NCERT Solutions for Class 12-science Biology Chapter 8 - Human Health and Disease

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Chapter 8 - Human Health and Disease Exercise 164

Solution 1

i. Education: People should be educated about infectious diseases so that they can protect themselves.

ii. Vaccination: People should be vaccinated against infectious diseases.

iii. Sanitation: Personal hygiene and public hygiene help in preventing the spread of various infectious diseases.

iv. Eradication of vectors: The destruction of vectors and their breeding places helps in preventing the spread of diseases. Avoid stagnation of water in residential areas.

Solution 2

i. The use of vaccines and immunisation programmes has enabled us to completely eradicate a deadly disease such as small pox.

ii. The number of other infectious diseases such as polio, diphtheria, pneumonia and tetanus has been controlled by using vaccines.

iii. The use of antibiotics and various other drugs has effectively treated many infectious diseases.

Solution 3

(a) Amoebiasis: By ingesting quadrinucleated cysts of Entamoeba histolytica with food and water. The cysts are carried from the faeces of the patient to food and water.

(b) Malaria: Plasmodium (malarial parasite) is transmitted from the patient to a healthy person when bitten by a female Anopheles mosquito.

(c) Ascariasis: The disease is transmitted by ingesting contaminated food and water with embryonated eggs of Ascaris.

(d) Pneumonia: It is a bacterial disease which is transmitted by the sputum and droplets released during coughing of the patient.

Solution 4

i. Drinking clean water.

ii. Periodic cleaning and disinfection of water tanks and reservoirs.

iii. Industries should not be allowed to discharge their wastes into water bodies.

Solution 5

The term 'suitable gene' refers to a specific segment of DNA which will be modified in the host to produce a specific protein to kill a specific disease-causing organism.

Solution 6

Primary lymphoid organs: Bone marrow and thymus

Secondary lymphoid organs: Spleen, lymph nodes, Peyer's patches (small intestine) and mucosal-associated lymphoid tissues (MALT).

Solution 7

(a) MALT - Mucosal-Associated Lymphoid Tissue

(b) CMI - Cell-Mediated Immunity

(c) AIDS - Acquired Immuno Deficiency Syndrome

(d) NACO - National AIDS Control Organisation

(e) HIV - Human Immunodeficiency Virus

Solution 8


Innate Immunity

Acquired Immunity

i.    It is non-specific in nature.


i.  It is specific in nature.

ii.   It is present from birth.

ii. It is acquired in response to a specific     pathogen.

iii.  It involves different types of barriers.

iii. It involves memory of antibody.

iv.  Example: Skin acts like a barrier.

iv. Example: Antibody response after           vaccination.













Active Immunity

Passive Immunity

i.  The body produces antigen in response to       pathogens in active immunity.

i.   Antigen is injected in the body to initiate           immunity.          

ii.  It is slow in action.

ii.  It is fast in action.

iii. Example:Antibody response after                   vaccination.  

iii.  Example: Yellow liquid in mother's milk           (colostrum) is full of antibodies.








Solution 9

Ncert Solutions Cbse Class 12-science Biology Chapter - Human Health And Disease

Solution 10

i.Sexual contact with infected person.

ii.Transfusion of contaminated blood and blood products.

iii.Organ transplantation from an infected person.

iv.From mother to child through the placenta.

Solution 11

After getting into the body of the person, the virus enters macrophages where the RNA genome of the virus replicates to form viral DNA by the enzyme reverse transcriptase. This viral DNA gets incorporated into the host cell's DNA and directs the infected cells to produce virus particles. The macrophages continue to produce the virus and in this way act like an HIV factory. Simultaneously, HIV enters helper T-lymphocytes (TH), replicates and produces progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. This is repeated leading to a progressive decrease in the number of helper T-lymphocytes in the body of the infected person.

Over a long term, there is a considerable decrease in the number of T-lymphocytes which leads to weakening of the defence mechanism of the body. This process is called acquired immunodeficiency.

