is developed when readymade antibodies are inserted or injected in the body by vaccination.
It shows no side-effect.	It shows some reactions.
It is slow but has long-lasting effects.	It is fast but has short-term effects.

Vaccination and Immunisation

Vaccination	Immunisation
In this process, the weakened or deactivated pathogens are injected into the body.	It is the process that occurs after injecting a vaccine when the body starts producing antibodies against pathogens.
It does not give complete protection against disease.	When the person fully recovers from a disease, gets immunity.
It is taken by injection or orally.	It is not taken orally or by injection, the body develops by its own capacity.

Allergies (Allergic Diseases)

These are the conditions caused by the hypersensitivity of the immune system to many harmless substances present around us. When the immune system responds to any foreign substances like pollen, dust, or any food which does not cause any reactions in most people, then allergies occur. The antibodies produced against these reactions are of IgE type (Ig stands for immunoglobulin-a class of protein).

Examples of Some Common Allergens (Allergens Cause Allergies)

Some common examples of allergens are outdoor pollutants including ozone and diesel exhaust, indoor pollutants like tobacco smoke and nitrogen dioxide, some food items like peanuts and eggs, microbial products, mites in dust, pollens, animal dander, etc.

Symptoms of Allergies

Symptoms of allergies include sneezing, nasal discharge, watery eyes, and difficulty in breathing.

Allergies are caused because of the production of histamine and serotonin.
Anti-histamines, adrenalin, and steroids reduce the symptoms of allergy.

Autoimmunity

It is a condition in which the body's immune system mistakes its own body tissues for foreign agents and starts attacking them. Autoimmune diseases cause inflammation which affects many parts of the body. Examples of such diseases are rheumatoid arthritis (attacks joints) and type 1 diabetes. In type 1 diabetes, the immune system starts destroying Islets of Langerhans, the cells in the pancreas which produce insulin hormone.

Immune System in the Body

It comprises lymphoid organs, cells, organs, and antibodies.

Role Played by the Immune System

It shows allergic reactions.
It distinguishes between self and non-self cells and fights against non-self or foreign antigens.
It is important in organ transplantation.
It is responsible for the production of memory cells or mast cells.

Lymphoid Organs

Primary, secondary, and tertiary lymphoid organs include different types of leukocytes or white blood cells which fight against infections. Bone marrow is the main lymphoid organ where all blood cells are produced including lymphocytes.

The thymus gland is found in the upper front part of the chest, behind the sternum which is made up of two lobes. It is also known as the ‘Throne of immunity’ or ‘training schools of T-lymphocytes.’
The spleen is an organ that filters blood. They are also known as the 'graveyard of red blood cells'.
The lymph nodes are the parts of the lymphatic system which trap antigens inside the tissue or lymph fluid. It leads to the activation of lymphocytes located in the lymph nodes. The lining of the major tracts, i.e., respiratory, digestive, and urogenital tracts, consists of lymphoid tissue. It is called 'Mucosal-Associated Lymphoid Tissue' (MALT).

AIDS (Acquired Immuno Deficiency Syndrome)

HIV-AIDS is Acquired Immunodeficiency Syndrome, which is a life-threatening condition caused by the human immunodeficiency virus (HIV), the genome of which is RNA, enclosed in an envelope and consists of reverse transcriptase (transcribes single-stranded RNA into DNA). It interferes with the protein synthesis machinery and the body's ability to fight against infection.

Modes of Transmission

The HIV virus is transmitted through contact with the infected blood, semen, or vaginal fluids.

Symptoms

Flu-like symptoms can be seen, e.g., fever, fatigue, and sore throat.
Other symptoms include weight loss, fever or night sweats, fatigue, and frequent infections.

Cure

There is no cure for AIDS but antiretroviral regimens can minimize the effects by preventing some secondary infections.

Transmission of HIV-Infection

Transmission of HIV infection can be happened by:

Direct contact with certain body fluids from a suffered person. These fluids are blood, semen, rectal fluids, vaginal fluids, breast milk, etc.
Having sexual contact with multiple partners.
Transfusion of contaminated blood and blood products. Contamination of blood can be considered if the person suffers from certain cancers, anemia, and thalassemia.
Sharing infected needles or syringes by drug addicts who take drugs intravenously.
Infected pregnant mother to her child through the placenta.

