CBSE Class 12 Biology Revision Notes Chapter 7: Human Health and Disease

Human health depends on physical, mental and social well-being, along with the body’s ability to prevent and fight disease. This chapter explains pathogens, immunity, AIDS, cancer and the harmful effects of substance abuse.

Health is influenced by genetic conditions, infections, nutrition, exercise, lifestyle and mental well-being. Disease develops when one or more organs or body systems cannot perform their normal functions.

These CBSE Class 12 Biology Revision Notes Chapter 7 follow the current 2026–27 chapter sequence. They organise important facts through concise explanations, process steps, comparisons and quick-revision tables.

Key Takeaways

• 39°C to 40°C: Typhoid can cause sustained high fever within this range.
• H2L2: An antibody contains two heavy and two light peptide chains.
• 5–10 years: HIV infection may remain without visible AIDS symptoms for several years.
• 50%: MALT constitutes nearly half of the lymphoid tissue in the human body.

Need help revising immunity, infectious diseases, AIDS and cancer?
Access interactive practice, chapter-wise notes and doubt-solving support on the Extramarks Learning App. Sign Up Free

Human Health and Disease Class 12 Notes Overview

The Human Health and Disease Class 12 Notes explain how health is maintained and how infections, abnormal cell growth and harmful habits affect the body.

The chapter also shows how immunity, vaccination, hygiene and early diagnosis help prevent disease.

Access Class 12 Biology Chapter 7 Human Health and Disease Notes in 30 Minutes

Use this order for rapid revision:

1. Learn the definition of health and disease.
2. Revise the pathogens, symptoms and transmission of major diseases.
3. Memorise the four barriers of innate immunity.
4. Compare acquired, active and passive immunity.
5. Recall the H2L2 structure of an antibody.
6. Revise primary and secondary lymphoid organs.
7. Trace HIV entry, replication and destruction of helper T-cells.
8. Compare benign and malignant tumours.
9. Learn major drug categories, sources and effects.
10. Finish with addiction, dependence and prevention measures.

Health and Disease in Class 12 Biology Chapter 7

Health is a state of complete physical, mental and social well-being. It means more than the absence of disease or physical weakness.

Healthy people generally:

• Work more efficiently
• Show higher productivity
• Live longer
• Face lower infant and maternal mortality

Health depends on:

• Genetic constitution
• Infections
• Food and water
• Rest and exercise
• Personal habits
• Mental state
• Social environment

Balanced nutrition, personal hygiene, regular exercise and yoga support physical and mental health.

A disease occurs when one or more organs or body systems cannot function normally. It produces identifiable signs and symptoms.

Infectious and Non-infectious Diseases

Diseases can be broadly grouped into infectious and non-infectious types.

Disease-causing organisms are called pathogens.

Pathogens include:

• Bacteria
• Viruses
• Fungi
• Protozoans
• Helminths

Common Diseases in Humans Class 12 Notes

The section on common diseases in humans covers pathogens, symptoms, transmission and prevention.

Pathogens enter the body, multiply and disturb normal physiological functions.

Typhoid

Typhoid is caused by the bacterium Salmonella typhi.

It usually enters the small intestine through contaminated food and water. It can then reach other organs through the blood.

Common symptoms include:

• Sustained fever of 39°C to 40°C
• Weakness
• Stomach pain
• Constipation
• Headache
• Loss of appetite

Severe cases may cause intestinal perforation and death.

The Widal test helps confirm typhoid.

Mary Mallon, known as Typhoid Mary, was a carrier who spread the infection through food she prepared.

Pneumonia

Pneumonia may be caused by:

• Streptococcus pneumoniae
• Haemophilus influenzae

These bacteria infect the alveoli of the lungs.

The alveoli fill with fluid, making breathing difficult.

Symptoms include:

• Fever
• Chills
• Cough
• Headache
• Bluish lips and fingernails in severe cases

Pneumonia spreads through droplets and aerosols. Sharing glasses or utensils may also transmit the infection.

Common Cold

The common cold is caused by rhinoviruses.

These viruses infect the nose and respiratory passage but generally do not affect the lungs.

