A student was conducting a scientific experiment with a plant. She cut out three 1-inch circles from construction paper and attached each circle to a different leaf of the plant. Finally, she set the plant in front of a sunny window with good air flow and left it there. She made sure that the plant was given enough water during her experiment. After 2 days, she removed one of the circles; after 4 days, she removed another circle; and at the end of the week, she removed the last circle.
Here are her results:
Day 2: slight mark where the paper covered the leaf; it is a lighter green than the rest of the leaf.
Day 4: yellow circle where the construction paper was.
Day 7: almost white circle where the paper covered the leaf.
Using your knowledge of photosynthesis, which answer choice explains her results the best?
A. The part of the leaves that were covered with paper didn't allow for water to be absorbed. Without water, photosynthesis was unable to take place because the phloem was not able to bring the needed water molecules to the roots.
B. The part of the leaves that were covered with paper didn't allow for gas exchange through the leaf's stomata. Without oxygen, photosynthesis was unable to take place because the needed reactant of oxygen was missing.
C. The part of the leaves that were covered with paper didn't get any light. Without light, cellular respiration was unable to take place because the mitochondria within the leaf cells were unable to absorb the ATP energy needed for the chemical reaction.
D. The part of the leaves that were covered with paper didn't get any light. Without light, photosynthesis was unable to take place because the chlorophyll within the leaf cells were unable to absorb the sunlight energy needed for the chemical reaction.
D. The part of the leaves that were covered with paper didn't get any light. Without light, photosynthesis was unable to take place because the chlorophyll within the leaf cells were unable to absorb the sunlight energy needed for the chemical reaction.
D. The part of the leaves that were covered with paper didn't get any light. Without light, photosynthesis was unable to take place because the chlorophyll within the leaf cells were unable to absorb the sunlight energy needed for the chemical reaction.
The correct answer is D. The part of the leaves that were covered with paper didn't get any light. Without light, photosynthesis was unable to take place because the chlorophyll within the leaf cells were unable to absorb the sunlight energy needed for the chemical reaction.
To arrive at this answer, we can consider the process of photosynthesis and how it is affected by the variables in the experiment. Photosynthesis is the process by which plants convert sunlight, water, and carbon dioxide into glucose (a form of energy) and oxygen. Chlorophyll, a pigment present in the chloroplasts of plant cells, is responsible for absorbing sunlight and initiating the photosynthesis process.
In the experiment, the student covered certain parts of the leaf with paper circles. The results show that the covered areas of the leaf were lighter in color, turning yellow and almost white over time. These changes indicate that the covered areas were not able to carry out photosynthesis effectively.
Option A is incorrect because the experiment ensured that the plant was given enough water. The student has not mentioned any signs of water deficiency in the plant, so lack of water absorption is not the reason for the changes observed.
Option B is also incorrect because the experiment did not affect gas exchange through the leaf's stomata. The experiment focused on blocking light, not the exchange of gases (oxygen and carbon dioxide) that are involved in photosynthesis.
Option C is incorrect because cellular respiration is a different process from photosynthesis. Cellular respiration occurs in the mitochondria of cells and involves the breakdown of glucose to produce ATP (energy) for cellular functions. The experiment did not directly affect cellular respiration.
Therefore, the most reasonable explanation for the observed results is that the covered parts of the leaf did not receive light. As a result, the chlorophyll within those cells could not absorb sunlight energy, thus hindering the photosynthesis process.