Human Health and Diseases Class 12 | Biology in Human Welfare| Term 2


Human Health and Diseases Class 12, Biology, Term 2


Health is a state of complete physical, mental and social well being. It is affected by many reasons. Some of them are;

  1. Genetic Disorders – Defect which child inherits from its parents.
  2. Infection from Microbes
  3. Life Style – It includes food and water we take, exercise and rest.
  • When people are healthy, they are efficient at work, it increases productivity and prosperity. It also increases longevity of people and reduces infant and maternal mortality.

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

Types of Diseases

There are basically two types of diseases.

a. Infectious Disease: Diseases which can be easily transmitted from infected person to healthy persons are called Infectious Disease

b. Non-Infectious Disease: Diseases which cannot be transmitted from one person to another are call Non-Infectious Disease.

Common Infectious Diseases in Man

The disease causing microbes like bacteria, virus, fungi, protozoa, helminths are called pathogens. Pathogens can enter the body by various means and multiply and interfere with normal vital activates resulting in morphological and functional damage.

Bacterial Diseases

a. Typhoid pathogen: Salmonella typhi mode of transmission: enters small intestine through food and water and migrates to other organ through blood. Symptoms:

  • High fever, weakness, stomach pain, constipation, headache and loss of appetite.
  • Intestinal perforation and death may occur.
  • Widal test is used for confirmation of disease.

b. Pneumonia pathogen: Streptococcus pneumonia and Haemophilus influenza mode of transmission: inhaling of droplets/aerosols released by infected person , sharing things with infected person. Symptoms:

  • Infects lung alveoli , alveoli get filled with fluid creating respiratory disorders.
  • Fever, chills, cough, headache.
  • Severe cases: lips and finger turn gray to blue colour.

Viral Diseases

a. Common Cold Pathogen: Rhinoviruses mode of transmission: inhaling droplets from cough or sneezes , through contaminated objects. Symptoms:

  • Infects nose and respiratory pathway
  • Nasal congestion and discharge, sore throat, hoarseness , cough , headache, tiredness etc.
  • Lasts for 3-7 days

Protozoan Diseases

A. Malaria Pathogen: plasmodium sp. (P. vivax, P. malaria , P. falciparum) mode of transmission: Anopheles mosquito biting.


  • Hemozoin causes chill and high fever recurring every 3-4 days

Life Cycle OF Plasmodium  

  1. Plasmodium targets the human body as a form of Sporozoites through the bite of female Anopheles mosquito.
  2. Sporozoites can infect the human’s liver cells that can rupture it and release merozoites as well.
  3. The parasites increase its number within the liver cells and further harm the red blood cells of the body.
  4. If the female Anopheles mosquito bites the infected person, then it again enters into the mosquito’s body and ultimately moves into further development.
  5. When these mosquitoes bite a human, the sporozoites are further spread into the body, thereby repeating the cycle and can increase the disease at the community level.Human Health and Diseases Class 12

B. Amoebiasis (Amoebic Dysentery) pathogen: Entamoeba histolytica mode of transmission: houseflies transmit parasites from faeces to food and water .

Helminth Diseases

A. Ascariasis

Pathogen: Ascaris(Intestinal parasite)

Mode of Transmission – Soil, water, vegetables, fruits etc. contaminated with eggs of parasites.


  1. Internal bleeding, muscular pain, fever, anemia.
  2. blockage of intestinal passage.


B. Filariasis ( Elephantiasis)

Pathogen: Filarial worms or WUCHERIA(W. brancrofti and W. malayi)

Mode of Transmission – Bite of female Culex mosquito.


  1. filarial worms live in lymphatic vessels causing chronic inflammation of the rogans in which they live for many years.
  2. limbs and genital organs may be deformed.

Fungal Diseases

a. Ring worms

Pathogen: Microsporum , Trichophyton and Epidermophyton.

Mode of transmission:

a. From soil or some personal item of infected person like comb , towel , clothes etc.

b. Moisture and heat develop to fungi to grow.


a. Dry, scaly, lesions on various body parts such as skin , nails and scalp.

b. Intense leaching

c. It is seen in groin, between the toes etc.

