What is plant anatomy?
• ANATOMY: study of the structure of
organisms… looking at cells, tissues
• (Morphology: Study of form)
What is plant physiology?
• PHYSIOLOGY: study of the function of
cells, tissues, organs of living things;
and the physics/chemistry of these functions…
Always keep in mind that in plant anatomy,
morphology & physiology…
“Structure correlates to function”
• How can water
move from
the ground
all the way
to the top
of a 100 m
tall redwood
tree?
Plant Anatomy: Cells
• Plant cells are basic building blocks
• Can specialize in form and function
• By working together, forming tissues, they can
support each other and survive
• Levels of organization
atoms > molecules > cells > tissues > organs > whole plant > pop.
Plant Tissues Types
All plant organs (roots, stems, leaves) are
composed of the same tissue types.
There are three types of tissue:
• 1. Dermal – outermost layer
• 2. Vascular – conducting tissue, transport
• 3. Ground – bulk of inner layers
1. Dermal tissue
• Epidermis is the outermost layer of cells
• Like the “skin” of animals
• In stems and leaves,
epidermis has cuticle,
a waxy layer that prevents
water loss.
• Some have trichomes, hairs.
• Root epidermis has root hairs, for
water and nutrient absorption
2. Vascular tissue
• Transports water and organic materials (sugars)
throughout the plant
• Xylem – transports water and
dissolved ions from the root
to the stem and leaves.
• Phloem – carries dissolved sugars
from leaves to rest of the plant
Xylem
• Transports water and dissolved minerals
• Tracheids: long, thin tube like structures
without perforations at the ends
• Vessel elements: short, wide tubes perforated at
the ends (together form a pipe, called vessel).
• Both cells have pits (thin sections) on the walls
Tracheids Vessel elements
Xylem cells
• Xylem cells are dead!
• They are hollow cells
and consist
only of
cell wall
Phloem
• Cells that transport organic materials (sugars)
• Phloem cells are ALIVE! (unlike xylem)
• However, they lack
nucleus and
organelles
Phloem: transports sugars
• Phloem composed of cells called sieve tube
members (STM)
• Companion cells join sieve tube members, are
related, and help to load materials into STM
• End walls of STM have large pores called
sieve plates
Companion cells
Sieve tube member Sieve plates
3. Ground tissue
• Makes up the bulk of plant organs.
• Functions: Metabolism, storage and support.
Root Stem Leaf
Plant Organs
Organs: tissues that act together to serve a
specific function
Dermal
• Roots Vascular
Ground
Dermal
• Stems Vascular
Ground
Dermal
• Leaves Vascular
Ground
Functions of plant organs:
• ROOTS: Anchorage, water/nutrient absorption
from soil, storage, water/nutrient transport
• STEMS: Support, water/nutrient transport
• LEAVES: Photosynthesis (food production)
ROOTS
• ROOTS “the hidden half”
• Functions of roots:
• Ancorage
• Absorption of water & dissolved minerals
• Storage (surplus sugars, starch)
• Conduction water/nutrients
Anatomy of a root
epidermis
cortex
vascular
Root Epidermis
• Outermost, single layer of cells that:
– Protects (from diseases)
– Absorbs water and nutrients
• ROOT HAIRS: tubular extensions
of epidermal cells.
• Increase surface area of root,
for better water/nutrient
absorption
Root Hairs: water and mineral
absorption
Root hairs
increase surface
area for better
absorption
Root Cortex
• Stores starch, sugars and other substances
Root Ground tissue
• In roots, ground tissue (a.k.a. cortex)
provides support, and
often stores sugars and starch
(for example: yams, sweet potato, etc.)
You‟re not a
yam, you‟re a Hey!
sweetpotato! I yam
what I
cortex yam,
man!
Root Cortex: Endodermis
• Endodermis: the innermost layer of the
cortex
Root cortex: Casparian strip
• The Casparian strip is a water-impermeable
strip of waxy material found in the
endodermis (innermost layer of the cortex).
• The Casparian strip helps to control the
uptake of minerals into the xylem: they have
to go through the cytoplasm of the cell!
STEMS
• Above-ground organs (usually)
• Support leaves and fruits
• Conduct water and sugars
throughout plant (xylem and phloem)
Stem anatomy
• Dermal, ground and vascular tissues…
epidermis
cortex
Vascular
pith
bundles
Types of Stems
Monocot stem Dicot stem Root
Types of stems
• Herbaceous vs. Woody stems
Tissues of stems
• Epidermis (Dermal tissue type)
• Provides protection
• Has cuticle (wax) prevents water loss
• Trichomes (hairs) for protection, to release
scents, oils, etc.
