2nd PUC Biology Question Bank Chapter 8 Human Health and Disease

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Karnataka 2nd PUC Biology Question Bank Chapter 8 Human Health and Disease

2nd PUC Biology Human Health and Disease One Mark Questions and Answers

Question 1.
Write the full form of LSD.
Answer:
LSD-Lysergic acid diethyl amide.

Question 2.
What are Psychotropic drugs.
Answer:
These are mood altering drugs which selectively affect behaviour perception and mental activity of a person using them.

Question 3.
Define addiction.
Answer:
Addiction is the state of succumbing and becoming dependent to a drug, alcohol or tobacco usage, as a result of becoming physically, physiologically and psychologically attached to its certain effects like euphoria and temporary feeling of well being.

Question 4.
What is immunity?
Answer:
Immunity could be defined as resistance to diseases. It can be natural or artificial.

Question 5.
What are interferons?
Answer:
Interferons are the proteins produced by the virus infected cells in our body.

Question 6.
When is a tumor referred to as malignant?
Answer:
Malignant tumor is a mass of proliferating neoplastic cells, which spread to distant sites through body fluids to develop secondary tumors.

Question 7.
What are oncogenic viruses?
Answer:
The viruses which cause cancer are called oncogenic viruses.

Question 8.

Which is the lymphoid organ in humans which produces blood cells?
Answer:
Bone (from the bone marrow).

Question 9.
Name the structure through which a newborn receives passive immunity?
Answer:
Placenta.

Question 10.
Define cancer?
Answer:
Cancer may be defined as the abnormal, uncontrolled growth of certain tissue cells.

Question 11.
What is carcinoma?
Answer:
Any cancer that arises in the epithelial tissue is called carcinoma.

Question 12.
What is sarcoma?
Answer:
Any cancer that arises in the connective tissues of the body is called a sarcoma.

Question 13.
What are oncogenes?
Answer:
Cancer genes that may arise from normal cellular genes (proto oncogenes) by somatic mutation and genetic rearrangement.

Question 14.
Which species of bacteria causes human typhoid?
Answer:
Salmonella typhi.

Question 15.
What is an antigen?
Answer:
A foreign substance which when introduced into a living body is capable of generating an immune response by stimulating the production of antibodies.

Question 16.
What is an antibody?
Answer:
Antibodies are the protective chemicals produced by the body in response to the presence of foreign substances like antigens.

Question 17.
Name the causative organism of amoebic dysentery?
Answer:
Entamoeba histolytica.

Question 18.
What are stimulants?
Answer:
Drugs that tend to stimulate and speed up body reactions causing alertness and hyperactiveness.

Question 19.
What are depressants?
Answer:
Drugs which depress the activity of the CNS.

Question 20.
Give an example of vaccine produced by recombinant DNA technology?
Answer:
Hepatitis – B vaccine.

Question 21.
What is the name given to the infectious stage of plasmodium?
Answer:
Sporozoites.

Question 22.
What is metastasis?
Answer:
Metastasis is a phenomenon in which cancer cells spread to different sites through body fluids and develop secondary tumors.

Question 23.
Name the process by which the genome of HIV replicates in the host cell.
Answer:
Reverse transcription.

Question 24.
Name a biological response modifier used in the treatment of cancer.
Answer:
Alpha interferon.

Question 25.
What is drug addiction?
Answer:
Psychological attachment to certain effects associated with drugs/alcohol is called addiction.

Question 26.
Mention the type of immunity provided by preformed antibodies when administered against snake bite.
Answer:
Passive immunisation.

Question 27.
Which is the diagnostic test used to confirm typhoid fever?
Answer:
Widal test.

Question 28.
What are oncogenic viruses?
Answer:
Cancer causing viruses are called oncogenic viruses.

Question 29.
Name the organism causing ringworm disease.
Answer:
Trichophyton or Microsporum or Epidermophyton.

Question 30.
Define allergy.
Answer:
The exaggerated responses of the immune system, to certain antigens present in the environment is called allergy.

2nd PUC Biology Human Health and Disease Two Marks Questions and Answers

Question 1.
Write the role of macrophages in providing immunity to humans.
Answer:
Macrophages are phagocytes and through phagocytosis they destroy the microbes which enter the body.

Question 2.
Write the symptoms of pneumonia.
Answer:
The symptoms include:

• fever,
• headache,
• cough and
• chills.

