Chapter 2: Science - Class 8
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A. Fill in the blanks.
1. The study of microorganisms is known as microbiology.
2. The bread dough rises because of the production of carbon dioxide.
3. Pathogens are the microorganisms that cause diseases.
4. Sodium benzoate and potassium metabisulphite are two chemical preservatives.
5. Aspergillus is a fungus that causes food poisoning.
B. Match the Following
| Column A | Column B |
|---|---|
| Ringworm | fungus |
| Clostridium | food poisioning |
| Anthrax | cattle |
| Lactobacillus | curd |
| Methane | biogas reactor |
C. Tick (✓) the correct option
1. The process, that helps milk to last longer but does not kill all microbes present in it, is known as-
- chloroplast
- chromoplast
- mitochondria
- vacuole
2. Rust of wheat is caused by-
- a cell organelle
- a tissue
- a single cell
- an organ
3. Medicines, containing killed or weakened pathogens, and used to prevent infectious diseases, are called-
- cytoplasm
- cell membrane
- nuclear membrane
- protoplasm
4. Which of the following reproduces only inside a host cell?
- ribosomes
- cell membrane
- mitochondria
- cell wall
5. A disease, caused by a virus, and spread by an insect, is-
- tissue → cell → organ → organ system
- organ → tissue → organ system → cell
- cell → organ → tissue → organ system
- cell → tissue → organ → organ system
D. Answer the following questions in brief
1. Why are viruses considered as being at the 'borderline' between living and non-living things?
ANSWER: Viruses are non-living outside a host cell but become active and behave like living things when inside a host cell. Hence, they are considered borderline between living and non-living.
2. What is fermentation? How is this process useful in the food and beverage industries?
ANSWER: Fermentation is a process where sugars are turned into alcohol or acids and carbon dioxide by microorganisms without oxygen. It's used in making dosa, bread, cakes, and wine.
3. 'In the absence of microorganisms the earth would become a heap of dead plants and animals'. Justify this statement.
ANSWER: Microorganisms break down dead plants and animals, recycling their materials into the environment. Without them, dead remains would pile up around us.
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.
(ii) How do you think growing peas will help in replenishing the soil?
ANSWER:
(i) Nitrogen.
(ii) Peas host Rhizobium bacteria, which fix nitrogen in the soil, helping replenish it.
5. Why does it take less time to prepare curd in summers as compared to preparing it in winters?
ANSWER: Microorganisms, like lactobacillus, reproduce faster in warmer temperatures. In summers, they multiply quickly, making curd faster.
6. How are the following diseases transmitted: (a) Malaria (b) Common cold (c) Tetanus (d) Typhoid
ANSWER:
(a) Malaria: By female Anopheles mosquito.
(b) Common cold: Through cough droplets in the air.
(c) Tetanus: Through cuts by rusted iron.
(d) Typhoid: Through contaminated food and water.
7. What are antibiotics? How are they produced? Give two examples of these.
ANSWER: Antibiotics are chemicals that stop harmful microorganisms from growing. They are made from microorganisms. Examples: Penicillin and Streptomycin.
E. Answer the following questions
1. 'Microorganisms are very useful in manufacturing different food items'. Explain the above statement.
ANSWER: Microorganisms play a crucial role in the food industry. They help in the fermentation process, which is essential for making foods like dosa, bread, and cake. Yeast is used to help the dough rise, making it soft and fluffy. Microorganisms also help in producing alcoholic beverages, wine, and acetic acid used in vinegar. Their ability to break down sugars and other substances contributes to the flavor, texture, and preservation of many food items.
2. Give reasons for the following.
(a) Yeast is added to the batter used to make 'dosas'.
(b) It is important to brush one's teeth before going to bed.
(c) Reducing the quantity of salt in pickle can cause it to go bad soon.
(d) Foods, from puffed or enlarged cans, should not be consumed.
(e) When using frozen food items, one should take out only the required quantities; thawed food should never be refrozen.
ANSWER:
(a) Yeast is added to dosa batter for fermentation. It produces gases that make the batter rise and become fluffy, giving the dosa its light texture.
(b) Brushing before bed removes food particles stuck between teeth. If not removed, bacteria can grow and produce acids, which damage tooth enamel and cause cavities.
(c) Salt helps preserve pickles by drawing out moisture and preventing the growth of harmful microorganisms. Reducing salt allows more bacteria to grow, leading to spoilage.
(d) A puffed can indicates bacterial growth inside, which could lead to the production of harmful toxins. Eating such food can cause food poisoning.
(e) Thawing and refreezing food can cause bacterial growth and spoilage. Additionally, nutrients in the food can be destroyed during this process.
3. How do communicable diseases spread? Suggest ways to prevent the following diseases: (a) Tuberculosis (b) Athlete's foot (c) Cholera
ANSWER:
(a) Tuberculosis: Tuberculosis (TB) spreads through the air when an infected person coughs or sneezes. Prevention includes vaccination and avoiding close contact with infected people.
(b) Athlete's foot: This fungal infection spreads through contact with infected surfaces like floors in gyms or swimming pools. Prevent it by maintaining good foot hygiene and wearing footwear in public places.
(c) Cholera: Cholera spreads through contaminated water or food. Prevent it by ensuring proper sanitation, using clean water, and washing hands regularly.
4. What are pathogens? Name two pathogens each that cause diseases in (i) plants and (ii) animals.
ANSWER: Pathogens are microorganisms that cause diseases.
In plants: Bacteria (e.g., Xanthomonas) and fungi (e.g., Puccinia).
In animals: Bacteria (e.g., Salmonella) and viruses (e.g., Rabies virus).
5. Mohan bought samosas from a road-side vendor and ate it. After sometime he felt nausea and started vomitting. He had severe pain in the abdominal region and suffered from diarrhoea. What could be the reason for his condition? What is it called? How could it be prevented?
ANSWER: Mohan most likely suffered from food poisoning caused by eating contaminated food. This can happen when food is not stored or prepared properly. Food poisoning can be prevented by ensuring food is cooked properly, stored at the correct temperature, and prepared in clean environments.
6. Which diseases the following children are most likely to suffer from?
(a) Ramu drinks water from a nearby lake. This water is neither boiled nor disinfected.
(b) Ashu does not take a bath every day. He maintains poor personal hygiene.
(c) Pulkit has been bitten by an infected street dog.
(d) Sohan is living in an area where the population is very high. He does not use a mosquito net (while sleeping), or insect-repellent creams (while playing in the open).
(e) Mohan was with two of his friends who were coughing and sneezing (they were suffering from common cold). One of these friends did not keep a handkerchief in front of his mouth while coughing and sneezing.
ANSWER:
(a) Cholera, as it spreads through contaminated water.
(b) Ringworm, a fungal infection spread by contact with infected skin.
(c) Rabies, which spreads through bites from infected animals.
(d) Malaria, transmitted by mosquitoes.
(e) Common cold, which spreads through droplets from coughing and sneezing.