What is the composition of air?
Air contains 21% of oxygen, 78% nitrogen, 0.03% carbon dioxide other gases like argon, dust particles, water vapours present in 0.01% quantity. Oxygen gas is very necessary for the respiration of organisms. Oxygen helps in burning; nitrogen gas is present in the large amount but it cannot help in burning process.
How will you prove that air supports burning?
How do plants and animals help each other in the exchange of gases in the atmosphere?
List five activities that are possible due to the presence of air.
The layer of air around the earth is known as ___________.
How will you show that air is dissolved in water?
Why does a lump of cotton wool shrink in water?
The component of air used by green plants to make their food, is ___________.
Which gas in the atmosphere is essential for respiration?
(a) Which kind of garbage is not converted into compost by the redworms?
(b) Have you seen any other organism besides redworms, in your pit? If yes, try to find out their names. Draw pictures of these.
Rearrange the boxes given below to make a sentence that helps us understand opaque objects.
To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Do you find that all living beings need the same kind of food?
Name the major nutrients in our food.
Classify the following fibres as natural or synthetic:
nylon, wool, cotton, silk, polyester, jute
Name five objects which can be made from wood.
Why do we need to separate different components of a mixture? Give two examples.
Correct the following statements and rewrite them in your notebook.
(a) Stem absorbs water and minerals from the soil.
(b) Leaves hold the plant upright.
(c) Roots conduct water to the leaves.
(d) The number of petals and sepals in a flower is always equal.
(e) If the sepals of a flower are joined together, its petals are also joined together.
(f) If the petals of a flower are joined together, then the pistil is joined to the petal.
Fill in the blanks:
(a) Joints of the bones help in the ——————— of the body.
(b) A combination of bones and cartilages forms the _______ of the body.
(c) The bones at the elbow are joined by a ______________________ joint.
(d) The contraction of the _____________ pulls the bones during movement.
When does a drought occur?
Name two foods each rich in:
(a) Fats
(b) Starch
(c) Dietary fibre
(d) Protein
Why can a pace or a footstep not be used as a standard unit of length?
Name the part of the plant which produces its food. Name this process.
Draw (a) a leaf, (b) a taproot and (c) a flower, you have studied for Table 7.3.
Is it possible for you to recognize the leaves without seeing them? How?
You are given an iron strip. How will you make it into a magnet?
Would the bulb glow in the circuit shown in Fig. 12.15?
A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?
How would you obtain clear water from a sample of muddy water?