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

Here we provide NCERT Solutions for Class 12 Biology Chapter 8 Human Health and Diseases for English medium students, Which will very helpful for every student in their exams. Students can download the latest NCERT Solutions for Class 12 Biology Chapter 8 Human Health and Diseases pdf, free NCERT solutions for Class 12 Biology Chapter 8 Human Health and Diseases book pdf download. Now you will get step by step solution to each question.

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

Question 1.
What are the various public health measures, which you would suggest as safeguard against infectious diseases ?
The various public health measures that could provide safeguard against infectious diseases are :

  1. Disposal of garbage – There should be regular collection and transport of garbage to disposal sites.
  2. Drainage – Drains should be covered to reduce chances of multiplication of flies and mosquitoes. Any blockage must be immediately attended.
  3. Isolation – A person suffering from an infectious disease should be segregated so that others do not catch infection from him.
  4. Sanitation – Clean surroundings can prevent spread of diseases. This includes: proper disposal of waste and excreta, periodic cleaning and disinfection of water sources and observing standard practices of hygiene in public catering.
  5. Eradication of vectors – It is necessary to eliminate the vectors and their breeding places. This can be achieved by – avoiding stagnation of water in and around residential areas.
    – regular cleaning of household coolers.
    – use of mosquito nets
    – introducing fishes like Gambusia in ponds that feed on mosquito larvae.
    – spraying of insecticides in ditches, swamps and drainage area.
    – doors and windows should be provided with wire mesh.
  6. Vaccination and immunization – This has enabled us to completely eradicate a deadly disease like smallpox. A large number of other infectious diseases like polio, diphtheria, pneumonia and tetanus have been controlled to a large extent by the use of vaccines.
  7. Pollution – Anti-pollution laws should be strictly enforced.
  8. Drinking water – Drinking water should be filtered and free from any contamination, suspended and dissolved matter.
  9. Education – People should be educated about the communicable diseases so that they can protect themselves against infection.

Question 2.
In which way has the study of biology helped us to control infectious diseases?
Study of biology has helped us to know about causes of diseases, carriers of diseases (vectors), effects of diseases on different body functions and above all, means to control diseases. Our immune system plays a major role in preventing diseases.

Question 3.
How does the transmission of each of the following diseases take place ?

  1. Amoebiasis
  2. Malaria
  3. Ascariasis
  4. Pneumonia


  1. Amoebiasis is caused by Entamoeba – histolytica. Infection occurs by ingesting cysts with food and drinks. These cysts are carried by flies from faeces to food and drinks.
  2. Malaria is caused by Plasmodium sp. Malarial parasites are carried from the infected to the healthy person by the female Anopheles mosquito.
  3. Ascariasis in man is caused by ingesting food and water contaminated with Ascaris eggs. Children become infected by ingesting soil.
  4. Pneumonia is spread by sputum (containing Streptococcus pneumoniae) of the patient. These microbes are inhaled and get lodged in the bronchioles.

Question 4.
What measure would you take to prevent water-borne diseases ?
Water-borne diseases can be prevented by drinking clean water. Water should be free from contamination, suspended and dissolved substances. If water is contaminated it should be boiled and filtered before drinking. Periodic cleaning and disinfection of water reservoirs, pools and tanks should be done.

Question 5.
Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.
Suitable genes refers to that gene (specific segment of DNA), encoding a protein associated with the target infectious organism, is spliced into plasmid, which is then copied & formulated as a vaccine.

Question 6.
Name the primary and secondary lymphoid organs.
Primary lymphoid organs are bone marrow and thymus. Secondary lymphoid organs are spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and mucosa associated lymphoid tissues (MALT).

Question 7.
The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form.

  1. MALT
  2. CMI
  3. AIDS
  4. NACO
  5. HIV


  1. MALT – Mucosa associated lymphoid tissue
  2. CMI – Cell mediated immunity
  3. AIDS – Acquired Immune Deficiency Syndrome
  4. NACO – National AIDS control organization
  5. HIV – Human immunodeficiency virus

Question 8.
Differentiate the following and give examples of each.

  1. Innate and acquired immunity,
  2. Active and passive immunity


  1. : Differences between innate and acquired immunity are as follows:
    NCERT Solutions for Class 12 Biology Chapter 8 Human Health and Diseases Q1.1
  2. Differences between active and passive immunity are as follows:
    NCERT Solutions for Class 12 Biology Chapter 8 Human Health and Diseases Q1.2

Question 9.
Draw a well-labeled diagram of an antibody molecule.
NCERT Solutions for Class 12 Biology Chapter 8 Human Health and Diseases Q9.1

Question 10.
What are the various routes by which transmission of human immunodeficiency virus takes place?
The various routes by which transmission of human immunodeficiency virus (HIV) takes place are –

  • Sexual contact with infected person.
  • Use of contaminated needles and syringes to inject drugs or vaccines.
  • Use of contaminated razors.
  • By transfusion of contaminated blood.
  • From infected mother to her child through placenta.
  • Organ transplantation.
  • Artificial insemination.

