Question

background
photosynthetic rate can be investigated by measuring the uptake of carbon dioxide (co₂) and production of oxygen (o₂) over time. measuring the rate of oxygen production provides an approximation of photosynthetic rate.
aim
to investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant, cabomba aquatica.
how fast it happens
hypothesis
if photosynthetic rate is dependent on light intensity, more oxygen bubbles will be produced by cabomba per unit time at higher light intensities.
method
▶ 0.8 - 1.0 g of cabomba stem were weighed. the stem was cut and inverted to ensure a free flow of oxygen.
▶ the stem was placed into a beaker filled with a 20°c solution of 0.2 mol l⁻¹ sodium bicarbonate (nahco₃) to supply co₂. an inverted funnel and a test tube filled with the nahco₃ solution collected the gas produced.
▶ the beaker was placed at distances (20, 25, 30, 35, 40, 45 cm) from a 60w light source and the light intensity measured with a lux (lx) meter at each interval. one beaker was not exposed to the light source (5 lx).
▶ before recording data, the stem was left to acclimatize to the new light level for 5 minutes. bubbles were counted for a period of three minutes at each distance.
the results

Explanation:

Step1: Calculate bubbles per minute

For each row, use the formula \( \text{Bubbles per minute}=\frac{\text{Bubbles counted in three minutes}}{3} \).
For light intensity \( 150\ (25\ cm) \): \( \frac{33}{3}=11 \).
For light intensity \( 190\ (20\ cm) \): \( \frac{35}{3}\approx12 \).

Answer:

Light Intensity In lx (distance)	Bubbles counted In three minutes	Bubbles per minute
13 (45 cm)	6	2
30 (40 cm)	9	3
60 (35 cm)	12	4
95 (30 cm)	18	6
150 (25 cm)	33	11
190 (20 cm)	35	12