NCERT Solutions Class 12 Biology Chapter 8

NCERT Solutions Class 12 Biology Chapter 8

Biology is vital because it enables us to comprehend how living things function and interact on various levels. The word “biology”  come from the Greek words “bios” (life) and “logos” (word) (meaning “study”). Other science oriented professions such as medicine, nursing and allied health, pharmacy and pharmacology, dentistry, and veterinary medicine also come under biology.

NCERT Class 12 Biology Chapter 8 is about Human Health and Disease. The effects of medicines are studied during medicine degrees. Human Health and Disease is a major subject in the NCERT syllabus for Class 12. This chapter covers important topics such as different diseases in humans, types of immunity, Cancer, HIV and AIDS, and many more.

Biology is an intricate subject and many students find it  challenging. Students can easily understand all the concepts through our NCERT Solutions Class 12 Biology Chapter 8. This encourages the students to master the topic and increases their confidence to achieve a high grade Extramarks introduces Chapter 8 Biology Class 12 NCERT Solutions to make this challenging subject easier. 

NCERT Solutions Class 12 Biology Chapter 8 students can easily understand all the concepts . This encourages the students to master the topic and increases their confidence to achieve a high grade

In addition to Class 12 Biology Chapter 8 NCERT Solutions, students can use the Extramarks website to access several other study resources.  For example, NCERT books, CBSE revision notes, CBSE sample papers, CBSE previous year question papers, and other materials are available for students.

Key Topics Covered in NCERT Solutions Class 12 Biology Chapter 8

Listed below are the key topics that are covered in NCERT Solutions for Class 12 Biology Chapter 8- Human Health and Disease:

Introduction to Health

NCERT Solutions Class 12 Biology Chapter 8 explains the concept of health and the factors affecting it. In layman’s language , health is the absence of all illnesses and infections. However, the World Health Organisation (WHO) defines health as more than just the absence of disease or sickness. It refers to a state of physical, mental, and social well-being that is active and energetic. Individuals can maintain excellent health by eating a well-balanced diet and exercising regularly. Several elements influence one’s health, including:

  • A diet that is not well balanced.
  • Disorders of the Gene.
  • Anxiety and stress.
  • Pathogen infection is when a person is infected with a pathogen.
  • Consumption of harmful and unsanitary foods.
  • Exercise and other physical activities are lacking.

A healthy and balanced diet, decent personal cleanliness, frequent exercise and other physical activity are essential components. In addition, everyone should be informed of the various illnesses and their consequences and preventive measures to manage their health.

Common Diseases in Humans

NCERT Solutions Class 12 Biology Chapter 8 explains disease as an undesirable condition that affects a living entity that is otherwise healthy. Infectious and non-infectious diseases are the two broad categories:

Infectious Disease: Pathogens such as bacteria, viruses, fungi, and parasites cause these diseases, which may be readily spread from one person to another, making them infectious or contagious. Infectious illnesses include the common cold, tuberculosis, influenza, ringworm, and malaria.

Non-Infectious Disease: Non-infectious diseases, also known as non-communicable diseases, cannot be transmitted from one person to another. Genetic abnormalities, bad diets, a lack of physical exercise, and a few environmental variables can all contribute to these diseases.

Some common Diseases in Humans:

  • Salmonella typhi, a pathogenic bacteria, is known to cause typhoid in humans. A widal test can be used to confirm this fever.
  • Streptococcus pneumoniae and Hemophilus influenza are the bacteria that cause pneumonia.
  • Rhinovirus is a virus that causes one of the most common viral diseases in humans, the common cold.
  • Plasmodium, a tiny protozoan, causes malaria. Entamoeba histolytica is another protozoan that causes amoebiasis (amoebic dysentery).
  • The intestinal parasite Ascaris causes ascariasis.
  • Filariasis or elephantiasis is caused by the filarial worm Wuchereria.


Immunity is the body’s capacity to protect, defend, and fight against infections such as bacteria, viruses, and other foreign bodies and poisonous chemicals. Immunity may be divided into two categories as explained by NCERT Solutions Class 12 Biology Chapter 8:

Innate Immunity

Innate immunity is  that has been present since birth and is non-specific. Pathogen penetration is limited by this immunity, which employs several barriers- psychological barrier, physical barrier, cytokine barrier and cellular barrier.

Acquired Immunity

Acquired immunity is pathogen-specific and develops over one’s life. Active immunity, which is acquired naturally or secondary or anamnestic response, occurs when a person suffers an illness or sickness due to their exposure to a pathogen, and their body becomes immune to the disease as a result of the formation of the immune response in the body.

