Class 12 Biology NCERT Solutions Chapter 8 Human Health and Disease

NCERT Solutions for Biology Chapter 8 Human Health and Disease

Table of Contents

NCERT Biology Chapter 8 Human Health and Disease Solved Textbook Questions

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

Ans- Health measures as a safeguard against infectious diseases. The public health measures that can be taken to avoid infectious diseases are as follows:

  • Vaccination- The populations should be vaccinated timely and properly so that they don’t develop diseases. For cholera. TB, hepatitis vaccinations are available.
  • Education and awareness- Everybody should be educated or made aware of the infectious diseases so that they can protect 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.
  • 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?

Ans- Various advancements that have occurred in the field of biology have helped us gain a better understanding to fight against various infectious diseases. Biology has helped us study the life cycle of various parasites, pathogens, and vectors along with the modes of transmission of various diseases and the measures for controlling them. Vaccination programmes against several infectious diseases such as small pox, chicken pox, tuberculosis, etc. have helped eradicate these diseases. Biotechnology has helped in the preparation of newer and safer drugs and vaccines. Antibiotics have also played an important role in treating infectious diseases.

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


DiseaseCausative organismMode of transmission
AmoebiasisEntamoeba histolyticaIt is a vector-borne disease that spreads by the means of contaminated food and water. The vector involved in the transmission of this disease is the housefly.
MalariaPlasmodium sp.It is a vector-borne disease that spreads by the biting of the female Anopheles mosquito.
AscariasisAscaris lumbricoidesIt spreads via contaminated food and water.
PneumoniaStreptococcus pneumoniaeIt spreads by the sputum of an infected person.

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

Ans- Drinking contaminated water is one of the main reasons for water born diseases such as typhoid, cholera etc. The measures that can be taken to prevent water-borne diseases are as follows,

  1. To prevent these diseases we should dispose of sewage, excreta, etc. properly.
  2. We should check our water reservoirs regularly.
  3. We should consume clean, pure, contamination free water only.

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

Ans- A ‘suitable gene’ refers to a specific DNA segment which can be injected into the cells of the host body to produce specific proteins. This protein kills the specific disease-causing organism in the host body and provides immunity.

6. Name the primary and secondary lymphoid organs.


  1. Primary lymphoid organs include the bone marrow and the thymus.
  2. Secondary lymphoid organs are the spleen, lymph nodes, tonsils, Peyer’s patches of small intestine, and appendix.

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 Organization
(e) HIV- Human Immuno Deficiency virus

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

Ans- (a) Innate and acquired immunity

Innate immunityAcquired immunity
It is a non−pathogen specific type of defense mechanism.It is a pathogen specific type of defense mechanism.
It is inherited from parents and protects the individual since birth.It is acquired after the birth of an individual.
It operates by providing barriers against the entry of foreign infectious agents.It operates by producing primary and secondary responses, which are mediated by B−lymphocytes and T-lymphocytes.
It does not have a specific memory.It is characterized by an immunological memory.

(b) Active and passive immunity

Active immunityPassive immunity
It is a type of acquired immunity in which the body produces its own antibodies against disease-causing antigens.It is a type of acquired immunity in which readymade antibodies are transferred from one individual to another.
It has a long lasting effect.It does not have long lasting effect.
It is slow. It takes time in producing antibodies and giving responses.It is fast. It provides immediate relief.
Injecting microbes through vaccination inside the body is an example of active immunity.Transfer of antibodies present in the mother’s milk to the infant is an example of passive immunity.

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


human health and disease

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

Ans- AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human immunodeficiency virus (HIV).

It has the following modes of transmission:

(a) Unprotected sexual contact with an infected person.
(b) Transfusion of blood from a healthy to an infected person.
(c) Sharing infected needles and syringes.
(d) From an infected mother to a child through the placenta.

