Exam Question for Class 12 Biology Chapter 8 Human Health and Diseases

Please refer to below Exam Question for Class 12 Biology Chapter 8 Human Health and Diseases. These questions and answers have been prepared by expert Class 12 Biology teachers based on the latest NCERT Book for Class 12 Biology and examination guidelines issued by CBSE, NCERT, and KVS. We have provided Class 12 Biology exam questions for all chapters in your textbooks. You will be able to easily learn problems and solutions which are expected to come in the upcoming class tests and exams for standard 12th.

Chapter 8 Human Health and Diseases Class 12 Biology Exam Question

All questions and answers provided below for Exam Question Class 12 Biology Chapter 8 Human Health and Diseases are very important and should be revised daily.

Exam Question Class 12 Biology Chapter 8 Human Health and Diseases

Objective Type Questions

Question. Entamoeba histolytica is a parasite of which human body part
(A) Stomach
(B) Small intestine
(C) Large intestine
(D) Liver



Question. Main source of infection of amoebiasis is
(A) Mosquito bite
(B) Contaminated water and food by faecal matter
(C) Droplets of nasal discharge of infected person
(D) All of these



Question. Ascaris is a parasite of
(A) Stomach
(B) Intestine
(C) Lungs
(D) Liver



Question. Healthy person gets infection of ascaris by
(A) Contaminated water, vegetable, fruits
(B) Mosquito bite
(C) Both (A) and (B)
(D) House fly contamination of food



Question. The vector for elephantiasis is
(A) Female mosquito
(B) Housefly
(C) Human
(D) Pig



Question. Ringworms is caused by
(A) Bacteria
(B) Helminths
(C) Viruses
(D) None of these



Question. Main symptom of ring worms is
(A) Stools with mucous and blood
(B) Dysentery
(C) Scaly lesions on skin, nails and scalps
(D) High fever with chills



Question. Which of the following is a measure for maintaining hygiene to control many infectious diseases?
(A) Keeping body clean
(B) Consumption of clean drinking water, food, vegetables, fruits etc
(C) Proper disposal of waste and excreta
(D) All of these



Question. Important measure to prevent disease that are transmitted through insect vectors
(A) Avoid stagnation of water in and around residential area
(B) Use of mosquito nets
(C) Spray of insecticides in drainage areas and swamp
(D) All of these



Question. Which of the following disease is spread by aedes mosquitoes?
(A) Malaria
(B) Chikungunya
(C) Amoebiasis
(D) None of these



Assertion and Reason Based Questions

Directions : In the following questions a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as :
(A) Both assertion (A) and reason (R) are trueand reason (R) is the correct explanation of assertion (A).
(B) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(C) Assertion (A) is true but reason (R) is false.
(D) Assertion (A) is false but reason (R) is true.

Question. Assertion (A) : Bone marrow and thymus are primary lymphoid orgAnswer :
Reason(R) : It is the organs, to which matured lymphocytes migrate, interact with antigens and then proliferate to become effector cells.
Answer : (C)

Question. Assertion (A) : Acquired immunity is pathogen specific.
Reason (R) : It is not present since birth.
Answer : (A)

Question. Assertion (A) : Opioids, also called opiates used to treat pain.
Reason (R) : Opioids are the drugs which bind to specific opioid receptors present in our central nervous system.
Answer : (A)

Question. Assertion (A) : Pathogens are disease causing organisms.
Reason (R) : Salmonella typhi is a pathogenic virus causing tuberculosis.
Answer : (C)

Question. Assertion (A) : Cocaine are drug of abuse.
Reason (R) : Cocaine interferes in the working of central nervous system.
Answer : (C)

Question. Assertion (A) : Diphtheria is caused by Corynebacterium diphtheriae.
Reason (R) : Corynebacterium diphtheriae produce a potent exotoxin that inhibits protein synthesis in epithelial cells.
Answer : (A)

Read the following text and answer the following questions on the basis of the same :
Health is defined as a state of complete physical, mental and social well being. Balanced diet, personal hygiene and regular exercise are very important to maintain good health. Any disturbance of structure or function of the body may be regarded as disease. Diseases can broadly be categorized into infectious (communicable) and non-infectious (non-communicable). A wide range of organisms belonging to bacteria, viruses, fungi, protozoans etc., could cause diseases in man.

Question. The nature of the spread of communicable diseases is known as _______ .
(A) Parasitology
(B) Immunology
(C) Epidemiology
(D) None of these.



Question. Which of the following diseases are communicable ?
(A) Infectious diseases
(B) Deficiency diseases
(C) Allergies
(D) Degenerative diseases.



Question. DPT vaccine is used for the immunization of :
(A) Cholera
(B) Bubonic plague
(C) Typhoid fever
(D) Diptheria.



Question. Which among the following is a set of bacterial diseases ?
(A) Cholera, typhoid and mumps
(B) Malaria, mumps and poliomyelitis
(C) Diphtheria, leprosy and plague
(d) Tetanus, Tuberculosis and measles.



Read the passage and answer any four questions.
A group of youth were having a ‘rave party‘ in an isolated area and was raided by police. Packets of ‘smack‘ and syringes with needles were found  ittered around. Syringes and needles are used to inject drugs intravenously, as this can have very quick and strong effect upon abuser. Higher  chances of addition can be seen through this mode of administration of drugs. Infected syringes may cause the user to catch deadly diseases.

