Final answer:
The rate of photosynthetic activity for tube 2 decreases over time due to various factors affecting plant metabolism and environmental conditions.
Step-by-step explanation:
The rate of photosynthetic activity for tube 2 can be determined by calculating the change in absorbance per minute or δa/min. As the numbers decrease over time, it indicates a decrease in photosynthetic activity. This can be due to factors such as limited light, depletion of nutrients, or metabolic changes in the plant.