Required Practical: Photosynthesis

Question 1

Why do we use an LED?

Answer 1

Minimal thermal energy dissipated so less risk of heat changing the temperature of the reaction and therefore the rate of photosynthesis.

Question 2

What can we use if we only have a normal lamp?

Answer 2

a water bath between the lamp and the test tube would absorb the thermal energy whilst still allowing the light through

Question 3

2. fill a test tube with ______________________ solution which contains CO2 used in photosynthesis

Answer 3

sodium hydrogen carbonate

Question 4

3. place a piece of a pondweed into the boiling tube with the…

Answer 4

cut end at the top

Question 5

4. leave the pondweed for 5 mins to….

Answer 5

acclimatise to the conditions in the boiling tube

Question 6

5. after 5 mins, one can observe bubbles of gas (X2) released, which shows that

Answer 6

O2

photosynthesis is taking place

Question 7

6. start a stopwatch once you see bubbles forming and…

Answer 7

count bubbles released per minute. Do this three times and take a mean.

Question 8

7. repeat all steps but each time put the test tube …

Answer 8

10cm further than the light source

Question 9

CONS of this practical

Answer 9

• the number of bubbles can be too fast to count accurately
• the bubbles are not always the same size

Question 10

Alternative more accurate way:

Answer 10

instead of counting bubbles, catch bubbles in a funnel and then into a measuring cylinder, then use this to measure the exact volume of oxygen produced.

Question 11

inverse-square-law equation

Answer 11

light intensity = 1/d^2