Human Health and Disease Question Answers: NCERT Class 12 Biology

Certain pathogens which are also known as biological agents; are tissue or organ specific as they are adapted to overcome the resistance mechanisms of those tissues and organs. E.g. the certain pathogens or disease producing organisms which enters the gut should know a way that how to survive in the stomach at the low pH and resistant to various digestive enzymes.

If a drug dependent person fails to get the drug, he feels severe physical and physiological disturbances, these are known as withdrawal symptoms. The withdrawal symptoms are as follows:

1. Anxiety
2. Shakiness
3. Sweating
4. Nausea   
5. Diarrhea
6. Perspiration
7. Running nose
8. Insomnia etc.

During the changing weather on the crowded places, we should avoid to go there because changing seasons are the time when infectious agents are more abundant and prevalent as moist condition favoures pathogen for their fast growth and people are more vulnerable as their body system is busy in adapting the changing environmental conditions of temperature humidity etc. and they get infected to these pathogen very easily.   

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Lymphoid organs: immune system of human beings consists of lymphoid organs. The organs where the maturation and proliferation of lymphocytes occurs are called lymphoid organs. Lymphoid organs are of two types. These are:

Primary lymphoid organs: It includes bone marrow and thymus whereas B- and T- cell lymphocytes mature and acquire their antigen specific receptor or we can say antigen sensitive lymphocytes. After the maturation, the lymphocytes migrates to secondary lymphoid organs.

Secondary lymphoid organs: The organs are site of interaction where lymphocytes interact with the antigen and proliferate to become the effector cells. E.g. spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix.

Lymph nodes are small, solid structures located at the specific sites along the lymphatic system. They trap the microorganisms or other antigens that enter the lymph and tissue fluid. Antigens enters into the lymph nodes and tissue fluid, activate the lymphocytes and produces an immune response.   

Each antibody molecule has four peptide chains, two small called light chains and two longer called heavy chains. Hence, an antibody is represented as H₂L₂.

When the pathogen enters into the body for the first time, it produces an immune response by generating antibodies. This response is of low intensity. By ensuring encounter with the same pathogen brings out a highly intensified secondary response.

This explained the fact that our body appears to have memory of the first encounter. This type of secondary immune response brings out by memory T- cells and B- cells which keep ready to produce a rapid and vigorous attack as soon as the same pathogen infects the body again.  

The patient is suffering from AIDS. The causative agent if HIV virus, a member of ‘retrovirus group’. AIDS is a disorder of cell- mediated immune system of the body. There is a reduction of T- helper cells which stimulates antibody production by B- cells.

In metropolitan cities life style of the human beings is responsible in the lowering of immunity and sensitivity to allergens. More polluted environment such as dust in the surroundings increases the chances of allergic reactions in children. Some symptoms of allergic reaction like sneezing, watery eyes, running nose and difficulty in breathing etc.  

The principle of vaccination is based on the property of immune system of memory cells.

In vaccination, a preparation of antigenic proteins or inactivated or live occurs but weakened pathogens are introduced into the body. The antigens generate or produces the primary immune response by producing antibodies along with memory B- cells and T- cells.

When the vaccinated person is attacked by the same pathogens again, the existing memory B- cells and T- cells recognize that antigen and overwhelm the invaders with massive production of lymphocytes and antibodies.

Hepatitis B vaccine is produced from yeast.  

An abnormal and uncontrolled growth of cells that causes malignant growth and enlargement of tissues is termed as cancer. Genes called cellular oncogenes or proto-oncogenes present in normal cells when activated under certain conditions lead oncogenic transformation of the normal cells that leads to cancer. A cancer cell is different from the normal cell in following ways:

The immune system of a person is suppressed. In the ELISA test, he was found positive to a pathogen.

1. The patient is suffering from AIDS. It is a disorder of cell- mediated immune system of the body. There is a reduction of T- helper cells which stimulates antibody production by B- cells.
2. AIDS is caused by Human Immuno Deficiency Virus (HIV). It is a retro virus containing RNA as genetic material.
3. Macrophages and helper T- cells are affected by the pathogen.   

