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Science [2 Mark Questions]

MODEL PAPER 2 · CBSE STD 10 (CBSE - English Medium). 8 questions.

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[2 Mark Questions]

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8 questions · timed · auto-graded

Question 22 Marks
Microorganisms are often referred to as the 'scavengers of the environment.' Explain.
Answer
Scavangers feed upon discarded and dead waste. Micro organisms are called scavengers of the environment because they decompose dead bodies of plants and animals present in the soil and help in cleaning the environment by removing waste products. They lie at the top of food chain.
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Question 32 Marks
List two reasons to show that the existence of decomposers is essential in an ecosystem.
Answer
Microorganisms like bacteria and fungi which helps in the breakdown of organic matter or biomass of dead plants and animals. into simple inorganic raw materials and replenish the environment are termed as decomposers. Their existence is thus, essential in an ecosystem because
i. They help in the natural replenishment of soil.
ii. They help in keeping the environment clean as they reduce environmental pollution.
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Question 42 Marks
An object is placed at a distance of 30 cm from a concave lens of focal length 15 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.
Answer
Object distance, u = - 30 cm
Focal length of concave lens = - 15 cm
We know that $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\frac{1}{v}-\frac{1}{-30}=\frac{1}{-15}$
$\frac{1}{v}=-\frac{1}{15}-\frac{1}{30}$
$\frac{1}{v}=\frac{-2-1}{30}=\frac{-3}{30}=\frac{-1}{10}$
v = -10 cm.
Characteristics of image:
i. The image is formed at a distance of 10 cm from the concave lens on the left side.
ii. Image formed is virtual.
iii. Image formed is erect.
iv. The size of the image formed is diminished.
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Question 52 Marks
Why is it not advisable to sleep under a tree at night while resting under it during mid$-$day is not bad?
Answer
During the day$,$ in presence of sunlight$,$ the plants use up the $CO_2$ and release $O_2$ in the process of photosynthesis. But during night$,$ plants won't perform photosynthesis so they are unable to use the $CO_2$ and this further leads to increase in the proportion of $CO_2$ in the air. During night the trees breathe in oxygen and release $CO_2$. If one sleeps under the trees$,$ the amount of increased $CO_2$ in the air around will certainly affect the health. So it is inadvisable to sleep under trees during night. He suffers from suffocation. He feels excess weight on his chest. For this reason$,$ some rural people imagine and fear that ghosts would come and sit on their chests if they sleep under Peepal or Banyan trees.
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Question 62 Marks
Chlorophyll is necessary for photosynthesis. Why?
Answer
The chlorophyll traps the solar energy and converts it into chemical energy which takes part the dark reaction of photosynthesis to form glucose. Hence chlorophyll is necessary for photosynthesis.
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Question 72 Marks
What will happen if the fallopian tubes are partially blocked and the ovulated eggs are prevented from reaching the uterus?
Answer
Fertilization may take place but the zygote may develop in the tube instead of uterus.
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Question 82 Marks
A mixture of oxygen and ethyne is bunt for welding. Can you tell why a mixture of ethyne and air is not used?
Answer
Ethyne is an unsaturated hydrocarbon. Since it has high carbon content, it burns in air with a sooty flame due to the presence of unburnt carbon in it. Due to its incomplete combustion, heat produced is not sufficient to attain the high temperature needed for welding. In order to ensure complete combustion and to obtain a high temperature needed for welding, a mixture of ethyne and oxygen is used.
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[2 Mark Questions] - Science STD 10 Questions - Vidyadip