How is food transported in plants?

The transportation of food (mainly sugars produced through photosynthesis) in plants is primarily facilitated by the phloem tissue, which is part of the plant’s vascular system. The movement of food substances, such as sugars, from the sites of production (usually the leaves) to other parts of the plant, is known as translocation.

1. Sugar Production in Source Tissues:

» Photosynthesis occurs in the green tissues of the plant, primarily in the leaves. During photosynthesis, carbon dioxide and water are converted into glucose (a type of sugar) and oxygen, using sunlight and chlorophyll.

2. Loading of Sugars into the Phloem:

» The sugars produced in the leaves are actively transported into the phloem sieve tube elements. This process involves the movement of sugars from the mesophyll cells (where photosynthesis occurs) into the companion cells associated with the sieve tubes.

3. Pressure Flow Mechanism:

» The movement of sugars in the phloem is explained by the pressure flow mechanism. Sugars are actively transported into the sieve tubes, creating a high concentration of solutes (sugars) in the phloem at the source (where sugars are produced).

» This high solute concentration creates an osmotic pressure that causes water to move into the phloem from surrounding cells. As a result, there is an increase in pressure in the phloem at the source.

4. Translocation:

» The increased pressure in the phloem at the source causes the sap (a mixture of water and dissolved sugars) to flow through the phloem tubes toward areas of lower pressure, which are the sinks (parts of the plant where sugars are needed, such as growing tissues, roots, and storage organs).

5. Unloading of Sugars at Sink Tissues:

» At the sink tissues, sugars are actively transported out of the phloem sieve tubes and are used for various purposes, including growth, energy, and storage. This unloading process decreases the solute concentration in the phloem at the sink.

6. Return Flow of Water:

» The decrease in solute concentration at the sink creates a lower pressure in the phloem, allowing water to move out of the phloem tubes. This water can then be reabsorbed by surrounding cells or returned to the xylem for transport back to the roots.
The entire process of sugar transport through the phloem, from source to sink, is a dynamic and continuous cycle known as translocation. It plays a crucial role in distributing the products of photosynthesis throughout the plant, supporting growth, development, and metabolic processes.