Question. Why is taking ‘smack‘ considered an abuse ?
(A) because it causes drug dependence
(B) because it affects nervous system
(C) because it impairs one’s psychological functions
(D) all of these
Answer : (D)

Question. Which of the following drug is commonly known as Smack?
(A) Heroin
(B) Morphine
(C) Codeine
(D) Pethidine
Answer : (A)

Question. ‘Smack’ is a drug obtained from the
(A) Latex of Papaver somniferum
(B) Leaves of Cannabis sativa
(C) Flowers of Datura
(D) Fruits of Erythroxylum coca
Answer : (A)

Question. Syringes and needles used by the youth for taking the drug could prove to be very fatal as :
(A) They can acquire serious infections.
(B) They can lead to malnutrition.
(C) They can cause transmission of parasitic disease.
(D) They can lead to cardiac arrest.
Answer : (A)

Question. Infected syringes disposes the user to catch which of the following disease :
(B) Hepatitis-B
(C) Hepatitis-C
(D) All of the above.
Answer : (D)

Very Short Answer Type Questions

Question. Retroviruses have no DNA. However the DNA of the infected host cell does possess the viral DNA. How is it possible?
Answer : After infecting the host cell, the viral DNA undergoes reverse transcription in the presence of an enzyme reverse transcriptase as a result of which viral DNA is formed. This DNA then gets incorporated into infected host DNA.

Question. The principle of vaccination is based on which property?
Answer : The principle of vaccination is based on the property of memory. 

Question. Trace the route of Sporozoite of Plasmodium when it enters the human body through the bite of infected female Anopheles mosquito till its entry into the R.B.C.
Answer : Sporozoites attack liver cells. Sporozoites reproduce asexually in liver cells by bursting them and then reach RBC.

Question. Name the category of disease in which ‘Rheumatoid arthritis‘ in human is put under.
Answer : Autoimmune disease.

Question. How drug abuse lead to stunted growth ?
Answer : It is due to premature closure of growth centres of the long bones.

Question. What is the function of Opioids ?
Answer : Opioids act as pain killers

Question. Suggest a method to ensure an anamnestic response in humAnswer :
Answer : Vaccination or Immunization (Active / passive) or weakened or inactive microbes or pathogens or proteins or antibodies introduced into the host body.

Question. Name any two physiological barriers that provide innate immunity.
Answer : Acid in stomach/Saliva in mouth/tears in eyes.

Question. Name two diseases whose spread can be controlled by the eradication of Aedes mosquitoes.
Answer : Dengue, Chikungunya//Yellow Fever / Eastern Equine Encephalitis / West Nile Fever / Zika /Zika Viral Disease

Short Answer Type Questions

Question. (i) Match the microbes listed under Column I with the products mentioned under Column II.   (Image 32)
(ii) Why is distillation required for producing certain alcoholic drinks?
Answer : (i) The correct matches are as follows  (Image 33)
(ii) Distillation is required to increase the alcohol content in alcoholic drinks. Whiskey, brandy and rum are produced by this process.

Question. Why are biogas plants considered more beneficial in rural areas?
Answer : The raw material for the biogas plant is mainly cow dung, which is available in plenty in rural areas where cattle are used. The biogas is used for lighting and cooking in these areas, as distribution is only in short distances. The spent slurry from the biogas plant is used as manure in agriculture; hence biogas plants are more suitable in rural areas.

Question. How do bioactive molecules of fungal origin help in restoring good health of humans?
Answer : Some bioactive molecules of fungal origin have been reported for their role in restoring good health of humans
For example, cyclosporin-A that is used as an immunosuppressive agent in organ transplant patients is produced by the fungus, Trichoderma polysporum.
Statins produced by yeast, Monascus purpureus have been commercialised as blood cholesterol lowering agents.

Question. What is sewage? In which way, it is harmful for us?
Answer : Sewage is the municipal wastewater collected from city or town homes that contain toilet, bathroom and kitchen waste. It contains large amounts of organic matter and many pathogenic microbes which are harmful to humans as they can cause diseases like cholera, typhoid, polio, etc.

Question. Give examples to prove that microbes release gases during metabolism.
Answer : Release of gases by microbes during metabolic activities can be justified by the following examples
(i) Puffed up appearance of dough, is due to the production of CO2 gas through fermentation by bacteria.
(ii) Swiss cheese has large holes due to production of CO2.
(iii) Methanogens produce methane.

Question. During the secondary treatment of primary effluents, how does a significant decrease in BOD occur? 
List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment. 
Answer : During secondary treatment, the primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it which allows vigorous growth of useful aerobic microbes into flocs, i.e. masses of bacterial cells in association with fungal filaments, forming mesh-like structure. As they grow, the microbes consume a major part of the organic matter in the effluent, which significantly reduces BOD.

Question. Distinguish between the roles of flocs and anaerobic sludge digesters in sewage treatments.
Answer : In sewage treatment, flocs consume major part of the organic matter, converting it into microbial biomass and releasing lot of minerals. It reduces the BOD of sewage.
While in anaerobic sludge digesters, many anaerobic bacteria are present, which digest the organic mass as well as aerobic microbes. During this digestion, methane,CO2, etc., are produced.

Question. Why is aerobic degradation more important than anaerobic degradation for the treatment of large volumes of wastewaters rich in organic matter. Discuss.
Answer : Aerobic degradation is more important than anaerobic degradation because naturally occurring aerobic and facultative microbes (bacteria, fungi, Protozoa and others) in the wastewater can rapidly oxidise soluble organic and nitrogenous compounds. Mechanical addition of oxygen makes the process faster and most of the pathogenic content of the effluent is removed.

