Explain how the internal structures of vascular and nonvascular plants transport food and water.
Vascular plants have a well-developed internal system called the vascular system, consisting of xylem and phloem tissues, which allows them to transport water, minerals, and nutrients throughout the plant.
Xylem is responsible for the transport of water and minerals from the roots to the stem and leaves. It is composed of long, hollow, and thick-walled cells called tracheids and vessel elements. Water uptake by the roots creates a suction force that pulls water up through the xylem vessels. This movement, known as transpiration, is driven by evaporation of water from the leaves through small openings called stomata. The cohesion and adhesion of water molecules also play a role in the upward movement of water in xylem.
Phloem, on the other hand, is responsible for the transport of sugars and other organic compounds throughout the plant. It consists of living cells called sieve elements, which are connected end-to-end to form sieve tubes. The movement of sugars in phloem is known as translocation and it occurs via a process called mass flow. Sugars are loaded into sieve elements in the source tissues, such as leaves, and are transported to the sink tissues, such as roots or developing fruits, where they are used for growth or storage.
Nonvascular plants, also known as bryophytes, lack a well-developed internal transport system. Instead, they rely on a simpler mode of transport called diffusion. Water and nutrients are absorbed directly through the cells of the plant's surface, which is usually in contact with moist environments. This diffusion mechanism, combined with the small size and simple structure of nonvascular plants, restricts their growth to moist areas and limits their ability to transport water and food over long distances.