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BOTANY
Plants are either woody (long
living) or herbaceous (short lived
and green). Woody plants have
both woody and herbaceous
structures.
Plant Organs and Tissues
There are two groups of plant organs:
1. Vegetative - which have leaves, roots
and stems
2. Reproductive - which have flowers, fruits
and seeds
Plant organs are made of several
types of tissues:
1. Meristematic - these tissues contain cells
that are capable of mitosis and can
develop into any tissue found in that
plant. They are found in growing areas of
the plant, like buds, root tips and stems.
a. Apical meristem - is found at the tips and
roots of stems
b. Lateral meristem - includes the vascular
cambium, cork cambuim and pericycle
2. Vascular - these tissues are composed of
different types of cells; the xylem, which
carries water and dissolved minerals
upward in the plant and the phloem which
carries water and dissolved food
3. Structural - these tissues produce food,
store food, cover, support and protect
plant.
The Leaf
The function of a plant’s leaves is to absorb
energy from the sun (photosynthesis).
The blade of the leaf is a large, flattened
area connected to the stem by a petiole (if
there is no petiole the leaf is sessile).
Stipules may cover the leaf during
development. They may be wing-like,
photosynthetic, or may be thorns. Make a
drawing of a leaf, including the blade,
petiole, stipules and stem.
Leaves may have several
shapes, or margins (the edge
of the leaf). Make drawings of
the following margins: entire,
lobed, serrate, and repand
See
http://www.fnr.purdue.edu/extension/kp/lm.
html
Leaves may also have several venations:
1.parallel - found in corn, grass, iris’ and
orchids
2.netted - where large veins branch to form
a network of smaller veins
a. pinnate - the veins branch off of one central
vein, as in oaks, African violets, and apple
trees
b.palmate - two or more main veins coming
from a single point, as in maples, ivies and
geraniums
See:
http://www.pssc.ttu.edu/pss1411cd/STRUCTU
R/leaves/venation.htm
Leaves may also be simple, where
there is one blade on one
petiole, or compound, with
leaflets. The difference between
a leaf and a leaflet is that leaves
have stipules and leaflets don’t.
The Covering of a Leaf
1. The upper and lower epidermis
are one cell layer thick. They
protect the leaf.
2. The cuticle consists of a waxy
substance secreted by the
epidermis. It helps the leaf retain
water in hot weather
3. The stomata are for gas exchange.
They are found on the underside of
the leaf and are regulated by the
guard cells. Guard cells make
sugars that will cause a change in
the turgor pressure of the cells.
When turgor pressure in the guard
cells is high, the stomata are open;
when the turgor pressure in the
guard cells is low, the stomata are
closed.
The Internal Structure of a Leaf
1. The parenchyma consists of the palisade
and spongy mesophylls. They are the
primary photosynthetic areas of the leaf.
The palisade mesophyll has a larger
number of cells in a smaller surface area.
The cells contain many chloroplasts. The
spongy mesophyll is involved in carbon
dioxide-oxygen exchange.
2. The vein is composed of the xylem, phloem and
the collenchyma. We have already discussed
the xylem and phloem; the collenchyma
strengthens the vein.
Draw and label a diagram of a leaf on your
paper. Include the palisade mesophyll, spongy
mesophyll, upper epidermis, lower epidermis,
cuticle, stomata, guard cells, xylem, and
phloem. See page 647 in your textbook.
Root Systems
Roots have four main functions:
1. They anchor the plant
2. They absorb water & minerals necessary
for plant growth
3. They transport absorbed substances to
where they are needed in the plant
4. They store food (in carrots, radishes, &
beets)
A taproot system has the original root that
sprouted from a seed. It continues to grow
as the predominant root. Taproots are
often long, thin, and produce small,
branching secondary roots. A fibrous root
system has no taproot but has many
secondary roots. In general, roots usually
spread outward more than they grow
downward. Why do you think this type of
growth would be beneficial for the plant?
Roots exhibit primary and secondary growth.
Primary growth of a root is growth of a root
in length. This growth results from the
manufacturing of cells in the meristematic
region. Lengthening, however, is due to
cell growth in the elongation region. Once
elongated, growth stops. The primary
tissues of a root are located above the
maturation region and are made during
primary growth. These tissues have root
hairs that are able to reach water that may
be out of the root’s reach.