In severe cases the lips and fingernails may turn greyish to bluish.

Question 3.
What measure would you take to prevent water-borne diseases?
Answer:
Water borne diseases can be prevented by

• Use of clean drinking water
• Periodic cleaning and disinfection of water tanks and reservoirs.
• Proper disposal methods of sewage and excreta.

Question 4.
Define the following diseases, causing agent and symptoms.
Amoebiasis, Ring worm, Ascariasis, Filariasis.
Answer:
(a) Amoebic Dysentery (Amoebiasis): It is caused by Entamoeba histolytica.
Infection is through contaminated food and water.
The pathogen resides in the large intestine.
Its symptoms include:

• Abdominal pain and cramps.
• Stools with excess mucus and blood clots.
• Constipation alternating with diarrhoea.

Houseflies act as mechanical carriers and transfer the parasite from the faeces of infected person to the food articles and water.

(b) Ringworms: These are caused by fungi like Microspomm, Epidermophyton and Trichophyton.
The symptoms include:

• dry scaly lesions on skin, nails and scalp.
• lesions are accompanied by itching.

Ringworms are generally acquired from soil or by direct contact with the contaminated articles used by the infected persons.

(c) Ascariasis: It is caused by Ascaris lumbricoides. (round worm).
Its symptoms include:

• Blockage of intestinal passage,
• Anaemia,
• Abdominal/muscular pain,
• Internal bleeding,
• Nausea and
• Headache.

Infection is through contaminated vegetables, fruits and water as eggs of parasite excreted by the infected persons contaminate soil, plants and water.

(d) Filariasis/Elephantiasis

• It is caused by Wuchereria bancrofti and Wuchereria malayi (filarial worms).
• They normally cause inflammation of the organs in which they live for many years.
• Genital organs may also be affected leading to gross deformities.
• Female Culex mosquito is the vector.

Question 5.
Name the primary and secondary lymphoid organs.
Answer:
Primary lymphoid organs-bone marrow and thymus, where immature lymphocytes differentiate into antigen sensitive lymphocytes.

Secondary lymphoid organs: Spleen, lymph nodes, tonsils, peyers patches of small intestine and appendix.

Question 6.
What is the mechanism by which the AIDS virus causes deficiency of the immune system of the infected person?
Answer:
1. On entering into the body of a person, HIV enters into macrophages where RNA genome of the virus replicates to form viral DNA with the help of reverse transcriptase enzyme. The viral DNA then gets incorporated into host cell’s DNA to direct the synthesis of virus particles.

2. HIV also enters into helper T lymphocytes. It replicates and produces viral progeny. These viruses are released into the blood and attack other helper T lymphocytes. It results in progressive decrease in the number of helper T lymphocytes in the body of the infected person, and the person starts suffering from number of infections.

Question 7.
How is a cancerous cell different from a normal cell?
Answer:
Cancer cells are different from normal cells as they,

• divide in an uncontrolled manner.
• do not undergo differentiation.
• are not confined to the part of the body, where they are initially formed
• invade other organs of the body forming secondary tumors.

Question 8.
Explain what is meant by metastasis.
Answer:
A phenomenon in which cancer cells spread to distant sites through blood and lymph and produce secondary tumors.

Question 9.
List the differences between antigen and antibody.
Answer:

Antigen	Antibody
They are foreign substances capable of generating an immune response and stimulate the production of antibodies.	They are protective chemicals which are produced in response to the presence of foreign substances called antigens.
Generally it is protein, but it may also be a polypeptide, complex lipid and certain other substances that combine with protein	It is a protein molecule.
They are present on the surface of micro-organisms or as free molecules	They are present on the surface of plasma cells and in body fluids.
They bind a macrophage to reach a helper T-cell to initiate an immune	They react with antigen directly to destroy them.

Question 10.
Give a brief account of a benign tumor?
Answer:
Benign tumors: Tumours result from abnormal and persistent cell division consists of cancer cells that remains localized at the spot of origin and do not spread to distinct sites. These are not great threat to life (non – fatal), but some can be fatal, as in brain tumor. Well-differentiated cells generally characterize benign tumors.

Question 11.
Write a note on the prevention and control of infectious diseases?
Answer:
The following practices can prevent/control most of the infectious diseases.

