NCERT Solutions for Class 12 Biology Chapter 7 Human Health and Disease

NCERT
SOLUTIONS
CLASS - 12th

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Class : 12th
Subject : Biology
Chapter : 8
Chapter Name : Human Health and Disease

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

Answer. Public health measures are preventive measures which are taken to check the spread of
various infectious diseases. These measures should be taken to reduce the contact with infectious
agents. Some of these methods are:
(1) Maintenance of personal and public hygiene:lt is one of the most important methods of
preventing infectious diseases. This measure includes maintaining a clean body, consumption of
healthy and nutritious food, drinking clean water, etc. Public hygienic includes proper disposal of
waste material, excreta, periodic cleaning,and disinfection of water reservoirs.
(2) Isolation: To prevent the spread of airborne diseases such as pneumonia, chicken pox,
tuberculosis, etc., it is essential to keep the infected person in isolation to reduce the chances of
spreading these diseases. (3) Vaccination: Vaccination is the protection of the body from
communicable diseases by administering some agent that mimics the microbe inside the body. It
helps in providing passive immunization to the body. Several vaccines are available against many
diseases such as tetanus, polio, measles, mumps, etc.
(4) Vector Eradication: Various diseases such as malaria, lariasis, dengue, and chikungunya
spread through vectors. Thus, these diseases can be prevented by providing a clean environment
and by preventing the breeding of mosquitoes. This can be achieved by not allowing water to
stagnate around residential areas. Also, measures like regular cleaning of coolers, use of mosquito
nets and insecticides such as malathion in drains, ponds, etc. can be undertaken to ensure a
healthy environment. Introducing sh such as Gambusia in ponds also controls the breeding of
mosquito larvae in stagnant water.

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

Answer. Various advancements that have occurred in the eld of biology have helped us gain a
better understanding to ght 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 smallpox, 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

Answer.

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 speci c DNA segment which can be injected into the cells of
the host body to produce speci c proteins. This protein kills the speci c 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

Answer. (a) MALT- Mucosa-Associated Lymphoid Tissue
(b) CMI- Cell-Mediated Immunity
(c) AIDS- Acquired Immunode ciency Syndrome
(d) NACO- National AIDS Control Organization
(e) HIV- Human Immunode ciency virus

Q8 Differentiate the following and give examples of each:
(a) Innate and acquired immunity
(b) Active and passive immunity

Answer. (a) Innate and acquired immunity

(b) Active and Passive immunity

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

Answer.

Q10 What are the various routes by which transmission of human immunode ciency virus takes
place?

Answer. AIDS (Acquired Immunode ciency Syndrome) is caused by the Human immunode ciency
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.

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

Answer. AIDS (Acquired Immunode ciency Syndrome) is caused by the human immunode ciency
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?

Answer.

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 bloodstream. From the bloodstream, 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. 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.

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

Answer. Yes, friends can in uence one to take drugs and alcohol. A person can take the following
steps for protecting himself/herself against drug abuse:
(a) Increase your willpower 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 dif cult 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 elds. 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:
(a) Parents should motivate and try to increase the will power of their child.
(b) 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.
(c) 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.
(d) Children should be encouraged to devote their energy in other extra- curricular and
recreational activities.
(e) Proper professional and medical help should be provided to a child if sudden symptoms of
depression and frustration are observed.