biology - photosynthesis

Question 1

describe how to investigate the effect of light intensity on the rate of photosynthesis of an aquatic plant?

Answer 1

• place cut pondweed in a test tube (containing sodium hydrogen carbonate solution) at a fixed distance from a light source (like a lamp)
• count the number of bubbles produced in one minute using a stopwatch
• repeat several times with different distances/light intensities, and calculate a mean for each distance
• plot a graph of light intensity (x axis) against rate of photosynthesis (bubbles per minute, y axis)

Question 2

why should you use an LED light rather than a lamp?

Answer 2

a lamp will emit more heat energy than an LED - therefore it may change the temperature of the experiment and affect the rate of photosynthesis

Question 3

what is the relationship between distance from a light source and light intensity?

Answer 3

inverse relationship

light intensity ∝ 1/distance^2

Question 4

how to make the measurement of oxygen production more accurate?

Answer 4

• place the pondweed under a filter funnel with an inverted measuring cylinder over the spout
• you can then determine the volume of oxygen produced more accurately

Question 5

why is sodium hydrogen carbonate used?

Answer 5

it releases CO2 which can be used by the pondweed for photosynthesis

Question 6

why can the number of bubbles produced be used to calculate the rate of photosynthesis?

Answer 6

oxygen bubbles are released as a product of photosynthesis, so the number of bubbles produced in a given time period is proportional to the rate of photosynthesis