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The Plant Body
•Plant body is made up of cells and tissues.
•Tissues are groups of cells that create a unit that has structure and a certain function.
•Simple tissues are made of one type of cell, while complex tissues are made or more than one kind.
•In plants, there are three tissue systems that each contains two or more kinds of tissues.
•Ground tissues provide both flexible and hard support and structure, storage, secretion, photosynthesis, and even differentiation into other types of cells (parenchyma only).
•It is composed of parenchyma, collenchyma, and sclerenchyma, which have different cell wall structures (see below for more).
• The cells secrete a thin primary cell wall that streches and expands. After growth, the cells often secrete a thicker and stronger secondary wall, which is inside the primary cell wall.
•Vascular tissues conduct water and dissolved nutrient minerals from the roots to the stems and leaves, conduct dissolved sugars to all parts of the plant, and also provide structural support for the plant.
•The tissue system consists of both xylem and phloem, which accomplish these tasks (see below for more).
•Dermal tissues provide a protective coating from the plant, help prevent water loss, control the diffusion of gas in and out of the plant, and allow light into the plant so that it can be absorbed in photosynthesis.
•It consists of the epidermis and periderm, which are complex tissues (see below for more).
•In herbaceous plants, the dermal tissue system is simply a layer of epidermis, while in wood plants, the initial epidermis splits as the plant grows and then periderm (which is much thicker) created the outer bark.
•Organs, such as roots, stems, leaves, flowers, and fruits, are made up of all three tissue systems. The tissue systems of different organs form a network throughout the plant.
Roots and Shoots:
•Usually an underground network of roots that helps anchor the plant into the ground.
•They provide the needed resources from the dark, moist soil by absorbing water and dissolved nutrient minerals from the soil.
•The vascular tissue system in the roots carries the water and nutrients to the areas of the plant that need it.
•The xylem of the vascular tissue carries the water and nutrients.
•The aboveground portion of the plant.
•Usually consists of a vertical stem with leaves.
•Flowering plants contain flowers or fruits with seeds in them.
•The stem allows the plant to grow and gives it structure.
•The leaves of the shoot system absorb the light and CO2 that is needed for photosynthesis to occur.
•The leaves contain mesophyll cells to trap in light and guard cells with stomata to let in CO2.
Vascular Plant Body
Ground Tissue System
•This tissue is found throughout the body of the plant and is the most common type of tissue in the plant.
•The soft parts of a plant (like the edible part of an apple or potato) consists mainly or parenchyma tissue.
•Have very thin and flexible primary cell walls and usually have large vacuoles. The thin cell wall consists mainly of cellulose with a bitof hemicelluloses and pectin.
•Many also have chloroplasts (the ones with chloroplasts are found in leaves and are involved in photosynthesis).
•The functions of the tissue are photosynthesis, storage, secretion, and also differentiation into other kinds of cells as a result of an injury to the plant.
•They store starch grains, oil droplets, water, and salts (sometimes visible as crystals)
•They secrete resins, tannins, hormones, enzymes, and sugary nectar.
•Tannins are polyphenols (contain phenol units) that either bind and precipitate or shrink proteins and other organic compounds.
Below are the parenchyma cells of an Irish potato.
•This tissue often occurs as long strands near stem surfaces and along leaf veins (the strings in a celery stalk)
•They have very thick primary walls but no secondary walls (have no lignin). The thickened areas of collencyma cell walls contain a lot of pectin in addition to cellulose and hemicelluloses.
•They have elongtaed cells with primary walls that are unevenly thickened and are especially thick in the corners
•They provide flexible support due to not having lignin in their cell walls- lignin is very stiff
•Its function is to support the plant, especially soft, nonwoody plants
•This support lets the plant grow upwards and compete with other plants for sunlight
Below are collenchyma cells.
•This tissue may be located in several areas of the plant body- sclerieds are found in the shells of nuts and in the pits of stone fruits. They also allow for the gritty texture of pears. Fibers are often found in wood, inner bark, and ribs (veins in leaves) of flowering plants.
•The cells have both primary and secondary walls (lack secondary walls at pits).
