Practise starch tests and water-plant investigations: destarch leaves, change one requirement, interpret iodine results and measure oxygen production reliably.
Photosynthesis is the process green plants use to convert light energy into chemical energy.
A student uses this method to show that carbon dioxide is needed for photosynthesis.
Step 1 place a plant in darkness for 48 hours
Step 2 remove a leaf and test it for starch
Step 3 enclose one leaf, still attached to the plant, in a flask containing a bag of solid sodium hydroxide (soda lime)
Step 4 place the plant in bright light for 24 hours
Step 5 test the leaf in the flask for starch
Step 6 test another leaf from the plant for starch
Explain why a leaf is removed from the plant and tested for starch in step 2.
An explanation that makes reference to two of the following
- show no starch present / starch is used up / leaf is destarched / eq
- by respiration / eq
- to make it a fair test / make test valid / any starch produced is from photosynthesis / eq
Explain the expected result of the starch test in step 5.
An explanation makes reference to two of the following
- no photosynthesis / no carbon dioxide / eq
- no carbohydrate / no starch / negative /eq
- iodine solution unchanged / leaf brown / yellow / orange /eq
requires CO2 for
photosynthesis
Light is also needed for photosynthesis.
Describe how the student's method could be modified to show that light is needed for photosynthesis.
A description that includes the following
- plant in dark / leaf with foil covering / leaf with stencil / eq
- access to CO2 / no soda lime / eq