If a person is hypersensitive to some substances that are present in the air, he may be allergic to it. Mast cells release some chemicals like histamine and serotonin, in response to these substance this results in the allergic reaction.

Precaution taken to prevent such reaction is to avoid the allergens responsible for particular allergy.

For an organ transplantation, it is an advantage to have an identical twin because the organ will have same surface markers and therefore, the recipient’s immune system will not identify it as foreign element and also will not react against it. In case of different surface markers, the immune system starts producing reaction and kills the foreign tissue or rejects it.  

Life style diseases which are caused by the specific food habits, work related posture or exposure to harmful radiations or substances, lack of physical exercise, mental stress etc. E.g. cancer, alcoholism, heart disease etc.  

RNA mutates faster than the DNA because DNA is more stable and also has better repair mechanisms that correct the changes in base pairs as soon as it is introduced.  

Both type of lymphocytes and other cells of the immune system are produced in the bone marrow. B and T lymphocytes are different from each other in the following aspects.

Wuchereria bancrofti and W. malayi, the filarial worm cause a slowly developing chronic inflammation of the organs in which they live for many years. Usually the lymphatic vessels of the lower limbs and the disease is called elephantiasis or Filariasis.

Fungi are responsible for causing common infectious diseases in man and it belongs to the genera Microsporium, Trichophyton and Epidermophyton that are responsible for ringworm in man.   

So, the (c) option is not matching or we can say is incorrect.

If thymus gland is removed from the body of a person, his immune system will become weak. As a result the person’s body becomes prone to infectious diseases. Thymus is a primary lymphoid organ where development and maturation of T- lymphocytes occurs, so if thymus gland is removed from the body, this will not occur.

Many microbial pathogens enter the gut of humans along with food. The preventive barriers to protect the body from such pathogens are as follows:

1. The coating of mucous of the epithelium lining of the gut, helps in trapping microbes that enters into the body.
2. Saliva in the mouth and hydrochloric acid in gastric juice is secreted by the stomach that prevents the microbial growth.

This type of immunity is innate immunity which is non- specific. It is present from birth and is inherited from parents which remains throughout the life. Many barriers are provided to the entry of foreign agents into our body. These are: physical barriers, physiological barriers, cellular barriers and cytokine barriers.

Colostrum which is mother’s milk during the initial days after the delivery; contains several antibodies (especially IgA) which are absolutely essential for developing resistance for the new- born babies. Infant’s immunity is another form of passive immunity.  

Interferons are the antiviral proteins produced by the cells when invaded by a virus. These are released from infected and dying host cells. On reaching the nearby uninfected cells, it makes them resistant to the viral infection by the formation of certain proteins which prevent viral multiplication.

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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: It 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 air-borne 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 immunizationto the body. Several vaccines are available against many diseases such as tetanus, polio, measles, mumps, etc.

(4) Vector Eradication: Various diseases such as malaria, filariasis, 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 Laxvivorous fish such as Gambusia in ponds also controls the breeding of mosquito larvae in stagnant water.

AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human immunodeficiency 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.

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.

y B��y0� ��� and T-lymphocytes.

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It does not have a specific memory.

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It is characterized by an immunological memory.

(b) Active and passive immunity

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 blood stream. From the blood stream, these cells reach distant parts of the body and therefore, initiate the formation of new tumors by dividing actively.

Alcohol and drugs have several adverse effects on the individual, his family, and the society.

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.

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 will power 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.

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.

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 fields. 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.

Various advancements that have occurred in the field of biology have helped us gain a better understanding to fight 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 small pox, 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.

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.

A ‘suitable gene’ refers to a specific DNA segment which can be injected into the cells of the host body to produce specific proteins. This protein kills the specific disease-causing organism in the host body and provides immunity.

(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.

(a) MALT- Mucosa-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

 (a) Innate and acquired immunity

(b) Active and passive immunity