Cells and Tissues of the Plant Body

Tissue Systems in Plants A tissue is a group of cells that forms a structural and functional unit There are three main tissue systems in plants: Ground tissue system used for photosynthesis, storage, and support Vascular tissue system Intricate plumbing system that conducts water, minerals, and food Dermal tissue system Covering of the plant body

Ground Tissue System This makes up the most of an herbaceous plant This system is composed of three tissues: parenchyma collenchyma sclerenchyma

Parenchyma Tissue Found throughout the plant body and is the most common type of cell and tissue The soft parts of the plant are mostly parenchyma Ex: edible part of an apple or potato

Parenchyma Tissue These cells contain chloroplasts to perform photosynthesis Starch grains, oil droplets, water, and salts can be stored in parenchyma cells Resins (sap), hormones, enzymes, and nectar can be secreted by these cells These cells have the ability to differentiate into other kinds of cells when a plant is injured (similar to a stem cell in the human body)

Collenchyma Tissue This is a flexible tissue that provides support in soft, nonwoody plants. This allows for plants to grow upward and receive adequate sunlight. These cells are elongated and have thicker corners The strings of celery have collenchyma tissue

Sclerechyma Tissue These cells have primary and secondary cell walls which means they have two support systems for the plant The secondary cell walls become strong and hard because of thickening of the wall around the cell. When sclerenchyma tissue provides support, the cells are often dead. Two types: sclereids and fibers

Sclerenchyma Tissue Sclereids: Fibers short cells that vary in shape Common in shells of nuts or the stones of fruits Ex: gritty texture of pears are sclereids Fibers Long tapered cells that occur in groups or clumps Abundant in the wood, inner bark, and veins of leaves

Vascular Tissue System Embedded in the ground tissue and transports materials through the plant Xylem and Phloem are the two main tissues within this system

Xylem and Phloem Xylem: moves water and dissolved minerals from the roots to the stems and leaves Contains four cell types: tracheids, vessel elements, parenchyma cells, and fibers Phloem: moves food (carbohydrates) throughout the plant and provides structural support Contains four cell types: sieve-tube elements, companion cells, phloem fibers, and phloem parenchyma cells

Dermal Tissue System Provides a protective covering for plant parts In herbaceous plants this is the epidermis In woody plants, an epidermis will split apart creating a periderm that is stronger and replaces the role of the epidermis

Epidermis Epidermis: tissue made of unspecialized cells with guard cells and trichomes included Cells are thicker on the outside for protection Release a waxy layer called the cuticle that covers surface to reduce water loss Between two guard cells are stomata that allow for gas exchange Contains trichomes which are outgrowths or hairs

Periderm Periderm: the outmost layer of cells covering a woody stem (the outer bark) Composed mostly of cork cells and cork parenchyma cells Cork cells are heavily coated with suberin which is waterproof helping to reduce water loss

Plant Meristems In order for plants to grow, they must go through Cell division Cell elongation Cell differentiation In animals, these processes occur everywhere, however in plants, there are only particular locations for growth, meristems

Two Kinds of Growth Primary growth: an increase in the length of a plant All plants have this type of growth Secondary growth: an increase in the girth (horizontal) of a plant Only woody plants have this type of growth

Primary Growth Primary growth occurs at apical meristems or areas at the tips of roots and shoots. Roots have a protective layer of cells called the root cap that protect the root during the division of cells

Secondary Growth Secondary growth occurs at the lateral meristems which occur at the entire length of stems and roots This growth is what allows for trees to form rings each year