Active and Passive Immunity

Active immunity is when the host is exposed to antigens, the host creates antibodies in the form of dead or live microorganisms. It’s a time-consuming process that takes a long time to complete. 

On the other hand, passive immunity is a type of immunity in which the body is supplied with ready-made antibodies to defend it from outside invaders.


Allergic illnesses are another name for allergies. They are a group of diseases induced by the immune system’s hypersensitivity to various normally innocuous chemicals in the environment. For example, allergies develop when the immune system reacts to a foreign substance such as pollen, bee venom, or a meal that causes no reaction in most people.

Sneezing, runny nose, watery eyes, and trouble breathing are all symptoms of allergic reaction, as stated by NCERT Solutions Class 12 Biology Chapter 8.

Immune System in the Body

Lymphoid organs, tissues, cells, and antibodies make up this system. The immune system works in the following way:

  • First, it aids in the distinction between self and non-self.
  • Second, it defends the body against foreign or non-self antigens.
  • Third, it is based on the development of memory cells and reacts to previously present antigens.
  • Fourth, it’s a component of allergic responses.
  • Fourth, it is critical in the treatment of auto-immune illnesses.
  • Finally, it’s crucial in the case of organ transplantation and graft rejection.


The Human Immunodeficiency Virus (HIV) causes Acquired Immunodeficiency Syndrome, impairing the body’s capacity to fight infection. The virus is spread by coming into contact with contaminated blood, sperm, or vaginal secretions. AIDS was first detected in 1981, and it has spread over the world in the subsequent twenty-five years, killing over 25 million people.

  • Fever, tiredness, and a sore throat are flu-like symptoms that develop within a few weeks of infection.
  • After that, the illness goes asymptomatic until it develops into AIDS. AIDS symptoms include weight loss, fever or night sweats, exhaustion, and recurring infections.
  • Although there is currently no cure for AIDS, antiretroviral therapy can help decrease the disease’s progression and avoid secondary infections and consequences.

Prevention and Control

  • Making blood transfusions HIV-safe.
  • To avoid using the same needles that have already been used.
  • Condoms are given away for free.
  • Keeping drug misuse under control.
  • Promoting the use of safe sex.
  • Promoting HIV testing in vulnerable communities regularly.
  • The role of society in stopping the disease’s spread.
    • Heartfelt sympathy for the people living with HIV/AIDS.
    • To raise public awareness about AIDS to prevent it from spreading.
    • To prevent the spread of this disease, society and medical facilities must work together. In addition, to avoid the transmission of HIV to other people, it is necessary to disclose one’s HIV status.

The concept of HIV-AIDS and its precautions have been explained by NCERT Solutions Class 12 Biology Chapter 8 in the above section. To obtain notes of the same, refer to the Extramarks website.


In our bodies, cell development is tightly regulated and coordinated. Still, when these systems fail, the differentiation of cells becomes uncontrollable, resulting in the creation of cancer cells and uncontrollable growth. These malignant cells will continue to divide, resulting in the creation of uncontrolled growth cells known as tumours.

Types of Tumours 

There are two types of tumours, as explained by NCERT Solutions Class 12 Biology Chapter 8:

  • The term “benign tumour” refers to a tumour that has been differentiated and encapsulated. Benign tumours develop at a slower rate, and they usually stay localised and do not migrate to other regions of the body, resulting in less harm.
  • The “malignant tumours”, on the other hand are a mass of proliferating cells called neoplastic or tumour cells. They form when cells proliferate out of control. The condition can become life-threatening if the cells continue to develop and spread. During metastasis, malignant tumours can develop swiftly and move to other areas of the body.

Drugs and Alcohol Abuse

The abuse of drugs, which are chemical compounds not prescribed by doctors and consumed in large doses, frequently results in the impairment of a person’s physical and psychological functioning, leading to drug addiction.

When a person achieves reproductive maturity, they enter adolescence. This is a period between childhood and adulthood.. Various physiological and psychological changes occur throughout this time, resulting in the individual’s emotional and behavioural development. Individuals are exceptionally emotional and vulnerable during this time. This may sometimes lead to Alcohol abuse.

Prevention and Control methods explained by NCERT Solutions Class 12 Biology Chapter 8:

  • But, first, avoid putting yourself under undue peer pressure.
  • Counselling and education
  • Seeking assistance from family and friends.
  • On the lookout for warning indicators.
  •  Looking for professional and medical assistance.

