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Plants, Tissues and Nutrition
Plant types and their evolution
• Terrestrial plants evolved from aquatic
green algae
• There are three main types:
• Bryophytes- mosses and hornwarts
• Ferns, Lycophytes and horsetails
• Gymnosperms and angiosperms
Fig. 15-1, p.245
charophytes
flowering
bryophytes lycophytes horsetails ferns cycads ginkgos conifers gnetophytes
plants
seed plants
plants with true leaves
vascular plants
land plants
(closely related groups)
Fig. 15-4, p.246
zygote only, no
sporophyte
green algae bryophytes
ferns
gymnosperms
angiosperms
Fig. 15-3, p.246
Bryophytes
• Mosses and Hornwarts
– “Leaves” have a cuticle to
conserve water
– A rudimentary root system
anchors them to substratum
and allows for absorption
– Need to live in moist
environment
– Produce spores and free
swimming sperm, need water
– Most can survive drying out
by going dormant
Ferns Lycophytes and Horsetails
• Share features with bryophytes
• Have rudimentary roots
• Have vascular system
Carboniferous Lycophytes
•Some formed vast forests
•Source of our modern “fossil
fuels”
•Extinct except for a few
groups
Lepidodendron
Fig. 15-7a, p.249
Ferns and Horsetails
• Have “true leaves”
• Root system
• Still need moisture
• Produce spores
(swimming sperm)
vegetative
stem
strobilus
on fertile
stem
Fig. 15-8c, p.249
Seed Producing plants:
Gymnosperms
Gymnosperms
Have all
adaptations for
living on land:
Produce seeds
Have a vascular
system
Well developed
roots
“true leaves”
conserve water
and exchange
gases with
atmosphere
Angiosperms (Flowering Plants)
• Flowers
– Ovules and (after fertilization) seeds develop in ovary
petal
stamen
(microspores
form here)
carpel
(megaspores
form here)
sepal
ovule
in an
ovary
Fig. 15-14, p.254
Flowering Plants
• Have all the same land adaptations as
gymnosperms plus flowers
• Dominate the plant kingdom
• Magnoliids, eudicots and monocots
Monocots and Eudicots
• Two major plant groups
• Same tissues, but arranged in different
ways
• Eudicots are the more diverse group
Monocots and Eudicots
• Differ in
– Cotyledon number
– Leaf venation
– Floral parts
– Pollen structure
– Arrangement of vascular bundles in stem
a Eudicots
Inside seeds, two cotyledons
(seed leaves of embryo)
Usually four or five floral
parts (or multiples of
four or five)
Leaf veins usually
in a netlike array
Three pores and/or
furrows in the pollen grain
surface
Vascular bundles organized
as a ring in ground tissue
b Monocots
Inside seeds, one cotyledon
(seed leaf of embryo)
Usually three floral parts
(or multiples of threes)
Leaf veins usually running
parallel with one another
One pore or furrow in
the pollen grain surface
Vascular bundles distributed
throughout ground tissue
Fig. 18-4, p.303
Plant Body
Plan
• Plant body plan is
divided into
• Shoots
• Roots
DERMAL TISSUES
VASCULAR TISSUES
GROUND TISSUES
SHOOT SYSTEM
ROOT SYSTEM
Body Plan
• Ground tissue
system- support
• Vascular tissue
system- transport
• Dermal tissue
system- conserve
water
Plant organ and tissue systems
• Shoots
– Produce food by photosynthesis
– Carry out reproductive functions
• Roots
– Anchor the plant
– Penetrate the soil and absorb water
and dissolved minerals
– Store food
shoot tip (terminal bud)
activity at
meristems
primary tissues
form as new
cells lengthen,
differentiate
primary tissues
form as new
cells lengthen,
differentiate
activity at
meristems
root tip
Fig. 29-3a, p.494
Meristems
• Regions where cell divisions
produce plant growth
• Apical meristems
– Lengthen stems and roots
– Responsible for primary growth
• Lateral meristems
– Increase width of stems
– Responsible for secondary growth
Simple Tissues
• Made up of one type of cell
– Parenchyma – alive
• Found in soft photosynthetic
tissues
– Collenchyma – alive
• Provides support
– Sclerenchyma – dead at
maturity
• Provides even more support
Simple Tissues
