Question

Identify plant organs that are sugar sources, sugar sinks, and organs that might be either. Explain.

Short answer

Mature leaves and storage roots produce sugar sources. Sugar sinks include growing leaves, flowers, fruits, and roots. Leaves and storing roots are two examples of organs that can be either (which are sinks in summer during the active growing season and sources in spring at the beginning of a growing season).

Step-by-step solution

Movement of sugar from source and sink 

A monosaccharide, mainly a sugar source, is a plant organ that is a net sugar generator, either through photosynthetic or starch degradation.

On the other hand, a sugar sink is an organ that is a net consumer or storehouse of sugar. Sinks differ in terms of energy requirements and capacity to offload sugars. There are sometimes more sinks than sources can support.

Role of sugar sink and source

Sinks typically get sugar from nearby sugar sources. For example, the top leaves on a branch may export sugar to the growing shoot tip, but the lower leaves may transfer sugar to the roots.

A developing fruit has the potential to monopolize the sugar sources that surround it. The sugar source determines the direction of movement for each sieve tube, and the sugar sink is interconnected by that tube.

Plant organs that are sugar sources, sugar sinks, and could be either

Sugar sinks include developing roots, buds, stems, and fruits. While developing leaves are sugar sinks, older leaves can be sugar sources if they are sufficiently illuminated.

Bulb or tuber, can be either a source or sink based on the season. It is a sugar sink while accumulating carbohydrates in the summer. After breaking dormancy in spring, it is a sugar source because its starch is converted down to sugar and delivered to the emerging shoot tips.