Overview of Plants 2

Plant Organs and Tissues Plants do have tissues that are organized into different organs. These organs of seed plants are roots, stems, and leaves. They also have 3 main types of tissues: dermal tissue, vascular tissue, and ground tissue.

Dermal Tissue The outer covering of the plant is made from dermal tissue – this is usually a single layer of epidermal cells. These surfaces are usually covered in wax to prevent water loss and injury, this is called the cuticle. Some epidermal cells have trichomes – tiny projections that help protect the leaf and give it a fuzzy appearance. In roots, dermal tissue also includes root hair cells that are very important for absorbing water.

Vascular Tissue This tissue form a transport system to move water and nutrients through the plant. Xylem is the water moving tissue. Phloem moves nutrients through the plant. Xylem is made of tracheids and vessel elements Phloem is made of sieve tube elements and companion cells.

Ground Tissue This is made of cells between dermal and vascular tissues. Ground tissue is made of mostly parenchyma cells – these cells have a thin cell wall and large central vacuole. Some ground tissue is made of collenchyma cells that have a thick cells wall to support the plant and sclerenchyma cells that make ground tissue tough and strong.

Plant Growth and Meristematic Tissue Most cells only have growth at their roots and stems. The new cells are produced in the meristems – this is the area where growth occurs. Meristemtic tissue is where new cells are located. At the tip off each growing shoot and root is an apical meristem. This provides cells that increase the length of stems and roots.

Roots Roots are responsible for absorbing water and dissolved nutrients. Roots also anchor the plant to the ground.

Types of Roots There are 2 main types – taproots and fibrous roots. Taproot is a primary root. Oak and hickory trees have large taproots to reach water. Carrots, dandelions, beets, and radishes have short, thick taproots that store sugars or starches. Fibrous roots have many branches and no single large root. Many weeds have fibrous roots.

Stems Stems are support systems for the plant body. It carries nutrients throughout the plants. It can also be a defense system that protects the plant against predators or disease. They also produce leaves, branches, and flowers. Xylem and phloem are major parts of a stem.

Monocot and Dicot Stems Monocots and dicots have the arrangement of vascular tissue in the stem different. In monocots – vascular bundles are scattered throughout the stem. A vascular bundle is both xylem and phloem. Dicots – vascular bundles are arranged in a cylinder. They are usually in a ringlike pattern.

Secondary Growth of Stems Secondary growth is how stems grow larger around. This is adding vascular tissue by vascular cambium and also the ability to produce cork through cork cambium.

Leaves The primary function of leaves is photosynthesis. Leaves can vary in shape but all share certain structural features. Most leaves have flattened sections called blades and then the blade it attached to the stem with a petiole.

Leaves have stomata – theses are porelike openings on the underside of a leaf that allow carbon dioxide and oxygen in and out of the cell. Each stomata is controlled by guard cells – they will open and close the stomata. This is also an area where transpiration can take place. Transpiration is the loss of water through its leaves. Plants need to control their stomata to allow gas exchange but not lose too much water.