Download I. Angiosperm Root, Stems and Leaves (Plant Organs)

III. Angiosperm Anatomy and Physiology
A. Kinds of Plant Tissue
1. Meristem- One of two types of plant
tissue capable of carrying on mitosis
a) Root meristem- tissues near the tip of the root
responsible for downward growth
b) Apical meristem- tissue near the tip of a stem that
produces upward growth
c) The lengthening of the roots and stems is called
primary growth.
d) Cell produced by the meristem are all alike until
they go through differentiation. This process
converts them to specialized tissues: Epidermis,
Vascular and ground tissue
2) Cambium-tissue responsible for secondary
growth- the widening of roots and stems
3) Epidermis- outermost layer of cells that develop
into a protective layer that produces cutin- waxy
material that prevents water loss
4) Vascular tissue- tissue that transports food and
water
A) Xylem- dead hollow cells that transport water and
provide strength
B) Phloem- tissue that transports food (glucose)
5) Ground tissue- tissues for the storage of food
and the protection of vascular tissue
A) Cortex- food storage cells
B) Endodermis- cells that determine what enter the
vascular tissue
B. Angiosperm Organs
1. Roots
a) Functions:
1) Absorb water
and minerals
2) Anchor the plant
3) Store food in the
form of starch
b. Root Morphology (external structure)
1) Taproot- one
large vertical root.
Found in many
dicots and provides
firm anchorage.
Can be modified to
store a large amount
of food
2) Fibrous Root3) Adventitious
highly branched, thin Roots- arise from the
root. Provides a large stem and leaves
area for water and
mineral absorption.
Found in many
monocots
c. Root Growth & Structure
1) Zone of Differentiation: Cells become
different tissues. (Outer cells become epidermis.
Inner cells become vascular tissue and the cells
in between become cortex)
2) Zone of Elongation- cells become full
sized and drive the root cap downward into the
soil
3) Zone of Cell division root meristem is
here. Contains quiescent center
4) Root cap- protects inner cells from damage.
The smashed cells produce a slimy coat that helps
ground penetration
d. Cross Section of a Root
1) Epidermisprotection
2) Root hairincrease surface
area for water
absorption
3) Cortex- food
storage
4) Phloem- food
transport
5) Xylem- water
transport
2. Stems
a) Functions:
1) transport food, water and
minerals between the roots and
the leaves.
2) support the plant growth above
ground
b) Stem Morphology
Herbaceous Stem
Woody Stem
1. Herbaceous Stems
a) Soft, green and fleshy
with little or no
secondary growth
b) Stem is supported by the
water that fills their
central vacuoles called
turgor pressure and the
slight lignification of
their cell walls
2. Woody Stems
a) Most dicots and
gymnosperms produce
woody stems which are
hard and long
b) Woody stems have a
vascular cambium that
allows for secondary
growth (width)
c) The vascular cambium
adds phloem cells
towards the outside and
xylem cells to the inside
d) The xylem added each year forms the tree rings
Woody Stems
e) The xylem that conducts water
is called sapwood.
f) The older xylem in the middle
that is non-functioning is
called heart wood.
g) Woody stems have a cork
cambium which fills in the
gaps in the bark caused by the
yearly addition of xylem
h) Bark is not air tight, gaps
called lenticels allow gas
exchange
c. Structure of Stems
1. In the stem, the vascular tissues are arranged
into groupings called Vascular Bundles
a) Monocotsvascular bundles
are in a random
order
b) Dicots- vascular
bundles are
arranged in a ring
between the pith
and the cortex
Which is the Monocot and which is the Dicot stem?
2. Buds and Branches
a) Buds protect the apical meristem from freezing
and drying during the winter
b) Buds develop in the fall and consist of 3 basic parts:
Bud Scales
Embryonic leaves
Apical
Meristem
c) Bud scales- protect the
meristem in the winter. When
the bud absorbs water in the
spring, it swells and the scales
fall off leaving scars
I
d) Terminal buds: at the
n
end of stems
t
e
e) Lateral buds: project
r
from the sides of stems
n
o
f) The distance between
d
bud scale scars is
e
called an internode
which equals one year
g) Apical Dominance- the presence of a terminal bud
inhibits the auxillary buds
3. Modified Stems
a) Stolons- horizontal stem growing
along the surface of the ground.
