Introduction: Plants are arguably the most important organisms on Earth. This is because they produce the oxygen that most other organisms need in order to survive. If all the animals on Earth were to disappear, the plants would never know it. However, if all the plants were to go, life as we know it would cease to exist fairly soon afterwards.

In the evolution of plants, three main structures have arisen that provide plants with all of the nutrients and other materials they need. These structures include roots, stems, and leaves. The roots anchor the plants into the soil and also are the primary site of water and nutrient absorption. The stems hold the plants upright and keep them closer to the Sun. They also serve as a highway for water going up and sugars coming down. The leaves are the main site of sunlight absorption, photosynthesis, and water and gas exchange.

In order to move water up from the ground and sugars back into the roots, vascular plants have evolved special tissues that serve at the channels through which these materials move. Xylem are the tubes that move water from the roots up to the leaves. Phloem move sugars from the leaves back to the roots for long term storage.

Examples of vascular plants include the world's tallest plant, the Giant Sequoia tree in California, which can grow to over 300 feet tall (see image left). Many vascular plants are used to make wood for houses, medicines, and produce food for humans.

Directions for this Lesson: Answer the practice questions and then watch the video to learn more about vascular plants.