How HIV Affects the Body?

HIV destroys T-cells or helper cells (CD4 cells), which are critical to the immune system. These cells are responsible to keep us healthy and protect against common diseases and infections. The macrophages, a type of WBCs are infected. The genomic RNA of the virus replicates with the help of an enzyme, reverse transcriptase, and forms viral DNA which enters the host cell and produces viral particles. HIV enters the T-cells and multiplies in the blood which further attacks other T-cells. This cycle goes on and the T-lymphocytes decrease in the infected person. HIV weakens the body’s natural defense mechanisms and then, symptoms appear.

Detection

AIDS can be detected by Enzyme-linked immunosorbent assay (ELISA), which is a biochemical test that helps in detecting the presence of an antibody or an antigen in a sample. Another test, i.e., Western Blot is done to check the result of ELISA.

Treatment

A person suffering from AIDS can be given anti-retroviral drugs to increase the lifespan of a person up to a natural death process.

Prevention and Control of AIDS

Choose safe sexual practices like the use of a condom
Limit the number of sexual partners
syringes or needles must be sterilized
Promoting regular check-ups for HIV
Get a test for Sexually transmitted diseases
Take precautions and double-check before having a blood transfusion
Awareness among people which is done with the help of the National AIDS Control Organization (NACO) and other non-governmental organizations (NGOs)

Cancer

Cancer is a disease in which the cells in the body grow in an uncontrollable fashion and spread to other parts of the body. Cancerous tumors spread and invade the surrounding tissues and can travel to distant places in the body to form new tumors. This process is called metastasis. Cancerous tumors may also be called malignant tumors.

Differences Between a Cancerous Cell and a Normal Cell

Cancerous cells grow in the absence of signals which instruct them to grow while normal cells only grow when they receive such instructions.
Cancerous cells ignore signals that normally instruct cells to stop dividing or to die (apoptosis or programmed cell death) while normal cells stop dividing after receiving signals.
Cancerous cells invade into surrounding areas and spread while normal cells stop growing when they come in contact with the other cells (contact inhibition).

Types of Tumors

Benign tumors	Malignant tumors
They are small	They are large
They are slow growing	They are fast-growing
They are non-invasive	They are invasive
They stay localized	They are metastasized

Causes of Cancer

The normal cells are transformed into cancerous cells through some agents, known as carcinogens.

Carcinogens

Ionizing radiations: X-rays and gamma rays.
Non-ionizing radiations: Both ionizing and non-ionizing radiations, cause DNA damage and mutations.
Some food items like chemicals, used in processed and cured meat may produce carcinogens.
The chemical carcinogens cause lung cancer, are present in tobacco smoke.
Oncogenic viruses (cancer-causing viruses) consist of viral oncogenes.

Detection and Diagnosis

Cancer detection is done by:

Biopsy: In this process, a small and thin section of the suspected tissue is taken out and examined.
Blood and bone marrow tests: This is done to detect leukemia or blood cancer.
Radiography: Here, X-rays are used to expose the infected cell.
CT (computed tomography): This is done to obtain a 3-D structure of an infected organ through X-rays.
MRI (magnetic resonance imaging): It involves the use of strong magnetic fields and non-ionizing radiations to detect the changes in the cells or tissues.
Techniques of molecular biology: It is used to identify the genes which prevent cancers.

Treatment of Cancer

There are different ways to treat cancer like surgery, radiation therapy, chemotherapy, and immunotherapy. In radiotherapy, the tumor cells are exposed to the X-rays, taking care of the normal cells surrounding them. There are certain drugs used to kill or burn cancerous cells, known as chemotherapeutics. These drugs show some side effects like hair loss, anemia, excessive weight loss, etc.

Drug Abuse

Drug abuse or substance abuse is the use of certain chemicals or use of illegal drugs in excessive quantities in order to have pleasurable effects on the brain.

Commonly abused drugs are opioids, cannabinoids, and coca alkaloids.

