Investigating photosynthesis Flashcards
What is starch?
Plants turn excess glucose in to starch which is stored in other parts of the plant and they also use it to make cellulose which is what the cell wall is made up of.
What would then happen to the amount of starch in a leaf if the plant was placed in the dark?
If there is no light, there is no photosynthesis. If there is no photosynthesis then glucose won’t be produced. Therefore the plant uses up the starch stored. Eventually it will run out and the plant will die as it has no food ( glucose)
Explain and describe how we test a leaf for starch
1- Kill the leaf. Break the cell wall. First, we are going to measure 100 ml of water and heat using a bunsen burner. Next, use forceps and place the leaf inside the boiling water. Boiling water stops any chemical reactions in the leaf and breaks up the cell wall making it easier to extract chlorophyll. DON”T FORGET TO TURN OFF THE BUNSEN BURNER AS ETHANOL IS FLAMMABLE.
2- Extract the chlorophyll to observe the color change for starch. Next, we measure 20 cm3 of ethanol and place in a tub of hot water for 10 mins. Next, use the forceps and place the leaf inside the boiling ethanol and wait for the leaf to bleach for 2-3 mins. This is the chlorophyll dissolving in the ethanol.
3- Next, take out the leaf from the ethanol using forceps and submerge it into cold water. This will soften the leaf and rinse off any ethanol.
4- Test for starch using iodine solution and observe any colour change : Lastly, spread the leaf on a petri dish and add a few drops of iodine. If starch is present their will be a colour change from yellow brown to blue black. If starch is not present, there will be no colour change and it will remain yellow-brown.
Do the white section of a variegated leaf have chloroplast?
No it does not so no starch is stored in them
Describe what happens when we test the variegated leaf for starch?
The white section of the leaf has no colour change when we add iodine solution so it remians yellow brown because no starch is present
Explain why you got these results-
The green section contained chloroplast so they carried out photosynthesis and stored glucose as starch therefore those sections turned blue black.
The white section has no chloroplast which is the organelle where photosynthesis takes place. Without chlorophyll, there is no photosynthesis.=, without photosynthesis, there is no production of glucose which is later stored as starch therefore their is no colour change.
What does the practical with variegated leaf prove about photosynthesis?
That chlorophyll is essential to carry out photosynthesis
Draw a labelled diagram of the leaf to describe results…
Green parts turn blue/black
(They contain starch)
White parts of leaf remain brown when tested with iodine.
(They contain no starch)
Green parts of leaf contain chlorophyll, so…
… they can photosynthesise and make starch
White parts of leaf contain no chlorophyll so…
… they cannot photosynthesise or make starch
How does a plant store the sugars that it makes?
As starch
How do we know if a plant has been photosynthesising?
If the plant contains starch which we test using iodine and turns blue-black if present
How can we show that a plant needs chlorophyll for photosynthesis?
Test a variegated leaf for starch
Only the green parts of the leaf contain starch as these are the only parts that can photosynthesise
State two uses of Glucose within plants. - 2 marks
Stored as starch, converted to cellulose which is used to make cell wall
- State the purpose of ethanol within the experiment? - 1 mark