NCERT Solutions Class 12 Biology Chapter 8 Exercise and Solutions

Extramarks Students can access previous years question papers, revision notes, extra problems, and more on the Extramarks website. Click on the  links below  to view NCERT Solutions Class 12 Biology Chapter 8:

Class 12 Science Biology 8: Very Short Answer Type Questions

Class 12 Science Biology 8: Short Answer Type Questions

Class 12 Science Biology 8: Long Answer Type Questions

Students may access NCERT Solutions Class 12 Biology Chapter 8 and other chapters by clicking here. In addition, students can also explore NCERT Solutions for other classes given below.

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By getting access to NCERT Solutions Class 12 Biology Chapter 8, students can easily understand all the concepts of Reproduction and its different concepts.

Key Features of NCERT Solutions Class 12 Biology Chapter 8

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Q.1 What are the various public health measures, which you would suggest as safeguard against infectious diseases?


Public health measures are very important for the prevention and control of various infectious diseases. These measures help to safeguard against infectious diseases. Some of these measures are:

a. Maintenance of personal and public hygiene: It is very important for the prevention and control of many infectious diseases. Personal hygiene includes keeping the body clean, consumption of clean drinking water, food, vegetables, fruits, etc. and public hygiene includes proper disposal of waste and excreta, periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks. These measures are particularly essential for water-borne diseases such as typhoid, amoebiasis and ascariasis.

b. Prevention of air-borne diseases: In cases of air-borne diseases such as pneumonia and the common cold, in addition to the above measures, close contact with the infected persons or their belongings should be avoided.

c. Prevention of vector-borne disease: For diseases such as malaria and filariasis that are transmitted through insect vectors, the most important measure is to control or eliminate the vectors and their breeding places. This can be achieved by

(i) avoiding stagnation of water in and around residential areas

(ii) regular cleaning of household coolers

(iii) use of mosquito nets

(iv) introducing fish like Gambusia in ponds that feed on mosquito larvae

(v) spraying of insecticides in ditches, drainage areas and swamps, etc.

(vi) doors and windows should have wire mesh to prevent the entry of mosquitoes.

d. Vaccination and Immunisation: In this, an antigenic protein of pathogen or inactivated/weakened pathogen (vaccine) is introduced into the body to generate antibodies that neutralise the pathogenic agents during actual infection. A large number of infectious diseases like polio, diphtheria, pneumonia and tetanus have been controlled to a large extent by the use of vaccines.

Q.2 In which way has the study of biology helped us to control infectious diseases?


Numerous advancements made in biological science have helped us to deal with many infectious diseases efficiently. Study of the biology of many disease-causing organisms has helped us to understand the lifecycle and disease-causing properties of the causative agent. This has helped in the production of new and safer vaccines. Through vaccines and immunisation programmes, many infectious diseases like polio, diphtheria, pneumonia and tetanus have been controlled to a large extent. Discovery of antibiotics and various other drugs has also enabled us to effectively treat infectious diseases.

Q.3 How does the transmission of each of the following diseases take place?
(a) Amoebiasis
(b) Malaria
(c) Ascariasis
(d) Pneumonia


Sl. No Disease Causative


Mode of transmission
a. Amoebiasis Entamoeba histolytica It is a vector-borne disease. The housefly is the vector which acts as a mechanical carrier and transmits the parasite.

The infection spreads through the drinking of contaminated water and food.

b. Malaria Different

species of Plasmodium

It is a vector-borne disease that spreads by biting of infected female Anopheles mosquito.
c. Ascariasis Ascaris lumbricoides A healthy person acquires this infection through contaminated water and food.
d. Pneumonia Streptococcus pneumoniae and Haemophilus influenzae A healthy person acquires this infection by inhaling the droplets/aerosols released by an infected person or by sharing glasses and utensils with an infected person.

Q.4 What measures would you take to prevent water-borne diseases?


Water-borne diseases such as amoebiasis, ascariasis, cholera, typhoid, hepatitis B are spread by drinking contaminated water. These water-borne diseases can be prevented by consumption of clean drinking water, food, vegetables, fruits, etc. Public hygiene measures like proper disposal of waste and excreta, periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks need to be done.

Q.5 Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.


A ‘suitable gene’ refers to a specific DNA segment which can be injected into the body of the host to produce specific proteins or antibodies. These antibodies can kill specific disease-causing organism in the host and provide immunity.

[Explanation: DNA introduced into the cells remains active for a long period and this therapy provides a long term protection from the disease. This powerful strategy is also used to reestablish the normal equilibrium and overcome a diseased condition in host.]

Q.6 Name the primary and secondary lymphoid organs.


(a) Primary lymphoid organs include the bone marrow and the thymus.

[Explanation: In these primary lymphoid organs, immature lymphocytes differentiate into antigen-sensitive lymphocytes.]

(b) Secondary lymphoid organs are the ‘Peyer’s patches of small intestine’, spleen, lymph nodes, tonsils, and appendix.

