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Subject:Mathematics Science English Social Studies Hindi Physics Chemistry Biology Computer Science

For setting curd, a small amount of curd is added to warm milk. The microbes present in the curd help in setting if the temperature of the mixture remains approximately between 35°C to 40°C. At places, where room temperature remains much below the range, the setting of curd becomes difficult. Suggest a way to set curd in such a situation.

Soln: In order to maintain the desired temperature container with curd should be wrapped with woollen or any other insulator. Curd can also be set in a room with temperature below optimum by keeping the container near the gas stove.

ScienceClass 7CBSE

In a mercury thermometer, the level of mercury rises when its bulb comes in contact with a hot object. What is the reason for this rise in the level of mercury?

Soln: Mercury gets expanded on heating; hence its level rises in the capillary when it comes in contact with a hot object.

ScienceClass 7CBSE

To keep her soup warm Paheli wrapped the container in which it was kept with a woollen cloth. Can she apply the same method to keep a glass of cold drink cool? Give a reason for your answer

Soln: Yes, the woolen cloth can be used to keep a glass of cold drink cool because woollen is an insulator that will not allow escape or entry of heat.

ScienceClass 7CBSE

Shopkeepers selling ice blocks usually cover them with jute sacks. Explain why.

Soln: Shopkeepers selling ice blocks usually cover them with jute sacks because materials like jute sacks sawdust and newspapers act as insulators and cannot allow escape or entry of heat through them.

ScienceClass 7CBSE

Paheli and Boojho measured their body temperature. Paheli found her’s to be 98.6 °F, and Boojho recorded 37°C. Which of the following statement is true? (a) Paheli has a higher body temperature than Boojho. (b) Paheli has a lower body temperature than Boojho. (c) Both have a normal body temperature. (d) Both are suffering from fever.

Soln: The answer is (c) Both have normal body temperature. Explanation: Degree Celsius and Fahrenheit are two scales of temperature measurement. Normal body temperature is 37º which is equal to 98.6 F. Hence both of them have normal body temperature.

ScienceClass 7CBSE

A beggar wrapped himself with a few layers of newspaper on a cold winter night. This helped him to keep himself warm because (a) friction between the layers of newspaper produces heat. (b) air trapped between the layers of newspaper is a bad conductor of heat. (c) newspaper is a conductor of heat. (d) newspaper is at a higher temperature than the temperature of the surrounding.

Soln: The answer is (b) air trapped between the layers of newspaper is a bad conductor of heat. Explanation: The heat from his body will not escape into the surroundings, and this will help him to keep his body warm.

ScienceClass 7CBSE

A marble tile would feel cold as compared to a wooden tile on a winter morning because the marble tile (a) is a better conductor of heat than the wooden tile. (b) is polished, while the wooden tile is not polished. (c) reflects more heat than the wooden tile. (d) is a poor conductor of heat than the wooden tile.

Soln: The answer is (a) is a better conductor of heat than the wooden tile.

ScienceClass 7CBSE

“Forests are our lifeline.” Write five sentences on this topic.

Soln: Forests are our lifeline for the following reasons (i) Forests give oxygen to keep us alive. (ii) Forests absorb carbon dioxide, a gas that contributes to climatic changes if its concentration increases in the atmosphere. (iii) Forests provide us with wood, gum, medicinal plants and spices. (iv) Forests save the soil from erosion. (v) Forests help in maintaining the groundwater level. vi) Forests avoid floods by increasing water holding capacity of the soil

ScienceClass 7CBSE

All the needs of animals living in a forest are fulfilled. Justify this statement in a few sentences.

Soln: Animals are dependent on plants in the forest for many things. Plants provide 02 to the animals to respire. Animals are dependent on plants for the food either directly or indirectly. Herbivores obtain food directly from plants, carnivores depend on herbivores for food. Trees in the forest provide shelter to forest animals. Hence it is said that the needs of animals living in a forest are fulfilled.

ScienceClass 7CBSE

Give any four factors which are responsible for the destruction of forests.

Soln: Factors responsible for the destruction of forests are (i) construction of roads. (ii) construction of buildings. (iii) industrial development. (iv) increasing demand for wood.

ScienceClass 7CBSE

People say that nothing goes waste in a forest. Can you explain, how?

Soln: Nothing goes waste in a forest for the following reasons Dry leaves and remains of dead animals are converted to a dark coloured substance called humus. This provides nutrients to the plants. Dead animals become food for vultures, crows, jackals and insects. Broken branches of trees are used as fuel by the people living in the vicinity of the forest.

ScienceClass 7CBSE

Name any four useful products other than wood, which we get from forests.

Soln: Gum, Spices, medicinal plants, catechu

ScienceClass 7CBSE

Deforestation may lead to floods. Why?

Soln: In the absence of trees, soil loses its water holding capacity this causes floods. Hence deforestation leads to floods.

ScienceClass 7CBSE

“A bunch of seedlings were seen sprouting on a heap of animal dropping in a forest.” How do you think is the seedling benefited from the animal dung?

Soln: Growing seedlings obtain nutrients from decaying animal heap.

ScienceClass 7CBSE

17. Match Column I with Column II Column I Column II a) Decomposers i) Dead plant and animal tissues b) Canopy iii) Habitat for wildlife c) Porcupine iii) Microorganisms d) Humus iv) Wild animal e) Forest v) Branches of tall trees

Soln: Column I Column II a) Decomposers iii) Microorganisms b )Canopy v) Branches of tall trees c) Porcupine iv)Wild animal d) Humus i) Dead plant and animal tissues e)Forest ii) Habitat for wildlife

ScienceClass 7CBSE

Two friends shared their experiences of their vacation trip to two different forests. Do you think they would have seen the same type of plants and animals during their respective trips? Give reason.

Soln: No, They might not see the same type of plants and animals in two different questions because climatic conditions in the two forests would be different which leads to variations in the types of plants and animals.

ScienceClass 7CBSE

Give names of any four birds which you expect to see in a forest.

Soln: Jungle crow, myna, dove, kingfisher

ScienceClass 7CBSE

Paheli wrote a food chain in the following way: frog → eagle → insects → grass → snake The chain is not in the correct order. Help her to write the food chain correctly.

Soln: grass→insects→frog→snake→eagle

ScienceClass 7CBSE

State whether the following statements are true or false. If false, give the correct statement. (a) Forests influence climate, water cycle and air quality. (b) In a forest, trees form the uppermost layer, followed by herbs. The shrubs form the lowest layer of vegetation. (c) The forest keeps on growing and changing and can regenerate. (d) Forests protect the soil from erosion.

Soln: a) True b) False- In a forest, trees form the uppermost layer, followed by shrubs. The herbs form the lowest layer of vegetation. c) True d) True

ScienceClass 7CBSE

Paheli while moving in a forest observed that there was no noise pollution, though lots of heavy vehicles were passing from the nearby highway. Explain why?

Soln: In Forests, there will be no noise pollution because forests absorb noise.

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