Modes of Disease Transmission - Questions & Answers

1. Fill in the blanks.

(i) Cleanliness, rest and sleep, and physical exercise are a part of personal hygiene.

(ii) One must always breathe by the nose and never by the mouth.

(iii) Fresh air brings oxygen into the living rooms.

(iv) One must never put a sharp pointed object into the ear, it may rupture the eardrum.

(v) For adults 6-7 hours of continuous undisturbed sleep is sufficient.

(vi) The municipal bodies must ensure the supply of clean germ-free drinking water and an efficient sewage disposal.

2. List any three advantages of a daily bath.

Answer: A daily bath keeps the skin clean and free of germs, opens the sweat pores, and removes the body odour given out by perspiration.

1. Tick-mark the correctly matched pairs of certain animals and their related diseases/habits.
(i) Culex — yellow fever
(ii) Aedes — filariasis
(iii) Anopheles — malaria
(iv) Gambusia — eat up mosquito larvae
(v) Rat flea — diarrhoea
(vi) Cockroaches — breed in man-holes

Answer: The correctly matched pairs are:
(iii) Anopheles — malaria
(iv) Gambusia — eat up mosquito larvae
(vi) Cockroaches — breed in man-holes

Mention if the following statements are True (T) or False (F)

(i) Contamination means entry of germs by insect bite T/F
Answer: False (F)

(ii) Sewage is the commonest source of contamination of water in the cities T/F
Answer: True (T)

(iii) Cholera is marked by acute diarrhoea and no urination T/F
Answer: True (T)

(iv) Typhoid is caused by a type of worm T/F
Answer: False (F)

(v) Mosquitoes are the source of dysentery germs T/F
Answer: False (F)

1. Choose the correct answer from the options given below :

(i) No urination due to shortage of water in the body is a typical symptom of :
(a) typhoid     (b) malaria
(c) dysentery     (d) cholera
Answer: (d) cholera

(ii) Which one of the following is an unhealthy habit?
(a) Removing wax from inside the ears
(b) Keeping the mouth closed while breathing
(c) Sleeping for only 6-7 hours
(d) Sharing towels with others
Answer: (d) Sharing towels with others

(iii) The protozoan that causes malaria is :
(a) Entamoeba histolytica
(b) Euglena
(c) Paramecium
(d) Plasmodium
Answer: (d) Plasmodium

(iv) The chemical substance mainly responsible for tooth disorders is :
(a) calcium     (b) chloride
(c) flourides     (d) iodides
Answer: (c) flourides

(v) Typhoid is caused by
(a) housefly     (b) bacteria
(c) virus     (d) None of the above
Answer: (b) bacteria

(vi) The germ causing Hepatitis is transmitted through :
(a) the bite of a mosquito
(b) contamination of food by a housefly
(c) personal contact with a patient
(d) contaminated water
Answer: (d) contaminated water

(vii) Which of the following is an agent that acts as an intermediate carrier of a pathogen ?
(a) Germs     (b) Water
(c) Vector     (d) None of these
Answer: (c) Vector

(viii) Which of the following is an insecticide ?
(a) DPT     (b) DCT
(c) DDT     (d) DPD
Answer: (c) DDT

(ix) Plasmodium is a :
(a) Virus     (b) Protozoan
(c) Bacterium     (d) Fungus
Answer: (b) Protozoan

(x) The fishes which selectively devour mosquito larvae are :
(a) Carps     (b) Sharks
(c) Dogfish     (d) Gambusia
Answer: (d) Gambusia

(xi) Identify the water-borne diseases based on their symptoms given below :
Water-borne disease P: Yellowish eyes, dark yellow urine (due to bile pigments).
Water-borne disease Q: Severe diarrhoea and vomiting followed by dehydration.
(a) P - Trachoma, Q - Hepatitis
(b) P - Trachoma, Q - Cholera
(c) P - Conjunctivitis, Q - Dysentery
(d) P - Hepatitis, Q - Cholera
Answer: (d) P - Hepatitis, Q - Cholera

1. Fill in the blanks :

(a) Taking stimulants and sedatives are unhealthy habits.

(b) Physical exercise should be systematic and regular.

(c) Public drains and garbage must be covered with bleaching powder or lime.

