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Q1. How does sugar help in preservation of squashes?

Solution

Sugar draws the water content of the microorganisms present in squash. This inhibits the growth of microorganisms and the squash can be preserved for long period of time.

Q2. Give two examples of leguminous plants.

Solution

Peas and beans

Q3. Name the causative organism of AIDS. How does it spread from an infected person to a healthy person?

Solution

Human immunodeficiency virus (HIV) is the causative agent of AIDS. HIV can only be transmitted from an infected person to another through direct contact of bodily fluids such as blood, semen, vaginal secretions, breast milk etc.

Q4. Give examples of 

Nitrifying bacteria 

Denitrifying bacteria 

Solution

Nitrifying bacteria: Nitrosomonas

Denitrifying bacteria: Pseudomonas 

Q5. Name the following: (i) A preparation of dead or weakened microbes that is introduced into a healthy person to protect them from a particular disease in future. (ii) The medicines obtained from microorganisms that are used to kill or stop the growth of the disease-causing microorganisms. (iii) The process of conversion of sugar into alcohol by yeasts. (iv) The product obtained by decomposition of plant and animal wastes by microorganisms.

Solution

(i) Vaccine(ii) Antibiotics(iii) Fermentation(iv) Manure

Q6. Name two organisms which fix atmospheric nitrogen in soil.

Solution

Rhizobium and Azotobacter are two organisms which fix atmospheric nitrogen in soil.

Q7. Discuss any two precautions for protection against diseases transmitted by mosquitoes.

Solution

The precautions for protection against diseases transmitted by mosquitoes are:a. We need to use mosquito nets and repellents.b. We should spray insecticides and control breeding of mosquitoes by not allowing water to collect in the surroundings.

Q8. For creating a fluffy dough of maida, we add warm water and yeast to the mixture. What is the importance of the warm water in this case?

Solution

In the mixture, yeast multiplies and releases carbon dioxide, which makes the dough fluffy. In this mixture, the warm water provides adequate moisture for the yeast to grow and also raises the temperature of the mixture, which favours the rapid growth of the yeast.

Q9. How the nitrates in the soil get decomposed?

Solution

Nitrates in the soil get decomposed by denitrifying bacteria into free nitrogen which escapes into the atmosphere.

Q10. Is Rhizobium a free living bacterium? Where is it found? How does it live there?

Solution

No, Rhizobium is not a free living bacterium. It is found in the root nodules of leguminous plants such as peas and beans. It lives there in a symbiotic relationship with the leguminous plants.

Q11. Malaria is caused by protozoa. Then, why destroying mosquitoes prevents the spread of malaria?

Solution

Destroying mosquitoes can prevent the spread of malaria as female Anopheles mosquito is a vector which carries Plasmodium from a diseased person to a healthy person.

Q12. Which form of nitrogen is used by plants?

Solution

Nitrates are a form of nitrogen used by plants.

Q13. What impact do plant disease causing microbes have on agriculture? How can such microbes be controlled?

Solution

The plant diseases caused by microorganisms reduce the yield of crops, thereby causing huge agricultural losses. Such microbes can be controlled by the use of certain chemicals which kill the microbes.

Q14. Who discovered the process of fermentation?

Solution

Fermentation was discovered by Louis Pasteur in 1857.

Q15. How can one preserve a liquid in the natural state without affecting its nutritional value?

Solution

Pasteurisation helps preserve liquids in the natural state without affecting the nutritional value.

Q16. How does a vaccine help in preventing a specific disease?

Solution

Vaccines create immunity which protects us from an infection caused by a disease. This allows the body to recognise and fight the vaccine-preventable disease in the future if a person comes into contact with it.

Q17. Using mosquito nets can help prevent which diseases?

Solution

Malaria and dengue spread through mosquitoes, and hence, the use of mosquito nets can help prevent the incidence of malaria and dengue.

Q18. After eating different foodstuffs at his friends birthday party, Raju fell sick on reaching home. He began vomiting and passing loose motions along with stomach ache. What is he suffering from? How is it caused?

Solution

He is suffering from food poisoning. Food poisoning could be due to the consumption of food spoilt by some microorganisms.

Q19. What are the three ways of preserving food at home?

Solution

Three ways of preserving food at home:

Salting: For preservation of meat, fish and vegetables

Pickling: For preservation of fruits and vegetables by vinegar and oil

Freezing: For preservation of vegetables, meat and eggs

Q20. How does sugar prevent the growth of harmful bacteria?

Solution

Sugar absorbs most of the water and reduces the moisture content, thus preventing the growth of spoilage bacteria.

Q21. What is the scientific term used for disease-causing microorganisms?

Solution

Disease-causing microorganisms are called pathogens.

Q22. What is pasteurisation? Who developed this process?

Solution

Pasteurisation is a process of heating milk to a temperature of 70^oC for 15 to 30 seconds and then quickly cooling it down to 10^oC. This kills any microorganisms present in the milk. Louis Pasteur developed the process of pasteurisation.

Q23. Microorganisms cause diseases in both animals and plants, yet they are considered friends. Why? Give two examples of microorganisms and how they act as friends.