Question 11.
What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
After the entrance of the virus into the body of the person, the virus enters into macrophages where RNA genome of the virus reverse transcribes to form viral DNA with the help of reverse transcriptase enzyme. This viral DNA gets incorporated into the host cell’s DNA and directs the infected cells to produce viruses. The infected macrophages produce virus and act like a HIV factory. Simultaneously, HIV virus enters into helper T lymphocytes where it replicates and produces other viruses. These viruses are then released into the blood and attack other helper T-lymphocytes. In this way, there occurs progressive decrease in number of helper T-lymphocytes in the body of the infected person. Due to decrease in the number of helper T-lymphocytes, the patient becomes so immunodeficient that he/she is unable to protect himself/herself against the infections of bacteria, fungi, viruses etc.

Question 12.
How is cancerous cell different from a normal cell?
Cancerous cell and normal cell are different in following aspects :
NCERT Solutions for Class 12 Biology Chapter 8 Human Health and Diseases Q12.1
NCERT Solutions for Class 12 Biology Chapter 8 Human Health and Diseases Q12.2

Question 13.
Explain what is meant by metastasis.
The non-regulated growth of the cells that accompanies cellular transformation produces tumours or neoplasms. Each tumour being the product of proliferation of a single abnormal cell. Malignant tumour cells are cancer cells that spread to mid take up residence in neighbouring tissues – a condition called metastasis.

Question 14.
List the harmful effects caused by alcohol/drug abuse.
Harmful effects caused by alcohol/drug abuse are as follows:

  • Among youth there is drop in academic performance, lack of interest in personal hygiene, isolation, depression, fatigue, aggressive and rebellious behavior, deteriorating relationships with family and friends, loss of interest in hobbies, change in sleeping and eating habits, fluctuations in weight, appetite, etc.
  • Excessive dose of drugs leads to coma and death due to respiratory failure, heart failure or cerebral haemorrhage.
  • Abusers become mental and cause financial distress to their entire family and friends.
  • They may acquire serious infections like AIDS and hepatitis by taking drugs intravenously.
  • Intake of alcohol/drugs damages nervous system, liver (cirrhosis) and kidney.
  • Drug abuse adversely affects foetus in case of pregnancy, leading to Foetal Alcohol Syndrome (FAS).
  • Continuous use of narcotics and stimulants cause impotency and chromosomal aberrations.
  • Heavy drinking can cause an acute alcoholic myopathy characterised by painful and swollen muscles and high levels of serum creatine phosphokinase (CK). Chronic alcoholic men may show testicular atrophy with shrinkage of the seminiferous tubules and loss of sperm cells.
  • Heavy drinking causes acute and chronic pancreatitis.
  • Alcohol increases RBC size causing a mild anemia.
  • Legal problems occur, such as arrest by police for obtaining and keeping drugs unlawfully.

Question 15.
Do you think that friends can influence one to take alcohol/drugs ? If yes, how can one protect himself/herself from such an influence ?
Yes, friends can influence person to take alcohol/drugs. One can protect himself/ herself from such an influence by avoiding experimental use of alcohol/drug for curiosity, pleasure, adventure and excitement, and avoiding the company of such friends

Question 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.
Once a person starts taking alcohol or drugs, it is difficult to get rid of this habit because he becomes addicted to it. Addiction is a psychological attachment to certain effects such as euphoria and a temporary feeling of well-being. These drive people to consume drugs / alcohol even when these are not needed, or even when their use becomes self-destructive. With repeated use, tolerance level of the receptors present in the body increases, which consequently leads to higher dose of drugs / alcohol and addiction.
Thus, the addictive potential of drugs and alcohol pull the user into a vicious circle leading to their regular use from which he / she may not be able to get out.

Question 17.
In your view what motivates youngsters to take alcohol or drugs and how can this be avoided ?
There are many factors that motivate youngsters to take alcohol or drug. These include:

  • Curiosity
  • Experimentation
  • Adventure and excitement
  • Peer pressure
  • Family history, i.e.,unstable or unsupported family structure
  • Frustration and depression
  • Relief from pain
  • Feeling of independence
  • Television, movies, newspapers and internet also help to promote this perception.
    This can be avoided by the following measures:
  1. Education and counselling : Educating and counselling people to face problems and stresses, and to accept disappointments and failures as a part of life.
  2. Seeking help from parents and peers: Help from parents and peers should be sought immediately so that they can guide appropriately. Help may even be sought from close and trusted friends.
  3. Looking for danger signs : Alert parents and teachers to look for and identify the danger signs. Even friends, if they find someone using drugs or alcohol, should not hesitate to bring this to the notice of parents or teachers in the best interests of the person concerned.
  4. Seeking professional and medical help : Lots of help is available in the form of highly qualified psychologists, psychiatrists, and deaddiction and rehabilitation programmes to help individuals who have unfortunately got in the quagmire of drug/alcohol abuse.
  5. Cross-checking before prescribing and selling drugs : The physicians should prescribe the habituating drugs only to the genuine persons and only for the essential duration. Pharmacists should not sell these drugs without the physician’s prescription.
  6. Discipline : Good nurturance with consistent discipline but without suffocating strictness reduces the risk of addictions.
  7. Communication : The child must be able to communicate with the parents seeking clarification of all doubts and discussing problems that arise in studies or develop in the class, with friends, siblings and others.
  8. Appreciation : For even the smallest achievement, good behavior and other activities, the child should be appreciated.
  9. Independent working : Giving responsibility to the child for small tasks and allowing him/her to perform independently. However, guidance should be provided where required.
  10. Avoid undue pressure : Every child has a specific personality with certain preferences and choices. They should be taken care of and respected. No child should be asked to perform beyond threshold limits whether in studies, sports or extracurricular activities.

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