Transcript Plant Stores

Plant Stores
D. Crowley, 2008
Monday, April 11, 2016
Plant Stores
To know that plants store glucose as starch, and how to test for this
Equations
The word equation for photosynthesis is
carbon dioxide + water  glucose + oxygen
The symbol equation for photosynthesis is
6CO2 + 6H2O  C6H12O6 + 6O2
Glucose & Starch
• During photosynthesis glucose is produced (a simple sugar)
• However, plants cannot store glucose, so they convert it into
starch (many small glucose molecules are joined together)
• Starch is insoluble, meaning it can be stored easily (when you
wash some rice you can see the starch wash off)
Starch Test
• How can we test for starch?
• How can we relate the presence of starch to the amount of
photosynthesis taking place?
• Iodine tests for starch – it turns blue/black in the presence of
starch
• If a plant photosynthesis a lot, then there should be more starch
present (as more glucose would have been made and converted
into starch)
Experiment
• Your task is to look at two
different types of leaf –one
normal leaf, and one which
has been kept in the dark
• You need to find out how
much starch is present in each
leaf…
• Follow the leaf starch
experiment worksheet
Starch Experiment
Boiling & Ethanol
• Why do we need to boil the leaf first, and then add it to the
ethanol?
• Boiling the plant damages the cell wall, and the ethanol extracts
the chlorophyll from the leaf allowing us to test if any starch is
present
Explanation
• Explain your results for the leaf in the light and the leaf in the
dark
• The leaf in the light has a good store of starch (photosynthesis
has taken place, converting the glucose produced to starch)
• The leaf in the dark cannot
photosynthesize, but has been
respiring (using up the starch
supply)
Storage
• Why store the glucose as starch?
• Remember, the starch is insoluble, so the plant can store it
conveniently without it getting dissolved within the cell which is
much more convenient than the soluble glucose