collenchyma
celery
parenchyma
Flax fibers
lignified secondary wall
Pear fruit
Complex Tissues
Composed of mixed cell types
Xylem
Phloem
Epidermis
Vascular Tissues
Xylem
Phloem
• Conducts water and
dissolved minerals
• Transports sugars
• Conducting cells are
dead and hollow at
maturity
• Main conducting
cells are sieve-tube
members
• Companion cells
assist in the loading
of sugars
one
cell’s
wall
pit in
wall
a
vessel of
xylem
parenchyma
b
Tissues in
a Stem
sieve plate
of sieve
tube cell
companion
cell
c
fibers of
sclerenchyma
phloem
Epidermis
• Covers and protects plant
surfaces
• Secretes a waxy, waterproof
cuticle
• Contains stomata
• In woody plants, periderm
replaces epidermis
Primary Shoot Structure
• Eudicot and monocot stems
petiole
axillary
bud
node
blade
sheath
blade
stem
node
Internal Structure of a
Eudicot Stem
• Outermost layer is epidermis
• Cortex lies beneath epidermis
• Ring of vascular bundles
separates the cortex from
the pith
• The pith lies in the center of
the stem
xylem
cell
epidermis
cortex
vascular
bundle
pith
companion
cell in
sieve tube phloem
in phloem
Fig. 18-5a, p.304
Internal
Structure of
a Monocot
Stem
• The vascular bundles
are distributed
throughout the ground
tissue
• No division of ground
tissue into cortex
and pith
collenchyma
sheath
air
vessel
space in xylem
epidermis
vascular
bundle
pith
sieve tube
in phloem
companion
cell in
phloem
Fig. 18-5b, p.304
Adapted to Photosynthesis
• Leaves are usually thin
– High surface area-to-volume ratio
– Promotes diffusion of carbon dioxide in,
oxygen out
• Leaves are arranged to capture sunlight
– Are held perpendicular to rays of sun
– Arranged so they don’t shade one another
Leaf Structure
UPPER
EPIDERMIS
cuticle
PALISADE
MESOPHYLL
phloem
SPONGY
MESOPHYLL
xylem
LOWER
EPIDERMIS
O2
CO2
one stoma
Leaf Veins: Vascular Bundles
• Xylem and phloem; often
strengthened with fibers
• In eudicots, veins are netlike
• In monocots, they are parallel
p.305
Leaf Epidermis
• Covers every leaf
surface
• Specialized cells
Stem Growth and Development
• Cells at tip of apical meristem divide
• Their descendents divide and
differentiate, giving rise to specialized
tissues
• Lateral buds are undeveloped
meristematic tissue that gives rise to
stems, leaves, and flowers
Stem
Development
immature leaf
shoot apical meristem
procambium
protoderm
procambium
ground meristem
epidermis
cortex
primary phloem
procambium
primary xylem
pith
Roots Structure
• Taproot system
– eudicots
• Fibrous root system
– monocots
Root Systems
taproot system of
a California poppy
fibrous root system
of a grass plant
Root Structure
• Root cap covers tip
• Apical meristem produces the cap
– Cell divisions at the apical meristem
cause the root to lengthen
– Farther up, cells differentiate and
mature
• Root Hairs-
– Provide large surface area for water
and mineral absorption
Internal Structure of a Root
• Outermost layer is epidermis
• Root cortex is beneath the epidermis
• Vascular cylinder contains xylem and phloem
• Endodermis, then pericycle surround the
vascular cylinder
• In some plants, there is a central pith
VASCULAR CYLINDER
endodermis
pericycle
xylem
phloem
cortex
epidermis
root hair
Vessel members are mature;
root hairs are about to form.
New root cells lengthen, sieve tubes
mature, vessel members start forming.
Most cells have stopped dividing
Meristem cells are dividing fast.
No cell division is
occurring here. root cap
root tip
Fig. 18-10a, p.307
epidermis
root
cortex
root cortex
endodermis
pericycle
primary
xylem
primary
phloem
b Vascular cylinder, cross section
Fig. 18-10b, p.307
Secondary Growth
• Woody plants
• A ring of vascular cambium produces
secondary xylem and phloem
• Wood is the accumulation of these
secondary tissues, especially xylem
Secondary Growth
Ongoing cell divisions
enlarge the inner core of
secondary xylem and
displace vascular cambium
toward the stem.