Question. Write the name of bacterium which is involved in setting milk into curd. Explain the process they carry in doing so. Write another beneficial role played by such bacteria.
Answer : Microorganisms like Lactobacillus and other commonly called Lactic Acid Bacteria (LAB) grow in milk and convert it into curd.
In this process, a small amount of starter is added to milk which turns it into curd. This starter is known as inoculum, which contains millions of LAB. These LAB produce acids that coagulate and partially digest the milk proteins. Thus, converting milk to curd. These bacteria also improve the nutritional quality by increasing vitamin-B 12 content in curd. A number of organic acids can also be found in curd.
LABalso play very beneficial role in checking disease causing microbes in our stomach.

Question. How does the application of the fungal genus–Glomus, to the agricultural farm increase the farm output?
Answer : The application of Glomus to agricultural field increases the farm output by increasing the nutrient availability to the crops. Glomus develops symbiotic association with the roots of plants, called mycorrhiza. It absorbs phosphorus from the soil and passes it to the plants it associates with. In return, it derives sugars from the host plant cells for its survival.

Question. How does the application of cyanobacteria help to improve agricultural output?
Answer : Cyanobacteria are autotrophic microbes found in aquatic and terrestrial environments.Most of these fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc.
In paddy fields, cyanobacteria serve as important biofertiliser. They also add organic matter to the soil, thus increasing the fertility.

Question. Name some traditional Indian food made of wheat, rice and Bengal gram, which involve use of microbes. (NCERT)
Answer : Some Indian traditional food made of wheat, rice and Bengal gram are Wheat–Bhature and nan Rice–Idli and dosa Bengal gram–Dhokla and khandvi.

Question. ‘Determination of Biological Oxygen Demand (BOD) can help in suggesting the quality of a water body’. Explain.
Answer : BOD refers to the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. The microbes biodegrade the major part of the organic matter in the effluent by using the dissolved oxygen. It reduces the BOD of the effluent.
When the BOD of sewage is reduced significantly the effluent is passed into a settling tank where the bacterial flocs are allowed to sediment forming the activated sludge. Thus, higher the value of BOD, more is the water polluted and more is the amount of biodegradable matter.

Question. How is primary sludge is different from activated sludge?
Answer : Primary sludge is different from activated sludge as primary sludge includes all solid substances which get setteled after primary treatment. It traps lots of microbes and debris while activated sludge is the sediment formed from effluent after secondary treatment which contains bacterial flocs.

Question. How has fungus, Trichoderma polysporum proved to be very essential to organ transplant patients?
Answer : Fungus, Trichoderma polysporum is used to produce cyclosporin-A which act as an immunosuppressive agent during transplantation. They supress the immune system of patient, so that it does not act against the organ transplanted.

Question. Give the name of the two different categories of microbes naturally occurring in sewage water.
Explain their role in cleaning sewage water into usable water. 
Answer : Two different categories of microbes naturally occurring in sewage water are aerobic and anaerobic microbes.
(i) Role of aerobic microbes in cleaning water Aerobic microbes grow excessively in the aeration tank and consumes a major part of the organic matter. It helps in reducing the BOD of the effluent.
(ii) Role of anaerobic microbes in cleaning water In the settling tank, anaerobic microbes digest the aerobic bacteria and fungi and produce gases like CH4, CO2,H2S, etc. It makes the water less polluted to be released in the water bodies.

Question. What are methanogens? How do they help to generate biogas? 
Answer : Bacteria which grow anaerobically on cellulosic material, produce large amounts of methane along with CO2 and H2 are called methanogens (one of the common bacterium is Methanobacterium).
Methanogens are found in anaerobic sludge and in rumen of cattle. These methanogens are grown in slurry which comprises of cattle dung, they act upon it by breaking it down and release gases like methane and CO2. Hence, methanogens help to generate biogas.

Question. Plasmodium falciparum is the causative agent of the most severe form of malaria. It is distributed throughout the tropics. Explain why malaria is restricted to the tropics?
Answer : Malaria is transmitted by Anopheles mosquito, which is insect vector for the Plasmodium falciparum parasite. This parasite needs warm conditions with temperatures above 20° C to complete its life cycle in the mosquito. Therefore, mosquitoes breed in warm conditions of tropics and in areas of stagnant water. Hence, malaria is restricted to the tropics.

Question. Explain any three preventive measures to control microbial infections.
Answer : Preventive measures to control microbial infections are as follows
1. Personal hygiene Keeping the body clean, consumption of clean drinking water, food, vegetables, fruits, etc.
2. Public hygiene Proper disposal of waste and excreta, periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks and observing standard practices of hygiene in public catering.
3. For vector borne diseases such as malaria Eradication of vectors and destroying their breeding sites, e.g. using mosquito nets and repellents, avoiding stagnation of water, regular cleaning of coolers, etc., introducing fishes like Gambusia in ponds that feed on mosquito larvae, spraying of insecticides in ditches, drainage areas and swamps, etc.

Question. ‘Prevention is better than cure’. Comment.
Answer : Prevention is always better than cure because some diseases cause extensive damage to the body tissues or organs and have a
(i) negative effect on their capacity to function.
(ii) permanent or long term debilitating effect.
(iii) negative mental and psychological effect.
(iv) financial burden.
Hence, it is said that prevention is easier and effective than cure of a disease.

