Question

Three tubes (A, B and C) As shown in the figure, were left in sunlight for one hour. Each test tube

was provided with a bicarbonate indicator. Bicarbonate indicator stays red if there is no change in

carbon dioxide concentration. The indicator becomes yellow if carbon dioxide is added and purple

if carbon dioxide is removed.The bicarbonate indicator in each tube was red at the start of the

experiment. Explain how the change in colour of the indicator occurs in different test tubes after

one hour.

Test Tube A: Plant is put inside a test tube of boiled water and a bicarbonate indicator.

Test Tube B: Plant and Snail is put in a test tube of normal water and a bicarbonate indicator.

Test Tube C: Snail is put in a test tube of normal water and a bicarbonate indicator.
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Answer 1

Test tube A will have the highest concentration of CO2. This is because test tube A contains snail. Snail is an organism that breathes in O2 and breathes out CO2. Hence, CO2 concentration increases in test tube A.

Test tube B contains a water plant, which takes in CO2 for food synthesis and gives out O2. Hence, more O2 concentration is found in test tube B.

Test tube C contains both a snail and a plant. The CO2 produced by the snail is utilized by the plant for its food synthesis and the O2 released by the plant is utilized by the snail for respiration.

Therefore, test tube A has the highest concentration of CO2.