CP6 - Photosynthesis Flashcards
What is photosynthesis?
The process by which plants synthesise
glucose using light energy from the Sun
Describe how you would investigate the effect of light
intensity on the rate of photosynthesis in an aquatic plant
● Place algal beads in a boiling tube at a fixed distance from a light source
● Fill the boiling tube with hydrogen carbonate indicator and record the initial colour
● After 30 minutes, record the final colour and find the pH using a colour
standard
● Repeat several times at different distances/light intensities, and calculate
a mean for each distance
● Plot a graph of light intensity (x) against rate of photosynthesis (bubbles
per minute, y)
Why is it best to use an LED light source
rather than a lamp?
Alamp will emit more heat energy than an LED -
therefore it may change the temperature of the
experiment and affect the rate of photosynthesis
What is the relationship between the distance
from a light source and light intensity?
Inverse square law - light intensity∝ 1 /
distance^2
How can the measurement of oxygen production be
made more accurate?
If the the pondweed is placed under a filter funnel with
an inverted measuring cylinder over the spout, the
volume of oxygen produced can be determined
Why is sodium hydrogen carbonate solution used
during this experiment?
It releases CO2
, which is used by the
pondweed during photosynthesis
Why can pH be used as an indication of
the rate of photosynthesis?
Carbon dioxide, which is acidic, is released as a
product of photosynthesis. The higher the rate of
photosynthesis, the greater the decrease in pH in
the given time.
What is a source of error in this practical?
The colour change may be subjective and
determining the pH using a colour standard may
be difficult.
