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Botany10
Chp 26 Plant Structure
235,000 species +/-, very diverse forms. Plant bodies divided into roots and
shoot systems. Contain diffentiatyed tissues and vascular systems.
herbaceous vs woody plants
herbaceous plants have no woody tissue, are either annuals, biennials or
perennials
woody plants are all perennials
root systems – fibrous and taproots (storage roots)
StemsNode – where leaf attaches
Internode – space on stem between nodes
Terminal bud – shoot at tip of stem
Bud scales- modified leaves that protect the dormant terminal bud
Lateral buds- located in the axils of leaves, if they grow they become
branches
Bud scale scars –
Leaf scarsLenticels- allow oxygen to diffuse into stem (woody stems)
LeavesBlade and petiole
Simple leaves have an undivided blade
Compound leaves have a blade divided into at least two or more leaflets
Use lateral buds to determine if a leaf is simple or compound…compound leaflets
form in a single plane.
Leaf arrangements (see figure 26-4 on page 509)
Alternate or opposite
Whorled
Venation
Parallel (moncots)
Netted – (dicots) palmately netted or pinnately netted (figure 26-6)
TISSUES
A tissue is a group of cells that form a structural and functional unit,
tissues may be comprised of just one type of cell or of several cell types.
(see discussion of tissue types on page 510) ground tissue system, vascular
tissue system and dermal tissue system.
Ground Tissues System –
Parenchyma found throughout the plant, perform important functions
such as photosynthesis, storage and secretion
Collenchyma cells combine to provide structural support, particular in
herbaceous plants
Sclerenchyma – hard structural support.
Vascular Tissue SystemXylem phloem
Dermal Tissue System –
Epidermis and Periderm
Epidermis usually single layer of cells, herbaceous plants and young
woody plants, epidermis secretes a waxy layer called a cuticle. Carbon dioxide,
oxygen and water vapor enter/escape through the cuticle via stomata. Guard
cells are found at the opening of the stoma, open during the day and closed at
night…usually. Epidermis may also have trichomes; outgrowths such as hairs or
spikes that serve a wide variety of purposes
Periderm many cell layers thick – woody plants…replaces epidermis as
woody plant matures
PLANT GROWTH (for interesting web site with info on recent advances in plant
development see www.edoc.com/plantcell/abs/v9n7/981.html or for a discussion on
germination and primary growth try http://research.umbc.edu/~farabaug/growth.htm)
3 different processes – cell division, cell elongation and cell
differentiation
Plants grow differently than animals…plants grow in localized areas called
meristems. Cells in meristems do not differentiate. Meristematic cells retain the
abiltiy to divie by mitosis. Plants continue to grow throughout their life spans.
Primary Growth – increase in the length of a plant, occurs at the apical
meristems (herbaceous plants)
Secondary growth – increase in the girth of a plant, occurs at the lateral
meristems (woody plants)
LEAVES – Chp 27
(for more information about leaf anatomy and morphology look at
www.botant.uwc.ac.za:80/sci_ed/std8/anatomy/leaves.htm or
http://koning,ecsu.ctstateu,edu/Plants_Human/MorpAnat.html or a leaf library at
www.onyxtree.com?leaf.html
Upper epidermis and lower epidermis. Because of large surface area
needed for photosynthetic processes (collection of light & gas exchange) the
surface area is prone to water loss. The cuticle reduces this tendency. Cuticle
thickness varies between upper and lower leaf surfaces.
Trichomes –
Stomata - guard cells open and close. Guard cells are the only sells in the
epidermis that have chloroplasts. There are more stomata on the lower surfaces
of leaves.
Mesophyll- photosynthetic tissue of the leaf, between upper and lower surfaces.
(see discussion on pg 528)
Vascular system of xylem and phloem pass through the mesophyll in leaves.
Xylem is usually toward the upper epidermis and phloem toward the lower., The
viens are surrounded by cells called a bundle sheaf
DICOTS AND MONOCOTS
Characteristic
Leaf shape
Attach to stem
Veins
Mesophyll
Monocot
Narrow leaves
Wrap around stem
Parallel
Not differentiated
Dicot
Broad flattened leaf
Petiole
Netted
Contains both palisade and
spongy layers
For more on monocots and dicots look at
www.ucmp.berkeley.edu/glossary/gloss8/monocotdicot.html
Structure is related to function in leaves – pg 530
Photosynthesis – epidermis is transparent allowing light to penetrate to the
interior of the leaf. The stomata allow carbon dioxide into the leaf and oxygen
back out (gas exchange). Water is transported to the leaf through the xylem and
sugars produced prom photosynthesis are distributed via the phloem.
Transpiration - 99% of the water absorbed from the soil by roots is lost from
evaporation, primarily through the leaves. Loss of water vapor from the above
ground portions of a plant is called transpiration.
Guttation – pg 534 when transpiration is low and water quantity is high
Abscission – leaves are lost because of reduced water availability, it is a
measure of water conservation…see abscission zone on pg 535.