Solution 12

Differences between cancer cells and normal cells:

Cancer cells

Normal cells

i. Divide in an uncontrolled manner.

i. Divide in a regulated manner.

ii. Do not show contact inhibition.

ii. Show contact inhibition.

iii. Do not remain confined in the area of formation.

iii. Remain confined.

iv. Do not undergo differentiation.

iv. Undergo differentiation.

Solution 13

It is the transference of malignant tumour from a primary to a secondary part of the body through the blood stream or lymph. The cells from the malignant tumour break away and migrate through the blood or lymph to other parts of the body. There on, they accumulate and form secondary tumour growth. This migrating and settling process of malignant tumour breaks is called metastasis.

Solution 14

The immediate adverse effects of drugs and alcohol abuse are manifested in the form of reckless behaviour, vandalism and violence. Excessive doses of drugs may lead to coma and death due to respiratory failure, heart failure or cerebral haemorrhage. A combination of drugs or their intake along with alcohol generally results in overdosing and even death.

i.Effect on society and family: There may even be some far-reaching implications of drug/alcohol abuse. If an abuser is unable to get money to buy drugs/alcohol, he/she may turn to stealing. The adverse effects are just not restricted to the person who is using drugs or alcohol. At times, a drug/alcohol addict becomes the cause of mental and financial distress to his/her entire family and friends.

ii.Effects of intravenous drug administration: Those who take drugs intravenously (direct injection into the vein using a needle and syringe) are more likely to acquire serious infections such as AIDS and hepatitis B.

iii.Long-term implications of alcohol abuse: The use of alcohol during adolescence may have long-term effects. It could lead to heavy drinking in adulthood. The chronic use of drugs and alcohol damages the nervous system and liver (cirrhosis).

The use of drugs and alcohol during pregnancy is also known to adversely affect the foetus.

iv.Implications of performance-enhancement drugs on athletes: The side-effects of the use of anabolic steroids in females include masculinisation (features like males), increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive hair growth on the face and body, enlargement of clitoris and deepening of voice.

In males, side-effects include acne, increased aggressiveness, mood swings, depression and reduction in the size of the testicles, decreased sperm production, potential kidney and liver dysfunction, breast enlargement, premature baldness and enlargement of the prostate gland. In the adolescent male or female, there is severe facial and body acne, and premature closure of the growth centres of the long bones, which may result in stunted growth.

Solution 15

Yes, friends can influence one in taking alcohol/drugs. Following measures can be taken:

(i) Avoid undue peer pressure.

(ii) Get counselling from a counsellor.

(iii) Practise good habits.

(iv) Seek medical help.

Solution 16

Once a person starts taking alcohol or drugs, he becomes addicted to these substances physically and mentally. Whenever he tries to get rid of this habit, he shows unpleasant 'withdrawal symptoms' and these include vomiting, diarrhoea, shivering, twitching, perspiration, abdominal and muscular cramps etc. So, it becomes difficult for a person to get rid of this habit.

Solution 17

People generally take drugs on the basis of the following factors:

i. People take drugs to escape from the realities of life and to overcome frustration and depression.

ii. Drugs act as a motivation factor for pleasure, fun, curiosity, adventure and to experience a different kind of awareness.

iii. People consume drugs under the influence of a peer group.

iv. People use drugs as a result of apathy arising from race, sex and age.

v. They take drugs to do more physical or mental work or to get relief from severe pain.

Alcohol or drug abuse can be avoided by the following:

i. Avoid undue peer pressure: Each child has stamina and personality which should be respected and nurtured. Children should not be pushed unduly to perform beyond their threshold limit.

ii. Education and counselling: Children should be properly counselled to face problems and stress, and to accept disappointments and failure as part of life.

iii. Seeking help from parents and peers: Parents and peers should guide youth and adolescents appropriately for sorting out their problems.

iv. Seeking professional and medical help: A lot of help is available in the form of highly qualified psychologists, psychiatrists and de-addiction and rehabilitation programmes to help individuals who have unfortunately become drug abusers.