To investigate the influence of light intensity or carbon dioxide on the rate of photosynthesis Flashcards
Name a suitable organism for this investigation?
elodea, pondweed
Why is elodea/pondweed suited for this experiment?
- aquatic plant
- bubbles can be seen
- gas can be measured
What do you do first before starting experiment?
set up water bath @25 degrees C with a thermometer
What is first step with the elodea?
cut the stem at an angle
Why cut elodea stem at an angle?
increase the surface area
Where do you put the cut stem?
in a beaker of water (under an inverted funnel), ((cut end upwards))
What do you saturate the water with to provide the carbon dioxide needed for dark stage of photosynthesis?
sodium carbonate
Why add sodium carbonate to water?
provide carbon dioxide
Where do you place the beaker?
into the water bath
Explain how you measured the rate of photosynthesis.
count the number of bubbles/measure volume
per unit time (minute)/over set period of time
How many times do you do this?
3, then find average
How do you include the factor of light intensity?
using a metre stick, place a lamp 1m away from the water bath and allow to stabilise for a few mins
How do you change the light intensity when repeating?
move lamp to 80cm rather than 1m then do distances 60cm, 40cm, 20cm
After finishing it all what do you do?
graph results with rate of photosynthesis vs. light intensity
What 3 things did you obtain in comleting the experiment (results)?
- rate of photosynthesis was slowest when lamp was 1m away
- as lamp moved closer to the water bath, the rate increased
- however, at 20cm the rate didn’t increase as the plant became saturated with light, couldnt absorb any more (graph levels)