Prevention and Control of Diseases

Personal Hygiene

a. Keep the body clean

b. Use clean water and food etc.

2. Public hygiene

a. Proper disposal of wastes and excreta .

b. Cleaning and disinfection of water reservoirs , pools etc.

c. Avoid contact with infected person.

d. Practices of hygiene.

e. Control and elimination of vectors.


  • It is the ability of immune system to fight against the disease causing organisms.
  • It is of two types:

a. Innate immunity

b. Acquired immunity

Innate immunity

  • This is non – specific defense present at the time of birth.
  • It provides different type of barriers to the entry of foreign agents into our body.
  • It is of four types:

a. Physical Barriers

It includes: skin( prevent entry of foreign bodies)

Mucus coating of epithelium lining the respiratory , gastro – intestinal and urino genital tracts to trap microbes.

b. Physiological Barriers:

It includes: acid in stomach , saliva in mouth, tears from eyes prevent microbial growth.

c. Cellular Barriers:

It includes: leucocytes  like WBC such as neutrophils or polymorpho-nuclear leucocytes (PMNL neutrophils), monocytes and natural killer lymphocytes , macrophages etc.

d. Cytokine Barriers :

It includes virus infected cells secrete protein called interferon which protect non- infected cells from further viral infection.

Acquired immunity

It is pathogen specific immunity.

  • It is characterised by memory i.e. during first encounter of a pathogen , our body produces primary response in low intensity. Second encounter with the same pathogen produces a secondary ( anamnestic) response in high intesity.
  • There are two types of lymphocytes

a. B-lymphocytes

b. T- lymphocytes


  • They produce proteins in response to pathogen into our blood to fight with them.
  • these proteins are called antibodies.


  • They help B- cells to produce antibodies.

Each antibody has four peptide chains namely

a. Two small chains called light chains

b. Two longer chains called heavy chains

It is represented as H2L2

Types of antibodies – IgG , IgA , IgM , IgE and IgD.

Acquired Immune Response 

Humoral and antibody mediated response / antibody mediated immunity (AMI)


T cells mediate CMI.

CMI is responsible for graft rejection.


a. Active immunity

b. Passive immunity


  • When a host is exposed to antigens antibodies are produced in the host body and is called active immunity.
  • it is slow and take more time to get fully effective.


  • when ready- made antibodies are directly given to the protect the body against foreign agents is called passive immunity.
  • colostrum- the yellowish fluid secreted by mother during the initial days of lactation has abundant antibodies(IgG) to protect from infant. The foetus also receives some antibodies from their antibodies from their mother, through the placenta during pregnancy .

Vaccination and immunization

  • Immunization is based on the memory of the immune system.
  • There are two types mainly ,

a. Active immunization

b. Passive immunization


Our immune system is designed to distinguish between self and non-self cells. Whenever some foreign cells or substance enters our body, our immune system recognizes it as non-self and then removes it. Sometimes, this system of immune response fails to function properly. It recognizes the self as non-self and starts destroying them, causing severe unnecessary reactions. These extra reactions are called hypersensitivity. Different allergic reactions occur due to different types of hypersensitivity.

The different types of hypersensitivities and their features are as follows:

Type I Hypersensitivity– It is an allergen-induced hypersensitivity causing the allergy. Small molecules called allergens enter the body and bind to specific antibodies in our bodies. The binding causes activation of immune cells causing anaphylaxis which further results in airway restriction or vasodilation, itching, or inflammation.


  • Due to genetic and other unknown reasons , body attacks self- cells resulting in auto-immune disease eg- Rheumatoid arthritis.


  • It is the system that gives immunity to the body by recognizing, responding, and remembering foreign agents.
  • It plays a role in allergic reaction , auto immune disease and organ transplantation.
  • It includes lymphoid organs, tissues , cells and soluble molecules like antibodies.

Lymphoid Organs

These are the organs where origin, maturation and proliferation of lymphocytes occur. It is of two types :

Primary Lymphoid Organs

The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen sensitive lymphocytes.