• Maintenance of personal hygiene (keeping the body clean, consumption of clean food and water).
• Maintenance of public hygiene (proper disposal of excreta/wastes, periodic cleaning and disinfection of water reservoirs; observing standard practices of hygiene in public catering).
• Eradication of vectors and their breeding places.
• Vaccination and immunisation for diseases like polio, diphtheria, tetanus, etc.
• Use of antibiotics and drugs to treat the infected persons.

Question 12.
Name the causative organism and symptoms of common cold?
Answer:
Common cold: It is caused by the rhino viruses.
These viruses infect the nasal and respiratory passages, but not the lungs.
Its symptoms include:

1. Nasal congestion and discharge,
2. Sore throat
3. Cough,
4. Headache
5. Tiredness and
6. Hoarseness which lasts for 3 – 7 days.

It spreads by,

1. Droplets released during cough and sneezing by an infected person and
2. Contaminated objects/articles.

Question 13.
Name the causative organism and symptoms of pneumonia?
Answer:
It is caused by Streptococcus pneumoniae and Haemophilus influenzae.
They infect the alveoli of lungs, where the alveoli become filled with a fluid resulting in severe difficulty in breathing/respiration.
The symptoms include:

• fever,
• headache,
• cough and
• chills.

In severe cases the lips and fingernails may turn greyish to bluish.
Infection is by

• droplets from an infected person and
• sharing the contaminated articles.

Question 14.
What are the various routes by which transmission of HIV takes place?
Answer:

• Sexual contact with an infected person.
• Transfusion of contaminated blood and blood plasma.
• Sharing of infected needles as in the case of intravenous injection.
• From an infected mother to her child through placenta.

Question 15.
Write causative organism and symptoms of Ascariasis.
Causative organism: Ascaris
Symptoms :
Answer:
Internal bleeding, Muscular pain, Fever, Anaemia and Blockage of intestinal passage.

Question 16.
What is a tumor? Mention the types of tumors.
Answer:
The extra mass of tissues produced by cancer cells or neoplastic cells is called a tumour.
Benign tumours (remain at their original location and do not spread to other parts of the body.) Malignant tumours (the tumour cells which damage, invade or migrate to surrounding tissues)

Question 17.
What is contact inhibition? What happens when this ability is lost in normal cells?
Answer:
The process which inhibits the uncontrolled growth of a normal cell due to its contact with the surrounding cells is called contact inhibition.

When a normal cell loses this ability, it starts uncontrolled division and develops a tumour/cancer.

Question 18.
Mention any four types of cancer treatments.
Answer:
Surgery, Radiotherapy, Chemotherapy and Immunotherapy.

Question 19.
Describe the effects of drug abuse.
Answer:

• Reckless behaviour, vandalism and violence.
• Excessive dose may lead to coma and death.

Question 20.
What are interferons? What is their significance?
Answer:
These are the anti-microbial proteins released by virus infected cells that protect other healthy tissue cells from infection. During viral infection, nucleic acid enters the host cell. This triggers the genes in most of the cells to produce interferons.

The host cell dies due to viruses, but interferons diffuse into other healthy cells and block the synthesis of viral proteins. When a new virus enters the cells it can’t multiply as the cell can’t produce the proteins. The virus needs to reproduce in order to spread infection.

Question 21.
Define disease and mention its types.
Answer:
Diseases can be broadly classified into two types:

1. Infectious diseases and
2. Non-infectious diseases.

The differences between them are as follows

Infectious diseases	Non-infectious diseases
These are the diseases which are easily transmitted from one person to the other.	These are the diseases which are not transmitted from one person to the other.
They are caused by pathogens.	They occur due to hereditary factors, deficiencies, habits, etc.

Some infectious diseases like AIDS and Hepatitis-B are fatal.
Cancer among non-infectious diseases, is the major cause of death.

2nd PUC Biology Human Health and Disease Three Marks Questions and Answers

Question 1.
Draw a well-labelled diagram of an antibody molecule.
Answer:

Question 2.
What are the various public health measures, which you would suggest as safeguard against infectious diseases?
Answer:
The public health measures which can safeguard against infectious diseases include the following.
1. Education: Public must be made aware about infectious diseases, mode of transmission and preventive measures so that they can protect themselves against infections.

2. Isolation: A person suffering from an infectious disease should be kept in isolation from other healthy persons. Healthy practices with good personal and public hygiene must be maintained.

