Human Health and DiseaseClass 12 Biology NCERT Solutions
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Q1EXERCISES
What are the various public health measures, which you would suggest as safeguard against infectious diseases?
Solution
Various public health measures that serve as safeguards against infectious diseases include:
- Proper disposal of waste and excreta: This prevents the contamination of soil, water, and food, which are common sources of pathogens for diseases like typhoid, amoebiasis, and ascariasis.
- Periodic cleaning and disinfection of water sources: Regular maintenance of water reservoirs, pools, cesspools, and tanks is crucial to prevent water-borne diseases.
- Observing standard practices of hygiene in public catering: This ensures that food and water served to the public are safe and free from infectious agents.
- Control and elimination of vectors: For vector-borne diseases like malaria and filariasis, it is essential to control the vector population. This can be achieved by:
- Avoiding water stagnation in and around residential areas.
- Regular cleaning of household coolers.
- Using mosquito nets.
- Introducing larvivorous fish like Gambusia in ponds.
- Spraying insecticides in ditches, drainage areas, and swamps.
- Using wire mesh on doors and windows to prevent mosquito entry.
- Vaccination and Immunisation Programmes: Large-scale immunisation programmes help in preventing and even eradicating infectious diseases like smallpox, polio, diphtheria, and tetanus.
Q2EXERCISES
In which way has the study of biology helped us to control infectious diseases?
Solution
The study of biology has been instrumental in helping us control infectious diseases in several ways:
- Understanding Pathogens: Biology has enabled us to identify and study various disease-causing organisms (pathogens) like bacteria, viruses, fungi, protozoans, and helminths. Understanding their life cycles, modes of transmission, and how they interact with the host is the first step in controlling them.
- Development of Vaccines: Based on the principle of immunological memory, biology has led to the development of vaccines. Immunisation programmes have successfully controlled diseases like polio, diphtheria, and pneumonia, and even completely eradicated smallpox.
- Discovery of Antibiotics and Drugs: The discovery of antibiotics and other drugs has provided effective treatments for many infectious diseases, significantly reducing mortality and morbidity.
- Advancements in Biotechnology: Modern biotechnology has allowed for the production of newer and safer vaccines. For example, the hepatitis B vaccine is produced from yeast using recombinant DNA technology.
- Diagnostic Tools: Biological knowledge is the basis for developing diagnostic tests like the Widal test for typhoid and ELISA for AIDS, which allow for early detection and treatment.
Q3EXERCISES
How does the transmission of each of the following diseases take place?
(a)
Amoebiasis
(b)
Malaria
(c)
Ascariasis
(d)
Pneumonia
Solution
(a) Amoebiasis (Amoebic dysentery): This disease is caused by the protozoan parasite Entamoeba histolytica. Transmission occurs through the faecal-oral route. Houseflies act as mechanical carriers, transferring the parasite from the faeces of an infected person to food and food products. The main source of infection is consumption of food and water contaminated by faecal matter.
(b) Malaria: This disease is caused by the protozoan Plasmodium. It is transmitted through the bite of an infected female Anopheles mosquito, which acts as the vector. The mosquito injects the infectious form of the parasite (sporozoites) into the human bloodstream when it bites.
(c) Ascariasis: This disease is caused by the roundworm Ascaris. The eggs of the parasite are excreted along with the faeces of an infected person, which then contaminate soil, water, and plants. A healthy person acquires the infection by consuming contaminated water, vegetables, or fruits.
(d) Pneumonia: This disease is caused by bacteria like Streptococcus pneumoniae and Haemophilus influenzae. It is transmitted from an infected person to a healthy person by inhaling the droplets or aerosols released during coughing or sneezing. It can also be transmitted by sharing glasses and utensils with an infected person.
Q4EXERCISES
What measure would you take to prevent water-borne diseases?
Solution
To prevent water-borne diseases like typhoid, amoebiasis, and ascariasis, the following measures should be taken:
- Consumption of Clean Drinking Water: Always ensure that drinking water is safe. This can be done by boiling, filtering, or using water purifiers.
- Proper Disposal of Waste: Sewage and other waste should be disposed of properly to prevent the contamination of water sources.
- Personal Hygiene: Wash hands with soap before eating and after using the toilet. Food, vegetables, and fruits should be washed thoroughly with clean water before consumption.
- Public Hygiene: Periodic cleaning and disinfection of community water sources like reservoirs, tanks, and wells are essential.
