A student investigated the requirements for photosynthesis using a destarched variegated plant. The leaves of this plant have a green central region containing chlorophyll and a white outer margin containing no chlorophyll.
Two leaves, Leaf 1 and Leaf 2, were prepared as shown in the diagram:
- Leaf 1 was left in the open air but had a strip of black paper secured across its middle to block out light.
- Leaf 2 was sealed inside a transparent conical flask containing concentrated potassium hydroxide (KOH\text{KOH}KOH) solution, which absorbs carbon dioxide (CO2\text{CO}_2CO2).
The plant was then placed under a bright light source for 24 hours. Following this, four discs (A, B, C, and D) were cut from different regions of the leaves and tested with iodine solution.
Which of the discs would test positive for starch by turning blue-black when treated with iodine solution?
Disc B
Disc A
Disc D
Disc C