3. Vaccination: People should be vaccinated against infectious diseases like small pox, chicken pox etc,

4. Sanitation: Proper sanitation of the surroundings can prevent spread of infectious diseases.

Question 3.
How does the transmission of each of the following diseases take place?
(a) Amoebiasis
(b) Malaria
(c) Ascariasis
Answer:
(a) Amoebiasis: By ingesting cysts of Entamoeba histolytica with water or food. The cysts are carried from faeces of an infected person to food and drinks.

(b) Malaria: Malarial parasite (Plasmodium sp.) is transmitted from the infected to the healthy person by the female Anopheles mosquito.

(c) Ascariasis: By ingesting Ascaris eggs with food and water. Children become infected by ingesting soil.

Question 4.
What is innate immunity? Mention the four types of barriers of innate immunity.
Answer:
It is a non -specific type of defence present at the time of birth.
The four types of barriers of innate immunity are,
(a) Physical barriers,
(b) Physiological barriers,
(c) Cellular barriers and
(d) Cytokine barriers.

Question 5.
What are carcinogens? Mention any two groups of carcinogens with an example for each.
Answer:
These include physical, chemical and biological agents, which transform normal cells by directly
causing changes in the DNA of this cells.

1. Physical agents: They include various forms of ionizing radiations. UV radiation is a powerful mutagen for skin cancer. The exposure of the thyroid glands to x – rays has shown to increase the incidence of thyroid cancer.

2. Chemical agents: The chemical carcinogens that have been found to be carcinogenic in humans include:
a. Chemical mixtures like soot (black carbon), tars, cigarette Smoke, etc.,
b. Industrial chemicals: Arsenic, nickel compound, benzidine, etc.,
c. Drugs: Mustard gas, phenacetin.

Question 6.
Mention the pathogen, causes and symptoms of pneumonia.
Answer:
Pneumonia: It is caused by Streptococcus pneumoniae and Haemophilus influenzae.
They infect the alveoli of lungs, where the alveoli become filled with a fluid resulting in severe difficulty in breathing/respiration.
The symptoms include:

• fever
• headache
• cough and
• chills.

In severe cases the lips and fingernails may turn greyish to bluish.
Infection is by

• droplets from an infected person and
• sharing the contaminated articles.

Question 7.
(a) Mention the pathogen and any two symptoms of typhoid,
(b) Name the diagnostic test used to confirm typhoid.
Answer:
(a) Common Infectious Diseases.
Depending on the pathogen, infectious diseases are as follows :

These pathogens enter our body by various means (direct contact, droplet infection, contaminated food and water, etc.), multiply there and interfere with the normal vital activities, resulting in morphological and functional disorders.

(b) It is caused by Salmonella typhi. The infection is by contaminated food and water. The pathogen enters the small intestine and then the other parts through body fluids. Its symptoms include :

• Sustained high fever (103 °- 104°F),
• Stomach pain
• Loss of appetite
• Constipation and
• Headache.

Intestinal perforation leading to death may occur in severe cases.
Typhoid can be confirmed by widal test.

2nd PUC Biology Human Health and Disease Five Marks Questions and Answers

Question 1.
What are the various routes by which transmission of human immunodeficiency virus takes place?
Answer:

• Unprotected (without condom) sexual intercourse with an infected partner.
• Use of contaminated needles and syringes.
• Use of contaminated razors for shaving.
• Transfusion of infected blood or blood plasma.
• Organ transplantation from an infected person.
• From infected mother to the baby at the time of child birth.

Question 2.
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
Answer:
(a) MALT – Mucosal associated lymphoid tissue
(b) CMI – Cell-mediated immunity
(c) AIDS – Acquired immunodeficiency syndrome
(d) NACO – National AIDS control organization
(e) HIV – Human immuno deficiency virus.

Question 3.
Give an account of non specific Immune responses.
Answer:
Non-specific body defences: Non-specific body defences are those that are present by birth in a healthy individual to protect from a wide range of harmful microorganisms in the environment, but not-specific against any particular pathogen.
These non-specific defence mechanisms are of two types.

1. Surface barriers
2. Cellular and Biochemical defences

1. Surface Barriers (Physical Barriers): They form the first line of defence. They include skin and mucus membrane.

Skin: It is the outermost body surface covering. It forms a barrier that prevents the entry of pathogens and other harmful substances into the body. Certain regions in the skin become heavily keratinized forming an impermeable physical barrier. Keratin is a sclero protein and is resistant to weak acids, bases, bacterial enzyme and toxins.

