The diagram given below represents an experiment to prove the importance of a factor in photosynthesis (a leaf partly covered with black paper held by clips). Answer the questions that follow: The diagram given below represents an experiment to prove the importance of a factor in photosynthesis (a leaf partly covered with black paper held by clips). Answer the questions that follow:
What will you observe in the experimental leaf after the starch test?
Topic: Result of the starch test
Answer
The COVERED portion remains BROWN (the colour of iodine), showing that NO STARCH is present, because it received no light and could not photosynthesise.
The UNCOVERED portion turns BLUE-BLACK, showing that starch IS present, because it received light and photosynthesised.
This proves that LIGHT IS NECESSARY for photosynthesis.
Describe BOTH portions and then state the CONCLUSION. An answer giving the two colours without saying what they prove has stopped one step short of what the question wants.
THE IODINE TEST: blue-black means starch is PRESENT; brown (unchanged) means it is ABSENT.
Remember the essential preliminary: the plant must be DESTARCHED by 24 to 48 hours in the dark beforehand, or any starch found might be left over from before and the result would prove nothing.