Photosynthesis RPA

Question 1

Method

Answer 1

1) Set up test tube rack 10cm away from light source
2) Fill boiling tube with fixed volume of sodium hydrogen carbonate and add a piece of pondweed
3) Leave for 5 mins
4) Start stopwatch and count number of bubbles produced in 1 minute- repeat this 2 more times to calculate a mean and record results in a table
5) Repeat steps 1 to 4 changing the distance of the boiling tube from the light source
6) plot graph to compare light intensity to rate of photosynthesis

Question 2

What type of light source is best to use and why

Answer 2

LED (not a lamp)
Emits less heat energy so prevents temperature affecting rate if photosynthesis

Question 3

Sources of error

Answer 3

Bubbles different sizes
Bubbles are too fast to count accurately
Other factors affecting rate of photosynthesis e.g temperature (if using lamp), CO2 concentration

Question 4

What are the bubbles produced that we count

Answer 4

Oxygen bubbles (released in photosynthesis)

Question 5

How to measure volume of oxygen produced more accurately than counting bubbles

Answer 5

Place filter funnel on top of pondweed with an inverted measuring cylinder over the spout and measure volume of oxygen

Question 6

Why use sodium hydrogen carbonate solution to place pondweed in

Answer 6

Releases CO2 which is needed for photosynthesis