Symptoms include:

• Nasal congestion
• Nasal discharge
• Sore throat
• Hoarseness
• Cough
• Headache
• Tiredness

Symptoms usually last three to seven days.

Transmission occurs through:

• Droplets from coughing or sneezing
• Contaminated objects
• Cups and utensils
• Books, pens and keyboards
• Door handles

Malaria and the Life Cycle of Plasmodium

Malaria is caused by protozoans belonging to the genus Plasmodium.

Important species include:

• Plasmodium vivax
• Plasmodium malariae
• Plasmodium falciparum

Malignant malaria caused by P. falciparum is the most serious form.

Life Cycle of Plasmodium

The life cycle of Plasmodium requires two hosts:

• Human
• Female Anopheles mosquito

The sequence is:

1. An infected female Anopheles mosquito bites a human.
2. Sporozoites enter the bloodstream.
3. They reach the liver and multiply inside liver cells.
4. Parasites enter red blood cells.
5. Infected RBCs rupture.
6. Haemozoin is released.
7. Haemozoin causes recurring chills and fever.
8. Another mosquito takes up the parasite while feeding.
9. Parasites multiply inside the mosquito.
10. Sporozoites reach its salivary glands.

The mosquito acts as both a host and a vector.

Amoebiasis

Amoebiasis, or amoebic dysentery, is caused by Entamoeba histolytica.

The parasite lives in the large intestine.

Symptoms include:

• Constipation
• Abdominal pain
• Abdominal cramps
• Stools containing mucus
• Blood clots in stools

Houseflies act as mechanical carriers.

The infection spreads through food and water contaminated with faecal matter.

Ascariasis

Ascariasis is caused by the intestinal roundworm Ascaris.

Symptoms include:

• Internal bleeding
• Muscular pain
• Fever
• Anaemia
• Intestinal blockage

The eggs leave the body through faeces and contaminate soil, water, fruits and vegetables.

A healthy person acquires the infection through contaminated food or water.

Filariasis

Filariasis, or elephantiasis, is caused by:

• Wuchereria bancrofti
• Wuchereria malayi

These worms cause chronic inflammation in the lymphatic vessels, particularly in the lower limbs.

The disease may cause:

• Swollen lower limbs
• Gross deformity
• Damage to genital organs

Female mosquitoes transmit filarial worms.

Ringworm

Ringworm is a fungal infection caused by species belonging to:

• Microsporum
• Trichophyton
• Epidermophyton

Symptoms include:

• Dry, scaly lesions
• Intense itching
• Infection of the skin, nails or scalp

The fungi grow well in warm and moist areas such as skin folds.

Ringworm may spread through:

• Contaminated soil
• Towels
• Clothes
• Combs
• Direct contact

Common Human Diseases Comparison

Prevention and Control of Infectious Diseases

The prevention of infectious diseases depends on personal hygiene, public sanitation, vaccination and vector control.

Important measures include:

• Keeping the body clean
• Drinking safe water
• Washing fruits and vegetables
• Proper waste disposal
• Cleaning water reservoirs
• Disinfecting public water sources
• Avoiding close contact with infected people
• Controlling mosquito breeding
• Using mosquito nets
• Installing wire mesh on doors and windows
• Using larva-eating fish such as Gambusia
• Following immunisation programmes

Vaccination has eradicated smallpox and controlled diseases such as polio, tetanus, diphtheria and pneumonia.

Immunity in Human Health and Disease Class 12 Notes

Immunity is the ability of the host to resist and fight disease-causing organisms.

The human immune system protects the body through innate and acquired defence mechanisms.

Innate and Acquired Immunity in Class 12 Biology

The two main forms of immunity are innate and acquired immunity.

Innate Immunity

Innate immunity provides non-specific protection from birth.

It includes four types of barriers.

Physical Barriers

Physical barriers prevent microbial entry.

Examples include:

• Skin
• Mucus lining the respiratory tract
• Mucus lining the digestive tract
• Mucus lining the urogenital tract

Physiological Barriers

Physiological barriers prevent microbial growth.

Examples include:

• Acid in the stomach
• Saliva in the mouth
• Tears from the eyes

Cellular Barriers

Some white blood cells destroy microbes through phagocytosis.

