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

We have compleed the NCERT/CBSE Solutions chapter-wise for Class 12 Biology Chapter 8 Human Health and Disease with Answers by expert subject teacher for latest syllabus and examination. Prepare effectively for the exam taking the help of the Class 12 Biology NCERT Solutions PDF free of cost from here. Students also can take a free NCERT Solutions of Human Health and Disease. Each question has right answer Solved by Expert Teacher. Download the Biology NCERT Solutions with Answers for Class 12 Biology Pdf and prepare to help students understand the concept very well.

NCERT Solutions for Class 12 Biology

Page No. 164


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

Answer: The measures that should be taken as safeguard against infectious diseases are:

(i) Proper disposal and treatment of sewage and excreta.
(ii) Periodic inspection and cleaning of the public water resources.
(iii) Vaccination to provide protection to the body from communicable.
(iv) Personal hygiene – Maintaining a clean body, consumption of healthy and nutritious food, drinking clean water, etc.
(v) Isolation and proper treatment of the infected persons to prevent the spread of disease.
(vi) Eliminating breeding grounds of the vectors of the infectious 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) Through contaminated food and water.
(b) Through Anopheles mosquito.
(c) Through contaminated food and water.
(d) By inhaling the droplets or aerosols released by infected persons.

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

Answer: Measures taken to prevent water-borne diseases are as follows:

  • Provision of clean water for drinking
  • Industries should be prohibited from discharging wastes into water bodies
  • Frequent cleaning and disinfecting water tanks and reservoirs

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.

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

(a) MALT (b) CMI (c) AIDS (d) NACO (e) HIV

Answer: The abbreviations with their full forms are as follows:

(a) MALT – Mucosa – Associated Lymphoid Tissue
(b) CMI – Cell-Mediated Immunity
(c) AIDS – Acquired Immunodeficiency Syndrome
(d) NACO – National AIDS control organization
(e) HIV – Human Immunodeficiency Virus

Q8. Differentiate the following and give examples of each:

(a) Innate and acquired immunity

Answer: Innate & acquired immunity

Innate immunity, also called inherent, natural, non specific immunity, comprises all those defence elements with which an individual is bom & which are always available to protect a living body. It acts on many organisms and does not show specificity, e.g. Lysozyme present in secretions such as tears, catalyzes the hydrolysis of molecules in the cell walls of bacteria & interferon induces antiviral state in non infected cells. They act as physiological barriers & check the growth of many pathogenic micro-organisms. Acquired immunity, also called adaptive or specific immunity, is the immunity obtained either from the development of antibodies in .response to exposure to an antigen, as from vaccination or an attack of an infectious diseases or from the transmission of antibodies as from mother to foetus through the placenta.

(b) Active and passive immunity

Answer: Active & passive immunity

Active immunity is acquired by catching & surviving an infectious disease or by vaccination with a weakened form of the diseases which makes the body to form antibodies. Whereas passive immunity is conferred by transfer of immune products like antibodies etc. from other individual

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

Answer: The diagram is as follows:

Q10. What are the various routes by which transmission of human immuno-deficiency virus takes place?

Answer: AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human immunodeficiency virus (HIV).
This is transmitted by following modes –
(a) Unprotected sexual contact with a diseased person.
(b) Transfusion of blood from a healthy to a diseased person.
(c) Sharing infected needles or syringes.
(d) infected mother to a child through the placental connection.

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

Answer: Upon managing to enter the body, this virus enters into macrophages where the RNA genome of the virus duplicates for the formation of viral DNA by the action of the reverse transcriptase enzyme. The viral DNA is then incorporated into the DNA of the cells of the host which targets the infected cells to synthesize virus particles. The macrophages continue to produce virus, serving as an HIV factory.

On the other hand, HIV enters the helper T-lymphocytes, replicating and producing progeny viruses, which when released in the blood, target other helper T-lymphocytes which is reiterated causing a progressive decrease in the count of helper T-lymphocytes in the patient’s body. In the long run, there is a significant decline in the count of helper T-lymphocytes resulting in weakening of the defense mechanism of the boy. This is referred to as acquired immunodeficiency.

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

Answer: Cancerous cell and normal cell are different in the following aspects:

Q13. Explain what is meant by metastasis.

Answer: 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.

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

Answer: Alcohol and drugs have several adverse effects on the individual, his family, and society. The list of harmful effects is given below:

(A) Effects of alcohol:

(a) Effects on the Individual: Alcohol harms the body of an individual. The consumption of excess alcohol by an individual causes damage to the liver and the nervous system. This results in the appearance of other symptoms such as depression, fatigue, aggression, loss of weight, and appetite in the individual. Sometimes, extreme levels of alcohol consumption may also lead to heart failure, resulting in coma and death. Also, pregnant women should avoid alcohol as it may inhibit the normal growth of the baby.

(b) Effects on the Family:

Consumption of excess alcohol by any family member is having devastating effects on the family. It may lead to several domestic problems such as quarrels, frustrations, insecurity, etc.

(c) Effects on Society:

(i) Rash behavior
(ii) Malicious mischief and violence
(iii) Deteriorating social network
(iv) Loss of interest in social and other activities

(B) Effects of Drugs: An individual who is addicted to using drugs can create several problems not only for himself but also for his family too.

(a) Effects on the Individual: Drugs harm the central nervous system of an individual which results in the malfunctioning of several other organs of the body such as the kidney, liver, etc. In these individuals, the spread of HIV is most common because they share common needles while injecting drugs into their bodies. On both males and females drugs have long-term side effects which include increased aggressiveness, mood swings, and depression.

(b) Effects on the Family and Society: A person addicted to drugs creates problems for his family and society too. That person becomes frustrated, irritated, and anti-social.

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:

(a) Increase your will power to stay away from alcohol and drugs. One should not experiment with alcohol for curiosity and fun.
(b) Avoid the company of friends who take drugs.
(c) Seek help from parents and peers.
(d) Take proper knowledge and counseling about drug abuse. Devote your energy in other extra-curricular activities.
(e) 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: Alcohol consumption and usage of drugs has a severe, addictive impact linked with euphoria, rendering a momentary feeling of well-being. Regular intake of drugs can increase the tolerance level of the receptors of the body which furthermore leads to more drug consumption.

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

Answer: Various factors are responsible for motivating youngsters towards alcohol or drugs. Curiosity, need for adventure and excitement, experimentation for fun are the initial causes for motivating youngsters.
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..such youngsters use to abuse alcohol due to their family pressure for academics .

Several mediums like television, internet, newspaper, movies promote various brend by the brand ambassadors like celebrities . Celebrities are also ideal of youngsters so the get much infiuenced by them.

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:

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

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