Learnwell science class 8 Solution
Question: Define these terms: Micro organism, Immunity, Fermentation, Pasteurization
Answer: Micro organisms are tiny living organism that cannot be seen with naked eyes. For example: Bacteria, fungi, algae, virus and protozoa
Immunity: The body of living organisms have ability to resist fight against disease. This is known as Immunity.
Fermentation: The conversion of sugar into alcohol in absence of oxygen using yeast is called Fermentation.
Pasteurization: Pasteurization is a heat-treatment process that destroys pathogenic microorganisms in certain foods and beverages.
Question: How do bacteria help in curd formation?
Answer: Lactobacillus bacteria present in curd that convert lactose present in milk to lactic acid
Question: Why does dough of bread rise when yeast is added to it?
Answer: When yeast is added to dough of bread, yeas reproduce rapidly and produce CO2 during respiration. The bubbles of CO2 fill the dough this make the bread porous and spongy.
Question: Viruses are considered as being on the border line between living and non-living organisms, Why?
Ans: Viruses is nonliving outside living cells but grows and multiplies inside living cell so, viruses are considered as being on the border line between living and non-living organisms. The study of viruses is called Virology.
Question: Write any two ways in which micro organism are useful and harmful for us?
Answer: Micro organisms are helpful in for us in following ways : Making curd, cheese from milk, bread from drought of bread and vinegar from alcohol.
Micro organisms are harmful for us in following ways: They can cause harmful diseases like polio, chicken pox etc
They can spoil our food called rancidity.
Question: Describe the role of micro organism in (i) cleaning environment (ii) sewage tratment
Answer : The role of micro organism in
(i) Cleaning environment: Bacteria and fungi breakdown dead and decaying plants and animals and help in cleaning environment.
(ii) Sewage treatment: Bacteria decompose municipal sewage into useful substance like methane gas or biogas.
Question: What are vaccines?
Answer : A small dose of dead and weekend microbes that produce immunity to diseases in the body is called vaccine.
Question: What are antibiotic?
Answer: Antibiotic are chemical prepared from bacteria and fungi Antibiotic either kill or stop the growth of disease causing microbes like penicillin.
Question: What is food poisoning?
Answer: Food poisoning is an illness caused by eating contaminated food. It's not usually serious and most people get better within a few days without treatment.
Question: Name the different methods of food preservation. Give one example of each?
Answer: The different methods of food preservation are:
Drying or dehydration: vegetable Freezing: Milk,fruit,meat etc
Pasteurization: milk Salting and adding sugar: pickles, jam,
Question: what are the advantages of food preservation?
Answer : The advantages of food preservation are:
(i) It reduces the wastage of food by avoiding its spoilage.
(ii) It help in retaining nutritive value of food.
(ii) It help to ensure avaibility of food item during off season and at distant palces.
Question: Why should you empty your water cooler during the rainy season?
Answer : We should empty our water cooler during the rainy season to prevent the breeding of mosquito in it.
Question: Why do sufficient amount of salt and oil added to pickles?
Answer: when salt and oil are added to pickles loose water that prevent their growth. This is why sufficient amount of salt and oil added to pickles to preserve it.
Question: Why are we preserving dead body in ice for long periods?
Answer: we preserving dead body in ice for long periods because freezing or lowering temperature stop growth and multiplication of micro organism.
Question: Why does sugar solution with yeast powder become alcoholic in taste?
Answer: Sugar solution with yeast powder become alcoholic in taste because yeast convert sugar solution into alcohol during anaerobic respiration.
Question: Why milk in polypacks does not get spoiled?
Answer: Milk in polypacks does not get spoiled because before storage milk is heated to about 70 degree C for 15 min then cool down quickly this sudden change in temperature kill microbes and prevents them from growth.
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