A. Fill in the blanks
- The study of microorganisms is known as microbiology.
- The bread dough rises because of the production of carbon dioxide.
- Pathogens are the microorganisms that cause diseases.
- Sodium benzoate and sodium metabisulphite are two chemical preservatives.
- Aspergillus is a fungus that causes food poisoning.
B. Match the following
| Column I | Column II |
|---|---|
| 1. Ringworm | (c) fungus |
| 2. Clostridium | (a) food poisoning |
| 3. Anthrax | (d) cattle |
| 4. Lactobacillus | (e) curd |
| 5. Methane | (b) biogas reactor |
C. Tick (✓) the correct option
- The process that helps milk to last longer but does not kill all microbes present in it, is known as—
✅ pasteurisation - Rust of wheat is caused by—
✅ fungus - Medicines containing killed or weakened pathogens and used to prevent infectious diseases are called—
✅ vaccines - Which of the following reproduces only inside a host cell?
✅ virus - A disease caused by a virus and spread by an insect is—
✅ dengue
D. Answer the following questions in brief
1. Why are viruses considered as being at the ‘borderline’ between living and non-living things?
Viruses are considered to be at the borderline between living and non-living things because they show characteristics of both.
Living characteristics:
- They reproduce inside the cells of a living host.
- They show heredity and mutation.
Non-living characteristics:
- Outside the host body, they remain inactive like non-living particles.
- They cannot grow, respire or reproduce on their own.
Thus, viruses behave like living organisms only when they enter a living cell. This unique nature makes them different from all other microorganisms.
2. What is fermentation? How is this process useful in the food and beverage industries?
Fermentation is the process in which microorganisms like yeast convert sugars into alcohol, carbon dioxide and other useful substances.
Uses in food and beverage industries:
- It is used in making bread and cakes. Carbon dioxide released during fermentation makes the dough soft and fluffy.
- It is used in preparing curd, cheese and vinegar.
- It is also used in the production of alcoholic beverages like wine and beer.
Fermentation has helped humans prepare nutritious and tasty foods for centuries. It is an excellent example of the beneficial use of microorganisms in daily life.
3. “In the absence of microorganisms the earth would become a heap of dead plants and animals.” Justify this statement.
Microorganisms act as decomposers in nature. They break down dead plants, animals and organic wastes into simpler substances.
If microorganisms were absent:
- dead bodies and wastes would keep accumulating everywhere,
- nutrients would not return to the soil,
- and the natural recycling process would stop.
As a result, the earth would become filled with heaps of dead matter. Therefore, microorganisms are essential for maintaining cleanliness and balance in nature.
This shows that even tiny organisms play a huge role in sustaining life on Earth.
4. Munna observes that the yield of wheat growing in his field has reduced in the current year. He gets the soil tested and the report confirms the deficiency of one particular nutrient. Accordingly, he is advised to grow peas after harvesting wheat.
(i) Name the nutrient found insufficient.
The nutrient found insufficient is nitrogen.
(ii) How do growing peas help in replenishing the soil?
Pea plants are leguminous plants. Their roots contain Rhizobium bacteria in root nodules.
These bacteria:
- convert atmospheric nitrogen into usable nitrogen compounds,
- enrich the soil naturally,
- and improve soil fertility.
Thus, growing peas helps farmers restore nitrogen in the soil without excessive use of chemical fertilizers. This method is eco-friendly and supports sustainable farming.
5. Why does it take less time to prepare curd in summers as compared to preparing it in winters?
Curd is formed by the action of Lactobacillus bacteria on milk.
During summers:
- the temperature is warm and suitable for bacterial growth,
- so bacteria multiply rapidly,
- and milk changes into curd quickly.
In winters:
- low temperature slows down bacterial activity,
- therefore curd takes more time to set.
This is why curd preparation is faster in summer than in winter.
6. How are the following diseases transmitted?
| Disease | Mode of Transmission |
|---|---|
| (a) Malaria | By the bite of infected female Anopheles mosquito |
| (b) Common cold | Through air droplets from coughing and sneezing |
| (c) Tetanus | Through cuts or wounds infected by bacteria present in soil or rusty objects |
| (d) Typhoid | Through contaminated food and water |
Proper hygiene, clean surroundings and vaccination help in preventing many of these diseases.
7. What are antibiotics? How are they produced? Give two examples of these.
Antibiotics are medicines that kill or stop the growth of disease-causing microorganisms.
They are produced by certain microorganisms such as bacteria and fungi in laboratories and industries.
Examples:
- Penicillin
- Streptomycin
Antibiotics have saved millions of human lives by helping doctors treat dangerous bacterial infections. However, they should be used only on medical advice because unnecessary use can reduce their effectiveness.
E. Answer the following questions
1. “Microorganisms are very useful in manufacturing different food items”. Explain the above statement.
Microorganisms play an important role in the preparation of many food items that we use in our daily life. Certain bacteria and fungi help in improving the taste, texture and quality of food through processes like fermentation.