These include:

• Neutrophils or PMNLs
• Monocytes
• Macrophages
• Natural killer cells

Cytokine Barriers

Virus-infected cells release proteins called interferons.

Interferons protect nearby non-infected cells against viral infection.

Acquired Immunity

Acquired immunity is pathogen-specific and possesses memory.

During the first encounter with a pathogen, the body produces a low-intensity primary response.

During a later encounter, the immune system produces a stronger secondary or anamnestic response.

Two types of lymphocytes participate:

• B-lymphocytes
• T-lymphocytes

Structure of an Antibody

B-lymphocytes produce antibodies.

Each antibody contains four peptide chains:

• Two heavy chains
• Two light chains

An antibody is therefore represented as:

H2L2

Common antibody classes include:

• IgA
• IgM
• IgE
• IgG

Humoral and Cell-Mediated Immunity

The acquired immune response occurs through humoral and cell-mediated immunity.

Humoral immunity is antibody-mediated because antibodies circulate in blood.

Cell-mediated immunity, or CMI, is controlled by T-lymphocytes.

CMI is important in organ transplantation. The body may recognise transplanted tissue as non-self and reject it.

Transplantation therefore requires:

• Blood group matching
• Tissue matching
• Immunosuppressant medicines

Active and Passive Immunity in Human Health and Disease

The difference between active and passive immunity depends on whether the body produces its own antibodies.

Active Immunity

Active immunity develops when antigens enter the body and stimulate antibody production.

It may result from:

• Natural infection
• Vaccination
• Exposure to weakened microbes
• Exposure to inactivated pathogens

Passive Immunity

Passive immunity develops when ready-made antibodies enter the body.

Examples include:

• IgA antibodies in colostrum
• Maternal antibodies crossing the placenta
• Antivenom after snakebite
• Antitoxin for tetanus

Vaccination and Immunisation Class 12 Biology Notes

Vaccination and immunisation use the memory of the immune system.

A vaccine may contain:

• Weakened pathogens
• Inactivated pathogens
• Antigenic proteins

Vaccination stimulates:

• Antibody production
• Memory B-cells
• Memory T-cells

During later infection, these memory cells generate a rapid and strong response.

Recombinant DNA technology allows antigenic proteins to be produced in bacteria or yeast.

The hepatitis B vaccine is produced using yeast.

Allergy and Autoimmunity in Human Health and Disease

Allergy and autoimmunity are abnormal immune responses.

Allergy

An allergy is an exaggerated immune response to harmless environmental antigens.

These antigens are called allergens.

Common allergens include:

• Dust mites
• Pollen
• Animal dander

Allergic responses commonly involve IgE antibodies.

Symptoms include:

• Sneezing
• Watery eyes
• Running nose
• Wheezing
• Breathing difficulty

Mast cells release histamine and serotonin during an allergic response.

Treatment may involve:

• Antihistamines
• Adrenaline
• Steroids

Autoimmunity

The immune system normally distinguishes self from non-self.

In autoimmune disease, the immune system attacks the body’s own cells.

Rheumatoid arthritis is an example of an autoimmune disease.

Human Immune System and Lymphoid Organs

The human immune system contains lymphoid organs, tissues, cells and soluble molecules such as antibodies.

Lymphoid organs are sites where lymphocytes develop, mature or interact with antigens.

Primary Lymphoid Organs

Primary lymphoid organs include:

• Bone marrow
• Thymus

The bone marrow produces blood cells, including lymphocytes.

The thymus lies near the heart and beneath the breastbone. It is large at birth but becomes smaller after puberty.

Secondary Lymphoid Organs

Secondary lymphoid organs include:

• Spleen
• Lymph nodes
• Tonsils
• Peyer’s patches
• Appendix

These organs allow lymphocytes to meet antigens and initiate immune responses.

Functions of Major Lymphoid Organs

Mucosa-associated lymphoid tissue, or MALT, occurs in the respiratory, digestive and urogenital tracts.

It constitutes nearly 50% of the lymphoid tissue in the body.

AIDS Class 12 Biology Notes

AIDS stands for Acquired Immuno Deficiency Syndrome.

It is caused by the Human Immunodeficiency Virus, or HIV.