- Preventing Contamination: Food should be kept covered to protect it from flies and dust, which can carry pathogens.
Q5EXERCISES
Discuss with your teacher what does 'a suitable gene' means, in the context of DNA vaccines.
Solution
In the context of DNA vaccines, a 'suitable gene' refers to a specific segment of DNA isolated from a pathogen that codes for an antigenic protein or polypeptide. This gene must have the following characteristics:
- It must be antigenic: The protein produced from this gene must be recognized as foreign by the host's immune system and be capable of triggering an immune response.
- It must be non-pathogenic: The gene should only produce the antigenic part of the pathogen, not the components that cause the disease itself. This ensures the vaccine is safe.
When a DNA vaccine containing this 'suitable gene' is introduced into the host, the host's own cells take up the DNA and use their cellular machinery to transcribe and translate it, producing the antigenic protein. This protein is then presented to the immune system, which mounts an immune response by producing antibodies and memory cells (B and T-lymphocytes). This process mimics a natural infection without causing illness, preparing the immune system to fight off the actual pathogen upon future exposure. An example of a vaccine produced using this principle (via recombinant DNA technology) is the Hepatitis B vaccine.
Q6EXERCISES
Name the primary and secondary lymphoid organs.
Solution
The primary and secondary lymphoid organs are:
-
Primary lymphoid organs: These are the organs where immature lymphocytes differentiate into antigen-sensitive lymphocytes. They are:
- Bone marrow
- Thymus
-
Secondary lymphoid organs: These organs provide the sites for the interaction of lymphocytes with antigens, which then leads to their proliferation into effector cells. They are:
- Spleen
- Lymph nodes
- Tonsils
- Peyer's patches of the small intestine
- Appendix
Q7EXERCISES
The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form:
(a)
MALT
(b)
CMI
(c)
AIDS
(d)
NACO
(e) HIV
Solution
(a) MALT: Mucosa-Associated Lymphoid Tissue
(b) CMI: Cell-Mediated Immunity
(c) AIDS: Acquired Immuno Deficiency Syndrome
(d) NACO: National AIDS Control Organisation
(e) HIV: Human Immuno deficiency Virus
Q8EXERCISES
Differentiate the following and give examples of each:
(a)
Innate and acquired immunity
(b)
Active and passive immunity
Solution
(a) Innate and Acquired Immunity
| Feature | Innate Immunity | Acquired Immunity |
|---|---|---|
| Presence | Present at the time of birth. | Acquired during one's lifetime after exposure to a pathogen. |
| Specificity | Non-specific; acts against all foreign agents in the same way. | Pathogen-specific; targets a particular pathogen. |
| Memory | Does not have immunological memory. | Characterised by immunological memory; subsequent responses are faster and more intense. |
| Components | Consists of physical barriers (skin, mucus), physiological barriers (stomach acid, saliva), cellular barriers (PMNL-neutrophils, monocytes), and cytokine barriers (interferons). | Mediated by B-lymphocytes and T-lymphocytes, which produce antibodies and mount cell-mediated responses. |
| Example | The skin preventing entry of microbes; acid in the stomach killing pathogens. | Immunity developed after a chickenpox infection or after receiving a polio vaccine. |
(b) Active and Passive Immunity
| Feature | Active Immunity | Passive Immunity |
|---|---|---|
| Source of Antibodies | Antibodies are produced by the host's own body in response to an antigen. | Ready-made antibodies are transferred to the host from an external source. |
| Speed of Response | Slow; takes time to develop a full and effective response. | Fast; provides immediate protection. |
| Duration | Long-lasting and provides effective protection. | Short-lived; protection lasts only for a few weeks or months. |
| Memory | Immunological memory is generated. | No immunological memory is generated. |
| Example | Immunity induced by natural infection (e.g., measles) or vaccination (e.g., tetanus toxoid vaccine). | Antibodies (IgA) transferred from mother to infant through colostrum; anti-venom injection for snakebites. |
Q9EXERCISES
Draw a well-labelled diagram of an antibody molecule.
Solution
A diagram of an antibody molecule cannot be drawn in text format. However, the structure can be described based on Figure 7.4 in the textbook.
An antibody molecule is a Y-shaped structure composed of four peptide chains. These are:
- Two identical Heavy Chains: These are longer polypeptide chains.
- Two identical Light Chains: These are shorter polypeptide chains.
These chains are held together by disulfide bonds. The overall structure is represented as .
