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Biology 2014-2015

Specialized Tissues in Plants
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SWS Life Science

Section 23-1

Specialized Tissues in Plants

 

Seed Plant Structures

    Seed plant cells are organized into three different tissues and organs:

            1. Roots

            2. Stems

            3. Leaves

    Linked together by systems that run the length of the plant performing functions such as:

v    Transport

v    Protection

v    Coordinating plant activities

 

Roots

1. absorbs water and dissolved nutrients

2. anchor plants in the ground, hold soil in place, and prevent erosion

3. store food (starch)

 

Stems

1. support system for the plant body

2. transport system that carries nutrients

3. defense system that protects the plant against predators and disease

 

Leaves

1. main photosynthetic system

2. contain subsystems to protect against water loss

 

Plant Tissue Systems

    Plants consist of three main tissue systems:

            1. dermal tissue - like the "skin" of a plant or the outermost layer of cells

            2. vascular tissue - like the plants "bloodstream", transporting water and

                      and nutrients throughout the plant

            3. ground tissue - everything else!

 

Dermal Tissue

    Dermal tissue (outer covering of a plant) consists of a single layer of epidermal cells, and covered with the cuticle, a thick waxy coating that protects against water loss.

    Examples:

            1. Trichomes are tiny projections which protect the leaf and give it a

                    fuzzy appearance.

            2. Root hair cells provide a large amount of surface area and aid in water

                    absorption.

            3. Guard cells are on the underside of leaves and regulate water loss

                    and gas exchange.

 

Vascular Tissue

    Vascular tissue forms a transport system that moves water and nutrients throughout the plant.

    Principle subsystems are:

            1. Xylem - a water-conducting tissue

w   Consists of tracheids (long, narrow cells with walls that are impermeable to water) and vessel elements (wider than tracheids and stack on top of one another for continuous water flow)

            2. Phloem - a food-conducting tissue

w   Consists of sieve tube elements, (arranged end to end and form a pipeline which sugars and other foods flow through) and companion cells (surround sieve tube elements and support phloem cells)

 

    They are both a network of hollow connected cells that carry fluids throughout the plant.

 

Ground Tissue

    Ground tissue lies between dermal and vascular tissues.

    Parenchyma is the main type of ground tissue.

w   cells have thin cell walls and large central vacuoles

w   in leaves, they are packed with chloroplasts and the main site of photosynthesis

    Collenchyma is thicker, strong, flexible cell which supports larger plants.

w   makes up the "strings" of a stalk of celery

    Sclerenchyma is an extremely thick, rigid cell that makes ground tissue tough and strong.

 

Plant Growth and Meristematic Tissue

    Most plants have indeterminate growth, which means they grow and produce new cells at the tips of their roots and stems for as long as they live.

    Meristems are clusters of tissue that are responsible for continuing growth throughout a plant's lifetime.

    Meristemtic tissue are the new cells produced and are undifferentiated (no specialized function yet).

    ONLY PLANT TISSUE THAT PRODUCES NEW CELLS BY MITOSIS.

    Apical meristem is a group of undifferentiated cells that divide to produce increased length of stems and roots.

    Differentiation, is the process where cells develop into mature cells with specialized structures and functions.

w   produce dermal, ground and vascular tissue

    Many plants also grow in width as a result of meristematic tissue that lines the stems and roots of a plant.