CHAPTER 35 PLANT FORM

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Meristems: They elaborate the plant body after germination

- act as stem cells for plants- rapidly divide into differentiated cells that make up the plant body- two types:    - apical meristems= elongate the root and stem of plant    - lateral meristems= produce and increase in

girth        - only present in vascular plants (shrubs

and trees)

Apical Meristems

 - located at the tips of stems and roots-  after germination, meristems produce primary tissues which becomes the primary plant body (soft shoots and roots) - develop into three types of embryonic tissue systems    - protoderm- forms the epidermis    - procambium- produces primary vascular tissue    - ground meristem- differentiates further into ground tissue(Think of the plant as if its still an embryo, these are the developmental stages of plant life)

Lateral Meristems

- lateral meristems produce what is called secondary growth= most of the trunk, branches, and older roots of trees- has the most dramatic effect in woody plants which have two lateral meristems    - cork cambium- produces the cork cells of the outer bark    - vascular cambium- produces secondary vascular tissue and lies between the xylem (wood) and phleom (cells close to woods surface) - interesting fact: removing the bark of a tree damages the phloem and may eventually kill the tree

Organization of the Plant Body

-- coordination of primary and secondary growth produces an adult plant- plants do not have a fixed size and vary between plants, even of the same species- number, size, structure, and location of leaves is dependent on plant environment- vascular plants have a root system ( grounds them and provides the plant with ions) and a shoot system (the stem, leaves, flowers, and fruit)- nodes and internodes on the shoot develop axillary buds that create new growth-

Types of Plant Tissue: Dermal Tissue

-Epidermal cells cover all the primary plant body- a number of specialized cells occur at the epidermis - guard cells flank the stomta (epidermal openings)     - contain chloroplast    - stomata only occur on the epidermal tissue of leaves    - exchange of CO2 and O2 occur at stomata- Trichomes- hair like outgrowths of the epidermis (the "fuzzy stuff" on stems and leaves)    - keep leaf surfaces cool and reduce transpiration     - some secrete sticky or toxic substances- Root hairs- occur at the tips of young roots    - keep the root in close contact with soil and increase absorption efficiency - in vascular plants, the cork cambium produces bark which replaces the epidermis

 

 

Types of Tissue: Ground Cells

- Parenchyma cells: most common type of cell, less specialized, mainly store food and water in large vacuoles- Collenchyma cells: relatively flexible, provide support for plant organs so they can bend without breaking (the strings of celery)- Scelrenchyma cells: two types    - fibers= long slender cells grouped in strands    - sclereids= form in branched bundles- cell wall of scelrenchyma cells contain ligin- branched polymer that causes the cell wall to become rigid

 

 

Types of Tissue: Vascular

- xylem cells: principle water conducting tissue of plants- a combination of dead hollow cells that make vessels and trachieds- water and other ions travel from the roots through the xylem to the leaves and diffuses as water vapor out of the stomata- Phloem cells: principal food conduction tissue of plants- carried out by sieve cells and sieve-tube members- sieve-tube memebers form sieve tubes and each cell is pared with a parenchyma cell (called compaion cells)-connected by plasmodesmata- which supplies the plant cells with organic materialsr

Root Structure

-there are three types vegetative organs in plants;       - roots, stems, and leaves-there are four parts recognized in developing roots;        -root cap, zone of cell division, the zone of elongation,                       and zone of maturation   -apical initials divide the cells that divide and end up on the tip become root cap cells-the other cells divide in opposite directions and pass through the three zones then they are fully differentiated      

  

The Root Cap

-the root cap consist of two types of cells; columella cells (the inner cells) and root cap cells (the outer cells)-the root cap cells are continuously replenished by the root apical meristem-there are golgi bodies in the root cap cells that secretes a slimy substance, this helps the root through the soil. It also helps with the growth of nitrogen-fixing bacteria-the root cap also functions as the perception of gravity-the inner (columella) cells are very specialized              -they have endoplasmic reticulum in the nucleus and the periphery which is located in the middle or top of the cell         -contain no large vacuoles         -contain amyloplasts which form on the sides of the cells towards the pull of gravitiy                

The Zone of Cell Division

-apical meristem is located in the center of the root tip , it is shaped like a inverted concave dome-cells divide every 12 to 36 hours at the edge of the dome-these new daughter cells go to one of the three tissues; protoderm, procambium, or ground meristem-in this section genes have been identified-the inner cell layer regulates the flow of water, the outer cell layer acts as storage-if a mistake occurs and a cell is not in the correct place the cell will develop according to the new postition

 

The Zone of Elongation

-the cells from the primary meristem become several times longer than they are wide, this causes the root to lengthen-the vacuoles inside these cells increasing until they occupy 90% of each cell-cells do not grow anymore in size above the zone of elongation

The Zone of Maturation

-the cells that elongated in the zone of elongation are differentiated into specific cell types-many epidermal cells develop roots hairs, increasing surface area to absorb nutrients and water-the ground meristem produces parenchyma cells, they are found in the interior of the epidermis        -this layer called the cortex can by many cell layers thick and it functions in storage-the endodermis has walls filled with suberin, suberin is produced in bands called Casparian strips-the stele is everything inside of the endodermis-the primary xylem conducts water

Modified Roots

-most plants either produce tap roots or fibrous roots, however there are plants with roots specific to the function needed for that plant-a root that comes from something other than a root is called a adventitious root        

Stem Structure: External Form

-the shoot apical meristem produces stem tissue that creates bulges (primordia) these bulges will form into leaves, shoots, and flowers-a node is the area where the leaf is attached-the area between two nodes is called an internode-the bud that is a product of the primary shoot apical meristem is called the axillary bud-a leaf scar is from the leaves falling off the trees in the fall, a bundle scar is where the vascular connections were

 

 

 

 

Internal Form

-from the apical meristem  three primary meristems develop; the protoderm,the ground meristem, and the procambium -cells of the vascular cambium divide indefinitely and create a secondary tissue

Leaf External Structure

- two morphological groups- microphyll- one gapless vein, andmegaphylls- several veins- leaves have evolved to have a flattened blade and slender stalk- mutant leaves have been foundto never flatten

Leaf Blades

 - simple leaves= undivided- compound leaves= divided into leaflets    - pinnate= lined leaflets    - palmate= radial leaflets- alternate leaves have one bud per leaf- compound leaves have two leaves per bud

 

 

 

Leaf Internal Structure

- entire surface covered with transparent epidermis and cuticle, lower epidermis contains stomata and guard cells- two layers of tissue ( the palisade and spongy mesophyll) rest between the upper and lower epidermis - veins, stomata, and intercellular spaces function together for gas exchange

 

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