NCERT Solutions For Class 12 Biology Human Health and Disease

NCERT Solutions For Class 12 Biology Human Health and Disease

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

Ans. The various public health measures against infectious diseases include the following –
1. Health Education – People should be educated about infectious diseases so that they may protect themselves against infections.
2. A person suffering from any infections should be isolated to avoid its transmission to any other person.
3. Vaccination – People should get a vaccination to avoid infection. Vaccination is available against cholera, typhoid, TB, etc.
4. Sanitation – Sanitary surroundings can prevent the spread of diseases. Public hygiene includes – suitable disposal of waste & human excreta; periodic cleaning and disinfection of water sources; observing normal practices of hygiene in public catering. Personal hygiene includes keeping the body clean and intake clean drinking water, vegetables, fruits, etc.
5. Eradication of vectors – The breeding places of vectors should be destroyed & adult vectors should be killed by appropriate methods.

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

Ans. Various studies that have taken place in the field of biology science have helped humans gain a better understanding of to fight against various infectious diseases. Biology has helped us analyze 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 programs 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.

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

Ans. (a) Amoebiasis – It is usually transmitted by consuming food or water contaminated by amoebic cysts.
(b)Malaria – It is transmitted by the female Anopheles mosquito. The mosquito picks up the parasite along with the blood when it bites an infected person. When this mosquito bites another healthy person, the parasites migrate into his blood with the saliva, which the mosquito injects before sucking up blood to prevent its clotting.
(c)Ascariasis – Transmitted through water, vegetables, fruits, etc. contaminated with the eggs of the parasites.
(d)Pneumonia – Spreads by cough & sneezes, by sharing drinking glasses & eating utensils with an infected person.

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

Ans: Water-borne diseases can be prevented by –
(i) Immunization
(ii) Educating people about health
(iii) Control of bad reservoirs
(iv) Oral dehydration
(v) General hygiene,

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

Ans- It refers to a specific DNA segment that can be injected into the body of the host so as to produce specific proteins and immunity which will kill the specific disease-causing organism present in the host body. 

6. Name the primary and secondary lymphoid organs.

Ans: Primary lymphoid organs – Bone marrow and thymus.
Secondary lymphoid organs – Spleen, lymph nodes, tonsils.

7. The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its fall form:
(a) MALT
(b) CMI
(c) AIDS
(e) HIV

Ans: (a) MALT – Mucosal 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

Innate immunity

Acquired immunity

1. It is a non- pathogen-specific type of defense mechanism.

1. It is a pathogen-specific type of defense mechanism.

2. It is inherited from a parent and protects the individual from birth.

2. It is acquired after the birth of an individual

3. It operates by providing barriers against the entry of foreign infectious agents.

3. It operates by producing primary and secondary responses, which are mediated by B−lymphocytes and T-lymphocytes.

4. It does not have a specific memory. 

4. It is characterized by an immunological memory


Active immunity


Passive 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

Ans- Refer NCERT Book

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

Ans: Various routes by which transmission of human immunodeficiency virus takes place are
(i) Sexual Contact without contraceptives.
(ii) Multiple sex partners.
(iii) Transfusion of the blood of infected person.
(iv) Intravenous drug users that shares needles are at high risk of contracting AIDS.

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 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. 

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

Ans: Cancer is a disease characterized by the excessive and abnormal growth of certain cells. In a healthy individual, the growth of cells is balanced by the rate of cell loss. Thus, when one attains adult age, the size and cellular contents of various body organs remain constant. The balance between the growth of the cells and the rate of cell class may be dislocated by certain chemicals, physical stresses and viral agents. As a result, the normal growth of the cells may be transformed into cancerous one. Cancerous cells acquire the ability to invade new sites, a phenomenon called metastasis. They exhibit a number of alterations on cell surface, in the cytoplasm, and in their genes. These features are used for the identification of cancers.

13. Explain what is meant by metastasis.

Ans: Metastasis is the phenomenon in which cancer cells due to unregulated proliferation spread to distant sites through body fluids to develop secondary tumors. Only malignant tumors show the property of metastasis.

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

Ans: Harmful effects caused by alcohol abuse are –
(i) Alcohol generates more energy mostly in the form of heat, but at the same time, it dilates the blood vessels. Consequently, the ‘heat generated is rapidly lost. Due to constant dilation, the arterial walls soon become brittle & rigid. Such a change in the property of blood vessels & deposition of alcoholic fat affects the working of the heart.
(ii) Alcoholism leads to gastric ulcers & gastritis.
(iii) In chronic alcoholism, the axon of the nerve inflame thus causing neuritis.
(iv) Permanent damage to liver cells occurs due to the deposition of fats. The liver dries up & hardens (cirrhosis).
Harmful effects caused by drug abuse are –
(i) Excessive doses of drugs may lead to coma & death due to respiratory failure, heart failure & cerebral haemorrhage.
(ii) Lack of interest in personal hygiene, withdrawal, isolation, depression, fatigue aggressive & rebellious behaviour etc.
(iii) Acquire serious infections like AIDS & hepatitis B, who take drugs intravenously.
(iv) The adverse effects of drugs are manifested in the form of reckless behaviour, vandalism & violence.

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:

(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 to other extra-curricular activities.

(e) 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: Psychological & physiological dependence of an individual to the intake of certain kinds of drugs and alcohol is called addiction. Once a person start taking alcohol & drugs, it is very difficult to get rid this habit because addiction drive people to take them even when these are not needed or even when their use becomes self destructive. With repeated use of drugs, the tolerance level of the receptors present in the body increases, consequently, the receptors responds only to higher doses of drugs or alcohal leading to greater intake & addiction. Thus, the addiction potential of drugs & alcohol, pull the user into a vicious circle leading to their regular use (abuse) from which he/she may not able to get out.

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

Ans- The root cause of addiction of man to drugs, smoking and drinking has been due to his inability to make mental adjustments with stresses and strains, drudgery and extreme misery in daily life.

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.

Important links

Leave a Comment

error: Content is protected !!