4. Take three test tubes. Fill ¾th 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?

5. Tick the correct answer:

(a) In cockroaches, air enters the body through

(i) lungs         (ii) gills           (iii) spiracles                 (iv) skin

(b) During heavy exercise, we get cramps in the legs due to the accumulation of

(i) carbon dioxide             (ii) lactic acid                    (iii) alcohol                      (iv) water

(c) Normal range of breathing rate per minute in an average adult person at rest is:

(i) 9–12                     (ii) 15–18                               (iii) 21–24                        (iv) 30–33

(d) During exhalation, the ribs

(i) move outwards                        (ii) move downwards                   (iii) move upwards           (iv) do not move at all