Living Science 2020 2021 Solutions for Class 7 Science Chapter 21 Half Yearly Test Paper are provided here with simple step-by-step explanations. These solutions for Half Yearly Test Paper are extremely popular among Class 7 students for Science Half Yearly Test Paper Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science 2020 2021 Book of Class 7 Science Chapter 21 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science 2020 2021 Solutions. All Living Science 2020 2021 Solutions for class Class 7 Science are prepared by experts and are 100% accurate.
Page No 115:
Question 1:
Are non-green plants autotrophs or heterotrophs?
Answer:
Non-green plants are heterotrophs because they can not perform photosynthesis.
Page No 115:
Question 2:
What kind of nutrition is seen in animals?
Answer:
Heterotrophic nutrition is seen in animals.
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Question 3:
By what methods-physical or chemical-is it possible to break a compound into its constituents?
Answer:
A compound can be broken into its constituents by chemical method. For example, water can be broken down into hydrogen and oxygen by passing electricity through it.
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Question 4:
What is the base of all plant fibres?
Answer:
Ans
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Question 5:
In which method of transfer of heat do molecules themselves travel from the hot portion to the cold portion?
Answer:
Convection is the method of transfer of heat in which molecules themselves travel from the hot portion to the cold portion.
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Question 6:
If a vegetable tastes bitter, what is it likely to have in it-a base or an acid?
Answer:
If a vegetable tastes bitter, it is likely to have base in it as bases are bitter and acids are sour in taste.
Page No 115:
Question 7:
Is rusting a physical or a chemical change?
Answer:
Rusting of iron is a chemical change because iron reacts with oxygen and forms iron oxide.
Iron cannot be easily obtained from iron oxide.
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Question 8:
Is heat a form of energy or a form of matter?
Answer:
Heat is a form of energy because it is emitted from a source. It flows from a hotter body to a colder body and this transfer is by thermal interactions.
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Question 9:
Fill in the blanks:
The nearer a place is to the equator the _______ (warmer/colder) it is expected to be.
Answer:
The nearer a place is to the equator the warmer it is expected to be.
Page No 115:
Question 10:
Humus is found in all layers of the soil. True or False?
Answer:
False. Humus is not found in all layers of soil. It is present only in the top soil.
Page No 115:
Question 1:
Name all the ingredients that are required for photosynthesis to occur.
Answer:
Photosynthesis requires carbon dioxide and water as raw materials. Photosynthesis in green plants takes place in the presence of light. Green plants have light absorbing pigment called chlorophyll.
Page No 115:
Question 2:
How does solid food travel down the oesophagus after it is swallowed?
Answer:
After the solid food is swallowed, it travels down the oesophagus by peristalsis, i.e., wave like action of muscles of oesophagus.
Page No 115:
Question 3:
What do you mean by the 'atomicity' of an element?
Answer:
Atomicity of an element can be defined as the number of atoms present in the molecule of an element.
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Question 4:
What is sericulture?
Answer:
Sericulture is the breeding and management of silk worms for the purpose of obtaining silk, i.e., silk production.
Page No 115:
Question 5:
What do you mean by 'temperature' of an object?
Answer:
Temperature of an object refers to the hotness or coldness of that object. Higher the temperature, hotter is the object.
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Question 6:
Water has higher heat capacity than stone. Compare the time taken by water and stone to heat up and cool down.
Answer:
Water has higher heat capacity than stone. Therefore, it takes more time to heat up and cool down as compared to stone.
Page No 115:
Question 7:
What effet does excess hydrochloric acid in the stomach cause?
Answer:
Excess of hydrochloric acid in the stomach causes acidity.
Page No 115:
Question 8:
Give a chemical reaction in which there is evolution of gas.
Answer:
Reaction of metals with acids forms salt and hydrogen gas.
Example:
Mg + 2HCl MgCl2 + H2 (gas)
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Question 9:
What protection does a polar bear have from the extreme cold weather in which it lives?
Answer:
Polar bear has a layer of fat under its skin which acts as an insulator. Further, it has two thick layers of fine fur which traps air for the protection from the extreme cold weather in which it lives.
Page No 115:
Question 10:
What is weathering?
Answer:
The formation of soil by the process of breaking up of large pieces of rock into smaller pieces by the action of natural agents such as water, air, glaciers and roots of the plants is termed as weathering.
Page No 115:
Question 1:
Describe the structure of a villus.
Answer:
The small finger-like projections present on the surface of a small intestine are called villi. The fine network of blood capillaries is present close to the surface of each villus. Food is first absorbed on the surface of a villus and then passed on to the blood capillaries.
Page No 115:
Question 2:
What is the difference between a mixture and a compound on the basis of their constituents?
Answer:
| Mixture | Compound |
| Ratio of the constituents is not fixed. | Ratio of the constituents is always fixed. |
| A mixture is a combination of two or more elements or compounds in which neither new molecules are formed and nor chemical reaction takes place. | A compound is a combination of two or more elements or compounds in which new molecules are formed. |
Page No 115:
Question 3:
Why does matter expand when heated?
Answer:
Matter expands when heated because on heating, movement of its molecules increases resulting in increasing the distance between the molecules. This increases the area occupied by them. Thus, the volume of the matter expands.
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Question 4:
What happens when sulphuric acid reacts with zinc metal?
