Testing a leaf for starch (photosynthesis)

O/L Science · G.C.E. Ordinary Level · Grades 10–11

Aim

To show with a starch test on leaves that photosynthesis needs light and chlorophyll.

Apparatus

• Leaves (sunlight, dark, variegated)
• Ethanol and hot water
• Iodine solution

Method

1. Dip the leaf in boiling water for 1 minute to kill the cells.
2. Boil in hot ethanol to remove chlorophyll.
3. Rinse in water and add iodine solution.
4. Record blue-black (starch) or brown (no starch).

Conclusion

Only the green parts exposed to light make starch: photosynthesis needs both light and chlorophyll.