Solution

Microorganisms are considered friends because they help us in daily life activities such as

Preparation of curd, bread and cakes

Commercial production of alcohol, wine and vinegar

Preparation of medicines

Used in agriculture to increase soil fertility

In cleaning up of the environment

Examples of microorganisms:

Lactobacillus helps promote curdling of milk (turning milk into curd).

Rhizobium bacteria help in nitrogen fixation.

Q24. Name the carrier organisms for malaria and dengue viruses.

Solution

Carrier for Malaria - Female Anopheles mosquito Dengue - Female Aedes mosquito

Q25. Why do we need to preserve food?

Solution

Food preservation slows down the activity of disease-causing bacteria or kills bacteria in food altogether. Preserving food keeps it from spoiling too quickly and allows it to last for weeks or even months.

Q26. (i) What are the two ways in which atmospheric nitrogen gets fixed into usable forms?(ii) How do herbivores obtain nitrogen for their body?

Solution

(i) (a) A few nitrogen fixing bacteria like Rhizobium and certain blue green algae can fix atmospheric nitrogen into usable forms like nitrates and nitrites.(b) Sometimes nitrogen gets fixed due to the high temperatures and pressures during lightning, thereby creating usable forms of nitrogen.(ii) Herbivores feed on plant parts and obtain the plant proteins and other nitrogen compounds from them which they use for building nitrogen compounds in their own bodies.

Q27. (i) What is meant by 'food poisoning'? What is its cause?(ii) Write the symptoms of food poisoning.(iii) Name two examples of bacteria which cause food poisoning.

Solution

(i) The disease caused due to the presence of a large number of micro-organisms (like bacteria and fungi) in the food, or due to the presence of toxic substances in food, formed by the action of micro-organisms, is called food poisoning. Food poisoning occurs due to the consumption of food spoilt by some micro-organisms. (ii) The major symptoms of food poisoning are: Vomiting, Diarrhoea (Loose motions), Pain in abdomen, headache and fever. (iii) The two most common examples of bacteria which cause food poisoning are bacteria Salmonella and bacteria Clostridium botulinum.

Q28. Who discovered penicillin mould?

Solution

Alexander Fleming discovered penicillin in 1929, while working on a culture of disease-causing bacteria.

Q29. Why are we advised to keep a safe distance from a person suffering from measles?

Solution

Measles is transmitted through air. If we remain in close proximity to a person suffering from measles then we have a high chance of getting the disease ourselves. Hence, we are advised to keep a safe distance from the person suffering from measles.

Q30. Fungi are useful in the fields of food and medicine. How?

Solution

The fungus, yeast is used in baking industry for producing bread and cakes as well as in the commercial preparation of alcohol and wine. Several fungi are used to prepare antibiotics, which can cure many infections. Thus fungi are useful in the fields of food and medicine.

Q31. How do herbivores obtain nitrogen for their body?

Solution

Herbivores feed on plant parts and obtain the plant proteins and other nitrogen compounds from them which they use for building nitrogen compounds in their own bodies.

Q32. How is atmospheric nitrogen utilized by plants?

Solution

First atmospheric nitrogen is fixed either by lightning or by living organisms like certain bacteria and blue green algae. As a result, nitrogen is converted into usable compounds of nitrogen. These can be utilised by plants from the soil through their root system for producing plant proteins and other compounds.

Q33. We have seen posters advising us to keep air coolers dry when not in use. Why?

Solution

The water in coolers if kept stagnant without use can serve as breeding grounds for mosquitoes. Preventing their breeding can protect us from diseases like malaria and dengue, which are spread by mosquitoes. Hence, we are advised to keep coolers dry when not in use.

Q34. Write any three advantages of food preservation.

Solution

Advantages of food preservation:

It decreases the food wastage.

It increases the storage period of perishable food materials.

It ensures the all year availability of seasonal food materials.

Q35. What is the vegetable Okra commonly called in India?

Solution

Okra is commonly known as bhindi in India.

Q36. How is a pathogen different from a carrier?

Solution

A pathogen actually causes the disease in another organism whereas a carrier only transmits the pathogen to another organism. A carrier does not cause the disease.

Q37. Study the following table and identify the terms numbered from 1 to 6.   Human Disease Causal Organism Mode of Transmission Measles 1 Air Typhoid Bacteria 5 Malaria 2 Mosquito Polio Virus 6 Tuberculosis 3 Air/Contact with infected person Hepatitis A 4 Water    

Solution

  Human Disease Causal Organism Mode of Transmission Measles Virus Air Typhoid Bacteria Water Malaria Protozoa Mosquito Polio Virus Air/Water Tuberculosis Bacteria Air/Contact with infected person Hepatitis A Virus Water    

Q38. Name the bacteria that promotes the formation of curd and cheese.

Solution

The bacterium, Lactobacillus promotes the formation of curd from milk and the bacterium, Renin is used in cheese production.

Q39. A child is given a shot of chicken pox vaccine. How does this vaccine help in the prevention of chicken pox?

Solution

When the child is given chicken pox vaccine, the dead or weakened microbes of chicken pox are introduced into the child's healthy body. The body fights and kills the microbes in vaccine by producing suitable antibodies. The antibodies against chicken pox remain in the body and recognizes the pathogen when it enters the body another time. Thus, the child is protected from all future attacks of the chicken pox microbe.

Q40. Name any two common preservatives.

Solution

Sodium benzoate and sodium metabisulphite are the two common preservatives.