One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be

(a) 80°C    (b) more than 50°C but less than 80°C
(c) 20°C    (d) between 30°C and 50°C

Classify the changes involved in the following processes as physical or chemical changes:
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f ) Digestion of food

Take three test-tubes. Fill æth of each with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO₂?

Sketch the cross section of soil and label the various layers.

Given below is a crossword puzzle based on this lesson. Use hints to fill in the blank spaces with letters that complete the words.
Down                                               Across
(D) 1 : Thorough washing           (A) 1 : Keeps warm
      2 : Animal fibre                            2 : Its leaves are eaten by silkworms
      3 : Long thread like structure      3 : Hatches from egg of moth

When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

Match the items in Column I with those in Column II:
Column I                                              Column II
(i) A home for living organisms         (a) Large particles
(ii) Upper layer of the soil                 (b) All kinds of soil
(iii) Sandy soil                                   (c) Dark in colour
(iv) Middle layer of the soil                (d) Small particles and packed tight                                                                                                                                               (v) Clayey soil                                  (e) Lesser amount of humus

Why does an athlete breathe faster and deeper than usual after finishing the race?

David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be

(i) 3 m        (ii) 5 m
(iii) 6 m      (iv) 8 m

Write one similarity and one difference between the nutrition in amoeba and human beings.

Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

(a) copper bottom makes the pan more durable.
(b) such pans appear colourful.
(c) copper is a better conductor of heat than the stainless steel.
(d) copper is easier to clean than the stainless steel.

Match the items in Column I with those in Column II:
Column I                             Column II
(a) Yeast                             (i) Earthworm
(b) Diaphragm                    (ii) Gills
(c) Skin                               (iii) Alcohol
(d) Leaves                          (iv) Chest cavity
(e) Fish                               (v) Stomata
(f) Frog                               (vi) Lungs and skin
                                           (vii) Tracheae

Distinguish between a parasite and a saprotroph.

In the circuit shown in Fig. 14.25

(i) Would any of the bulb glow when the switch is in the ‘OFF’ position?
(ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Why do we often sneeze when we inhale a lot of dust-laden air?

Explain why holes are made in hanging banners and hoardings.

Make sketches of the two stages in the life history of the silk moth which are directly related to the production of silk.

Draw a diagram of the human excretory system and label the various parts.

Draw the circuit diagram to represent the circuit shown in Fig.14.21.

State similarities and differences between the laboratory thermometer and the clinical thermometer.

Explain how groundwater is recharged?