Question. The harmful allele of sickle-cell anaemia has not been eliminated from human population. Such afflicted people derive some other benefit? Discuss.
Answer : Sickle-cell anaemia still persists in the population despite being harmful because this mutation can also be beneficial in certain conditions. The mutant HbS type haemoglobin is found at high frequencies (upto 20% and above) in the tropical Africa.
It is known that heterozygotes (HbS / HbA), having both types of haemoglobin show resistance to malarial infection as the body targets the Plasmodium falciparum infected cell for destruction. In contrast, individuals homozygous for normal haemoglobin (HbA / HbA) suffer high mortality rates in early childhood due to malarial infection. Thus, the allele for sickle-cell has been maintained because heterozygotes have a higher reproductive success than either of the two possible homozygotes.

Question. ‘Maintenance of personal and public hygiene is necessary for prevention and control of many infectious diseaes’. Justify the statement giving suitable examples.
Answer : Diseases which are easily transmitted from one person to another, are called infectious diseases.
For prevention and control of such diseases, maintenance of personal and public hygiene is necessary, for this purpose, some common preventive measures should be taken as follows
(i) Education People should be educated about communicable disease to protect themselves from such diseases.
(ii) Isolation The infected person should be kept isolated to minimise the spread of infection.
(iii) Vaccination People should get vaccination on time to avoid infection.
(iv) Sanitation The sanitation should be improved to avoid infection from polluted water, contaminated food, etc.
(v) Eradication of Vectors The breeding places of vectors must be destroyed and adult vectors should be killed by suitable methods.
(vi) Sterilisation The patient’s surroundings and articles of use should be completely sterilised to reduce the chances of infection.

Question. How does the transmission of each of the following take place? Ringworm, Malaria, Ascariasis, Pneumonia.
Answer : The mode of transmission of the above diseases are
(image) 13

Question. What are lifestyle diseases? How are they caused? Name any two such diseases.
Answer : Lifestyle diseases are ailments that are primarily based on the day-to-day habits of people.
Lifestyle diseases are caused by specific food habits, work related posture or exposure to harmful radiations or substances, lack of physical exercise, mental stress, etc.
Two lifestyle diseases are
• Hypertension • Heart disease

Question. Compare the symptoms of ascariasis, amoebiasis and elephantiasis.
Answer : Comparison between the symptoms of ascariasis, amoebiasis and elephantiasis are as follows (image) 14

Question. What measures would you take to prevent the water-borne diseases? 
Answer : To prevent water-borne diseases, water bodies, like ponds, water tanks, reservoirs in the city or village should be cleaned periodically. The proper disposal of domestic waste, excreta, sewage should be done. At personal level, boiling of water, using water purifier, washing hands before meals should be practiced.

Question. Why is it that during changing weather, one is advised to avoid closed, crowded and air conditioned places like cinema halls, etc?
Answer : During changing weather, one is advised to avoid crowded places because changing seasons are the time when infectious agents are more active as moist conditions favours the growth of pathogens. Also, people are more vulnerable as their body system is busy in adapting to the changing environmental conditions of temperature, humidity, etc. Thus, this increases the chances of getting easily infected by various pathogens.

Question. Community service department of your school plans a visit to a slum area near the school with an objective to educate the slum dwellers with respect to health and hygiene.
(i) Why is there a need to organise such visits?
(ii) Write the steps you will highlight as a member of this department, in your interactions with them to enable them to lead a healthy life.
Answer : (i) Slums are generally unauthorised and encroached colonies having no public facilities. Due to lack of public facilities and education, the living standards there are very low and people are always at risk. Thus, there is a need to organise visits to educate people of slum about sanitation and other health related issues.
(ii) Development of healthy life is a bidirectional process and needs the cooperation of both authorities and public of slum area. Interacting with people, understanding their needs, availability of funds, interaction with all concerned authorities, making a concrete plan of development are required to handle the situation of slums.

Question. Certain attributes of innate immunity are given in the table below. Identify A, B, C, D, E and F respectively in it.
(image) 15
Answer : (i) A–Physiological barriers, B–Acid in stomach.
(ii) C–Cellular barriers, D–Phagocytose and destroy microbes
(iii) E–Interferons, F–Prevention of viral infections

Question. (i) What is the functional difference between B and T-cells?
(ii) Name the source used to produce hepatitis-B vaccine using rDNA technology.
Answer : (i) Functional differences between B and T-cells are as follows
(image) 16
(ii) Hepatitis-B vaccine is produced from surface antigens of transgenic yeast by rDNA technology. The antigens represent whole protein vaccine.

Question. Many microbial pathogens enter the gut of humans along with food. What are the preventive barriers to protect the body from such pathogens? What type of immunity do you observe in this case?
Answer : Many microbial pathogens enter the gut of humans along with food. The preventive barriers to protect the body from such pathogens are as follows
(i) The mucus coating of the epithelium lining of the gut helps in trapping microbes entering the body.
(ii) Saliva in the mouth and hydrochloric acid in gastric juice secreted by stomach prevent microbial growth.
This type of immunity is innate immunity. It is present from birth and is inherited from parents. The innate immunity remains throughout the life.

