Kingdom Plantae:
Plant Structure
Life Science
Chapter 12
Form and Structure
• Plants: living organisms which are eukaryotic
and multicellular, with organized tissues
(especially conducting tissues), plastids (such
as green chloroplasts), and cell walls
containing cellulose.
http://videos.howstuffworks.com/hsw/9763-the-world-of-plants-plants-and-the-planet-video.htm
Form and Structure
• Morphology – the shape or form of an
organism
• Anatomy – the bodily structure of an
organism; how the cells and tissues are put
together
• Important because the exterior shape and
interior structure of plants often determine
where a plant can grow, how it functions, and
how it can be used by man.
Plant Organs
• Most plants have four main types of organs:
– Roots
– Stems
– Leaves
– Flowers
Plant Organs
• Determined by their relationships to Nodes:
– Node – a region where a leaf is or was attached
• Roots DO NOT have nodes
• Stems DO have nodes
• Leaves DO NOT have nodes but are attached
to stems at nodes
Roots
• Two main systems:
– Tap root – has one or only a few main roots that
are thicker and longer than other roots of the plant
• Lateral roots – smaller roots which branch from the
main root
– Fibrous root – has a cluster of roots that are about
equal in size; may branch several times
Stems
• Two main types of stems:
– Woody – very hard, firm, and inflexible; capable
of supporting a lot of weight; often start as
herbaceous but grow into woody stems
– Herbaceous – softer and more flexible; contains
some supporting cells in the stems but not as many
as the woody stem; uses Turgor pressure to stand
straight
Leaves
• Three main parts of a leaf:
– Blade – the flat, green part
– Vein – the water- and sugar-conducting tissues
– Petiole – the part of the leaf between the node and
the blade
• Simple – one leaf
• Compound – many leaflets
Leaves
• Blade edges:
– Lobed – several indentations within leaf
– Toothed – edge is saw-like or has jags
– Smooth – no teeth
Veins
• Three main types of venation:
– Parallel – veins run parallel to each other
– Palmate – veins meet at a common point at the
petiole
– Pinnate – one main vein running the length of the
leaf with smaller veins extending to the edge
Petiole
• The point of connection between the node and
the leaf
– The veins the leaf blade converge and follow
through the petiole to the stem
Leaf Arrangements
• Three common arrangements:
– Alternate – one leaf per node
– Opposite – two leaves per node
– Whorled – three or more leaves per node
• Leaf arrangements help in identifying plants.
Plant Anatomy
• Support:
– Cellulose creating stiff cell walls
– Turgor Pressure caused by the presence of water in
the cells
• Plant:
– All living plant cells contain plastids, though not
necessarily green chloroplasts.
• Some green or red (Tomatoes) chloroplasts, some store
starch or oil
Plant Tissues
• Xylem – made of long, hollow cells; carries
water from roots through the stem to the leaves
– Wood – a collection of layers of xylem that have
been formed during several years; tree rings
• Phloem – carries sugar solution from the
leaves to the growing plants
• Vascularized bundles – a grouping of xylem
and phloem tubules
– leaves, young plants, and non-woody plants
contain vascularized bundles
– Fibers – long, narrow cells (not hollow) that are
VERY strong; often found grouped together to
form a fiber tissue
• Can be used to make rope and cloth
• Epidermis – thin, flat cells; effective barrier
against loss of water; the outermost tissue of
leaves, young roots, and young stems;
– Secretes a waxy substance that forms the cuticle –
protective coating
– Bark – layer just outside the xylem; innermost
layer of bark makes newest xylem and phloem
cells
– Cork – dead cells with thick cell walls; form a
tough, waterproof coating that keeps harmful
organisms out and moisture in.
• Cork cambium – layer of living cells just inside the dead
cell; constantly dividing and producing new cells
Major Plant Groups
• Three main categories:
– Nonvascular
– Seedless Vascular
– Seeded Vascular
Nonvascular
• Diffusion is used to transport water and other
materials
• Fairly short
• Live near water and in shady places
• Bryophytes
– Mosses – have structures that resemble leaves and
roots but are not true leaves and roots because they
do not have vascular tissue
– Two parts always present:
• Green part – used for sexual reproduction
• Rootlike part – anchors plant
Seedless Vascular
• Plants can grow taller because of the water and
material transport system; require water for
sexual reproduction
– Ferns
• “leaves” are called fronds; appear as coils; spores are
produced on the underside of the frond
• Rhizome – underground stem
• Roots – grow from rhizome into
ground
Seeded Vascular
• Reproduce by seeds not spores
– Do not rely on water for sexual reproduction
therefore can live in wet or dry areas.
– Seeds are multicellular; contain a young plant
(embryo); abundant energy reserves; barriers for
protection
• Gymnosperm – “naked seed” - limited barriers
– Pine trees – seeds are exposed
• Angiosperm – “covered seed” – completely protected
seed inside of the fruit
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