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NCERT Solutions for Class 12 Biology Chapter 8 - Human Health and Disease

Aakash NCERT Solutions for Chapter 8 of Class 12 makes students about Biology Health, maintenance of optimum health and diseases. Students are also taught about types, treatment and prevention of diseases, immunity and its types in an easy yet detailed manner.

Human Health and Disease Class 12 Biology Chapter 8 NCERT Question and Answers - Download PDF


1.What are the various public health measures, which you would suggest as safeguard against infectious diseases?
Health measures as a safeguard against infectious diseases.
The public health measures that can be taken to avoid infection of diseases are as follows:
(a)Vaccination - The populations should be vaccinated timely and properly so that they don't develop diseases. For diseases like cholera, TB, hepatitis vaccination are available
(b)Education and awareness - Everybody should be educated or made aware of the infectious diseases so that they can protected themselves from infectious diseases
Sanitation - Adopting public sanitation measures is good for avoiding infectious diseases. We should maintain cleanliness in our surroundings. One should also maintain cleanliness and consume only clean drinking water and contamination-free fruits and vegetables.
(d)Eradication - The vectors of diseases must be eradicated by destroying the breeding sites of many vectors.

2.In which way has the study of biology helped us to control infectious diseases?
Biological research and tools have always been helpful in controlling and eradicating infectious or communicable diseases. biology helps us in various ways, some of them are:
(a)By using the knowledge of biology we can know the nature of the diseases.
(b)To find out the mode of transmission of disease, biology plays a very important role, for example, if a person shows symptoms like vomiting or diarrhea, the mode of transmission can be through contaminated food. and disease will take the -faecal route.
(c)To provide treatment and cure the infected person by medicines.
(d)Provide vaccines and immunization treatment for preventing further spread of disease.

3.How does the transmission of each of the following diseases take place?

Amoebiasis- It transmits via consumption of water and food contaminated by amoebic cysts.

Malaria- It transmits from one person to another by means of female Anopheles mosquito. When this mosquito bites a diseased person, along with blood it takes the parasite and while biting a healthy person, the parasite transfers to the healthy person.

Ascariasis- It transmits through food and water contaminated with eggs of the parasite.

Pneumonia- It transmits through droplet infection i.e. through sneeze,cough,sharing utensils etc.

4.What measure would you take to prevent water-borne diseases?
Drinking contaminated water is one of the main reasons for water borne diseases such as typhoid, cholera etc. The measures that can be taken to prevent water-borne diseases are as follows
(a)To prevent these diseases we would dispose of sewage, excreta, etc. properly
(b)We should check our water reservoirs regularly.
(c)We should consume clean, pure, contamination free water only.

5.Discuss with your teacher what 'a suitable gene' means, in the context of DNA vaccines.
A suitable gene means that special DNA segment which can be injected into the host body to produce specific proteins. These specific proteins should be such that they can kill the particular disease-causing organism present in the host body.

6.Name the primary and secondary lymphoid organs.
Lymphoid organs are the organs in which origin, maturation and proliferation of lymphocytes occur. Lymphoid organs are of two types i.e.primary lymphoid organs and secondary lymphoid organs. In primary lymphoid organs, the origin of lymphocytes occurs. These include bone marrow and thymus.
After maturation, lymphocytes migrate to a secondary lymphoid organ-like spleen, lymph nodes, tonsils, peyer’s patches of small intestine and appendix. They provide the sites for interaction of lymphocytes with antigens.

7.Expand well-known abbreviations
MALT- Mucosal Associated Lymphoid Tissue

CMI- Cell Mediated Immunity

AIDS- Acquired Immunodeficiency Syndrome

NACO- National AIDS Control Organisation

HIV- Human Immunodeficiency Virus

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

Innate immunity

Acquired immunity

It is a non-specific type of defence present at the time of birth and provides different kinds of barriers to the entry of foreign agents into the body.

It is pathogen specific

defence characterised

by memory.

It remains throughout the life

It is short-lived

Innate immunity is inheritable

Acquired immunity is not inheritable

(b)Active and passive immunity

Active immunity

Passive immunity

Active immunity develops in a

person’s own body in

response to an infection or any


Passive immunity develops   a

person's body when antibodies

from outside are  injected into

the body

Active immunity does not  have side effects

It may have side effects

It is long lasting

It has a short span

Active immunity takes a long

period to provide show effect

Passive immunity immediately

show effects and provides relief.