Question. (i) List any two situations, when a medical doctor would recommend injection of preformed antibodies into the body of a patient. Name this kind of immunisation and mention its advantages.
(ii) Name the kind of immunity attained when instead of antibodies, weakened antigens are introduced into the body.
Answer : (i) The two situations in which doctor will recommend injection of preformed antibodies into the body can be
(a) in case of snake bite
(b) in case of tetanus
This type of immunisation is called passive immunisation.
Advantages of passive immunisation are as follows
(a) It helps to prevent and slow down the course of disease.
(b) Passive immunisation with preformed antibodies leads to promote the availability of large amount of antibody thus act quickly.
(ii) Passive immunity attained when instead of antibodies, weakened antigens are introduced into the body.

Question. (i) It is generally observed that the children who had suffered from chickenpox in their childhood may not contact the same disease in their adulthood. Explain giving reasons the basis of such an immunity in an individual. Name this kind of immunity.
(ii) What are interferons? Mention their role.
Answer : (i) When the boy suffered from chickenpox, first time his body’s immune system exhibited primary response. Along with that, the memory of chickenpox virus was stored by the immune system. Now, whenever the same virus will attack this boy, the immune system will produce an intense response, preventing the body from getting chickenpox again. Thus, protecting the boy from getting infected by chickenpox ever again in life. It is known as acquired immunity.
(ii) Interferons are special kind of proteins secreted by virus infected cells. These protect the healthy cells from the virus attack.

Question. What does the term ‘memory of the immune system’ mean?
Answer : Memory of the immune system is an unique feature, which helps in producing an intensive secondary/anamnestic response when the pathogen attacks the second time.

Question. Mention any four symptoms of dengue fever.
Answer : Four characteristic features of dengue fever are high fever, severe front headache, joint pain, nausea and vomiting.

Question. Name the types of acquired immune responses and the special types of lymphocytes involved in providing them.
Answer : Types of acquired immune responses are
(i) Humoral immune response provided by B-lymphocytes.
(ii) Cell-mediated immune response provided by T-lymphocytes.

Question. Name any two secondary lymphoid organs in a human body and state the function of any of them.
Answer : Spleen, lymph nodes, tonsils, Peyer’s patches of small intestine, vermiform appendix.
Spleen : They act as sites for interaction of lymphocytes with the antigen and cause immune response.
Function :
Spleen : Trap blood-borne micro-organisms and worn out RBCs, thus filters blood.
Lymph nodes : Trap the micro-organisms / antigens (which happen to get into the lymph and tissue fluid). The trapped antigens activate lymphocytes and cause immune response.

Question. (i) It is generally observed that the children who had suffered from chickenpox in their childhood may not contract the same disease in their adulthood. Explain giving reasons on the basis of such immunity in an individual. Name this kind of immunity.
(ii) What are interferons ? Mention their role.
Answer : (i) The first infection of chickenpox produce a primary response and antibodies are generated against the chickenpox virus, subsequent encounter with the same virus elicits a highly intensified secondary response, due to the memory cells formed during the first encounter, (active immunity).
(ii) Proteins secreted by virus infected cells,which protects non-infected cells from viral infection / when a – interferon is given to cancer patient (it activates immune system),
destroys tumour.

Question. Name two drugs obtained from poppy plant. “These drugs are medically useful but are often abused“. Taking the mentioned examples justify by giving reasons.
Answer : Heroin / smack, morphine; morphine obtained from latex of unripe capsules of poppy plant (Papaver somniferum) is an effective pain killer and sedative. Heroin (a derivative of morphine) is used as drug. If these drugs are taken for the purpose other than medicinal or taken in larger doses, that may impair the physical and mental state of a person, then it is said to be abused.

Question. Mention the chemical nature of an antibody and name the type of cells they are produced by. Write the difference between active and passive immune responses on the basis of antibodies. A
Name the cells that act as HIV factory in humans when infected by HIV. Explain the events that occur in these infected cells.
Answer : Chemically antibodies are proteins. They belong to the immunoglobulin family of proteins which are Y shaped large molecules produced by plasma cells.
They are important constituents of the immune system.
Antibodies are produced by specialized white blood cells called B-lymphocytes (or B cells). When an antigen binds to the B-cell surface, it stimulates the B-cell to divide and mature into a group of identical cells called a clone.
Differences between active and passive immune responses : 

Active immunityPassive immunity
It is a type of acquired immunity in which the body produces
its own antibodies against disease-causing antigens
It is a type of acquired immunity in which ready-made antibodies are transferred from one individual to another.
It has a long-lasting effectIt does not have a longlasting effect.
It is slow. It takes time in producing antibodies and giving responses.It is fast. It provides immediate relief.
e.g., Injecting microbes through vaccination inside the body.e.g., Transfer of antibodies present in
the mother’s milk to the infant.

Macrophages cells acts as an HIV factory in human when infected by HIV, where RNA of virus replicates to form viral DNA with the help of enzyme reverse transcriptase.
Events that occur in these infected cells are :
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 give 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 the helper T-lymphocytes. It replicates and produces viral progeny here. These newly formed progeny viruses get released into the blood, attacking
healthier 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 the body. 

Question. (i) Differentiate between benign and malignant tumours.
(ii) Why is colostrum a boon to the newborn baby ?
Answer : (i) Benign tumour remains confined to original location / does not spread to another part of the body / not cancerous.
Malignant tumour is mass of proliferating (neoplastic) cells that invade and damage surrounding tissue / cancerous tumour /tumour showing property of metastasis.

