RP measuring the rate of photosynthesis Flashcards
equipment
-lamp/light source
-a 10cm piece of pondweed
-boiling tube
-ruler
-a stopwatch
-sodium hydrogen carbonate solution
-funnel
-measuring cylinder
method
- Fill a boiling tube with a set volume of sodium hydrogen carbonate
- place the pondweed in the tube, with the cut end at the top
- Place a boiling tube 10cm away from the light source, using the metre ruler
- leave the boiling tube for 5 minutes so the pondweed can acclimatise the the conditions in the tube
- start the stopwatch and count the number of bubbles in a minute
- repeat the experiment at 10cm intervals (20cm, 30 cm etc.)
errors
if the temp is too hot, it would change the experiment
bubbles may be too fast to count
inverse square law
light intensity ∝ 1/distance²
results
as the light intensity is decreased, the oxygen given off is less, so the rate of photosynthesis is decreased
what does the inverse square law mean?
if you halve the distance, the light intensity will be four times greater
how can the measurement of oxygen production be made more accurate?
place the pondweed under a filter funnel, with an inverted measuring cylinder to determine volume of oxygen produced
why is sodium hydrogen carbonate used?
it releases CO₂ which is used by pondweed in photosynthesis
why can the number of bubbles produced be used to calculate the rate of photosynthesis?
oxygen bubbles are formed as a product of photosynthesis, number of bubbles is proportional to the rate of photosynthesis
variables
independent- distance away from light source
dependent- number of oxygen bubbles produced /volume of oxygen
control- volume of sodium hydrogen carbonate, light source
safety
- keep water away from electrical wiring
- lamp may get hot
why is it best to use an LED source rather than a lamp?
-lamp will emit more heat energy therefore would affect temperature changing the result