(d) The housefly is often designated as public enemy no. 1.

(e) Rat-flea is a parasite which lives on rat's skin.

2. Name the following :

(a) The bacterium which causes cholera.
Answer: Vibrio cholerae

(b) The liquid domestic wastes from the kitchen, toilet, etc.
Answer: Sewage

(c) The chemical substances used to kill rats.
Answer: Raticides (rat poisons)

(d) The disease caused due to the inflammation of liver.
Answer: Hepatitis

(e) The disease caused due to the bacilli bacteria released in tannery wastes from leather industries.
Answer: Anthrax

3. Complete the blanks in the table given below :

1. Define :

(a) Health
Answer: Health is the state/condition of the body of a person who depicts/portrays physical, mental, social and emotional fitness.

(b) Hygiene
Answer: Hygiene is defined as the science and practice of maintaining good health.

(c) Pathogen/germ
Answer: A pathogen or germ is a disease-causing organism that enters the body and causes illnesses.

(d) Vector
Answer: Vector is any agent that acts as an intermediate carrier of a pathogen.

(e) Contamination
Answer: Contamination means unwanted entry of disease-causing germs into drinking water or edible foods.

2. Give suitable explanations for the following : (LS)

(a) One should breathe by nose and never by mouth.
Answer: One should breathe by the nose to filter out dust and prevent direct entry of germs, maintaining respiratory health.

(b) Hands must be washed before eating food.
Answer: Hands constantly handle objects that carry germs. Washing hands with soap ensures that these germs are not picked up by our fingers and transferred into the mouth through food.

(c) Eating places must be kept free of flies.
Answer: Flies act as vectors by picking up filth and depositing their saliva, vomit, or excreta on food, which spreads diseases like cholera, typhoid, and dysentery.

3. How are cockroaches and rats harmful to humans ?
Answer: Cockroaches breed in manholes, eat and spoil food and clothes, and are suspected carriers of viral diseases, including cancer-causing viruses. Rats eat grains and foods and carry the rat-flea, a parasite which can carry and spread plague germs.

4. Name the two types of dysentery and their causative germs and give one main precaution against them.
Answer: The two types are Bacillary dysentery (caused by the bacterium Shigella) and Amoebic dysentery (caused by the protozoan Entamoeba histolytica). One main precaution is drinking safe (boiled) water and keeping food covered and free from flies.

5. Mention three symptoms of the disease Hepatitis.
Answer: Three symptoms are body ache, yellowish eyes, and deep yellow urine (due to bile pigments).

6. Suggest any two methods of controlling flies.
Answer: 1. Elimination of breeding places by covering refuse and removing all animal and human excreta at frequent intervals. 2. Spraying houses and breeding places with DDT and other insecticides.

7. List any three effective methods for controlling mosquitoes.
Answer: 1. Spraying dwelling places with DDT and other insecticides to kill adult mosquitoes. 2. Spraying stagnant water with kerosene or oily substances to kill larvae and pupae. 3. Biological control by introducing Gambusia fish in ponds to selectively devour mosquito larvae.

8. Mention any three ways by which potable water can be contaminated.
Answer: 1. Improperly disposed sewage leaking into sub-soil and groundwater. 2. Defecating or urinating near lakes, rivers, or ponds. 3. Draining animal wastes and washings from dairies/poultries into water bodies.

1. Describe the different ways by which the housefly contaminates our food.
Answer: The housefly contaminates our food by:
1. Hairy body and legs pick up filth: They easily pick up filth containing germs from dirty places and contaminate food by sitting on it.
2. Pouring out saliva: They moisten the foodstuffs by pouring out their saliva on it or vomiting (regurgitating) food swallowed from dirty places.
3. Excreta: They deposit their excreta while they feed, directly contaminating human food.
4. Direct transmission: Sometimes germs are conveyed directly when a fly sits on an infected person and then on a healthy person's body parts (like eyes).

2. What are the four major aspects of personal hygiene?
Answer: The four major aspects of personal hygiene are:
1. Cleanliness: Regular cleaning of hands, skin, hair, teeth, nose, eyes, and ears.
2. Physical exercise: Regular and systematic exercise to improve blood circulation.
3. Rest and sleep: Allowing adequate rest for all body organs by getting 6-7 hours of continuous undisturbed sleep.
4. Healthy habits: Maintaining regular timings for eating and sleeping, clearing bowels every morning, and avoiding unhealthy habits like using tobacco, alcohol, stimulants, or sedatives.