Ie. Strawberries
b) Rhizomes- horizontal stem
underground. Ie Irises and Irish
potatoes
c) Bulbs- vertical underground shoots
with leaves modified for food
storage. Ie. Onion
3. Leaves
a. Function: organs that have the ability to
make food (glucose) in photosynthesis
(Leaves stomates)
(Enters stomates)
(From Roots)
(To Roots)
b. Structure of the leaf
Leaf Parts
1. Cuticle- waxy layer that prevents water loss
2. Palisade layer- major photosynthetic layer
3. Upper Epidermis- protects underlying cells
and secretes cuticle
4. Chloroplast- organelle responsible for
photosynthesis
5. Spongy Layer- allow gas exchange and moves
food to phloem
6. Lower epidermis- protection, contain stomates
for gas exchange
Leaf Parts
7. Guard Cells- flank stomates and open and
close them
8. Stomate- gap through which air actually
passes
9. Phloem- carries food
10. Xylem- carries water
11. Vein- holds xylem and phloem
C. Transport in Vascular Plants
1. Transport at the Cellular
Level
a) Passive Transport- doesn’t
require cellular energy input
1) Diffusion- solutes move down the
concentration gradient from areas of high
concentration to areas of low concentration
2) Facilitated Diffusion- protein form selective
channels to allow specific solutes through the
membrane
3) Osmosis- the diffusion of water from areas of
high water potential to low water potential
b) Active Transport- requires
energy input from the cell
1) Transport Proteins- embedded in the cell
membrane bind to a specific substrate, change
conformation and release the substrate on the
other side of the membrane
2) Proton Pumps- hydrolyze ATP and use the
energy to pump protons across membrane to
create an electrochemical gradient
•
•
Cations will be driven into the cell by membrane
potential
Anions are accumulated by the cell through
cotransport with hydrogen ions
2. Short Distance (Lateral) Transport
a) From Cell to Cell- out of one cell through the cell
membrane and cell wall into the next cell through the
cell membrane and cell wall
b) Symplast- a continuum of cytoplasm within the plant
formed by plasmodesmata- cytoplasmic channels
formed through pores in the cell wall
c) Apoplast- the extracellular pathway between cell walls
3. Pathway of Water and Minerals
a) Water and dissolved solutes gain access to the
roots through root hairs with hydrophilic cell
walls
b) Water and minerals enter apoplastic routes;
however, the entrance to the stele is blocked by a
ring of wax called the casparian strip which
lies tangential to the stele
c) Minerals must be extracted from the
extracellular fluid into cortex cells and follow a
symplastic pathway into the stele
d) Therefore, the endodermal cells regulate the
composition of the sap
SoilEpidermisCortex
EndodermisStele
4. Transpiration-Cohesion-Tension Mechanism
a) Transpiration- water evaporates out of the leaf
through the stomate. This causes water to leave the
cells surrounding the air spaces in the leaf.
b) The tension, or negative pressure causes water to move
from the xylem in the leaf petiole to the cells.
c) Cohesion- hydrogen bonding between water molecules
pulls water up the stem from the root to replace water
lost by the leaf
d) Adhesion- water molecule clings to xylem cell walls
which prevents back flow due to gravity.
e) Root Pressure- water is pushed up the root xylem
tubes as water enters the root hairs
f) Plants can regulate transpiration by opening or closing
stomates
5. Control of Transpiration
(Plants strike a balance between gas exchange and water loss.
When stomates are open, both gas exchange and water loss are
greatest)
a) Guard cells flank stomata and control
stomatal diameter by changing shape
1) When turgid, guard cells buckle due to
microfibrils. This causes the stomate to open
2) When flaccid, guard cells sag and close
stomate
b) Change in turgor pressure is accomplished
by the uptake of potassium ions
1) Uptake of potassium lowers water potential
causing water to enter
2) Closing occurs when potassium ions leave
c) Stomates open at dawn because:
1) Light induces guard cells to uptake
potassium due to the activation of a light
receptor which activates proton pumps in
the plasma membrane
2) Decrease in carbon dioxide in the leaf air
space due to photosynthesis in the
mesophyll
3) Internal clocks in the guard cells
d) Guard cells will close if:
1) Water deficiency results in flaccid guard
cells
2) Production of abscisic acid by mesophyll
cells
3) High temperature increases carbon
dioxide in the leaf air space due to
increased respiration
6. Transport in Phloem
a) Translocation- process of transporting
sugar from a source to a sink through
phloem
1) Source- sugar producing cells
2) Sink- cell requiring sugar
b) Loading sugar from a source
1) Sugar may be loaded via the symplast
2) Proton pumps can actively load sugar
against the concentration gradient
c) Increased sugar concentration lowers water potential which
causes water from the surrounding tissues to enter the phloem
d). The resulting increase in pressure drives the sap to the sink
cell. This is called bulk flow
IV. Nutrition in Plants
A. Nutrition Requirements in Plants
1. Water- the most abundant compound in most
plants is an essential nutrient for photosynthesis
2. Carbon dioxide- is incorporated into a plants
organic material
3. Minerals- (inorganic ions) are selectively
absorbed by the roots
4. Macronutrients- needed in large amounts
5. Micronutrients- are needed in small quantities
Macronutrients
Micronutrients
B. Nitrogen Assimilation in Plants
1. Plant growth and crop yield are often limited by
nitrogen, an essential ingredient of proteins and
nucleic acids
2. Although the atmosphere is rich in nitrogen, plants
require the assistance of bacteria living in soild to
supply them with the forms of nitrogen they need
a) Nitrogen-fixing bacteria posses nitrogenase an enzyme
that converts atmospheric nitrogen into ammonia
b) The ammonia is then converted to nitrate or ammonium,
which can be used by the plant
3. The roots of legumes have nodular swellings that house the
nitrogen-fixing bacteria
4. Improving the quality and quantity of protein crops and can help
alleviate the problem of human malnutrition
5. Agricultural research in developing protein-rich plants and
enhancing nitrogen-fixing capabilities may yield practical
benefits to the world
C. Some Nutritional
Adaptations in Plants
1. Parasitic Plants- either
supplement their
photosynthetic nutrition or
give up photosynthesis
entirely by tapping the
vascular system of the host
plant
Nutritional Adaptations
2.
Carnivorous Plantsusually found in poor
soil or acid bogs.
Obtain nitrogen by
killing and digesting
insects
Nutritional Adaptations
3. Mycorrhizaemutualistic
associations between
root and fungi help the
plant by enhancing
mineral nutrition,
water absorption and
disease resistance