HIV belongs to the retrovirus group and contains an RNA genome enclosed within an envelope.

HIV Transmission and Replication in Class 12 Biology

HIV spreads through specific body fluids and gradually weakens the immune system.

HIV Transmission

HIV can spread through:

• Sexual contact with an infected person
• Transfusion of infected blood
• Sharing contaminated needles
• Transmission from mother to child through the placenta

People at greater risk include:

• Individuals with multiple sexual partners
• Intravenous drug users
• People requiring repeated blood transfusions
• Children born to infected mothers

HIV does not spread through casual touch or ordinary physical contact.

HIV Replication

The process of HIV replication weakens the immune system step by step.

1. HIV enters the body.
2. It infects macrophages.
3. Reverse transcriptase converts viral RNA into viral DNA.
4. Viral DNA enters the host-cell DNA.
5. The infected macrophage produces new viruses.
6. HIV also infects helper T-lymphocytes.
7. Viral particles multiply inside these cells.
8. New viruses infect additional helper T-cells.
9. The number of helper T-cells decreases progressively.
10. The immune system becomes unable to fight opportunistic infections.

Macrophages continue to produce virus particles and act as HIV factories.

Symptoms and Diagnosis of AIDS

The time between HIV infection and the appearance of AIDS symptoms may range from a few months to several years.

It commonly lasts about five to ten years.

Symptoms may include:

• Repeated fever
• Diarrhoea
• Weight loss
• Recurrent infections

As helper T-cells decline, infections caused by bacteria, viruses, fungi and parasites become difficult to control.

The ELISA test is commonly used to detect HIV infection.

Antiretroviral medicines may prolong life but do not eliminate the virus.

AIDS Prevention

Prevention measures include:

• Safe sexual practices
• Screening donated blood
• Using disposable needles
• Avoiding shared syringes
• Preventing intravenous drug abuse
• Regular testing in high-risk groups
• Public education
• Medical care without discrimination

NACO and other organisations work to prevent HIV transmission and educate communities.

People living with HIV require medical care, support and social acceptance.

Cancer Class 12 Biology Notes

Cancer develops when normal control over cell growth and differentiation breaks down.

The cancer Class 12 Biology section covers tumour formation, metastasis, carcinogens, diagnosis and treatment.

Normal Cells and Cancer Cells

Normal cells show contact inhibition.

When normal cells touch neighbouring cells, their division slows or stops.

Cancer cells lose contact inhibition and continue dividing.

This produces a mass of cells called a tumour.

Benign and Malignant Tumours in Human Health and Disease

The two main tumour types are benign and malignant tumours.

Metastasis

Malignant tumour cells may separate from the original tumour.

They travel through blood and lodge in distant organs.

They then form secondary tumours.

This spread is called metastasis.

Causes of Cancer

Agents that cause cancer are called carcinogens.

They may be:

• Physical
• Chemical
• Biological

Physical carcinogens include:

• X-rays
• Gamma rays
• Ultraviolet radiation

Chemical carcinogens include substances present in tobacco smoke.

Biological agents include oncogenic viruses.

Normal cells also contain proto-oncogenes. Their activation under certain conditions can cause oncogenic transformation.

Cancer Detection and Diagnosis

Early detection improves the success of treatment.

Diagnostic methods include:

• Biopsy
• Histopathological examination
• Blood tests
• Bone marrow tests
• Radiography
• CT scans
• MRI scans
• Detection of cancer-specific antigens
• Molecular testing for inherited susceptibility

In a biopsy, a small tissue sample is removed, stained and examined under a microscope.

Cancer Treatment

Cancer treatment may involve:

• Surgery
• Radiotherapy
• Chemotherapy
• Immunotherapy

Radiotherapy uses radiation to destroy tumour cells while protecting surrounding tissue.

Chemotherapy uses drugs to kill cancer cells. Side effects may include hair loss and anaemia.

Biological response modifiers such as alpha-interferon activate the immune system against tumour cells.

Several cancers require a combination of surgery, radiation and chemotherapy.

Drugs and Alcohol Abuse Class 12 Biology Notes

The misuse of drugs and alcohol can damage physical, physiological and psychological functions.