1. The figure given below represents an organism. Study the same and answer the following questions :

(a) Identify the organism and write its scientific name.
Answer: The organism is Entamoeba histolytica.

(b) Is it a causative agent of any disease? If yes, name the disease.
Answer: Yes, it is the causative agent of Amoebic dysentery.

(c) Label the guidelines 1, 2 and 3.
Answer: 1 - Pseudopodium, 2 - Nucleus, 3 - Blood cell.

(d) Is it a unicellular or a multicellular organism ? Mention the specific category of organisms to which it belongs.
Answer: It is a unicellular organism. It belongs to the specific category of protozoans.

(e) Write one important function of the part numbered 1.
Answer: The pseudopodium is used for moving and for engulfing red blood cells from the patient's intestine for feeding.

2. Mosquitoes have become a nuisance in the lives of people. Several steps are recommended to destroy mosquitoes in different stages. One of the step is 'Biilogical control' in which a kind of fish is introduced in the ponds, as shown below in the figure.

(a) What are the four stages in the life cycle of a mosquito ?
Answer: The four stages are egg, larva, pupa, and adult.

(b) Name the fish which selectively devours mosquito larvae.
Answer: Gambusia.

(c) Give an example of insecticide (full form) which can be sprayed in ponds and marshy places to kill the larval stages of mosquitoes.
Answer: Dichloro-diphenyl-trichloroethane (DDT).

(Choose the answer based on the codes given below.)
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

(i) Assertion (A) : Malaria is caused by Plasmodium which is spread by Culex mosquito.
Reason (R) : There are two hosts in the life cycle of a malarial parasite which are Anopheles mosquito and humans/monkeys/birds, etc.
Answer: (d) A is false but R is true.

(ii) Assertion (A) : Gambusia is a kind of fish which should be introduced in ponds as a biological control measure for mosquitoes.
Reason: (R) : Gambusia fishes selectively devour mosquito larvae from the ponds. Hence used to control the growth of mosquitoes.
Answer: (a) Both A and R are true and R is the correct explanation of A.

(iii) Assertion (A) : Bacillary dysentery is caused due to infection by a protozoan which occurs frequently in children.
Reason: (R) : Shigella is a kind of bacillus bacteria which causes bacillary dysentery.
Answer: (d) A is false but R is true.

(iv) Assertion (A) : Hygiene is defined as the science and practice of maintaining good health.
Reason: (R) : Hygiene can be maintained by taking vaccines and antibiotics regularly to keep a person away from diseases.
Answer: (c) A is true but R is false.

1. During the monsoon, Jennifer noticed that mosquitoes were everywhere, especially near the puddles outside her house. A few days later, her cousin fell sick with a high fever, and the doctor explained that it was caused by a mosquito bite. Jennifer learned that different types of mosquitoes can cause illnesses such as dengue and malaria which are often characterised by high fever. (LS)

(a) Name three types of mosquitoes along with the specific disease they cause.
Answer: 1. Anopheles mosquito causes malaria. 2. Culex mosquito causes elephantiasis (filariasis). 3. Aedes mosquito causes yellow fever and dengue.

(b) Write the pathogens which cause malaria and dengue fever.
Answer: Malaria is caused by a protozoan called Plasmodium. Dengue fever is caused by viruses.

(c) Do these mosquitoes suffer from the same disease which they spread from an infected person to the healthy person ? Explain.
Answer: No, the mosquitoes do not suffer from the disease. They simply act as vectors (intermediate carriers) for the pathogens. The germs grow and multiply within the mosquito's body, and are safely introduced into a healthy person's bloodstream through the mosquito's saliva.

(d) How can mosquito breeding be controlled in ponds and other stagnant bodies ?
Answer: Mosquito breeding can be controlled by completely filling up small ponds and puddles, pouring kerosene or other greasy oils on stagnant water to suffocate and kill larvae and pupae, and introducing biological control fishes like Gambusia to devour the mosquito larvae.