Living Science 2019 2020 Solutions for Class 7 Science Chapter 21 - Half Yearly Test Paper

Answer:

Non-green plants are heterotrophs because they can not perform photosynthesis.  

Answer:

Heterotrophic nutrition is seen in animals.

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.

Answer:

Ans

Answer:

Convection is the method of transfer of heat in which molecules themselves travel from the hot portion to the cold portion.

Answer:

If a vegetable tastes bitter, it is likely to have base in it as bases are bitter and acids are sour in taste.

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.

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.

Answer:

The nearer a place is to the equator the warmer it is expected to be.

Answer:

False. Humus is not found in all layers of soil. It is present only in the top soil. 

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.

Answer:

After the solid food is swallowed, it travels down the oesophagus by peristalsis, i.e., wave like action of muscles of oesophagus.

Answer:

Atomicity of an element can be defined as the number of atoms present in the molecule of an element.

Answer:

Sericulture is the breeding and management of silk worms for the purpose of obtaining silk, i.e., silk production.

Answer:

Temperature of an object refers to the hotness or coldness of that object. Higher the temperature, hotter is the object.

Answer:

Water has higher heat capacity than stone. Therefore, it takes more time to heat up and cool down as compared to stone.

Answer:

Excess of hydrochloric acid in the stomach causes acidity.

Answer:

Reaction of metals with acids forms salt and hydrogen gas.
Example:
Mg + 2HCl $\to$MgCl₂ + H₂ (gas)

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.

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.

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.

Answer:

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.

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 $\to$ZnSO₄ + H₂

Answer:

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.

Answer:

(b) nitrogen
Nitrogen is an integral part of all proteins. Therefore, plants need nitrogen in addition to glucose to synthesise proteins. 

Answer:

(d) four
Stomach of a cow is complicated and has four chambers.

Answer:

(a) atom
Atom is the smallest particle of an element that can take part in a chemical reaction.

Answer:

(b) wool
Wool, when burnt, smells like hair because it is nothing but thick hair of animals like sheep.

Answer:

(c) $-$40 ͦ
As calculated from the formula C= ($\frac{5}{9}$) (F$-$32), the temperature at which Celsius and Fahrenheit thermometer read the same is −40°.

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.

Answer:

(a) acetic acid
Mineral acids are inorganic acids as they do not have carbon. Acetic acid is an organic acid. 

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.

Answer:

(b) clayey soil
Clayey soil have very little space between its particles and thus, it can absorb and retain maximum water.

Answer:

(b) 2
Compound X needs two electrons to fulfil its octet. Therefore, its valency is two.

Answer:

b. small intestine

The process of digestion as well as absorption take place in small intestine. 
 

Answer:

A thermos flask prevents loss of heat by minimizing heat loss by conduction, convection, and radiation.

Hence, the correct answer is option "d".
 

Answer:

The chemical name of caustic soda is sodium hydroxide(NaOH).

Hence, the correct answer is option "a".

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".

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.