Question

A pulse of sugars labelled with a fluorescent dye is supplied to leaves of young plants. After a brief interval, tissue sections are obtained from the plant and examined under the fluorescence microscope. Tissues are scored for the presence of fluorescence and ranked from very high to low fluorescence. Which cells would contain the most fluorescence?

a) Cells with low metabolic activity
b) Cells with chloroplasts
c) Cells undergoing mitosis
d) Cells with high metabolic activity

Answer 1

Cells with high metabolic activity would contain the most fluorescence when pulsed with fluorescently-labeled sugars, as they actively use these sugars for various biochemical processes.

Step-by-step explanation:

The cells that would contain the most fluorescence following a pulse of sugars labeled with a fluorescent dye would be those with high metabolic activity. This is because cells with vigorous metabolic functions utilize more sugars to fuel various biochemical processes. In the context of plant cells, these metabolically active cells are primarily involved in photosynthesis and active transport mechanisms, such as loading of sucrose into the phloem.

Photosynthates, like sucrose, are produced in the mesophyll cells and are then translocated through the phloem. The process of moving these photosynthates requires energy in the form of ATP, indicating high metabolic activity in the cells that are involved in this process. Therefore, when examining a plant under a fluorescence microscope after it has been fed fluorescently labeled sugars, the cells in areas like the phloem tissues would show high levels of fluorescence compared to other tissues.