Question

1. Sam picked healthy leaves from a house plant and placed them into a pot filled halfway with boiling water. He left the leaves in the boiling water for five minutes. Then he filled a glass jar with half a cup of rubbing alcohol. Using tweezers, he removed the leaves from the pot and placed them in the glass jar containing the rubbing alcohol. Sam then took the glass jar and put it in the middle of the pot of hot water. Sam let the leaves sit in the alcohol for 15-30 minutes until they turned white. What color will the jar of alcohol turn and why?
2. Using the tweezers Sam carefully removes the leaves from the alcohol and dips them in the rinse water. He blots the leaves gently of a piece of paper towel and places them in a different area of light on the plate. Using the tweezers gently spreads the leaves back into their normal shapes. He uses a syringe to flood the leaves with iodine. After two minutes what are the colors of the leaves?
3. Circle one answer: The results of the iodine test were positive/negative for starch.

_____________ molecules formed during the process of __________ are converted to starch storage.

Based on your knowledge of photosynthesis, list and explain at least two factors that could lead to a negative iodine test.

Answer 1

The colour of the jar containing alcohol turns green because alcohol disrupts chloroplast thereby dissolving chlorophyll pigment . As a result leaf turns into pale colour.

When leaf is put into a pot filled with boiling water no further chemical reactions takes places as the cells become softened and when boiled in alcohol chlorophyll pigment will be dissolved and the leaf becomes brittle. when rinsed with water it again becomes soft.

The portion of the leaf exposed to light will turn blue-black in colour when iodine solution is added  indicating the presence of starch and the portion of the leaf which is not exposed to light will retain reddish brown colour of iodine indicating the absence of starch synthesis.

The results of the iodine test were positive indicating the presence of starch.

Glucose formed during the process of photosynthesis is converted into starch for storage.

The factors that could lead into a negative iodine test are availability of sunlight, water and CO2 .

When sunlight is not adequate plants could not perform photosynthesis and water and CO2 are essential reactants for the process of photosynthesis to take place.

Photosynthesis can be defined as the process of synthesis of glucose from carbondioxide and water in the presence of sunlight and chlorophyll and liberating oxygen.