2 required practicals

Practical : evolution of oxygenMETHOD

Take some pondweed and submerge in a beaker of water underneath an upside down funnel. Fill a boiling tube with water and place it over the end of the funnel. As oxygen is produced bubbles of gas will collect in the boiling tube and displace the water. use thermometer to moniter temp.

Practical : evolution of oxygen RESULTS AND ANALYSIS

prove gas is oxygen by relighting a glowing splint. Amount of bubbles per minute can also be used to measure rate of photosynthesis.

How do we test for photosynthesis?

test for starch as some of glucose produced from photosynthesis is converted to starch

Why is it hard to test for glucose?

It is quickly used up or converted into other substances

Method to test for presence of starch - PRE-PREP (destarching)

Place the plant in a dark cupboard for at least 24 hours before practical to ensure leaves have no starch.

Method to test for presence of starch - PREP (prepare the leaf)

Boil the leaf to kill cells and break down cell wall and membrane.
Place the leaf in hot ethanol to remove chlorophyll for clear colour change later
When doing this turn off bunsen burner as ethanol is flammable
Rinse leaf in water to soften
Spread leaf over white tile and do iodine test for starch.

How do we test whether light is needed for photosynthesis?

Cover part of the leaf with aluminium foil and place in sunlight
Exposed parts of the leaf should photosynthesis
Do test for presence of starch process
Covered part will remain orange-brown and non covered part will be blue black.

What should we apply to evaluation as usual?

CORMMS

How do we heat ethanol as it is extremely flammable

electric water bath.

Practical : investing need for carbon dioxide in photosynthesis PRE-PREP (Destarch)

Place the plant in a dark cupboard for at least 24 hours before practical to ensure leaves have no starch.

Practical : investing need for carbon dioxide in photosynthesis method

Enclose 1 leaf using a clamp and clamp stand from the destarched plant in a conical flask containing potassium hydroxide to remove carbon dioxide from the air and then enclose 1 leaf with nothing to act as a control. Finish with iodine test

Practical : investigating the need for chlorophyll in photosynthesis METHOD

Use a variegated leaf where the white areas contain no chlorophyll.
Do test for presence of starch process