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

The well-labelled diagram of an antibody molecule is as follows

10.What are the various routes by which transmission of human immunodeficiency virus takes place?
Acquired immunodeficiency syndrome is caused by the human immunodeficiency virus. The various routes by which transmission of human immunodeficiency virus takes place are:
(a)Through sharing of infected needles.
Having sex with an infected person without using condoms.
(c)Infected mother to baby through the placenta.
(d)Through the transfer of blood from an infected person to normal person

11.What is the mechanism by which the AIDS virus causes deficiency in the immune system of the infected person?
AIDS is a viral disease caused by the HIV virus. It is considered to be one of the most dangerous diseases with no cure until now. HIV affects the immune system of the body and makes it unable to perform its usual functions. The mechanism by which HIV virus causes deficiency of the immune system is as follows:
(a)After entering into the system, HIV binds itself to the surface receptors present on helper T-cells and introduces its RNA and reverse transcriptase enzyme into these cells.
(b)After this, by utilizing the host cell's machinery, HIV produces a copy of DNA itself through reverse transcription.
(c)This copy of DNA gets incorporated into the genome of the host cell. This is called the provirus form, which directs the viral genome to produce new virus particles.
(d)The subsequent formation and release of viral particles destroy the host cell. As a result, the number of T helper cells decreases.
(e)AIDS occurs when the count of helper T-cells falls very much and the body is unable to fight against diseases.

12.How are cancerous cells different from a normal cell?
Differences between cancerous cells and normal cells

Cancer cells

Normal cells

Cancerous cells divide at a faster rate forming a mass of cells called tumour.

Normal cells divide at a normal rate and do not cause the formation of tumors

They spread, move to another tissue

and affects their normal functions.

Thus, they are not restricted to one


These are restricted to

one location.


13.Explain what is meant by metastasis.
Metastasis - It refers to the process of formation of secondary tumors from the fragments of primary tumors.The pieces Primary tumors are carried to neighbouring tissues via blood. Metastasis is the last stage of cancer.

14.List the harmful effects caused by alcohol/drug abuse.
Harmful effects caused by alcohol/drug abuse.
(a)These reduce the efficiency of all the tissues of our body. Long time use of drugs and alcohol can cause many mental and physical diseases.
(b)These dilate the blood vessels and affect the normal functioning of the heart.
(c)Excessive drug/alcohol abuse can lead to cirrhosis in the liver.
(d)Excessive drug/alcohol abuse may increase the workload of kidneys and cause kidney failure.
Long time use of alcohol /drugs can cause impotence.
(f)Alcoholics lose their image in society because of their nature created under the influence of alcohol.
(g)Drug/alcohol abuse increases family violence which affects their family and social life.

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 alcohol/drugs. However, we can avoid those conditions in the following ways:
(a)We should avoid the company of those friends who take drugs or alcohol.
(b)We should increase our willpower to stay away from these things.
(c)We should have knowledge about the bad results of taking alcohol or drugs.
(d)We should take the help of our parents if any question arises in our mind regarding this.
(e) We should immediately consult a doctor if any symptoms like depression or frustration are felt.

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.
Once a person starts taking alcohol or drugs, it becomes very difficult to get rid of this habit. It is mainly because according to this person, alcohol is the only way to attain a normal state. Alcohol does not affect any organ other than the nervous system of a human body. However, due to the effect on the nervous system other organs also get affected. Prolonged use of alcohol can make a person so addicted that his nervous system works normally only in the presence of alcohol or drugs. Even when someone starts withdrawing alcohol or drugs, the body gets affected badly and withdrawal symptoms are seen. Due to these withdrawal symptoms, people often do not get rid of alcohol.

17.In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
There are several reasons which motivate youngsters to take alcohol. Some of these are given here under:
(a)Appreciation from friends on the use of such things.
(b)Sometimes youngsters start taking these things just for pleasure
(c)To get rid of depression and frustration, youngsters often move to drugs/alcohol.
(d)After watching it in movies, adolescents think that taking alcohol or drugs is a sign of being cool and royal. So, they also start following these.
(e)Sometimes the company of wrong friends makes us alcoholic.
(f)We can avoid all these, by sharing our problems with our parents. We should understand the bad effects of alcohol and should not look at alcohol as a sign of royalty or greatness. There are many other ways to solve problems other than alcohol intake. Youngsters should be taught about moral values.

NCERT Related Links

NCERT Solutions for Class 12 Biology: Download Chapterwise PDFs

Chapter 1 Reproduction in Organisms

Chapter 2 Sexual Reproduction in Flowering Plants

Chapter 3 Human Reproduction

Chapter 4 Reproductive Health

Chapter 5 Principles of Inheritance and Variation

Chapter 6 Molecular Basis of Inheritance

Chapter 7 Evolution

Chapter 8 Human Health and Disease

Chapter 9 Strategies for Enhancement in Food Reproduction

Chapter 10 Microbes in Human Welfare Solutions

Chapter 11 Biotechnology: Principles and Processes

Chapter 12 Biotechnology and its Applications

Chapter 13 Organisms and Populations

Chapter 14 Ecosystems Solutions

Chapter 15 Biodiversity and Conservation

Chapter 16 Environmental Issues

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