Each chain has a variable region and a constant region. The variable regions of one heavy chain and one light chain together form the antigen-binding site. Since an antibody molecule has two such pairs, it can bind to two antigen molecules simultaneously. The antigen-binding site is specific to a particular antigen, which gives the immune response its specificity.
Q10EXERCISES
What are the various routes by which transmission of human immunodeficiency virus takes place?
Solution
The transmission of Human Immunodeficiency Virus (HIV) occurs through contact with infected body fluids. The various routes are:
- Sexual Contact: Unprotected sexual contact with an infected person is the most common mode of transmission.
- Transfusion of Contaminated Blood and Blood Products: Receiving blood or blood products (like plasma) from an HIV-infected donor.
- Sharing of Infected Needles: This is common among intravenous drug abusers who share needles and syringes.
- From Infected Mother to Child (Vertical Transmission): The virus can be transmitted from an infected mother to her child through the placenta during pregnancy, during childbirth, or through breastfeeding.
Q11EXERCISES
What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
Solution
The AIDS virus, HIV, causes a deficiency of the immune system by systematically destroying a crucial component of it. The mechanism is as follows:
- Entry into Host Cells: After entering the body, HIV first infects macrophages. The viral RNA genome replicates to form viral DNA using an enzyme called reverse transcriptase. This viral DNA then gets incorporated into the host cell's DNA.
- HIV Factory: The infected macrophage continues to produce new virus particles, acting like an 'HIV factory'.
- Attack on Helper T-cells: Simultaneously, HIV enters and infects helper T-lymphocytes ( cells), which are essential for coordinating the immune response. Inside the cells, the virus replicates and produces progeny viruses.
- Destruction of Helper T-cells: The newly formed viruses are released from the infected cell (often destroying it in the process) and proceed to infect other helper T-lymphocytes.
- Progressive Decline: This cycle is repeated, leading to a progressive and severe decrease in the number of helper T-lymphocytes in the body.
Since helper T-cells play a central role in activating both B-cells (for antibody production) and other T-cells, their depletion cripples the entire adaptive immune system. The person becomes severely immuno-deficient and unable to protect themselves against common infections, leading to the condition known as AIDS.
Q12EXERCISES
How is a cancerous cell different from a normal cell?
Solution
A cancerous cell differs from a normal cell in several fundamental ways:
| Feature | Normal Cell | Cancerous Cell |
|---|---|---|
| Cell Growth and Division | Highly controlled and regulated. Cells divide only when needed. | Uncontrolled and unregulated proliferation. Cells divide continuously. |
| Contact Inhibition | Exhibit contact inhibition; they stop dividing when they come into contact with other cells. | Have lost the property of contact inhibition; they continue to divide and pile up, forming masses called tumors. |
| Differentiation | Differentiate to perform specific functions. | Often lose their differentiation and become non-specialized. |
| Nutrient Competition | Use nutrients for normal metabolic functions. | Grow very rapidly and compete with normal cells for vital nutrients, starving them. |
| Metastasis | Remain at their original location in the body. | Malignant cancerous cells can invade surrounding tissues and spread to distant sites through blood or lymph to form new tumors (metastasis). |
Q13EXERCISES
Explain what is meant by metastasis.
Solution
Metastasis is the process by which cancer spreads from the primary site where it originated to other, distant parts of the body. It is the most feared property of malignant tumors.
The process involves several steps:
- Cancer cells from the primary tumor break away (slough off).
- These cells invade surrounding tissues and gain access to the bloodstream or the lymphatic system.
- They travel through these circulatory systems to distant locations in the body.
- Wherever they get lodged, they exit the vessel, begin to divide uncontrollably, and establish a new, secondary tumor.
This ability to spread and form new tumors in different organs is what makes cancer so dangerous and difficult to treat, especially in its advanced stages.
Q14EXERCISES
List the harmful effects caused by alcohol/drug abuse.
Solution
The harmful effects of alcohol/drug abuse are wide-ranging and affect the individual, their family, and society.
Immediate Effects:
- Reckless behaviour, vandalism, and violence.
- Excessive doses can lead to coma and death due to respiratory failure, heart failure, or cerebral hemorrhage.
Long-term Effects on the Individual:
- Addiction and Dependence: The user becomes psychologically and physically dependent on the substance.
- Damage to Organs: Chronic use damages the nervous system and can cause liver cirrhosis.