Bone Marrow and Thymus

  • Bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced.
  • Thymus is a lobed structure located near the heart and beneath the breastbone
  • The thymus is large at time of birth but keeps reducing in size with age and by time puberty is attained it reduces in size
  • Both bone marrow and thymus provide micro- environments for the development and maturation of T – lymphocytes.


They include organs like spleen, lymph nodes, tonsils , payer’s patches of small intestine and appendix. after maturation lymphocytes migrate in these organs.

The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen , which then proliferate to become effector cell.


  • It is largest bean shaped organ.
  • It mainly contains lymphocytes and phagocytes.
  • It is large reservoir of erythrocytes.


  • They are small solid structures located at different points along lymphatic system.
  • they serve to trap the micro-organisms or other antigens which happen to get into lymph and tissue fluid.
  • antigens trapped in the lymph nodes are responsible for the activation of the immune response.

MALT ( Mucosal Associated Lymphoid Tissue)

  • there is lymphoid tissue also located within the lining of the major tracts ( respiratory , digestive and urogenital tracts) called MALT.
  • it constitutes about 50 percent of the lymphoid tissue in human body.


Full form of AIDS is Acquired Immuno Deficiency Disorder.

  • It means deficiency of immune system acquired during the lifetime of an individual indicating that its not congential.
  • Syndrome- group of symptoms
  • Ut was first reported in 1981.
  • It varies from months to years(5-10 yrs)

Causes of AIDS

  • By having sex, you may become infected if you have vaginal anal or oral sex with an infected partner whose blood, semen or vaginal secretions enter your body.
  • By sharing needles.
  • From blood transfusions.
  • During pregnancy or delivery or through breast-feeding.

Symptoms of AIDS

  • The person suffers from bouts of fever, diarrhoea and weight loss.

The person become so immuno deficient that he/she is unable to protect these against infections.

Test For Identification of AIDS

It can be identified by ELISA (Enzyme Linked Immuno  – Sorbent Essay)test.

Process of AIDS

Prevention of AIDS

  • AIDS has no cure but can be prevented.
  • The only excuse may be ignorance and it is rightly said ” don’ t  die of ignorance “
  • NACO (National AIDS Control Organisation) and NGO’s(Non – Fovernmental Organisation) are educating people about AIDS.
  • WHO (World health Organisation) has started the number of programmes to prevent the HIV infection

Steps to prevent AIDS

  • Use condoms. Male latex condoms are the most effective way to prevent HIV and other STIs when you have sex.
  • Get tested. Be sure you and your partner are tested for HIV and other STIs.
  • Be monogamous.
  • Limit your number of sexual partners.


There is no uncontrolled growth of the body cells by virtue of the contact inhibition property displayed by the cells of the body. When the body cells lose this property and show an abnormal growth with a breakdown of the regulatory mechanism in the cells, then it leads to mass of continuously growing cells. This is nothing but cancer. Cancer cells divide continuously and make this mass of cells called tumours.

A tumour is classified into one of these three types based on its ability to undergo metastasis (spreading)

Benign Tumour

These tumours are localized at a particular location in the body. Moreover, it does not spread to the other parts of the body and is generally harmless. However, when a benign tumour occurs in areas such as the brain, it can turn fatal. Treatment often involves surgery and it does not grow back.

Malignant Tumour

These tumours are cancerous – meaning that they will grow quickly and spread to other normal tissues of the body. This ability to spread is called metastasis. Usually, cancer cells metastasize when it gets into the bloodstream or the lymph nodes and form secondary tumours across various sites in the body.

Diagnosis of Cancer

The detection and diagnosis of cancer are very important before it spreads to other parts of the body. Identification of cancer genes is pivotal to prevent cancer.

The following methods are used to detect cancer;

  1. Biopsy.
  2. Histopathological studies of tissue.
  3. Radiography technique.
  4. Computed tomography.
  5. Magnetic resonance imaging.
  6. Molecular biology techniques.

Treatment of Cancer

Commonly, three types of treatment are available for cancer.

