Difference between Source and Sink in Plants

The photosynthetically active parts of a plant are referred to as the source. The areas of active growth and areas of storage are referred to as sinks. However, a source is not always a source, and a sink is not always a sink. For example, leaves that act as sources when the plant is fully grown are known to act as sinks when the plant is growing. The stems and branches act as a sink, but when they are young, then tender stems are green and perform photosynthesis. Thus they act as sources when they are young.

Plants are autotrophs, i.e., they cook their own food. However, this food needs to be transported to different parts of the plant. A phloem is a conducting tissue in plants that transports food to all the parts of a plant. The movement of food from the source to the sink is known as phloem translocation.

Leaves photosynthesise and are, therefore, sources of plants. The sugar produced through photosynthesis is translocated with the help of phloem sieve elements to parts such as roots, flowers, seeds, fruits and storage organs like tubers and bulbs. Simply put, leaves and stems are the exporters of organic solutes, and the rest of the plant parts are the importers of those solutes.

Let us now differentiate between source and sink in plants.

Source in Plants
Sink in Plants
The photosynthetically active parts of the plants are referred to as the sources. The areas of active growth and the areas of storage are referred to as the sinks.
The phloem elements are loaded at these sites. The phloem elements are unloaded at these sites.
The source in the plant is responsible for synthesising the sugars required for plant growth. The sinks in the plants use the sugars for immediate use and store the rest for future metabolic needs.
The leaves act as a source when photosynthesising. Seeds, fruits, flowers, roots, and storage organs act as sinks in fully grown plants.

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Frequently Asked Questions


What is the source-sink theory?

The source-sink theory is an ecological model that says that a variation in habitat is likely to bring a downfall or rise in the population graph.


What is the importance of source-sink relationships in plants?

The source and sink relationships in plants determine the yield and nutritional quality of the crops produced.


Is fruit a source or sink?

Fruits act as a sink in plants because they depend on the source for their supply of sugars.


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