When do you think the chloroplasts will be aligned with their flat surfaces parallel to the walls? When would they be perpendicular to the incident light?
(i) The chloroplasts will be aligned with their flat surfaces parallel to the walls of mesophyll cells when the light intensity is moderate or low. This orientation allows them to receive the optimum quantity of incident light for efficient photosynthesis, as the flat surfaces provide maximum area for light absorption.
(ii) The chloroplasts would be perpendicular to the incident light when the light intensity is very high or intense. This orientation helps reduce the amount of light absorbed by the chloroplasts, preventing potential damage from excessive light exposure. This is a protective mechanism to avoid photodamage while still maintaining photosynthetic activity.
Explanation
The textbook context states that chloroplasts align themselves along the walls of mesophyll cells to get the optimum quantity of incident light. From this statement, students can infer that chloroplasts adjust their orientation based on light intensity. When light is moderate, they position flat surfaces parallel to walls to maximize light absorption. When light is too intense, they turn perpendicular to reduce exposure and protect themselves from photodamage. This demonstrates the dynamic nature of chloroplast movement in response to environmental conditions.