Question. Two children, A and B aged 4 and 5 years respectively visited a hospital with a similar genetic disorder. The girl A was provided with enzyme replacement therapy and was advised to revisit periodically for further treatment. The girl B was, however, given a therapy that did not require revisit for further treatment.
(a) Name the ailments the two girls were suffering from?
(b) Why did the treatment provided to girl A required repeated visits?
(c) How was the girl B cured permanently?
Answer : (a) Adenosine deaminase (ADA) deficiency 
(b) In Enzyme Replacement Therapy functional ADA is introduced to the patient (by injection), this therapy is not completely curative as enzyme can act only for a limited time period.
(c) [As there is no permanent cure at the age of five hence 1 mark of this answer allocated to part (b)]

Question. A child is born with ADA – deficiency (a) Suggest and explain a procedure for possible life-long (permanent) cure.
(b) Name any other possible treatment for this disease.
Answer : (a) Gene therapy, lymphocytes from the blood of a patient are grown in a culture outside the body, functional ADA, cDNA is introduced into these lymphocytes, these cells are returned to the patient’s body at early embryonic stage. 
(b) Bone marrow transplantation, enzyme replacement therapy.

Question. Certain attributes of innate immunity are given in the table below. Identify A, B, C, D, E and F respectively in it. 

Sr. No.Type of barrierExample of the barrierFunction
(i)ABPrevent microbial
nuclear leucocytes

Answer : A. Physiological barrier.
B. Acid in Stomach/Saliva in mouth/Tears.
C. Cellular Barrier.
D. Phagocytose / Destroy microbes.
E. Interferons.
F. Protect non-infected cells from virus attack.

Question. (a) Write the scientific names of the causative agent and vector of malaria, and write its symptoms.
(b) Name any two diseases spread by Aedes sp.
Answer : (a) Plasmodium vivax / P. falciparum / P.malariae, vector-Female Anopheles mosquito Symptoms – chill , high fever
(b) Dengue, Chikungunya. 

Question. Medically it is advised to all young mothers that breastfeeding is the best food for their newborn babies. Do you agree? Give reasons in support of your answer.
Why is breastfeeding recommended during the initial period of an infant’s growth ? Give reasons.
Answer : Yes, Breast freeding is considered to be the best food for infants because it provides nutrition (calcium, fats, lactose) / provides (passive) immunity / provides antibodies / Ig A which heps the new born grow healthy and strong. This also protects the infants against allergies, sickness,infections etc.

Question. Name one airborne and a waterborne disease in humAnswer : List one specific symptom of each one of them. 
Answer : Air-borne diseases : Tuberculosis (TB), Influenza Symptoms : Pain and difficulty in breathing/ Coughing. Water-borne diseases : Diarrhoea, Typhoid. Symptoms : Loose motions/ Watery stool. 

Question. Name a human disease, its casual organism, symptoms (any three) and vector, spread by intake of water and food contaminated by human faecal matter.
Answer : Amoebiasis (Amoebic dysentery), Entamoeba histolytica, constipation / abdominal pain / cramps / tools with excess mucus / blood clots (Any three symptoms), Housefly.
Ascariasis, Ascaris, internal bleeding / muscular pain / fever / anaemia / blockage of intestinal passage (Any three symptoms), Housefly.
Typhoid, Salmonella typhi, high fever / weakness /stomach pain / constipation / headache / loss of appetite, Housefly. (Any three symptoms)

Question. List two diseases that spread through inhaling droplets or aerosols. Write one prominent symptoms for each one of them.
Answer : Diseases that spread through inhaling droplets and aerosols are Diphtheria and Common cold. Symptoms of Diphtheria : Sore throat and swollen lymph nodes. Symptoms of Common cold : Nasal congestion and sneezing. 

Question. A farmer while working on his farm was bitten by a poisonous snake. The workers in the farm immediately rushed him to the nearby health centre. The doctor right away gave him an injection to save his life. What did the doctor inject and why ? Explain.

Answer : (i) Antitoxin / Antivenoms / Preformed antibodies. 
(ii) Whenever quick immune response is required, we need to directly inject preformed antibodies / Antitoxins. 
(iii) To neutralize snake venom quickly, passive immunity is provided.

Question. (i) What is an ‘‘allergic reaction’’ ?
(ii) Name any two drugs used to quickly reduce the symptoms of allergy.
(iii)Why do more and more children in metro cities of India suffer from allergies and asthma?
Answer : (i) The exaggerated response of the immune system to certain antigens present in the environment is called allergic reaction. 
(ii) Anti-histamine, adrenaline, steroids. (Any two)
(iii) Due to deteriorating air quality, sensitivity to the environment, allergens, lowering of immunity due to modern day lifestyle (which could be due to the protected environment
provided largely in life).

Question. Name the type of immunity a baby is born with. How is it different from the one he getsfrom the mother’s milk after birth ? 
Answer : Innate Immunity-Acquired Immunity that a baby acquires from his mother’s milk after birth is an example of passive immunity.

Question. How does the HIV breakdown the immune system of the AIDS patients ?
Answer :
(i) Virus enters in macrophages.
(ii) RNA genome replicates to form viral DNA with help of reverse transcriptase.
(iii) Viral DNA gets incorporated into host cells DNA to produce virus particles.
(iv) HIV enters into helper ‘T’ lymphocytes and produces progeny virus.
(v) These are released in the blood and attack another helper ‘T’ lymphocytes.
(vi) This leads to progressive decrease in the number of helper ‘T’ lymphocytes and the person starts suffering from infections (loss of immunity).