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

Ans- AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human immunodeficiency virus (HIV) via sexual or blood-blood contact. After entering the human body, the HIV virus attacks and enters the macrophages. Inside the macrophages, the RNA of the virus replicates with the help of enzyme reverse transcriptase and gives rise to viral DNA. Then, this viral DNA incorporates into the host DNA and directs the synthesis of virus particles. At the same time, HIV enters helper T- lymphocytes. It replicates and produces viral progeny there. These newly formed progeny viruses get released into the blood, attacking other healthy helper Tlymphocytes in the body. As a result, the number of T-lymphocytes in the body of an infected person decreases progressively, thereby decreasing the immunity of a person.

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

Ans- Differences between cancerous cells and normal cells,

Cancer cells  Normal cells
Cancerous cells divide at a faster rate forming a mass of cells called tumor.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 location.These are restricted to one location.

13. Explain what is meant by metastasis.

Ans- The property of metastasis is exhibited by malignant tumors. It is the pathological process of spreading cancerous cells to the different parts of the body. These cells divide uncontrollably, forming a mass of cells called tumor. From the tumor, some cells get sloughed off and enter into the blood stream. From the blood stream, these cells reach distant parts of the body and therefore, initiate the formation of new tumors by dividing actively.

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

Ans- Alcohol and drugs have several adverse effects on the individual, his family, and the society.

A. Effects of alcohol:

Effects on the individual: Alcohol has an adverse effect on the body of an individual. When an individual consumes excess alcohol, it causes damage to the liver and the nervous system. As a result, other symptoms such as depression, fatigue, aggression, loss of weight and appetite may also be observed in the individual. Sometimes, extreme levels of alcohol consumption may also lead to heart failure, resulting coma and death. Also, it is advisable for pregnant women to avoid alcohol as it may inhibit normal growth of the baby.

Effects on the family: Consumption of excess alcohol by any family member can have devastating effects on the family. It leads to several domestic problems such as quarrels, frustrations, insecurity, etc.

Effects on the society:

(a) Rash behavior
(b) Malicious mischief and violence
(c) Deteriorating social network
(d) Loss of interest in social and other activities

B. Effects of drugs: 

An individual who is addicted to drugs creates problems not only for himself but also for his family.

Effects on the individual: Drugs have an adverse effect on the central nervous system of an individual. This leads to the malfunctioning of several other organs of the body such as the kidney, liver, etc. The spread of HIV is most common in these individuals as they share common needles while injecting drugs in their body. Drugs have long-term side effects on both males and females. These side effects include increased aggressiveness, mood swings, and depression

Effects on the family and society: A person addicted to drugs creates problems for his family and society. A person dependant on drugs becomes frustrated, irritated, and anti-social.

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?

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

  1. Increase your will power to stay away from alcohol and drugs. One should not experiment with alcohol for curiosity and fun.
  2. Avoid the company of friends who take drugs
  3. Seek help from parents and peers.
  4. Take proper knowledge and counseling about drug abuse. Devote your energy in other extra-curricular activities.
  5. Seek immediate professional and medical help from psychologists and psychiatrists if symptoms of depression and frustration become apparent.

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.

Ans- Once a person starts taking alcohols or drug, 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?

Ans- Many factors are responsible for motivating youngsters towards alcohol or drugs. Curiosity, need for adventure and excitement, experimentation are the initial causes of motivation. Some youngsters start consuming drugs and alcohol in order to overcome negative emotions (such as stress, pressure, depression, frustration) and to excel in various fields. Several mediums like television, internet, newspaper, movies etc. are also responsible for promoting the idea of alcohol to the younger generation. Amongst these factors, reasons such as unstable and unsupportive family structures and peer pressure can also lead an individual to be dependant on drugs and alcohol.

Preventive measures against addiction of alcohol and drugs:

  1. Parents should motivate and try to increase the will power of their child.
  2. Parents should educate their children about the ill-effects of alcohol. They should provide them with proper knowledge and counselling regarding the consequences of addiction to alcohol.
  3. It is the responsibility of the parent to discourage a child from experimenting with alcohol. Youngsters should be kept away from the company of friends who consume drugs.
  4. Children should be encouraged to devote their energy in other extra- curricular and recreational activities.
  5. Proper professional and medical help should be provided to a child if sudden symptoms of depression and frustration are observed.

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