Sweat (sudorific gland) secreted by skin makes the surface acidic. This inhibits the growth of bacteria. Sebum (Oily secretion of sebaceous glands) contains chemicals that are toxic to bacteria.

Mucous membrane: They are the membranes found in the lining of the various entry points of the human body like, lyes, respiratory paths, genital openings, anus etc. The mucus (fluids) produced by these linings trap the micro-organisms and immobilizes them. Skin and mucus membranes also produce a variety of chemicals which serve the following functions.

Protective functions:

• Saliva produced in the oral cavity contains lysozyme that destroys bacteria.
• Vaginal secretions of adult females are acidic, inhibiting the growth of bacteria and fungi in the female reproductive tract.
• The mucosa of stomach secretes hydrochloric acid and protein digesting enzymes that destroy pathogens in the stomach.
• Lacrimal fluid (tear) which washes and lubricates the eyes continuously also contains bactericidal lysozyme.
• Mucus produced in the respiratory tract traps micro-organisms that try to enter the lungs.
• Urine normally with acidic PH of 6-5 inhibits bacterial growth.
• Earwax secreted by the ceruminous glands in the ear canal traps dust, microorganisms and insects that enter the ear.
• Human milk is rich in antibacterial substances namely lactoferrin and Neuraminic acid.

2. Cellular and Bio-chemical defences:
They are the internal defence barriers present in the body and form the second line of defence.
They include.

1. Phagocytosis
2. Natural killer cells (NK Cells)
3. Interferons
4. Inflammatory response

Phagocytosis: It is a process in which the phagocytic leucocytes (WBC) engulf the pathogen (disease causing agent) and digest it with the help of lytic enzymes. The cells involved in Phagocytosis are called phagocytes. The chief phagocytes are macrophages which are derived from a type of WBC called monocytes and neutrophils.

A phagocyte engulfs the particulate matter through the formation of pseudopodia. The vesicle thus formed inside the phagocyte is called phagosome. The phagosome then fuses with the lysosome containing hydrolytic enzymes to form phagolysosome. Inside the phagolysosome, the particulate matter is broken down.

Natural killer cells (NK Cells): Natural Killer Cells are non-phagocytic larger lymphocytes which have large granules. These cells show natural cytotoxicity and are able to kill a range of tumor cells. NK Cells are not phagocytic but promote cell lysis by direct attack on target cell membrane and releasing of several cytolytic chemicals like cytolysin and perforin.

Interferons: These are the anti-microbial proteins released by the virus infected cells that protect other healthy tissue cells from infection. During viral infection, nucleic acid enters the ( host cell. This triggers the genes in most of the cells to produce interferons.

The host cell dies due to viruses, but interferons diffuse into other healthy cells and block the further synthesis of viral proteins. When a new virus enters the cells, it cannot multiply as the cell cannot produce f the proteins. The virus needs to reproduce in order to spread infection.

Inflammatory response: It is a biochemical local defensive response of the non-specific defence mechanism, to infection and tissue damage, (such as cuts, insect bites, etc.) It is expressed in the form of swelling, pain, and irritation. It is also brought about by phagocytes.

Question 4.
Explain the role of B – lymphocytes in humoral Immunity?
Answer:
Role of B-lymphocytes in humoral immunity: B-lymphocytes undergo maturation and become immunity competent in the bone marrow.

The B-lymphocytes are responsible for humoral immunity. In this type of immunity, the body fights against the pathogen by producing antibodies, in the fluids like plasma, lymph, etc.

1. When an antigen enters the body, it is recognized by the B-cells which get activated with the help of the helper T – cells, which secrete specific substances called lymphokines for the activation. The cell surface membrane of B-cells is capable of forming only one type of antibody.

2. Once the B-cell is activated, it is bound to the specific antigen and responds by producing 2 types of cells namely plasma cells and memory cells.

3. Plasma cells secrete large quantities of anti-bodies into the general circulation (Blood and lymph) specific for that antigen.

4. These antibodies act on the antigens and destroy them.

5. The memory cells survive for long periods and persist in the body, ready to mount a secondary response against the pathogen, if a reinfection occurs.

Question 5.
Explain the role of T-lymphocytes in cell mediated Immunity?
Answer:
The T-cells are responsible for the cell mediated immunity. In this type of immunity antibodies are not formed but the body produces large number of activated T-cells that are specially designed to destroy the foreign organisms.