Question. (i) Why is there a fear amongst the guardians that their adolescent wards may get trapped in drug/alcohol abuse ?
(ii) Explain ‘addiction‘ and ‘dependence‘ in respect of drug / alcohol abuse in youth.
Answer : (i) Adolescents are easily affected by (Vulnerable to) peer pressure, adventure, curiosity, excitement, experimentation and media.
(Any two) = 
(ii) Addiction : Psychological attachment to certain effects such as Euphoria or temporary feeling of well – being. 
Dependence : Tendency of the body to show withdrawal syndrome or symptoms if regular doses of drug or alcohol are abruptly discontinued.

Question. On a visit to a Hill station, one of your friends suddenly became unwell and felt uneasy.
(i) List two symptoms you would look for to term it to be due to allergy.
(ii) Explain the response of the body to an allergy.
(iii) Name two drugs that can be recommended for immediate relief.
Answer : (i) Sneezing, watery eyes, running nose,difficulty in breathing. (Any two)
(ii) Body releases antibodies, lgE type and chemicals like histamine and serotonin from mast cells which produce symptoms of allergy
(iii) Antihistamine, adrenalin, steroids.

Question. (a) Name the causative agents of pneumonia and common cold.
(b) How do these differ in their symptoms ?
(c) Mention two symptoms common to both.
Answer : (a) Streptococcus pneumoniae/ Haemophilus influenzae, Rhinoviruses.
(b) Different symptoms (any two) 

PneumoniaCommon cold
Infects alveoli of lungsInfects nose & respiratory passage
chillsSore throat
Lips /fingers may
turn grey to black.

Question. State the three characteristics of Acquired Immunity. List the different ways by which it can be attained by humAnswer :
Answer : Characteristics of Acquired Immunity : Pathogen specific / characterized by memory /Acquired after birth / are of two types : Active and passive/humoral and cell mediated/includes primary response and secondary response. (Any two)
Way by which it can be attained by humans :Active Immunity by encountering a pathogen /virulent microbe/suffering from contagious disease.
Passive Immunity through immunization / readymade antibodies.

Long Answer Type Questions

Question. (i) Cancer is one of the most dreaded disease. Explain ‘contact inhibition’ and ‘metastasis’ with respect to  the disease.
(ii) Name the group of genes that have been identified in normal cells that could lead to cancer. How dothese genes cause cancer?
(iii) Name any two techniques that are useful in detecting cancers of internal organs
(iv) Why are cancer patients often given a-interferon as part of the treatment? (Delhi 2014)
Answer : (i) Contact inhibition Normal cells have the property of contact inhibition (stoppage of growth on coming in contact with other cells), but cancer cells do not have this property. As a result, cancer cells divide continuously to give rise to a mass of cells (tumours).
Metastasis This property is exhibited by malignant tumours. It is the pathological process of spreading of cancerous cells to different parts of the body. These cells divide uncontrollably, forming a mass of cells called tumour.

From the tumour, some cells get sloughed off and enter the bloodstream. From the bloodstream, these cells reach near by as well as distant parts of the body therefore, initiating the formation of new tumours by dividing actively.
(ii) There are cancer causing viruses called oncogenic viruses. They have genes called viral oncogenes.
Certain other genes called cellular oncogenes (c-onc) or proto-oncogenes have been identified in normal cells, which when activated can lead to tumour formation.
(iii) Techniques that are useful in detecting cancers of internal organs are
(a) Computed Tomography (CT) is done to generate a 3-D image of internal tissue. It uses X-rays. 
(b) Magnetic Resonance Imaging (MRI) involves the use of non-ionizing radiations and strong magnetic fields to detect pathological and physiological changes in a living tissue.
(iv) The biological response modifiers such as a-interferons are given to cancer patients as a part of their treatment because it activates patients’s immune system and helps in destroying the tumour.

Question. Explain the adaptive immunity with emphasis on its properties, activation and its role in vaccination.
Answer : Adaptive immunity is pathogen specific immunity. It is not present from birth and develops during an individual’s lifetime. This type of immunity is acquired,either by encountering the disease or by vaccination. It has the following characters 
(i) Specificity It is the ability to distinguish different foreign molecules.
(ii) Memory It is a unique feature, which helps in producing an intensive secondary/ anamnestic response when the pathogen attacks the second time.
(iii) Discrimination between self and non-self This type of immunity is able to recognise and respond to foreign molecules (non-self) and can avoid response to those molecules that are present within the body (self).
Vaccination is based on the property of memory of adaptive immune system. In vaccination, an antigen or pathogen which is in inactive form is introduced in human body which induces mild immune response. The vaccine is therefore generating antibodies along with memory B and T-cells that recognise the pathogen on subsequent exposure.

Question. What are recombinant DNA vaccines? Give two examples of such vaccines. Discuss their advantages. (NCERT Exemplar)
Answer : Recombinant DNA vaccines are made up of a small circular DNA (plasmid) that has very tiny piece of pathogen DNA incorporated in it to produce one or two specific proteins of the pathogen.
This recombinant DNA is introduced into the bacteria or yeast cells, where it can use cell’s machinery to produce polypeptides of pathogen. These are used as vaccines to trigger a range of immune responses. Vaccines produced by using this approach allow large scale production, e.g.
(i) Hepatitis-B vaccine produced from yeast.
(ii) Bird flu DNA vaccine.

