Moving Sugars in Plants

Plants are every bit as complex as animals. Just as you may stretch in the morning sun, some plants are able to unfold their leaves, or even turn to face the sunlight. Just like us, they have specialized cells and tissues that help them live and grow. Yet, one of the biggest differences between us is that we have to find food to eat, while plants make their own. Most plants do this in their leaves through a process called photosynthesis.

A cross-section of some plant stems reveals phloem tissue. Click for more detail.

Plants have chlorophyll that uses sunlight to gather energy. The energy is then used to change carbon dioxide from the air into sugars like glucose and fructose. The plants then load the sugars from the leaves into the phloem in preparation for transport to other areas of the plant. Phloem are tissues that look like tubes. They transport sugars throughout the plant and supply it to tissues like roots, flowers and fruits that depend on this sugar to grow. Think of them like the veins in our body that move blood.

Moving sugars from cells in the leaves to cells in the phloem is difficult for plants. The concentration of sugar molecules can affect how the sugar acts. Different parts of plants have different concentrations of sugars. These different concentrations form what are called concentration gradients. To move sugars to some areas or cells, up concentration gradients, plants need to use proton pumps, many which require phosphorus and other enzymes. If there isn't enough phosphorus, the plant can be weak or stunted, or may even die.

Additional images via Wikimedia Commons. Plant seedling image by Bff.