Uses of microorganisms in food preparation
(a) Preparation of curd
The bacterium Lactobacillus converts milk into curd. It multiplies rapidly in warm conditions and changes milk sugar into lactic acid, giving curd its sour taste.
(b) Bread and cakes
Yeast is used in baking bread and cakes. It produces carbon dioxide gas during fermentation, which makes the dough rise and become soft and fluffy.
(c) Cheese and paneer
Different microorganisms are used in preparing cheese and improving its flavour and texture.
(d) Idli, dosa and dhokla
Fermentation by microorganisms makes the batter soft, light and easy to digest.
(e) Beverages
Yeast is used in preparing beverages like wine and beer.
Thus, microorganisms are extremely beneficial for humans and contribute greatly to the food industry.
2. Give reasons for the following.
(a) Yeast is added to the batter used to make ‘dosas’.
Yeast helps in the fermentation of the batter. During fermentation, carbon dioxide is produced, which makes the batter soft, spongy and fluffy. This improves the taste and texture of dosas.
(b) It is important to brush one’s teeth before going to bed.
Food particles remain trapped between the teeth after eating. Bacteria present in the mouth act on these food particles and produce acids. These acids can damage teeth and cause tooth decay.
Brushing before sleeping removes food particles and reduces bacterial growth, helping to keep the teeth healthy.
(c) Reducing the quantity of salt in pickle can cause it to go bad soon.
Salt acts as a preservative. It prevents the growth of microorganisms that spoil food.
If the amount of salt is reduced:
- microorganisms can grow easily,
- the pickle gets spoiled quickly,
- and its shelf life decreases.
Therefore, sufficient salt is necessary for preserving pickles.
(d) Foods from puffed or enlarged cans should not be consumed.
Puffed cans indicate the growth of harmful microorganisms inside the food. These microbes may release poisonous gases and toxins that can cause food poisoning.
Eating such food can seriously affect health. Therefore, food from swollen cans should always be avoided.
(e) When using frozen food items one should take out only the required quantities; thawed food should never be refrozen.
When frozen food is thawed:
- microorganisms become active and begin multiplying.
If the food is refrozen:
- microbes may continue surviving,
- food quality decreases,
- and chances of food poisoning increase.
Hence, only the required quantity should be taken out, and thawed food should not be refrozen.
3. How do communicable diseases spread? Suggest ways to prevent the following diseases:
Communicable diseases spread through:
- air,
- water,
- contaminated food,
- direct contact,
- insects and other carriers.
Maintaining cleanliness, proper hygiene and vaccination helps in preventing many diseases.
(a) Tuberculosis
Spread:
Through air droplets from coughing or sneezing of an infected person.
Prevention:
- Cover mouth while coughing or sneezing.
- Avoid close contact with infected persons.
- Take proper vaccination (BCG vaccine).
(b) Athlete’s Foot
Spread:
Through direct contact and use of infected towels, socks or floors.
Prevention:
- Keep feet clean and dry.
- Avoid sharing towels and shoes.
- Maintain personal hygiene.
(c) Cholera
Spread:
Through contaminated food and water.
Prevention:
- Drink clean and boiled water.
- Eat hygienic food.
- Maintain proper sanitation and cleanliness.
4. What are pathogens? Name two pathogens each that cause diseases in (i) plants and (ii) animals.
Pathogens are disease-causing microorganisms.
(i) Pathogens causing diseases in plants
- Fungus causing rust of wheat
- Bacteria causing citrus canker
(ii) Pathogens causing diseases in animals
- Bacteria causing anthrax
- Virus causing foot-and-mouth disease
Pathogens can spread rapidly and harm plants, animals and humans if proper care is not taken.
5. Mohan bought samosas from a road-side vendor and ate it. After sometime he felt nauseated and started vomiting. He had severe pain in the abdominal region and suffered from diarrhoea. What could be the reason for the condition? What is called? How could it be prevented?
The samosas eaten by Mohan were probably contaminated by harmful microorganisms. These microbes may have produced toxins in the food.
As a result, Mohan suffered from:
- nausea,
- vomiting,
- stomach pain,
- and diarrhoea.
This condition is called food poisoning.
Prevention of food poisoning
- Eat fresh and hygienic food.
- Avoid uncovered roadside food.
- Wash hands before eating.
- Store food properly.
- Avoid stale or contaminated food.
This shows the importance of cleanliness and safe eating habits in daily life.
6. Which diseases are the following children most likely to suffer from?
| Situation | Disease |
|---|---|
| (a) Ramu drinks untreated lake water. | Cholera / Typhoid |
| (b) Ashu does not maintain personal hygiene. | Athlete’s foot / Skin infection |
| (c) Pulkit was bitten by an infected street dog. | Rabies |
| (d) Sohan does not use mosquito net or repellent creams. | Malaria / Dengue |
| (e) Mohan stays close to friends suffering from common cold. | Common cold |
These examples teach us that cleanliness, hygiene and awareness are very important for protecting ourselves from diseases.
Also Read: Chapter 1 Cell and Its Structure solutions
Class 8th Social ScienceSolutions