Stem Vascular tissue
• Vascular bundles – composed of both
xylem and phloem
• Xylem
– Conducts water
– Support
• Phloem
– Conducts food Vascular
– Support cambium
Vascular cambium
• Occurs in woody stems
• Vascular cambium located in the middle
of the vascular bundle, between xylem and
phloem
Vascular tissue: Trees
• Vascular tissue is located on the outer layers
of the tree.
bark
phloem
Vascular
cambium wood
xylem
Girdling: cutting around a tree
• Damages the phloem and xylem, eventually
killing the tree!
Vascular tissue forms rings in trees
• Annual rings: xylem formed by the
vascular cambium during one growing
season
• One ring = one year
History of the tree: annual rings
Dendrochronology : tree time-keeping
1917 & 1945: Tree
Survives two World
1776: Declaration Wars 1969: Man
of US independence lands on Moon
1492: Columbus lands in
the Americas
1620: Pilgrims land 1861: Start of
in Plymouth, Mass. Civil War
1489: Tree is planted 1971: Birth Year
by Native American
of the IDIOT
who cut down
this tree!!!
Ground tissue: Cortex & pith
• Stores food (e.g. potato)
• Site of Photosynthesis (when green)
• Support cells
cortex
pith
LEAVES:
• „Photosynthetic factories‟ of the plant…
• Function: Photosynthesis – food
production for the whole plant
• Blade: Flat expanded area
• Petiole: stalk that connects
leaf blade to stem, and
transports materials
BLADE
Leaf Anatomy
• Leaf anatomy is correlated to photosynthesis:
Carbon dioxide + Water sugars + oxygen
dermal
ground
vascular
dermal
Leaf epidermis
• Is transparent – so that sun light can go through.
• Waxy cuticle protects against drying out
• Lower epidermis: stomata with guard cells –
for gas exchange (CO2, H2O in; O2 out)
Leaf epidermis
• Trichomes (give fuzzy texture)
(“Panda plant”)
Leaf vascular tissue
• VEINS vascular tissue of leaves.
• Veins are composed of xylem (water transport)
phloem (food transport)
and bundle sheaths,
cells surrounding the
xylem/phloem for
strength & support
Leaf Mesophyll
• Middle of the leaf (meso-phyll)
• Composed of photosynthetic ground cells:
• Palisade parenchyma
(long columns below epidermis;
have lots chloroplasts for
photosynthesis)
Spongy parenchyma
(spherical cells)
with air spaces around,
(for gas exchange)
Plant water transport
• How can water move from
the ground
all the way
to the top
of a 100 m
tall redwood
tree?
Water transport in plants:
• The same way we drink soda
from a straw!
• Water‟s great
cohesive forces (molecules
sticking to each other)
and adhesive forces
(attaching to walls of xylem cells)
Transpiration-cohesion Theory
for water transport in the xylem
• Evaporation of water in the leaves
(through stomates) generates the „sucking
force‟ that pulls adjacent water molecules
up the leaf surface
Water transport (cont.)
• Like a long chain, water molecules pull each
other up the column.
• The column goes from roots leaves.
• What‟s amazing is that the
water moves up by using the sun‟s
evaporative energy…
• Plants control transpiration by opening/closing
stomata
Sugar translocation
• 1. Sugars made in leaf mesophyll cells (source)
diffuse to phloem cells in the vascular bundles.
• 2. Companion cells load dissolved sugars into
the phloem STM using energy (ATP).
• 3. Water moves into cells with high sugar
concentration.
• 4. Osmotic water flow generates a high
hydraulic pressure that moves dissolved sugars
through the phloem to the rest of the plant
(sink).
Pressure flow in phloem
• Sugars made in the
leaves are loaded into
companion cells and
into phloem STM.
• Water (from xylem)
moves in by osmosis,
creating pressure flow
down the phloem.
Plant Hormones
• Chemical compounds produced by plants
• Effective at very low concentrations
• Five major hormone groups are:
1. Auxins
2. Gibberellins
3. Cytokinins
4. Abscisic Acid
5. Ethylene
1. AUXINS
• Promote cell growth
• Involved in
gravitropism
and phototropism
• Control fruit development
2. Gibberellins
• Promote stem elongation
3. Cytokinins
• Promote cell division and
organ differentiation
4. Abscisic Acid
• Promotes seed dormancy
• Causes stomata closing
5. ETHYLENE
• Gaseous hormone,
very simple formula (C2H4)
• Ethylene promotes
fruit ripening!
Air Ethylene
“One rotten apple spoils the barrel”
• Why?
Probably due to ethylene!
Rotten apple producing
lots of ethylene!
• Autocatalytic
• As a response to injury
Avocado ripening…
• Place in a paper bag, with a ripe banana!