[Explanation: The secondary lymphoid organs provide the sites for interaction of lymphocytes with the antigen, which then proliferate to become effector cells.]

Q.7 The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form:
(a) MALT
(b) CMI
(c) AIDS
(d) NACO
(e) HIV


(a) MALT- Mucosa-Associated Lymphoid Tissue

(b) CMI- Cell-Mediated Immunity

(c) AIDS- Acquired Immuno Deficiency Syndrome

(d) NACO- National AIDS Control Organisation

(e) HIV- Human Immuno Deficiency virus

Q.8 Differentiate the following and give examples of each:
(a) Innate and acquired immunity
(b) Active and passive immunity



Innate immunity Acquired immunity
Innate immunity is a non-specific type of defence that is present at the time of birth. Acquired immunity is pathogen-specific. It is characterised by memory.
It is inherited from parents. It is acquired after the birth when the host encounters a pathogen.
It functions by providing various barriers such as

(i) Physical barriers (ii) Physiological barriers (iii) Cellular barriers and (iv) cytokine barriers against the entry of foreign infectious agents.

It functions by producing primary and secondary immune responses, which are mediated by B−lymphocytes and


It does not have a specific memory. It is characterised by an immunological memory upon encounter with the antigen.


Active immunity Passive immunity
It is a type of acquired immunity wherein the body produces its own antibodies against living or dead microbes or other proteins. It is a type of acquired immunity where readymade antibodies are administered directly to protect the body against foreign agents.
It is slow and takes time in generating antibodies and giving responses. It is fast and provides immediate relief.
For example: Injecting the microbes deliberately during immunisation or infectious organisms gaining access into the body during natural infection induces active immunity. Transfer of antibodies from the mother’s milk to the infant through yellowish fluid colostrums during the initial days of lactation is an example of passive immunity.

Q.9 Draw a well-labelled diagram of an antibody molecule.


A well-labelled diagram of an antibody molecule is depicted below:

Q.10 What are the various routes by which transmission of human immunodeficiency virus takes place?


AIDS is caused by the Human Immuno deficiency Virus (HIV), a member of a group of viruses called retrovirus, which has an envelope enclosing the RNA genome. Transmission of HIV-infection generally occurs in the following ways:

(a) Sexual contact with an infected person.

(b) Transfusion of contaminated blood and blood products.

(c) Sharing infected needles like in the case of using intravenous drug abusers.

(d) From an infected mother to her child through the placenta.

Q.11 What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?


AIDS is caused by the Human Immunodeficiency Virus (HIV), via sexual or blood-blood contact. After getting into the body of the person, the virus enters into macrophages where the RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase. This viral DNA gets incorporated into the host cell’s DNA and directs the infected cells to produce virus particles. The macrophages continue to produce virus and in this way, they act as an HIV factory. HIV enters into helper T-lymphocytes (TH), replicates and produces progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. This repeated process leads to a progressive decrease in the number of helper T-lymphocytes in the body of the infected person, thereby decreasing the immunity of a person.

Q.12 How is a cancerous cell different from a normal cell?


Normal cell

Cancerous cell

Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibit their uncontrolled growth and they stop dividing.

Cancerous cells lack the property of contact inhibition. Therefore, they continue to divide, giving rise to masses of cells called tumors.

Normal cells undergo differentiation after attaining specific growth.

Cancerous cells do not undergo differentiation.

These cells remain confined at a particular location.

When the cancerous cells become malignant, they grow very rapidly, invading and damaging the surrounding normal tissues.

Q.13 Explain what is meant by metastasis.


The pathological process of spreading cancerous cells to the different parts of the body is called metastasis. The property of metastasis is exhibited by malignant tumours. The malignant tumours are a mass of proliferating cells called neoplastic or tumour cells. These cells grow very rapidly, invading and damaging the surrounding normal tissues. As these cells actively divide and grow, they also starve the normal cells by competing for vital nutrients. Cells sloughed from such tumours travel through blood and lymph, reach distant sites and rise to a new tumour.

[Explanation: Metastasis is a complex process and to successfully colonise a distant area in the body, the cancer cell must complete a series of steps to form a clinically detectable lesion. The most common sites of cancer metastasis are the bone, liver and lung ].

The steps of metastasis include:

Separation from the primary tumour.
Invasion through tissues around the initial lesion.
Entry into the blood vessels and lymphatic vessel.
Reaching the distant organ like lungs, liver, bone.
Formation of a new tumour along with new blood vessels feeding the tumour.

Q.14 List the harmful effects caused by alcohol/drug abuse.


