2.45B: Practical: Investigate the Effect of Light on Net Gas Exchange from a Leaf, Using Hydrogen-Carbonate Indicator

HYDROGENCARBONATE INDICATOR: Indicator of Carbon Dioxide Concentration in a Solution

COLOUR AND CARBON DIOXIDE LEVELS:

COLOUR	CARBON DIOXIDE CONCENTRATION
YELLOW	High
RED	Atmospheric
PURPLE	Low

INVESTIGATING EFFECT OF LIGHT ON GAS EXCHANGE

Diagram showing the Apparatus to Investigate the Effect of Light on Gas Exchange

METHOD: Place pondweed in a beaker of Hydrogen Carbonate indicator Place light source at a set distance to adjust light intensity (the smaller the distance between the light source and plant, the higher the light intensity) Allow plant to adapt to adjusted environment for a few minutes Observe and record the colour of indicator Change light intensity and repeat process

RESULT: When light source is placed close to the plant, high light intensity will allow Photosynthesis to occur due to the presence of light, therefore increasing the rate of Photosynthesis involving the absorption of Carbon Dioxide (produced as a waste product of Respiration) Given that the rate of Photosynthesis is greater than the rate of Respiration, the concentration of Carbon Dioxide in solution will decrease, causing the indicator to turn Purple When light source is placed distant to the plant, low light intensity will prevent Photosynthesis to occur due to the absence of light, therefore decreasing the rate of Photosynthesis involving the absorption of Carbon Dioxide (produced as a waste product of Respiration) As the rate of Respiration will therefore be greater than the rate of Photosynthesis, the concentration of Carbon Dioxide in solution will increase, causing the indicator to turn Yellow