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Science Give scientific reasons:

Cell Structure and Micro-organisms · Maharashtra Board STD 7 (MSBSHSE - English Medium). 10 questions.

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10 questions · timed · auto-graded

Question 12 Marks
Cells are the basic structural units of living organism.
Answer
  1. Cells are the smallest unit from which a living organism is made.
  2. A cell contains all the necessary structures which are required to carry out various biological processes.
  3. A group of cells makes a tissue, which further makes an organ and many organs together make an organ system and finally organism. Thus, the cells are the basic structural units of living organism.
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Question 22 Marks
A compound microscope is used for observing cells.
Answer
  1. Cell are extremely minute in size.
  2. We cannot see cells with naked eye.
  3. An object when kept on a glass slide is magnified many times by the lenses of this microscope.
  4. Hence, compound microscope is used for observing cells.
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Question 32 Marks
Mitochondria are called the power houses of the cell.
Answer
  1. Mitochondria are tiny organelles inside the cells that are involved in releasing energy from food.
  2. This process is known as cellular respiration.
  3. It is for this reason that mitochondria are often referred to as the power houses of the cell.
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Question 42 Marks
Fodder is soaked in water before offering to cattle.
Answer
  1. In dry fodder only some part of it is useful for cattle and rest is wasted.
  2. When fodder is soaked in water, it sprouts.
  3. So, to make the fodder more nutritious and more easy to digest it is soaked in water before offering to cattle.
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Question 52 Marks
Bread rises during baking.
Answer
  1. The process of fermentation is used in baking, for example, in making bread. Yeast is added to make the dough rise.
  2. The fermentation is a chemical process of conversion of one type of carbon compound into another type of carbon compound by the action of micro-organisms.
  3. Heat is generated in this process. Carbon dioxide $(CO_2)$ and some other gases are released.
  4. These gases cause an increase in volume so the bread dough rises.
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Question 62 Marks
A refrigerator is used in almost every home.
Answer
  1. Refrigerator is used to keep food item in healthy condition and to keep them fresh.
  2. If the food items are kept outside, they spoil very fast due to growth of micro-organisms and they make food spoiled and harmful.
  3. The optimum temperature for the growth of micro-organism is 15°C to 35°C.
  4. In refrigerator the temperature is kept very low. So, the food is preserved in refrigerator.
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Question 72 Marks
Fungus grows quickly in moist or humid condition.
Answer
  1. Fungus needs water and moisture for its growth.
  2. Humidity brings about spore germination and the fungus is able to grow and reproduce quickly in moist or humid condition.
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Question 82 Marks
Soil is turned over during tilling.
Answer
  1. Tilling is done to loosen the soil in initial agricultural practice.
  2. Loose soil allows the penetration of roots of the plant.
  3. By turning of soil, it allows uniform mixing of manure and fertilizer.
  4. It increases the fertility of soil. Seeds also germinate easily in aerated soil. Hence, soil is turned during tilling.
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Question 92 Marks
There is a possibility of food poisoning if we eat stale food.
Answer
  1. Fungus grows quickly on moist and stale food. Micro-organisms grown on the food release toxic materials like enterotoxin into the food.
  2. Such toxins spoil the food.
  3. Eating such spoiled food may cause loose motions and vomiting. So, we should eat food which is freshly prepared.
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Question 102 Marks
Diseases spread on a large scale during periods of heavy rainfall and floods.
Answer
  1. Due to floods there is shortage of clean, safe drinking water.
  2. It gets contaminated with sewage and dirt having disease causing pathogens, causing disease of alimentary canal, typhoid, cholera, dysentery.
  3. Due to stagnant water, many mosquitoes breed on it and cause diseases like malaria, dengue, etc.
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Give scientific reasons: - Science STD 7 Questions - Vidyadip