Addiction to alcohol/drugs is a very serious problem the present-day society is facing and is a cause of real concern.

Effects of alcohol:

On an individual: Alcohol causes short-term as well as the long-term effect on an individual.

  1. Short-term effects include Slurred speech, drowsiness, vomiting, diarrhoea, headaches, breathing difficulties, unconsciousness etc.
  2. Long-term effects include High blood pressure, stroke, liver disease, nerve damage, vitamin B1 deficiency, ulcers, malnutrition etc.

Also, it is advisable for pregnant women to avoid alcohol as it may retard the growth of the baby.

On the family: Long term consumption of alcohol by any family member can have negative effects on the family. It may lead to several domestic problems like quarrels, sexual assault, domestic violence, frustrations, insecurity, etc.

On the society: Increased on-the-job injuries and loss of productivity, rash behaviour, violence and loss of interest in social activities.

Similarly, an individual who is addicted to drugs creates problems for himself as well as for the family and society.

Effects of drugs:

On an individual: It weakens the immune system and causes cardiovascular diseases. Injected drugs can cause infections of the blood vessels and heart valves, dramatic fluctuations in appetite and increase in body temperature. Susceptibility of HIV infection is most common in these individuals as they share common needles while injecting drugs in their body.

On the family and society: A person addicted to drug creates a family as well as a social problem as he becomes frustrated, irritated, confused and may become anti-social.

The most common warning signs of drug and alcohol abuse among youth include drop in academic performance, unexplained absence from school/college, lack of interest in personal hygiene, withdrawal, isolation, depression, fatigue, aggressive and rebellious behaviour, deteriorating relationships with family and friends, loss of interest in hobbies, change in sleeping and eating habits, fluctuations in weight, appetite, etc.

Q.15 Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?


Yes, friends can influence one to take drugs and alcohol. A person can take the following steps to protect himself/herself against drug abuse:

(a) Increase your will power to say no to alcohol and drugs. One should not experiment with alcohol for adventure and excitement.

(b) Avoid the company of friends who take drugs and alcohol.

(c) Seek help from family and peers to get rid of the habit.

(d) Take proper counselling and professional help about drug and alcohol abuse.

(e) Utilise your energy in constructive extra-curricular activities.

Q.16 Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.


Drug and alcohol consumption has an addictive nature associated with a temporary feeling of well-being. With repeated use of drugs, the tolerance level of the drug receptors present in our body increases. Consequently, the receptors respond only to higher doses of drugs or alcohol leading to greater intake and addiction.

Q.17  In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?


There are several factors responsible for motivating youngsters towards alcohol or drugs. Curiosity, need for adventure, excitement and experimentation constitute common causes, which motivate youngsters to try drugs and alcohol. Television, movies, newspapers, the internet also help to promote the perception that drugs and alcohol can solve many big problems. Other factors that are associated with rampant drug and alcohol abuse among adolescents are unstable or unsupportive family structures and peer pressure.

Preventive measures against alcohol and drug abuse are as follows:

(i) Avoid undue peer pressure – A child should not be pressurised unduly to perform beyond his/her threshold limits be it studies, sports or other activities.

(ii) Education and counselling – Educating and counselling him/ her to face problems and stresses, and to accept disappointments and failures as a part of life. Children should channelise their energy into healthy pursuits like sports, reading, music, yoga and other extracurricular activities.

(iii) Seeking help from parents and peers – Help from parents and peers should be sought immediately so that they can guide appropriately.

(iv) Looking for danger signs – Alert parents and teachers need to look for and identify the danger signs. Appropriate measures would then be required to diagnose the malady and the underlying causes.

(v) Seeking professional and medical help – Youngsters who have become drug/alcohol addicts should take help from highly qualified psychologists, psychiatrists, and attend de-addiction and rehabilitation programmes to help themselves.

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FAQs (Frequently Asked Questions)

1. What is the gist of Class 12 Biology Chapter 8?

The chapter -Human Health and Diseases covers various facets of health-related topics in an easy-to-understand manner.. It defines health as a person’s mental, bodily, and social well-being and the diseases that detract from it. It also discusses the importance of a proper diet and a healthy lifestyle. Besides, this chapter discusses illnesses, both communicable and non-communicable disorders, and the addictive nature of alcohol and drugs. A person may get addicted and require professional and medical help to deal with the situation.

2. What does immunity mean?

Everyday our body is exposed to a large number of infectious agents from our surroundings. However, there are only a few times when these infectious exposures will result in any disease. This is due to the ability of our body to defend itself from most of these foreign infectious agents. The self-defence ability of the host (body) to fight the disease-causing agents or organisms, conferred by the immune system is called immunity.