Plant Tissue Systems

Stomata

the cuticle does not let gases pass through it. Pores called stomata permit plants to exchange oxygen and carbon dioxide. Stomata (extend through the cuticle and outer layer of cells) are found on at least some parts of most plants. Guard cells, a pair of specialized cells border each stoma. Stomata open and close as guard cells change shape. When the stomata are open, a plant is able to gain carbon dioxide from the air, but the plant loses water vapor through the open stomata. When the stomata are closed plant conseres water, but photosynthesis slows down or stops because of a shortage of carbon dioxide.

Plant Tissues

vascular plants have three tissue systems. The dermal tissue system, the vascular tissue system and the ground tissue system.Ground Tissue makes up much of the inside of the nonwoody parts of a plant, including roots, stems, and leaves. The tissue that forms strands that conduct water, minerals, and organic compounds throughout a vascular plant is vascular tissue.

Dermal Tissue

2. The Dermal Tissue is the covering of the outside of the body of a plant. The epidermis is a "skin" formed by the dermal tissue in the nonwoody parts of a plant. The epidermis of the majority of plants is made of a single layer of flat cells. The epidermis commonly has hairlike extensions. These extensions on leaves and stems often assist with helping slow water loss by trapping moisture near the surface of the leaf. Root hairs are epidermis extensions on root tips that help increase water absorption. There is a waxy cuticle that coats the epidermis of stems and leaves that protects the plant and prevents water loss. When the cuticle was developed, it made it possible for plants to be in drier environments. The cuticle has a function of protecting the leaves an repelling water. When the dermal tissue in on woody stems and roots, it consists of several layers of dead cells referred to as cork. These cork cells have a waterproof chemical and are not covered by a waxy cuticle. In addition to its role in protection, dermal tissue also functions in absorbing mineral nutrients and gas exchange.

Ground Tissue System

4. The inside of most nonwoody plants is where ground tissue is and it surrounds and supports vascular tissue. They are thin-walled cells that remain alive. They keep their nucleus after maturing. There can be ground tissue that are thick-walled and lose nucleus. Ground tissue in leaves have cells with chloroplast for photosynthesis. When in stems and roots they support in the storage of water, sugar and starch. They often have large vacuoles for storage. Angiosperms have ground tissue that makes up fruit flesh. It isn't normal in woody parts of plants.

Phloem

The cells in Phloem conduct sugars and nutrients throughout the plant's body. The conduction cells of phloem have a cell wall, cell membrane, and cytoplasm. They lack organelles or have modified versions. Sieve-tube members are the conducting cells in phloem. These cells link to form sieve tubes. There are pores in the walls between sieve-tube members near each other that cnnect the cytoplasms and allow substances to pass from cell to cell. There are rows of companion cells beside the sieve tubes that have organelles. These companion cells carry out cellular respiration, protein synthesis and metabolic functions for sieve tubes.

Vascular Tissue System

There are two types of vascular tissue, xylem and phoelem, that transport water, minerals, and nutrients throughout the plant. The development of vascular tissue was one of the most important changes as plants evolved. The tissues are composed of cells that are stacked end to end. The two types, xylem and phloem allow most vascular plants to grow to much larger sizes than nonvascular plants.

Xylem

Xylem is made of thick-walled cells. These cells conduct water and mineral nutrients from plant's roots through it's stems to its leaves. At maturity, xylem cells are dead. They are left with their cell walls, that are strong. Tracheids and vessel elements are the two types of conducting cells in xylem. Water flows from one tracheid to the next through pits, or thin areas in the cell walls. Vessel elements link to form vessels. The vessel elements have large perforations in their ends that allow water to flow more quickly between vessel elements.