Selina Concise Solutions for ICSE Class 9 Biology Chapter 15 Hygiene A Key To Healthy Life

Exercise 1

Question A:
1. (d) cholera
2. (d) Sharing towels with others
3. (d) Plasmodium
4. (c) Fluorides
5. (b) Bacteria
Answer: (Answers listed above verbatim).
Maintaining good hygiene helps prevent the spread of harmful germs from one person to another. Choosing the right habits, like using clean towels and drinking pure water, keeps our bodies safe from dangerous infections.
Teacher's Tip: Remember the "ABC" of health: Always Be Clean!
Exam Tip: Read all options carefully before marking the answer to ensure you pick the most accurate one according to the textbook.

Question B.1:
Column I Column II
(a) Eggs (iii) White cylindrical
(b) Adult (i) Sucking proboscis
(c) Pupa (ii) Barrel-shaped
(d) Larva (iv) Legless
Answer:
(a) Eggs - (iii) White cylindrical
(b) Adult - (i) Sucking proboscis
(c) Pupa - (ii) Barrel-shaped
(d) Larva - (iv) Legless
Houseflies go through four distinct stages during their life cycle, from eggs to flying adults. Each stage has a unique physical structure that helps it survive and develop in its environment.
Teacher's Tip: Think of the "P" in Pupa as standing for a "Package" because it looks like a hard, sealed case.
Exam Tip: In matching questions, rewrite the correct pairs side-by-side in your answer sheet rather than drawing lines.

Question B.2:
The different ways by which the housefly contaminates our food:
1. Hairy body and legs: Hairy or spiny body and legs easily pick up dirt containing germs from unhygienic places such as rotten materials, infected wound or faecal matter. When these flies sit on our food, they rub their legs continuously dropping the particles of dirt onto the food, thereby contaminating it.
2. Pouring out saliva: When the housefly pours its saliva or regurgitates on food, foodstuffs get moistened and pathogens get deposited on them. This results in their contamination.
3. Excreta: While feeding on food items, houseflies may deposit their excreta on food, contaminating it.
4. Direct transmission of germs: In some cases, houseflies directly transmit the pathogens. In case of eye disease trachoma, pathogens are transferred from an infected person to a healthy person, when a fly settled on an infected eye of a person sits on the eyes of a healthy person.
Answer: (Steps listed above verbatim).
Flies act like tiny vehicles that transport dangerous germs from waste materials directly to the things we eat. Because they feed on both filth and fresh food, they are one of the biggest threats to kitchen hygiene.
Teacher's Tip: Visualize the fly like a "germ-carrying taxi" that drops off unwanted passengers on your meal.
Exam Tip: Use the four distinct headings like "Hairy body" and "Saliva" to organize your answer and score full marks.

Question B.3:
Two methods of controlling flies:
1. Spraying of insecticides
2. Elimination of breeding grounds
Answer: (Methods listed above verbatim).
We can stop flies by using chemicals that kill them instantly and by keeping our surroundings clean. Removing rotten trash means flies have no place to lay their eggs, which stops new flies from growing.
Teacher's Tip: No garbage equals no flies, so always keep your trash bins tightly closed.
Exam Tip: When asked for control methods, focus on the "elimination of breeding grounds" as it is the most effective long-term solution.

Question B.4:
Effective methods for controlling mosquitoes:
1. Spraying insecticides
2. Food should be protected by covering it
3. Eliminating breeding places of mosquitoes
Answer: (Methods listed above verbatim).
Controlling mosquitoes is vital because they spread serious diseases like malaria directly into our blood. The most successful strategy is to get rid of standing water where they like to lay their eggs.
Teacher's Tip: Use the "Net, Spray, and Drain" rule for a mosquito-free home environment.
Exam Tip: Be sure to specify that mosquitoes breed in "stagnant water" to show you understand their biological needs.

