Translocation of Organic Solutes

Plants not only move water and minerals from their roots to their leaves, but they also transport organic nutrients to different parts of the plant that need them, such as young leaves, flowers, seeds, fruits, and roots. This transportation of organic nutrients is done through special tissues called phloem.

To understand how this works, we can look at the feeding habits of aphids, which are small insects that suck the juice of plants. When an aphid feeds on a plant, it inserts its mouthparts, called stylets or proboscis, into a sieve tube, which is a part of the plant's phloem tissue that contains sugary fluid.

The sieve tubes in plants are under high pressure, known as turgor pressure. As a result, the sugary sap from the sieve tube is forced through the gut of the aphid. The sap then comes out of the posterior end of the aphid's gut as droplets, which are called honeydew.

This process of aphids feeding on plant sap and excreting honeydew provides valuable information about how organic nutrients are transported within plants. It shows that phloem tissues play an important role in translocating, or moving, organic nutrients from one part of the plant to another, allowing the plant to distribute essential nutrients to where they are needed for growth and development.