The drug and alcohol abuse section covers opioids, cannabinoids, coca alkaloids, tobacco and adolescent vulnerability.

Commonly Abused Drugs

Opioids

Opioids bind to receptors in the central nervous system and gastrointestinal tract.

Heroin is chemically called diacetylmorphine.

It is produced by acetylating morphine obtained from the latex of Papaver somniferum.

Heroin:

• Is commonly called smack
• Is taken by snorting or injection
• Acts as a depressant
• Slows body functions

Morphine has legitimate medical use as a sedative and painkiller.

Cannabinoids

Cannabinoids interact with receptors mainly present in the brain.

They are obtained from Cannabis sativa.

Products include:

• Marijuana
• Hashish
• Charas
• Ganja

They may be inhaled or consumed orally.

Cannabinoids can affect the cardiovascular system.

Coca Alkaloids

Cocaine is obtained from Erythroxylum coca.

It interferes with dopamine transport.

Cocaine:

• Is also called coke or crack
• Is usually snorted
• Stimulates the central nervous system
• Produces euphoria and increased energy
• May cause hallucinations at high doses

Tobacco and Nicotine

Tobacco contains nicotine.

Nicotine stimulates the adrenal glands to release adrenaline and noradrenaline.

This:

• Raises blood pressure
• Increases heart rate

Smoking is associated with:

• Lung cancer
• Throat cancer
• Urinary bladder cancer
• Bronchitis
• Emphysema
• Coronary heart disease
• Gastric ulcers

Tobacco chewing increases the risk of oral cancer.

Smoking also increases carbon monoxide in the blood. This reduces oxygen transport by haemoglobin.

Addiction and Dependence in Adolescents

Adolescence generally covers the period from 12 to 18 years.

It is a vulnerable stage of physical, mental and behavioural development.

Factors encouraging substance use include:

• Curiosity
• Experimentation
• Adventure
• Peer pressure
• Academic stress
• Desire to escape problems
• Unsupportive family conditions
• Media influence
• The belief that substance use is fashionable

Addiction and Dependence Compared

Addiction and dependence are related but different consequences of repeated substance use.

Addiction

Addiction is a psychological attachment to the pleasurable effects of drugs or alcohol.

Repeated use increases tolerance.

The body then requires a higher dose to produce the same effect.

This may create a cycle of increasing use and self-destructive behaviour.

Dependence

Dependence occurs when stopping the substance produces withdrawal symptoms.

Symptoms may include:

• Anxiety
• Shaking
• Nausea
• Sweating

Severe withdrawal may require medical supervision.

Effects and Warning Signs of Drug and Alcohol Abuse

Immediate effects may include:

• Reckless behaviour
• Violence
• Vandalism
• Respiratory failure
• Heart failure
• Cerebral haemorrhage
• Coma
• Death

Combining drugs with alcohol increases the risk of overdose.

Warning signs include:

• Falling academic performance
• Unexplained absence
• Poor personal hygiene
• Social withdrawal
• Depression
• Fatigue
• Aggressive behaviour
• Rebellious behaviour
• Damaged relationships
• Changes in sleep
• Changes in appetite
• Sudden weight change
• Loss of interest in hobbies

Sharing needles increases the risk of HIV and hepatitis B.

Long-term substance abuse can damage:

• The nervous system
• The liver
• Family relationships
• Social functioning

Alcohol use during pregnancy can harm the developing foetus.

Prevention and Control of Drug and Alcohol Abuse

Early intervention is important because these habits often begin during adolescence.

Preventive steps include:

1. Avoiding excessive pressure on adolescents
2. Providing education and counselling
3. Encouraging sports, music, reading and yoga
4. Seeking support from parents and trusted friends
5. Identifying warning signs early
6. Informing parents or teachers when help is needed
7. Seeking professional medical treatment
8. Using rehabilitation and de-addiction services

Supportive parenting combined with consistent discipline can reduce substance abuse risk.

Human Health and Disease Class 12 Quick Revision Tables

The following tables summarise the main concepts from the Class 12 Biology Chapter 7 Notes.

Pathogens and Diseases

Immunity Summary

Important Abbreviations

Major Chapter Comparisons

Useful Links for Class 12 Biology