Question C.1:
Kind of mosquito Disease caused by it
Anopheles Malaria
Culex Filariasis
Answer: (Pairs listed above verbatim).
Different mosquito species carry different types of parasites and germs that cause specific illnesses. For example, only the female Anopheles mosquito can transmit the malaria parasite to humans.
Teacher's Tip: Match the "A" in Anopheles with the "M" in Malaria by remembering they both involve high fevers.
Exam Tip: Scientific names like Anopheles should always start with a capital letter and be written clearly.

Question C.2:
Stages of life cycle: Culex - Anopheles
Egg: Culex - Eggs have no air spaces and are laid in rafts. Anopheles - Eggs have small air spaces on their either sides, which makes them buoyant.
Larva: Culex - Larva floats obliquely with its head hanging downward. Anopheles - Larva floats parallel to the surface of water.
Adult: Culex - Adult keeps its body more or less parallel at rest. Anopheles - Adult always rests with its straight body, making an angle against the surface.
Answer: (Comparisons listed above verbatim).
Identifying these physical differences is the first step scientists take to track which mosquitoes are in a certain area. These structural traits, like how a larva hangs in the water, are very reliable markers for classification.
Teacher's Tip: Remember: Anopheles rests at an "Angle," while Culex rests "Completely" flat against the surface.
Exam Tip: When drawing comparisons, mention specific structures like "rafts" versus "buoyant air spaces" to show detailed knowledge.

Question D.1:
(i) One should breathe by nose and never by mouth because nose contains hair and mucous to trap dust and micro-organisms, so that the inhaled air becomes pure and the respiratory passage is free of dust and micro-organisms.
(ii) We handle a variety of things like books, coins, furniture, tools and machinery in workshops, seats and supporting rods in buses and even pets and other domestic animals in our day-to-day life. Many of these objects carry germs. These germs can be picked up by us, when we touch these objects and get transferred to other parts of our body or into our mouth, when we eat our food. Therefore, it is necessary to wash our hands before eating food to avoid the spread of diseases caused due to these germs.
(iii) Flies are carriers of many disease-causing germs and bacteria. Therefore, eating places must be kept free of flies to avoid possible contamination of food.
Answer: (Reasons listed above verbatim).
Breathing through the nose acts as a natural air filter to protect your lungs from pollution. Washing hands is the easiest way to remove pathogens before they have a chance to enter your digestive system.
Teacher's Tip: Think of your nose hair as a "natural air filter" and soap as your "invisible shield."
Exam Tip: In "Give Reason" questions, clearly state the benefit (e.g., pure air or germ removal) to get full points.

Question D.2:
Cockroaches and rats are common household pests.
1. Cockroaches are involved in spoiling food, paper and cloth. They may act as carriers of viruses, especially those which cause cancer.
2. Rats eat grains and other foods. They also act as carriers of certain pathogens. A parasite named rat-fleas lives on rat’s skin. It possibly carries the germs of plague.
Answer: (Details listed above verbatim).
Household pests like rats and roaches are serious health hazards that contaminate our living space and food. Keeping your home dry and sealing food containers helps prevent these animals from moving in.
Teacher's Tip: Remember the "Rat-Flea-Plague" connection to understand how animals spread disease indirectly.
Exam Tip: Explicitly mention specific diseases like "plague" to prove the danger of household pests.

Question D.3:
TYPE OF DYSENTERY - CAUSATIVE GERM - PRECAUTION
1. Bacillary dysentery - Bacterium: Shigella dysenteriae - Drinking safe (boiled) water
2. Amoebic dysentery - Protozoan: Entamoeba histolytica - Avoiding contaminated water and food
Answer: (Table data listed above verbatim).
Dysentery is a serious illness that can be caused by either tiny bacteria or microscopic protozoa. Boiling your drinking water is the best precaution because high heat kills most of these harmful organisms instantly.
Teacher's Tip: Just remember: "B" is for Bacillary and "B" is for Bacteria!
Exam Tip: Ensure you spell scientific names like "Entamoeba histolytica" correctly for maximum credit.