(i) Recombinant DNA vaccines are advantageous over killed or attenuated vaccines, since they do not get virulent or mutated again as it is seen in case of attenuated vaccines.
(ii) Secondly these are highly pure, specific and elicit show strong immune response.

Question. Explain the process of replication of a retrovirus after it gains entry into human body. (All India 2014)
Or What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person? (NCERT)
Answer : The process by which retrovirus gains entry into human host body or the mechanism by which AIDS virus causes immunodeficiency is as follows. (Image 20)

Question. Drugs like LSD, barbiturates, amphetamines, etc., are used as medicines to help patients with mental illness. However, excessive doses and abusive usage are harmful. Enumerate the major adverse effects of such drugs in humans (NCERT Exemplar)
Answer : Harmful effects of drugs like LSD, barbiturates, etc., are (i) Anxiety, shakiness, nausea and sweating, loss of mind control.
(ii) Reckless behaviour, vandalism and violence.
(iii) Lack of interest in personal hygiene, fluctuations in weight and appetite.
(iv) Social adjustment problems.
(v) Withdrawal, isolation, depression, fatigue, aggressive behaviour. 
(vi) Withdrawal symptoms can be severe and life threatening.
(vii) Excessive doses of drugs may lead to coma and death due to respiratory failure, heart failure or cerebral haemorrhage.

Question. In your view what motivates youngsters to take alcohol or drugs and how can this be avoided?
Or Why do some adolescents start taking drugs. How can this be avoided? (NCERT Exemplar)
Answer : Adolescents take drugs/alcohol due to following reasons
(i) Social and peer pressure.
(ii) Curiosity and need for adventure, excitement and experiment.
(iii) To avoid stress, depression and frustation.
(iv) To overcome hardships.
(v) Avoid unsupportive or unstable family structure.
(vi) Perception that it is cool or progressive. This perception is further promoted by TV, movies, newspapers and internet.
This can be avoided by
(i) Avoid undue peer pressure Parents must understand the abilities and personality type of the child. A child should not be pushed unduly for studies or sports or other activities. Pressure from parents and teacher beyond threshold is not healthy for children.
(ii) Education and counselling Parents and teachers should educate and counsel the child to face difficult situations as part of life. Stress, disappointments and failure must be taken in a healthy way. Involvement in extracurricular activities is a good distraction from daily stress. It channelises the child’s energy in right direction.
(iii) Seeking help from parents and peers In case of any academic or emotional problem, advice and guidance should be sought out from parents or trusted friends.
Besides solving problems, it also helps in venting out feelings of anxiety, fear and guilt.
(iv) Looking for danger signs Danger signs must be brought in light and must be told to parents and teachers if they find someone using drugs or alcohol.
There should be no hesitation in informing the same to the elders. This helps in preventing the person from drug abuse and initiating remedial steps.
(v) Seeking professional and medical help Affected people have a lot of help available in the form of doctors, psychologists, psychiatrists and rehabilitation programmes. An addicted person can get completely rid of the problem and lead a perfectly normal and healthy life by getting help.

Case Based Questions

Question. (i) How does a Human Immunodeficiency Virus (HIV) replicate in a host ?
(ii) How does an HIV-infected patient lose immunity?
(iii) List any two symptoms of this disease.
Answer : (i) Diagram : Refer Topic 1 / Revision Notes /Important Diagrams / Fig 1.3
(ii) Loss of T-lymphocytes.
(iii) Fever / diarrhoea / susceptibility to other diseases, prone to microbial infection.

Question. (i) Name the drug used
(a) As an effective sedative & pain killer.
(b) For helping patients to cope with mental illness like depression but often misused.
(ii) How does the moderate and high doses of cocaine affect human body R [O.E.B.]
Answer : (i) (a) Morphine, which is obtained from the latex of the poppy plant is used as an effective sedative and pain killer.
(b) LSD (Lysergic acid dimethyl amide) or Barbiturates are used to help the patients to cope with mental illness like depression.
LSD is a hallucinogenic substance, it is synthetically derived from the fungus, Claviceps purpurea.
(ii) Cocaine is a powerful addictive stimulant drug. The source of cocaine is coca leaves (Erythroxylum coca). It can alter brain structure and function if used repeatedly.
Effect of moderate doses of cocaine :
1. Feeling of euphoria and increased energy.
2. Increased in heart beat, respiration rate and blood pressure.
3. Dilated pupils.
4. Feeling of wellness and increased confidence. Effect of high doses of cocaine :
1. Panic attacks
2. Irritability
3. Anxiety
4. Paranoia.
Long term use of high doses of cocaine can result in weight loss and malnutrition. It may cause Parkinson’s disease. 5

Question. Define adolescence. Why are adolescents advised not to smoke ? How smoking affects the functioning of the body. Explain in reference to the rise in blood pressure and emphysema.
Answer : Adolescence refers to the period and process of rapid growth and physical and mental development from childhood to adulthood. Adolescents are advised not to smoke because of it’s addictive nature, it is hard to get rid of the use of tobacco. Smoking produces negative effect on the body. Smoking of tobacco is associated with cancer of lungs, urinary bladder, bronchitis, coronary heart diseases, etc. Smoking increases the content of carbon monoxide in the blood which interferes, with the oxygen-carrying capacity of the blood. The nicotine (of tobacco) stimulates adrenal glands to secrete adrenaline and nor-adrenaline; these ormones increase the blood pressure and heart rate.

Exam Question for Class 12 Biology Chapter 8 Human Health and Diseases

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