VASCULAR CAMBIUM
stem
surface
primary xylem
primary phloem
VASCULAR CAMBIUM
secondary xylem
secondary phloem
Fig. 18-11b, p.308
outer surface
of stem root
division
One of the
cells
vascular
cambium at
the start of
secondary
growth.
division
One of the
two daughter
cells
differentiates
into a xylem
cell (coded
blue), and the
other remains
meristatic.
One of the
two daughter
cells
differentiates
into a phloem
cell (coded
pink), and the
other remains
meristatic.
The same pattern of cell
division and differentiation
into xylem and phloem
cells continues through
the growing season.
Fig. 18-11c, p.308
Formation of Bark
• All tissues outside vascular cambium
• Periderm
– Cork
– New parenchyma
– Cork cambium
• Secondary phloem
Woody Stem
periderm
BARK
vascular cambium
secondary
phloem
HEARTWOOD
SAPWOOD
Tree Rings
• Form as a result of xylem tubes with
different diameters
– Wide tubes develop during wet season
– Narrow tubes develop during dry season
– Different diameters create discernable
pattern of year’s growth
vessel in
xylem
direction
of growth
early wood
late wood
early wood
Fig. 18-12b, p.309
Tree
Rings
cork
2° phloem
vascular
cambium
Annual
Growth Ring
2° xylem
Late wood
Early wood
1° xylem
Pith
Woods
a. Pine
b. Oak
c. Elm
Fig. 18-13b, p.309
Plant Nutrition, Transport and Gas
Exchange
Soil
• Minerals mixed with humus
– Minerals come from weathering of rock
– Humus is decomposing organic material
• Composition of soil varies
• Suitability for plant growth depends largely
on proportions of soil particles
Macronutrients
Mineral elements that are required in amounts
above 0.5% of the plant’s dry weight
Carbon
Nitrogen
Magnesium
Hydrogen
Potassium
Phosphorus
Oxygen
Calcium
Sulfur
Micronutrients
Elements that are required in trace amounts
for normal plant growth
Chlorine
Zinc
Iron
Copper
Boron
Molybdenum
Manganese
Leaching
• Removal of nutrients from soil by water
that percolates through it
• Most pronounced in sandy soils
• Clays are best at holding onto nutrients
Soil Erosion
• Loss of soil to wind and water
• Often the result of deforestation
• Nutrient loss affects entire food chain
O HORIZON
Fallen leaves and other
organic material littering
the surface of mineral soil
A HORIZON
Topsoil, with decomposed
organic material; variably deep
(only a few centimeters in
deserts, elsewhere extending
as far as thirty centimeters
below the soil surface)
B HORIZON
Compared with A horizon, larger
soil particles, not much organic
material, more minerals;
extends thirty to sixty
centimeters below soil surface
C HORIZON
No organic material, but partially
weathered fragments and grains
of rock from which soil forms;
extends to underlying bedrock
BEDROCK
Fig. 18-14a, p.311
Fig. 18-14b, p.311
p.311
Root Hairs
• Extensions from
the root epidermis
• Greatly increase
the surface area
available for
absorption
Root Nodules
• Swelling on roots of some plants
• Contain nitrogen-fixing bacteria
• Bacteria convert nitrogen gas to forms
plants can use
Root Nodules
a Root
nodule
Fig. 18-17a, p.312
Root Nodules
Fig. 18-17b, p.312
Mycorrhizae
• Symbiosis between young plant
root and fungus
• Fungal filaments may cover or
penetrate root
• Fungus absorbs sugars and
nitrogen from plant
• Roots obtain minerals absorbed
from soil by fungus
Mycorrhizae
Root Structure and Absorption
• Roots of most flowering plants have
– Endodermis (innermost skin): surrounds
vascular cylinder
– Exodermis (outer skin): just below surface
• Both layers contain a Casparian strip
– Controls the flow of water and nutrients
Epidermis: (surface skin) in contact with
outside environment (leaves and roots)
Casparian Strip
exodermis
root hair
epidermis
• Prevents water and
solutes from passing
between cells into
vascular cylinder
• Water and solutes must
flow through cells
• Flow is controlled by
transport proteins
forming
vascular
cylinder
cortex
Casparian
strip
Fig. 18-18, p.313
Plant Nutrient Transport
• Simple Diffusion
Plant Nutrient Transport
• Osmosis
Active Transport
• Active Transport –
uses ATP to move
substances across
a membrane
• ATP - high energy
molecule
Gas Exchange & Nutrient Exchange
• Small Cells –
Simple diffusion
is adequate
Amoeba
• Larger Cells –
Cytoplasmic
Streaming
Elodea
Water Use and Loss
• Plants use a small amount of water for
metabolism
• Most absorbed water lost to
evaporation through stomata in leaves
• Evaporation of water from plant parts is
transpiration
Transpiration
• Much water is transpired
from leaves
• How does water get up to
the top of a 300 ft tall tree?
