NCERT Solutions for Class 12 Biology Chapter 8: Human Health And Disease

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Chapter8. Human Health And Disease
CategoryNCERT Solutions for Class 12

Our NCERT Solutions for Class 12 Biology is a great resource for students preparing for boards or competitive exams, such as the NEET. These Biology Class 12 Solutions are made by expert faculties, keeping the latest curriculum in mind. Besides helping students with understanding the concepts of Biology, these solutions are also helpful in writing accurate answers that are vital to score full marks in examinations. On this page, we have given the Class 12 Biology Chapter 8: Human Health And Disease Solutions.

NCERT Solutions for Class 12 Biology Chapter 8

Human Health And Disease Solutions

Q1) What are the various public health measures, which you would suggest as safeguard against infectious diseases?

Answer) Public health measures which should be taken to afeguard against infectious diseases are:

  • Maintenance of personal and public hygiene: It is one of the most important methods for prevention of various infectious diseases. This measure consists of maintaining a hygienic body, taking of healthy and nutritious food, drinking clean water, etc. In public hygiene their is proper disposal of garbage, excreta, periodic cleaning of society, and cleaning of water reservoirs.
  • Isolation: To prevent the spread of air-borne infectious diseases like pneumonia, chicken pox, tuberculosis, etc., it is essential measure to keep the infected person in isolation with others to reduce the chances of spreading these infectious diseases.
  • Vaccination: Vaccination is the protection of the body from communicable diseases by injecting some agent that makes copy of the microbe inside the body. It helps in providing passive immunity to the body. Several vaccines are available against many diseases such as tetanus, polio, measles, mumps, etc.
  • Vector Eradication: Various diseases such as malaria, filariasis, dengue, and chikungunya spread through vectors. Thus, these diseases can be prevented by providing a clean environment and by the prevention of breeding of mosquitoes. This can be achieved by not allowing water to stagnate around public areas. Also, measures like periodic cleaning of coolers, use of mosquito nets and spreading of insecticides in drains, ponds, etc. can be undertaken to ensure a healthy environment. Introducing fish such as Gambusia in ponds also controls the breeding of mosquito larvae in still water against diseases.

Q2) In which way has the study of biology helped us to control infectious diseases?

Answer) 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.

Q3) How does the transmission of each of the following diseases take place?

(a) Amoebiasis
(b) Malaria
(c) Ascariasis
(d) Pneumonia


a) Amoebiasis: It is a vector transmitted disease that spreads by the means of contaminated food and water. The vector involved in the transmission of this disease is the housefly. Its mode of transmission is Entamoeba histolytica.

b) Malaria: It is a vector transmitted disease that spreads by the biting of the female Anopheles mosquito. Its mode of transmission is Ascaris lumbricoides.

c) Ascariasis: It spreads through contaminated food and water. Its mode of transmission is Ascaris lumbricoides

d) Pneumonia: It spreads by the sputum of a diseased person. Its mode of transmission is Streptococcus pneumonia

Q4) What measure would you take to prevent water-borne diseases?

Answer) Water-borne diseases such as cholera, typhoid, hepatitis B, etc. spread by drinking contaminated water. These water-borne diseases can be prevented by ensuring proper disposal of sewage, excreta, periodic cleaning. Also, measures such as disinfecting community water reservoirs, boiling drinking water, etc. should be observed.

Q5) Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.

Answer) 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.

Q6) Name the primary and secondary lymphoid organs.


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

Q7) The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form:

(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

Q8) Differentiate the following and give examples of each:

(a) Innate and acquired immunity
(b)Active and passive immunity

Answer a) Differences between 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.

Answer b) Differences between 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.

Q9) Draw a well-labelled diagram of an antibody molecule.


NCERT Solutions for Class 12 Biology Chapter 8

Q10) What are the various routes by which transmission of human immunodeficiency virus takes place?

Answer) The various routes by which transmission of human immunodeficiency virus(HIV) takes place is as follows:

  • Sexual relation with the person infected
  • Organ transplantation from an infected person
  • Transfusion of contaminated blood products and blood
  • Transmitted from mother to the child through the placenta

Q11) What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?

Answer) 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 T-lymphocytes 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.

Q12) How is a cancerous cell different from a normal cell?


Normal cellCancerous cell
Normal cells show the property of contact inhibition. Therefore, when these cells come into contact with other cells, they stop dividing.Cancerous cells lack the property of contact inhibition. Therefore, they continue to divide, thereby forming a mass of cells or tumor.
They undergo differentiation after attaining a specific growth.They do not undergo differentiation.
These cells remain confined at a particular location.These cells do not remain confined at a particular location. They move into neighboring tissues and disturb its function.

Q13) Explain what is meant by metastasis.

Answer) Metastasis is a pathological process that is observed in malignant tumors. In this process, the cancerous cells spread to different body parts and divide indefinitely to form a cluster of cells known as tumor. Some of these cells from the tumor get sloughed off and manage to enter into the blood stream from where they arrive at the distant parts of the body and thus the formation of new tumors is initiated as they actively divide.

Q14) List the harmful effects caused by alcohol/drug abuse.

Answer) The harmful effects of alcohol and drug abuse are as follows:

  1. Harmful effects of alcohol:
    • On individual – has an adverse effect on the body. When excess alcohol is consumed, it damages the nervous system and the liver, which is a vital organ. This leads to other symptoms such as fatigue, depression, weight loss, aggression, loss of appetite. In extreme cases, heart failure leading to coma and death is also observed.
    • On family – excess alcohol consumption by any family member can have destructing effects on the family members as it may lead to domestic violence, verbal abuse, irritation, insecurity etc
    • On society – impulsive behavior, fading social web, violence, lack of interest in social activities.
  2. Harmful effects of drugs:
    • On individual – effect of drugs on one’s body is severe, more so on the central nervous system. It can lead to malfunctioning of different organs of the body such as liver, kidney etc. in such individuals, HIV spreads rapidly as they share used needles while they inject drugs into the body. Drug addicts face both short-term and long-term effects, some of which are mood swings, aggressiveness, depression etc

Q15) Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?

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

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

Q16) 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.

Answer) Drug and alcohol consumption has an inherent addictive nature associated with euphoria and a temporary feeling of well-being. Repeated intake of drugs increases the tolerance level of the body’s receptors, leading to more consumption of drugs.

Q17) In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?

Answer) 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 dependent on drugs and alcohol.

Preventive measures against addiction of alcohol and drugs:

  • Parents should motivate and try to increase the will power of their child.
  • 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.
  • 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.
  • Children should be encouraged to devote their energy in other extra- curricular and recreational activities.
  • Proper professional and medical help should be provided to a child if sudden symptoms of depression and frustration are observed.

That’s it. These were the solutions of NCERT Class 12 Biology Chapter 8 – Human Health And Disease. Our team hopes that you have found these solutions helpful for you. If you have any doubt related to this chapter then feel free to comment your doubts below. Our team will try their best to help you with your doubts.

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