•The thick secondary cell walls have a lot of lignin in them (along with cellulose, hemicelluloses, and pectin).
•The secondary cell walls become strong and hard due to thickening- thus they cannot stretch or elongate.
•Cells that provide support are often dead.
•Main function is to provide strength and support as the tissue is hard and inflexible
•Sclereids are of various shapes and form hard shells and pits
•Fibers are long and tapered cells that are often in patches or clumps.
•They are found throughout the plant, as they provide strength for stems and veins in certain leaves
Below are sclerenchyma cells.
•It is continuous throughout the plant body.
•Its function is to conduct water and dissolved nutrient minerals from the roots to the stems and leaves and to provide structural support for the plant.
•It is a complex tissue made up of four different cell types: tracheids, vessel elements, parenchyma cells, and fibers.
•Fibers provide support and strength.
•Parenchyma cells store materials for the plant.
•Tracheids and vessel elements conduct water and minerals. They are dead at maturity and are hollow so that only their cell walls are left.
•Tracheids are long and tapering cells that are in groups of clumps. Water passes from one to another as it moves up a plant.
•Vessel elements are also hollow, but their end walls have holes in them and their diameters are larger than tracheids’. They are stacked and water is able to travel through them as it moves up the plant. A stack of vessel elements forms a vessel, which is like a pipe for water.
•Vessel elements also have side walls with pits in them that allow for the sideways movement of water from one vessel to another.
A cross section of xyl;em can be seen to the right.
•Its function is to conducts food materials (the carbohydrates produced by photosynthesis that are dissolved in water) to all places in the plant and to provide structural support.
•It is a complex tissue made up of sieve tube elements, companion cells, fibers, and phloem parenchyma cells.
•Fibers are usually very long in herbaceous plants and provide support.
•Parenchyma cells store materials for the plant.
•Sieve tube elements join end-to-end to create sieve tubes. They have cell end walls called sieve plates. These plates have a series of holes that allow the cytoplasm to extend from one sieve tube element to another.
•They are living when mature, but many of their organelles disintegrate at this point. They can function without nuclei.
•Adjacent to each sieve tube element is a companion cell that helps the sieve tube element work.
•It has a nucleus that directs the actions of the sieve tube element and the companion cell.
•Plasmodesmata are cytoplasmic connections between companion cells and their adjoining sieve tube elements.
•Overall, the companion cell helps move sugar into the sieve tube element so that the sugar can be sent to other parts of the plant.
A close up of phloem can be seen to the right.
•In herbaceous plants, it is a single layer of cells that provides a protective coating for the plant.
•Woody plants initially make an epidermis too but it splits apart during growth.
•Epidermis is a complex tissue made up of mostly unspecialized living cells. There are some specialized guard cells and trichomes in the layer of cells, too.
•They are flattened, transparent cells that allow light to pass through so chloroplasts of other cells can absorb the light.
•They secrete a waxy cuticle over the surface of their exterior walls to prevent water loss.
•Since the cuticle slows diffusion of CO2, stomata, or small pores in the epidermis, control the CO2. They are surrounded by guard cells that usually open during the day and close at night. They are opened or closed based on the amount of water in them (they close the stomata when they have little water in them and open it when they are filled with water)
•Epidermis also contains little hairs, called trichomes that come in a variety of sizes and have a variety of functions.
•In salty environments, they can remove excess salt from plants.
•In desert plants, they can increase reflection of light so that the plant stays cooler and doesn’t lose as much water.
•Others serve for protection, as they prevent animals from eating the plant.
•Root hairs are unbranched trichomes that increase the surface area of the root epidermis so that more water and minerals can be absorbed more efficiently.
Epidermis can be seen to the right.
•It replaces the epidermis in the stems and roots of old woody plants as they grow in size and girth, providing a protective coating.
•It creates the outer bark of old stems and roots and is a complex tissue made or cork cells and cork parenchyma cells.
•Cork cells are dead when mature and have walls coated with the waterproof suberin to reduce water loss and protect.
•Cork cambium cells are meristematic and help form new cells.
•Cork parenchyma cells function mainly in storage.
Periderm can be seen to the right.
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