Water Transport
• Water moves through xylem
• Xylem cells are tracheids or vessel
members
• Both are dead at maturity
Tracheids
pits in
tracheid
Tracheids have tapered,
unperforated end walls.
Pits in adjoining tracheid
walls match up.
Fig. 18-19a, p.314
vessel member
Three adjoining members of a vessel. Thick,
finely perforated walls of these dead cells
connect to make long vessels, a type of waterconducting tube in xylem.
Vessel
Members
Fig. 18-19b, p.314
perforation plate
Vessel
Members
Perforation plate at the end wall of one type of
vessel member. The perforated ends allow
water to flow unimpeded.
Fig. 18-19c, p.314
Cohesion-Tension
Theory of Water Transport
• Transpiration creates negative tension
in xylem
• Tension extends downward from
leaves to roots
• Hydrogen-bonded water molecules are
pulled upward through xylem as
continuous columns
The Role of Hydrogen Bonds
• Hydrogen bonds hold water molecules
together in conducting tubes of xylem
• Weak bonds still allow water to
evaporate through stomata during
transpiration
Transpiration
Drives Water Transport
Water evaporates
from leaves
through stomata
Creates a tension
in water column in
xylem
mesophyll (photosynthetic cells)
vein
upper epidermis
a Transpiration
is the evaporation of
water molecules from
aboveground plant
parts, especially at
stomata. The process
puts the water in
xylem in a state of
tension that extends
from roots to leaves.
stoma
The driving force of evaporation in air
Fig. 18-20a2, p.315
Replacement Water Is Drawn in
through Roots
Fig. 18-20a1, p.315
Wilting
• Water regulation maintains turgor
Cuticle
• Translucent coating secreted by
epidermal cells
• Consists of waxes in cutin
• Allows light to pass through but
restricts water loss
Plant Cuticle
leaf surface
cuticle
epidermal cell
photosynthetic cell
Fig. 18-22, p.316
Stomata
• Openings across the cuticle and
epidermis; allow gases in and out
• Guard cells on either side of a stoma
• Turgor pressure in guard cells affects
opening and closing of stomata
Stomata
guard cells
open stoma
chloroplast
closed stoma
Fig. 18-23, p.316
CAM Plants
• Most plants
– Stomata open during day and
photosynthesis proceeds
• CAM plants are better at
water conservation
– Stomata open at night and carbon dioxide
is fixed
– Next day, stomata remain closed while
carbon dioxide is used
Stomata and the Environment
Phloem
Phloem
• Carry organic compounds
• Conducting tubes are sieve tubes
– Consist of living sieve-tube members
• Companion cells
– Lie next to sieve tubes
– A type of parenchyma
– Help load organic compounds into
sieve tubes
Transport through Phloem
• Driven by pressure
gradients
• Companion cells
supply energy to
start process
sieve tube of the phloem
Pressure
Flow Theory
SOURCE
Active transport
moves solutes
into sieve tubes.
Pressure pushes
bulk
solutes by bulk
flow
flow between
source and sink.
Solutes unloaded
into sink cells,
lowering their
water potential;
water follows.
WATER
Water moves
in, increasing
turgor
pressure.
Pressure and
solute
concentrations
decrease
between source
and sink.
SINK
Phloem
one cell of
a sieve tube
companion
cells in the
background
perforated
end plate
of sieve
tube cell
Transportable
Organic Compounds
• Carbohydrates are stored as starches
• Starches, proteins, and fats are too
large or insoluble for transport
• Cells break them down to smaller
molecules for transport
– Sucrose is main carbohydrate
transported