Plant Tissue SystemsLike other organisms, plant cells are grouped together into various tissues. These tissues can be simple, consisting of a single cell type, or complex, consisting of more than one cell type. Above and beyond tissues, plants also have a higher level of structure called plant tissue systems. There are three types of tissue systems: dermal tissue, vascular tissue, and ground tissue systems.
Plant Tissue Systems: Dermal TissueThe dermal tissue system consists of the epidermis and the periderm. The epidermis is generally a single layer of closely packed cells. It both covers and protects the plant. It can be thought of as the plant's "skin." Depending on the part of the plant that it covers, the dermal tissue system can be specialized to a certain extent. For instance, the epidermis of a plant's leaves secretes a coating called the cuticle that helps the plant retain water. The epidermis in plant leaves and stems also contain pores called stomata. Guard cells in the epidermis regulate gas exchange between the plant and the environment by controlling the size of the stomata openings.
The periderm, also called bark, replaces the epidermis in plants that undergo secondary growth. The periderm is multilayered as opposed to the single layered epidermis. It consists of cork cells (phellem), phelloderm, and phellogen (cork cambium). Cork cells are nonliving cells that cover the outside of stems and roots to protect and provide insulation for the plant. The periderm protects the plant from pathogens, injury, prevents excessive water loss, and insulates the plant.
Plant Tissue Systems: Ground TissueThe ground tissue system synthesizes organic compounds, supports the plant and provides storage for the plant. It is mostly made up of parenchyma cells but can also include some collenchyma and sclerenchyma cells as well. Parenchyma cells synthesize and store organic products in a plant. Most of the plant's metabolism takes place in these cells. Parenchyma cells in leaves control photosynthesis. Collenchyma cells have a support function in plants, particularly in young plants. These cells help to support plants while not restraining growth due to their lack of secondary cell walls and the absence of a hardening agent in their primary cell walls. Sclerenchyma cells also have a support function in plants, but unlike collenchyma cells, they have a hardening agent and are much more rigid.
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