• When an antigen enters the body, T-cells get activated and individually respond to the antigen by producing their clones called lymphoblasts and memory cells.
• These clones of T-cells are similar but perform different functions.
• They do not produce antibodies but develop further to produce one of the following. 3 types of T-cells, namely.

(a) T-killer cells: These destroy the antigen before it can spread an infection by secreting certain substances like cytolysin.

(b) T-helper cells: These activate B-cells (to produce antibodies) and T-Killer cells (To kill the antigens by secreting certain substances called lymphokines).

(c) T-suppressor cells: These inhibit the immune response of both T and B lymphocytes to foreign antigens, when infection is controlled.

4. The memory cells persist in the body and readily mount a secondary response against the pathogen if reinfection occurs.

Question 6.
List the harmful effects caused by alcohol drug abuse.
Answer:
Effects of alcohol on the body parts: Alcohol addiction or alcoholism: Regular consumption of alcohol leads to dependency on alcohol, which is known as alcoholism or alcohol addiction. Alcohol addiction in modem days is mainly due to many social, psychological and physical problems.

Effect of alcohol on the nervous system: Alcohol has direct effect on brain and leads to dis co-ordination of movement, dementia, and partial loss of memory (amnesia). During this period, the person is unable to remember anything. There is a loss of moral sense and indulgence in antisocial behaviour and loss of body balance.

Effect on the stomach: Alcohol stimulates excessive secretion of gastric juice which may lead to inflammation of gastric mucosa and also leads to hyperacidity and ulcer.

It also affects food intake and digestion. It may lead to loss of appetite (hunger), indigestion, vomiting and diarrhea.

Effect on the liver: Excessive consumption of alcohol affects the normal functioning of liver. It includes fibrosis. (Formation of fibrous tissue on liver) and cirrhosis (degeneration of liver tissue). It can also lead to jaundice.

Effect on the kidney: It affects the normal functioning of kidney and leads to kidney failure.

Effect on the foetus: Consumption of alcohol during pregnancy, affects the normal growth and development of foetus and leads to congenital defects such as heart diseases, abnormal limb development, etc.

In addition to all these bodily effects, it also affects the social life i.e. family in particular and society in general.

Question 7.
Describe the ill-effects of drug abuse in males and females. Also mention the preventive measures that is to be taken to reduce such effects.
Answer:
1. III – effects in males: Acne, increased aggressiveness, mood swings, depression, reduction of size of testicles, decreased sperm production, kidney and liver dysfunction, premature baldness.

2. III – effects in females: Masculinisation, increased aggressiveness, mood swings, depression, abnormal menstrual cycle, excessive hair growth on face and body and deepening of voice.

The following measures are need to be taken to prevent such problems:
(a) Education and counselling to face problems or stress, to accept failure as a part of life and to channelise child’s energy some health promoting activities.
(b) Avoid undue peer pressure and stop pressurising a child to perform beyond its capabilities.
(c) Seeking help from parents and peers by sharing the feelings of anxiety and guilt.
(d) Seeking professional counsel for medical help available in the form of highly qualified psychiatrists, psychologists etc.

Question 8.
Write the schematic representation of the life cycle of HIV.
Answer:

Question 9.
Represent schematically replication of retrovirus.
Answer:

Question 10.
Define innate immunity. Explain the barriers of innate immunity.
Answer:
Non-specific body defences are those that are present by birth in a healthy individual to protect from wide range of harmful microorganisms in the environment, but not-specific against any particular pathogen.
Then non-specific defence mechanisms are of two types.

1. Surface barriers
2. Cellular and Biochemical defences

Surface Barriers (Physical Barriers):
They form the first line of defence. It includes skin and mucus membrane.
Skin: It is the outermost body surface covering which forms a barrier, that prevents the entry of pathogens and other harmful substances into the body. Certain regions in the skin become heavily keratinized forming an impermeable physical barrier.

Keratin is a sclero protein and resistant to weak acids, bases, bacterial enzyme and toxins. Sweat (sudorific gland) secreted by skin makes the surface acidic. This inhibits the growth of bacteria. Sebum (Oily secretion of sebaceous glands) contains chemicals that are toxic to bacteria.

Mucous membrane:
They are the membranes found, lining the various entry points of the body like, eyes, respiratory paths, genital openings, anus etc. The mucus (fluids) produced by these linings trap the micro-organisms and immobilizes them. Skin and mucus membranes also produce a variety of chemicals which serve the following functions.