Secondary growth of a root is growth in
diameter, and it usually occurs in woody
plants. Secondary growth occurs when
secondary xylem and phloem are
produced. Because the vein is enlarged,
the epidermis is crushed (remember the
epidermis is important for water
absorption). Cork cells will protect the
enlarged veins but the vein must grow in
length if it is to continue absorbing water.
Secondary growth leads to the production
of extensive root systems.
Stems
Stems have two major functions:
1. They manufacture, support and display
leaves
2. They conduct many of the materials
needed for and manufactured by
photosynthesis to and from the leaves
How Plants Use Water
Plants use water in four ways:
A. For photosynthesis (think about the
equation)
B. For turgor-using water to stiffen parts of
the herbaceous plant
C. For hydrolysis-adding water to break
large molecules apart
D. For translocation-moving dissolved
materials from one place to another
What causes the movement of
water in plants?
Translocation is the movement of water and
dissolved minerals within a plant. The
movement of water may result from:
A. Root pressure - which causes the
movement of water up the xylem
B. Passive absorption - which is the
movement of water according to a
concentration gradient
C. capillarity - which is the tendency of water
to move up a thin tube (like the xylem)
D. transpiration - which is the release of
water vapor, by the plant, into the
atmosphere
E. cohesion - which is the “sticking together”
of a group of water molecules
F. transpiration-cohesion theory - which
states that as water molecules are
removed from the top of the plant (due to
transpiration) additional water molecules
that are “stuck together” rush into the
bottom
Plant Hormones
Plant hormones are chemical growth
regulators produced by the meristematic
regions of a plant. There are two main
groups of plant hormones:
A. Auxins - which are found in stems,
seeds, leaves, fruits and roots, Auxins
cause elongation of cells, cause
unfertilized flowers to develop into
seedless fruits, and stimulate the
formation of roots in wood stem cuttings.
B. Gibberellins
- stimulate cell
division and elongation, growth of
seeds, flower formation, pollen
formation and fruit formation.
Tropisms
A tropism is a growth response in plant that
is caused by hormonal action. There are
four kinds of tropisms:
A. phototropism - a growth response to light
B. thigmotropism - a growth response to
touch
C. chemotropism - a growth response to
chemicals; for example, hydrotropism is
a growth response to water
D. geotropism - a growth response to gravity
In general, a positive tropism is a growth
response toward a particular factor and a
negative tropism is a growth response
away from a particular factor.
Plants and Light
Light is important for plants. A plant that
does not receive enough light may be pale
green, yellow or white. The stem
elongates abnormally and the plant bends
toward any available light. Such a plant is
said to be etiolated.
• Photoperiodism is the response of a plant
to changes in light intensity and length of
days.
• Short day plants flower when the period of
light is less than 12 hours.
• Long day plants flower when the period of
light is more than 12 hours.
• Neutral day plants flower independently of
the photoperiod; they usually flower
continuously if proper conditions are met.
Reproduction of Flowering
Plants
Accessory Flower Parts
A. Sepals – leaflike, green structures that
encircle the flower stem beneath the
petals
B. Petals – leaflike, colorful structures
arranges in a circle called a corolla
around the top of a flower stem
Reproductive Flower Parts
A. Stamen (male)
• filament – the long structure that
supports the anther
• anther – the structure at the tip of the
filament that produces pollen containing
sperm
B. Pistil (female)
• stigma – at the top of the pistil; a sticky or
feathery surface on which the pollen
grains land and grow
• style – the slender stalk of the pistil that
connects the stigma to the ovary
• ovary – eventually becomes the fruit;
contains the ovules
• ovules – will become seeds if they are
fertilized
Use the diagram on
page 656 to draw a
typical flower and
label the accessory
and reproductive
parts.
Kinds of Flowers
•
•
•
•
Complete – a flower that has all 4 organs
(sepals, petals, stamens and pistils)
Incomplete – a flower that lacks one or
more organs
Male – have stamens but no pistils
Female – have pistils but no stamens