Name of the Drug	Sources	Taken By	Action on the body
Opioids	Latex of poppy plant (Paper somniferum)	Injection or snorting	It acts as a depressant
Cannabinoids	Inflorescence of Cannabis sativa plant	Inhalation/orally	It shows effects on the cardiovascular system
Coca Alkaloids/cocaine	Coca plant (Erythroxylum coca)	Snoring	It disturbs neurotransmitters and CNS, also causes hallucination

Smoking

Smoking is a practice in which a substance is burned and the smoke is breathed in which is absorbed into the bloodstream. Smoking causes cancer, heart disease, stroke, lung diseases, diabetes, and chronic obstructive pulmonary disease (COPD), which includes emphysema and chronic bronchitis. Smoking also enhances the risk for tuberculosis, eye disorders, and problems related to the immune system, e.g., rheumatoid arthritis.

Adolescence and Drug/Alcohol abuse

The period of adolescence starts when an individual reaches reproductive maturity, which is different in both girls and boys. During this period, the persons undergo certain changes resulting in emotional and behavioral growth. Adolescents lead towards drug abuse because of the following reasons:

Curiosity
Need for adventure
Experimentation
Perceived benefits of alcohol and drug use
Stress and academic pressure
Peer pressure
Unstable family structure

Also Read: Adolescence and Drug/Alcohol Abuse Prevention

Addiction and Dependence

Addiction and Dependence consists of the temporary feeling of well-being which makes people have drug or alcohol when there is no need even. Dependence is the ability of the body to unpleasant syndrome if the regular dose of drug/alcohol is discontinued for some time.

Effects of Drug/Alcohol Abuse

Reckless behavior.
Vandalism and violence.
The use of excessive doses of drugs may lead to coma and death due to respiratory failure, heart failure, or cerebral hemorrhage.
Injecting drugs could lead to increased susceptibility to diseases like AIDS, Hepatitis, etc.
Damage to the nervous system and Liver cirrhosis.
Adverse effects on the fetus due to consumption during pregnancy.

Side Effects of Performance-Enhancing Drugs for Sports

A feeling of a fast heartbeat
A heartbeat that is a too fast, too slow or irregular rhythm
Excessive weight loss
High blood pressure
Hallucination
Stroke

Common Warning Signs of Drug and Alcohol Abuse

Personality changes
Changes in the friend circle
School performance becomes down
Social withdrawal
Pills or medication bottles become lost
Taking overdosage of the medication
Abrupt changes in the finance/money loss
Mood swings
Disturbed sleep or appetite

Prevention and Control

Avoid undue peer pressure
Counseling sessions
Seeking help from parents and professionals

Common Diseases In Humans

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NCERT Notes on Class 12 Biology Chapter 7 - Human Health and Disease

Health

How Can We Achieve a Good Health?

Disease

Causes of Diseases

Diseases Can Be Classified Into

Effect of Pathogens on Our Body

Adaptations of Pathogens in Our Body

Some Examples of the Pathogens in Our Body

Examples of Bacterial Diseases

Example of a Viral Disease

Example of Diseases Caused by Protozoans

Life Cycle of Plasmodium

Stages Involved

Steps Involved

Diseases Caused by Helminthes

Diseases Caused by Fungi

Prevention and Control

Immunity

Types of Immunity

Some Examples of Barriers to Innate Immunity

Special Cells Provide Acquired Immunity by Producing Antibodies

Antibody Structure

Active Immunity and Passive Immunity

Vaccination and Immunisation

Allergies (Allergic Diseases)

Examples of Some Common Allergens (Allergens Cause Allergies)

Symptoms of Allergies

Autoimmunity

Immune System in the Body

Role Played by the Immune System

Lymphoid Organs

AIDS (Acquired Immuno Deficiency Syndrome)

Modes of Transmission

Symptoms

Cure

Transmission of HIV-Infection

Transmission of HIV infection can be happened by:

How HIV Affects the Body?

Detection

Treatment

Prevention and Control of AIDS

Cancer

Differences Between a Cancerous Cell and a Normal Cell

Types of Tumors

Causes of Cancer

Carcinogens

Detection and Diagnosis

Treatment of Cancer

Drug Abuse

Smoking

Adolescence and Drug/Alcohol abuse

Addiction and Dependence

Side Effects of Performance-Enhancing Drugs for Sports

Common Warning Signs of Drug and Alcohol Abuse

Prevention and Control

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