  1. Surgery – Surgically removing localized cancerous mass (Effective for benign tumours)
  2. Radiation therapy – In this therapy, radiation is used to kill the cancer cells.
  3. Chemotherapy – Chemotherapeutic drugs are used to kill cancer cells.

Many chemical drugs have side effects in cancer patients like hair loss. So, interferons are injected into cancer patients to develop immunity against these side effects.

Drug Abuse 

  • The surveys and statistics show that the use of drugs has been increased among youths.
  • Proper education and guidance would enable youth to safeguard themselves against the drug abuse by following healthy life styles.
  • the drugs commonly opioids , cannabinoids and coca alkaloids.
  • these drugs are obtained from flowering plants and fungi.


Opioids work by blocking the pain signals sent from the brain. They bind to opioid receptors on the nerve cells and block the release of neurotransmitters from the neuron ending.

A. Morphine

  • it is obtained from the latex of poppy plant ( Papaver somniferum ).
  • it is sedative and pain killer
  • it is to reduce pain after after surgery.

B. Heroin

  • it is commonly called smack and chemically diacetylmorphine.
  • it is bitter, white, odourless and crystalline compound obtained from acetylation of morphine which is extracted from the latex of poppy plant.
  • it is a depressant and slows down the body function.


Cannabinoids are a group of chemicals, which interact with cannabinoid receptors present mainly in the brain.

  1. Cannabinoids are obtained from the inflorescences of plant Cannabis sativa.
  2. Leaves, flower tops, resins of C. sativa in various combinations produce hashish, charas, marijuana and ganja.
  3. These are inhaled or ingested orally.
  4. These drugs affect cardiovascular system of the body

Tobacco contains nicotine, which stimulates the adrenal gland to release adrenaline and noradrenaline which in turn increases the blood pressure and heart rate.

  1. It is obtained from tobacco plant.
  2. Its mode of intake is smoking, chewing or used as a snuff.
  3. Tobacco can induce lung cancer, bronchitis, emphysema, coronary heart disease, cancer of throat, oral cancer and cancer of urinary bladder, etc.
  4. Smoking of tobacco leads to increase in carbon monoxide content of blood and reduces the concentration of haem-bound oxygen. This leads to oxygen deficiency in the body.

Alcohol has an anaesthetic effect on nervous system, affecting cerebrum, cerebellum and other parts.

  1. It is taken orally.
  2. Effect of alcohol is euphoria, peptic ulcer, gastric carcinoma, hepatitis, liver failure, liver cell carcinoma, etc.

Addiction is a psychological attachment to certain effects such as; euphoria and a temporary feeling of well-being associated with drugs and alcohol. These drive people to take them without need or even when it becomes self destructive.

Dependence on drug/alcohol is the tendency of the body to manifest a characteristic and unpleasant Withdrawl Syndrome, if regular dose of drugs/alcohol is discontinued abruptly.

  1. Withdrawl symptoms are characterised by anxiety, shakiness, nausea and sweating.
  2. Sometimes, withdrawl symptoms can be so severe that they may be life threatening.
  3. It leads the patient to ignore all social norms in order to get sufficient funds to fulfil his/her needs. These results in social adjustment problems.

Drugs Exert have following effects on males

  • Acne
  • Aggressiveness
  • Reduction in size of testes
  • Sperm production is low
  • Premature baldness
  • Enlargement of prostate gland.

Drugs have effects on females also in the following ways

  • Aggressiveness
  • Masculinization (features like males)
  • Mood swings.
  • Depression
  • Irregularities in menstrual cycles.
  • Excessive growth of facial and body hair.

Drugs/alcohol addiction can be prevented and controlled by the following ways:

  • Avoid undue peer pressure.
  • Avoid disappointments and failures in life.
  • Discuss and seek help of parents and elders.
  • Discourage friends to take drugs/alcohol.
  • Take medical help whenever required.


# Human Health and Diseases Class 12

# Human Health and Diseases Class 12 Notes

# Human Health and Diseases Class 12 Biology

# Human Health and Diseases Class 12 NCERT Solutions

# Human Health and Diseases Class 12 Solutions


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