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

charophytesbryophytes lycophytes horsetails cycads ginkgos conifers gnetophytes

flowering

plants

seed plants

plants with true leaves

vascular plants

land plants

(closely related groups)

Fig. 15-4, p.246

ferns

green algae bryophytes ferns gymnosperms angiosperms

zygote only, no

sporophyte

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

Lepidodendron Fig. 15-7a, p.249

Carboniferous Lycophytes

•Some formed vast forests

•Source of our modern “fossil

fuels”

•Extinct except for a few

groups

vegetative

stem

strobilus

on fertile

stem

Fig. 15-8c, p.249

Ferns and Horsetails

• Have “true leaves”

• Root system

• Still need moisture

• Produce spores

(swimming sperm)

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

stamen

(microspores

form here)

carpel

(megaspores

form here)

petal

sepal

ovule

in an

ovary

Fig. 15-14, p.254

Angiosperms (Flowering Plants)• Flowers

– Ovules and (after fertilization) seeds develop in ovary

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

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

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

MonocotsEudicotsa b

Plant Body

Plan

VASCULAR TISSUES

GROUND TISSUES

SHOOT SYSTEM

ROOT SYSTEM

DERMAL TISSUES

• Plant body plan is

divided into

• Shoots

• Roots

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

root tip

Fig. 29-3a, p.494

primary tissues

form as new

cells lengthen,

differentiate

activity at

meristems

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

collenchyma parenchyma lignified secondary wall

Simple Tissues

celery Flax fibers Pear fruit

Complex Tissues

Composed of mixed cell types

Xylem

Phloem

Epidermis

Vascular Tissues

Xylem

• Conducts water and

dissolved minerals

• Conducting cells are

dead and hollow at

maturity

Phloem

• Transports sugars

• Main conducting

cells are sieve-tube

members

• Companion cells

assist in the loading

of sugars

Tissues in

a Stem

one

cell’s

wall

pit in

wall

sieve plate

of sieve

tube cell

companion

cell

a bc

fibers of

sclerenchyma

phloemparenchyma

vessel of

xylem

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

blade

petiole

axillary

bud

node

stem

blade

sheath

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

cortex

epidermis

vascular

bundle

pith

xylem cell

sieve tube

in phloem

companion

cell 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

epidermis

vascular

bundle

pith

vessel

in xylemcollenchyma

sheath

sieve tube

in phloemcompanion

cell in

phloem

air

space

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

PALISADE

MESOPHYLL

SPONGY

MESOPHYLL

LOWER

EPIDERMIS

one stoma

cuticle

O2CO2

phloem

xylem

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

Developmentimmature leaf

ground meristem

primary phloem

primary xylempith

procambium

cortex

procambium

protoderm

shoot apical meristem

procambium

epidermis

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

xylem

phloemcortex

epidermis

pericycle

endodermis

VASCULAR CYLINDER

root hair

root tip

root cap

Vessel members are mature;

root hairs are about to form.

New root cells lengthen, sieve tubes

mature, vessel members start forming.

Fig. 18-10a, p.307

Most cells have stopped dividing

Meristem cells are dividing fast.

No cell division is

occurring here.

primary

xylem

primary

phloem

epidermis

pericycle

Vascular cylinder, cross section

root cortex

endodermis

root

cortex

Fig. 18-10b, p.307b

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.

primary xylem

primary phloem

VASCULAR CAMBIUM

VASCULAR CAMBIUM

secondary xylem

secondary phloem

stem

surface

Fig. 18-11b, p.308

outer surface

of stem root

divisiondivision

One of the cells vascular cambium at the start of secondary growth.

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

peridermsecondary

phloem

BARK

HEARTWOOD SAPWOOD

vascular cambium

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

early wood late wood early wood

vessel in

xylem

direction

of growth

Fig. 18-12b, p.309

Tree

Rings

Pith

2° xylem

1° xylem

vascular

cambium

cork

2° phloem

Annual

Growth Ring

Early wood

Late wood

Fig. 18-13b, p.309

a. Pine

b. Oak

c. Elm

Woods

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 HORIZONFallen leaves and other organic material littering the surface of mineral soil

A HORIZONTopsoil, with decomposed organic material; variably deep (only a few centimeters in deserts, elsewhere extending as far as thirty centimetersbelow the soil surface)

B HORIZONCompared with A horizon, larger soil particles, not much organic material, more minerals; extends thirty to sixty centimeters below soil surface

C HORIZONNo 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

Fig. 18-17a, p.312

a Root nodule

Root Nodules

Fig. 18-17b, p.312

Root Nodules

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 Stripexodermis

root hair

epidermis

forming vascular cylinder

cortex

Casparian

strip

• Prevents water and

solutes from passing

between cells into

vascular cylinder

• Water and solutes must

flow through cells

• Flow is controlled by

transport proteins

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

• Larger Cells –

Cytoplasmic

Streaming

Elodea

Amoeba

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

pits in

tracheid

Tracheids have tapered,

unperforated end walls.

Pits in adjoining tracheid

walls match up.

Fig. 18-19a, p.314

Tracheids

vessel member

Three adjoining members of a vessel. Thick,

finely perforated walls of these dead cells

connect to make long vessels, a type of water-

conducting tube in xylem. Fig. 18-19b, p.314

Vessel

Members

perforation plate

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

Vessel

Members

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

stoma

The driving force of evaporation in air

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.

Fig. 18-20a2, p.315

a

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

leaf surface

Fig. 18-22, p.316

cuticle epidermal cell photosynthetic cell

Plant Cuticle

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

Fig. 18-23, p.316

open stomaguard cells chloroplast closed stoma

Stomata

CAM Plants

• Most plants– Stomata open during day and

photosynthesis proceeds

• CAM plants are better atwater 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

Pressure

Flow TheorySOURCE

WATER

SINK

bulkflow

sieve tube of the phloem

Active transport moves solutes into sieve tubes.

Water moves in, increasing turgor pressure.Pressure pushes

solutes by bulk flow between source and sink.

Pressure and solute concentrations decrease between source and sink.

Solutes unloaded into sink cells, lowering their water potential;water follows.

one cell of

a sieve tube

companion

cells in the

background

perforated

end plate

of sieve

tube cell

Phloem

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