- Health Risks: Those who inject drugs intravenously are at high risk of acquiring serious infections like AIDS and Hepatitis B.
- Mental Health: Can lead to depression, anxiety, isolation, and aggressive behaviour.
- During Pregnancy: Use of drugs and alcohol during pregnancy adversely affects the foetus.
- For Sportspersons (Anabolic Steroids): Side-effects include masculinisation in females, depression, reduced sperm production and kidney/liver dysfunction in males, and stunted growth in adolescents.
Social and Economic Effects:
- Drop in academic or professional performance.
- Financial distress for the individual and their family, sometimes leading to stealing.
- Deteriorating relationships with family and friends.
- Social adjustment problems.
Q15EXERCISES
Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
Solution
Yes, friends and peer pressure can significantly influence an adolescent to take alcohol or drugs. During adolescence, there is a strong desire to fit in and be accepted by one's peer group. If the peer group considers smoking, drinking, or using drugs as 'cool' or progressive, an individual may feel pressured to participate to avoid being left out.
One can protect himself/herself from such an influence in the following ways:
- Avoid Undue Peer Pressure: It is important to have self-confidence and a strong will to say 'no'. Every child has their own choice and personality which should be respected.
- Choose Friends Wisely: Associate with friends who have healthy habits and are supportive of positive life choices.
- Education and Counselling: Being educated about the harmful effects of drugs and alcohol can strengthen one's resolve to avoid them.
- Seeking Help: If feeling pressured, one should immediately seek help and guidance from parents, trusted elders, or school counsellors. Talking about the pressure can help in finding ways to deal with it.
- Channelise Energy into Healthy Pursuits: Engaging in healthy activities like sports, music, yoga, or other hobbies can boost self-esteem and reduce the time and inclination for negative activities.
Q16EXERCISES
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.
Solution
Once a person starts taking alcohol or drugs, it becomes difficult to get rid of the habit due to two main phenomena: addiction and dependence.
-
Addiction: This is a psychological attachment to the effects of drugs and alcohol, such as euphoria and a temporary feeling of well-being. This creates a strong craving and drives the person to use the substance repeatedly, even when they know it is harmful. The desire to experience these pleasant feelings becomes a powerful motivating force.
-
Dependence: This is a physical phenomenon. With repeated use, the body's receptors adapt to the presence of the drug, and their tolerance level increases. This means the person needs progressively higher doses to achieve the same effect. The body becomes dependent on the drug to function 'normally'.
-
Withdrawal Syndrome: If the regular dose of the drug or alcohol is abruptly discontinued, the body manifests a characteristic and unpleasant withdrawal syndrome. Symptoms can include anxiety, shakiness, nausea, and sweating. These symptoms are very uncomfortable and can sometimes be life-threatening. The person often resumes using the substance simply to relieve these withdrawal symptoms.
This combination of psychological craving (addiction) and the need to avoid physical discomfort (dependence and withdrawal) creates a vicious circle that traps the user, making it extremely difficult to quit without professional and medical help.
Q17EXERCISES
In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
Solution
Motivations for youngsters to take to alcohol or drugs:
- Curiosity and Experimentation: A child's natural curiosity and a desire for adventure and excitement can motivate them to experiment with drugs and alcohol.
- Peer Pressure: The desire to be accepted by friends and the perception that it is 'cool' or progressive to smoke or drink is a major cause.
- Stress Relief: Youngsters may turn to drugs and alcohol to escape from stress related to academic pressures, examinations, or personal problems.
- Media Influence: Television, movies, and the internet often glamorize the use of alcohol and drugs, promoting a false perception of their use.
- Family Environment: Unstable or unsupportive family structures can also contribute to a youngster's vulnerability to substance abuse.
How this can be avoided:
- Education and Counselling: Educating adolescents about the harmful effects of drugs and alcohol is crucial. They should be counselled on how to handle stress and failure in a healthy way.
- Parental Responsibility: Parents should foster a supportive and communicative environment, maintain consistent discipline, and be alert to any danger signs in their children.
- Avoid Undue Peer Pressure: Children should be taught to have self-respect and confidence to say 'no' to negative influences, without feeling pressured to conform.
- Channelising Energy: Encouraging participation in healthy activities like sports, yoga, music, and other extracurricular activities helps in channelising their energy positively.
- Seeking Professional Help: If a problem is identified, help should be sought immediately from parents, teachers, psychologists, or de-addiction and rehabilitation programmes. Early intervention can prevent the situation from worsening.