NCERT Solutions for Class 12 Biology Chapter 8: Human Health and Diseases

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

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

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

Ans. Biology imparts knowledge about causative agents of various diseases, their mode of transmission, life cycle of pathogens and their vectors.
All this information helps to avoid the tentative cause of diseases and to take preventive health care to alleviate the chances of infections. 

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 contracted by ingesting water or food contaminated by amoebic cysts.
(b) Malaria: It is transmitted from one person to another 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 an other 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: It is a bacterial disease which is transmitted by the scutum and droplets released during coughing up the patient.

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

Ans. Water borne diseases can be prevented in following ways:
(i) Drink only boiled water. If not boiled, water should be chlorinated and filtered.
(ii) Take food safety precaution like proper washing and cooking of food.
(iii) Use disposable glass and plants while eating food outside.

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

Ans. The term ‘suitable gene’ refers to that gene which can be injection in the cells of host body to produce specific proteins. These proteins kills the specific disease causative agent in the host body and provides immunity

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
(d) NACO
(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

Ans. Innate immunity and Acquired immunity

Innate Immunity Acquired Immunity
  1. It is non specific to antigen.
It is specific to antigen.
  1. It is inherited from parents (before birth)Example: Stomach acid and skin.
It is acquired after birth.Example: Antibody.

(b) Active and Passive immunity

Active Immunity Passive Immunity
  1. Body produces antibodies in response to antigen.
The antibodies are produced outside and then injected into body.
  1. It develops for long duration. Example: Vaccine
It does not develop of long duration. Example: IgG

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

antibody molecule

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 with the infected person.
(ii) Sexual contact with multiple partners.
(iii) Transfusion of the blood of infected person.
(iv) Intravenous drug users that shares needles are at high risk of contracting AIDS.
(v) From an infected mother to her children via the placenta.

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

Ans. Mechanism of HIV infection in human: HIV is the virus, which causes a disease in human called AIDS. HIV is a DNA virus, once it enters in the body it acquired to host machinery to produce enormous copy of DNA by the enzyme called reverse transcriptase. Then it attacks on helper T-Lymphocytes cell and starts rupturing the cell. The result in the destruction of T-Lymphocyte making the person’s immune system weak.

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

Ans. Difference between normal cell and cancerous cell:

Normal Cell Cancerous Cell
  1. Growth of cells occurs in regulated manner.
Growth of cells occurs in excessive and abnormal or uncontrolled manner.
  1. It shows contact inhibition.
It does not show contact inhibition.
  1. It remains confined in area of formation.
It does not confined in area of formation.

13. Explain what is meant by metastasis.

Ans. Metastasis is the phenomenon in which cancer cells spread from one organ or part of body to another through body fluids to develop secondary tumours. 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 and deposition of alcoholic fat affect the working of heart.
(ii) Alcoholism leads to gastric ulcers and gastritis.
(iii) In chronic alcoholism, the axon of the nerve inflame thus causing neuritis.
(iv) Permanent damage to liver cells occur due to deposition of fats. The liver dries up and harden (cirrhosis).
Harmful effects caused by drug abuse are:
(i) Excessive doses of drugs may lead to coma and death due to respiratory failure, heart failure and cerebral haemorrhage.
(ii) Lack of interest in personal hygiene, withdrawal, isolation, depression, fatigue aggressive and rebellious behaviour etc.
(iii) Acquire serious infections like AIDS and hepatitis B, who take drugs intravenously.
(iv) The adverse effects of drugs are manifested in the form of reckless behaviour, vandalism and 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. Following measures can be taken:
(i) Avoiding the company of friends, who take drugs.
(ii) Not taking undue pressure of failures beyond its threshold.
(iii) Getting counselling from some counsellor
(iv) Seeking help from parents and peers
(v) Seeking medical help

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 alcohol as drugs, he become addict to these substances physically as well as mentally. Repeated intake of drugs or alcohol increases the tolerance level of body’s receptor, leading to more consumption. So, it becomes difficult for a person to get rid of this habit.

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

Ans.Major factors which motivate youngsters to take to alcohol or drugs are:
(i) Curiosity due to  dvertisements and pleasure.
(ii) Desire for excitement.
(iii) False belief of enhanced performance.
(iv) Monotony of daily life.
It can be avoided by:
(i) To identify to reason of addiction and take remedial measures.
(ii) By giving proper education and counselling to addict.
(iii) Parents and teachers should be alert the activities of children.

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