Answer:
When sulphuric acid (H2SO4) reacts with zinc metal, zinc sulphate (ZnSO4) and hydrogen gas (H2) are formed. The chemical reaction is as follows:
H2SO4 + Zn ZnSO4 + H2
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Question 5:
What is the difference between weather and climate?
Answer:
| Weather | Climate |
| The daily atmospheric conditions of a place with respect to factors like temperature, rainfall, humidity etc., is termed as weather of that place. | The weather pattern of a place, on an average over a long span of time like 30 years or so, is termed as climate of that place. |
Page No 115:
Question 6:
Draw a labelled diagram to show a fire alarm that uses the principle of expansion of heat.
Answer:
A fire alarm that uses the principle of expansion of heat:
This fire alarm uses the fact that different solids expand by different amount of heating. The alarm contains two metal strips, one of the iron and other of brass, firmly bolted together. Brass expands more on heating, therefore the bimetallic strip bend on the side of iron upon heating and the circuit is completed. Hence, the fire alarm bell rings.
Page No 115:
Question 1:
Which of these elements do plants need in addition to glucose to synthesise proteins?
(a) carbon
(b) nitrogen
(c) hydrogen
(d) oxygen
Answer:
(b) nitrogen
Nitrogen is an integral part of all proteins. Therefore, plants need nitrogen in addition to glucose to synthesise proteins.
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Question 2:
How many chambers does the stomach of a cow have?
(a) one
(b) two
(c) three
(d) four
Answer:
(d) four
Stomach of a cow is complicated and has four chambers.
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Question 3:
Which is the smallest particle of an element that can take part in a chemical reaction?
(a) atom
(b) molecule
(c) compound
(d) either atom or molecule depending on the element
Answer:
(a) atom
Atom is the smallest particle of an element that can take part in a chemical reaction.
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Question 4:
Cloth made out of which of these when burnt will smell like burning hair?
(a) cotton
(b) wool
(c) jute
(d) flax
Answer:
(b) wool
Wool, when burnt, smells like hair because it is nothing but thick hair of animals like sheep.
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Question 5:
At what temperature will the reading on a Celsius thermometer be the same as the that on a Fahrenheit thermometer?
(a) 0°
(b) 100°
(c) −40°
(d) 212°
Answer:
(c) 40 ͦ
As calculated from the formula C= () (F32), the temperature at which Celsius and Fahrenheit thermometer read the same is −40°.
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Question 6:
How does the dark or light colour of an object affect the amount of heat it radiates or absorbs?
(a) Dark colour objects absorb and radiate more heat than light coloured objects.
(b) Dark colour objects absorb more but radiate less heat than light coloured objects.
(c) Dark colour objects absorb less and radiate more heat than light coloured objects.
(d) Dark colour objects absorb and radiate the same amount of heat as light coloured objects.
Answer:
(a) Dark-coloured objects absorb and radiate more heat than light-coloured objects.
Dark-coloured objects absorb and radiate more heat than light-coloured objects.
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Question 7:
Which of these is not a mineral acid?
(a) acetic acid
(b) hydrochloric acid
(c) sulphuric acid
(d) nitric acid
Answer:
(a) acetic acid
Mineral acids are inorganic acids as they do not have carbon. Acetic acid is an organic acid.
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Question 8:
If a chemical equation has '+ heat' on its right hand side, it is definitely a
(a) endothermic reaction.
(b) exothermic reaction.
(c) combination reaction.
(d) neutralization reaction.
Answer:
(b) exothermic reaction
The '+ heat' on the right side of reaction shows that heat is released in the reaction. Hence, the reaction is exothermic.
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Question 9:
Which of these soils absorbs and retains the maximum water?
(a) sandy soil
(b) clayey soil
(c) loam soil
(d) sandy-loam soil
Answer:
(b) clayey soil
Clayey soil have very little space between its particles and thus, it can absorb and retain maximum water.
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Question 10:
In a compound XO2, the valency of X is
(a)1.
(b) 2.
(c) 4.
(d) cannot be determined from this fromula.
Answer:
(b) 2
Compound X needs two electrons to fulfil its octet. Therefore, its valency is two.
Page No 116:
Question 11:
Which organ in the human body does both – digestion as well as absorption of digested food?
a. stomach
b. small intestine
c. large intestine
d. all of these
Answer:
b. small intestine
The process of digestion as well as absorption take place in small intestine.
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Question 12:
A thermos flask prevents loss of heat by
a. conduction
b. convection
c. radiation
d. all of these
Answer:
A thermos flask prevents loss of heat by minimizing heat loss by conduction, convection, and radiation.
Hence, the correct answer is option "d".
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Question 13:
The chemical name of caustic soda is
a. sodium hydroxide
b. ammonium hydroxide
c. potassium hydroxide
d. magnesium hydroxide
Answer:
The chemical name of caustic soda is sodium hydroxide(NaOH).
Hence, the correct answer is option "a".
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Question 14:
The reaction MN + OP → MP + ON is a
a. combination reaction
b. decomposition reaction
c. single displacement reaction
d. double displacement reaction
Answer:
Following reaction is an example of double displacement reaction.
There is an exchange of substances in reacting species.
Hence, the correct answer is option "d".
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Question 15:
It is very hot near the equator because
a. sun rays strike vertically.
b. sun rays travel through lesser thickness of the atmosphere.
c. days are longer.
d. all of these.
Answer:
d. all of these.
It is hot near the equator because days are long near the equator, sun rays strike vertically on the equator and sun rays travel through lesser thickness of the atmosphere near the equator.
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