Plant Structures

Plant cell structure (Review)

Differences between plant & animal cells? Unlike animal cells, plant cells

have . . . chloroplasts.a central vacuole.a cell wall of cellulose (angular cells not rounded).

Plant taxonomy (Review)

Of ~19 plant phyla, only 4 are wide-

spread.

Know a dichot- omous key to separate the plant phyla.

Plant structure (Dicotyledonous angiosperms)

ShootAbove- ground

RootBelow-ground

Note the ring of vascular tissue.

Plant tissues

Plants consist of 4 types of tissue.Dermal tissue – epidermal cells, often covered with a waxy layer called the cuticle.Vascular tissue – xylem and phloem cells transport water and nutrients throughout the plant.Ground tissue – parenchyma cells lying between dermal and vascular tissue provide support with thickened cell walls.Meristematic tissue – undifferentiated cells that produce all others by mitosis.

Plant tissues

Plants consist of 4 types of tissue.Dermal tissueVascular tissue

= xylem & phloem

Ground tissueMeristematic tissue creates new cells

Meristem

Plant meristemsDicotyledonous

plants have apical and

lateral meri- stems that

give birth to

new cells.Apical = at tips.Lateral = at side.

Plant meristemsGrowth due to apical and lateral

meristemsApical meristems increase plant length.

Undifferentiated cells in shoot and root.

bud

Buds will also develop their own apical meristems

Plant meristems Growth due to apical

and lateral meristemsLateral meristems increase plant girth.

Vascular cambium makes xylem and phloem.

Cork cambium makes bark (constantly

replaced).

Vascularcambium

Diagram of a dicot plant stem

Stems hold leaves toward light & transport nutrients from

roots.

As the dicot plant ages, the vascular tissues form a ring.

Young

Older

Diagram of a dicot plant stem

As the dicot plant ages, meristematic cells form a ring called vascular cambium.

Be able to draw this. (functions of tissues later)

The vascular cambium gives riseto the xylem & phloem tissues.

Vascularcambium

Diagram of a dicot plant stem

A new ring of xylem and phloem forms each year in perennial plants like trees.

Xylem rings are useful for telling the age of a tree.

Monocot vs. dicot plant stem

Recall that monocot stems (like corn & palms) have their vascular tissues in scattered bundles, not in rings (as do dicots like oak trees).

Transport within stemsWater moves from root to leaf as sap

through xylem tissue that is composed of non-living tubular cells. Xylem vessels have lateral pits and perforations at top & btm.

Diameter of xylem vessel = 50 to 100 μm

Transport within stems

Water moves by transpirational pull aided by cohesion, adhesion, & evaporation.

Evaporation removes water from the leaf surface as a result of the lower humidity in the air compared to the leaf.

Transport wihin stems

Water has polarity (the effect of having dis-tinct ends, or poles, like a magnet); water has opposite charges on opposite ends of the molecule. One pulls another.

Transport within stems

Water moves by transpirational pull aided by cohesion, adhesion, & evaporation.

Cohesion is the attractive force that one water molecule has for another (due to hydrogen bonding).

Cohesion lets the insectwalk on water.

Water ispulledup thexylemvessels.

Transport within stems

Water moves by transpirational pull aided by cohesion, adhesion, & evaporation.

Adhesion is the attractive force that one water molecule has for another substance – such as hydrophilic cellulose – (also due to hydrogen bonding).

Xylem walls are cellulose and adhere water.

Water is pulled up.

Transport within stemsSo, transpirational pull is the

movement of water up a plant against gravity aided by attractive forces on water molecules and resulting from evap- oration of water va-

por from the leaves and stems.

The tallest trees, Coast Redwoods in northern Cali-fornia, (Sequoia sempervirens),

can be nearly 380’ tall).

Transport within stems

Phloem is a vascular tissue that moves sap from sugar sources to sugar sinks.

Phloem sap contains sucrose & amino acids.Sources (where

the sugar is made) include photosynthetic tissues and storage organs.

Sinks (where the sugar is need-ed) include thefruits, seeds, &roots.

Transport within stems

Phloem is made of living cells called sieve tube members and companion cells.

(Recall: xylem cells are dead.)

Sieve tube mem-bers are stack-ed to form tubes.

Companion cells lie along each sieve tube mem-

ber & help loadsugar into the sieve tube.

Transport within stems

Active translocation of sugars from source to

sink in phloem.

1) Sugars are actively transported from source cells into sieve tube elements, so cells must be alive.

2) Because of the high sugar concen- tration in the phloem, water dif- fuses into the sieve tube elements, raising the water pressure.

3) Pressure causes the sap – sugar water – to flow through the phloem.

4) Sugars are transported out of the phloem into sink cells; water dif- fuses into the xylem, reducing the water pressure in the phloem.

Transport within stems

Active translocation of nutrients from source to sink.

Transport within stems

Review: water flows in a plant due to differences in water potential (% H2O).

Positive pressure pushes, as in the phloem.Negative pressure pulls, as in the xylem.

Plant Structures

Plant structure (Dicotyledonous angiosperms)

ShootAbove- ground

RootBelow-ground

Note the ring of vascular tissue.

Plant roots

Plant roots anchor plants in the ground and absorb water

and dissolved minerals from the soil.

Uptake by roots

Roots provide a large area for uptake of water and nutrients.

• Thousands of root hairs on each root.

• Dozens of lateral roots.• Mycorrhizae

(mutualistic fungi) grow out into soil.

Root hairs

Uptake by roots

How do minerals reach the roots?Mass flow of the water in the soil.

The roots intercept ions as they pass by.

Transport within rootsMineral ions are absorbed from the

soil into roots passively & by active transport.

Apoplast – non-living route of transport through cell walls to xylem.Symplast – transport route through the living cytoplasm to the xylem.

Absorption can create so much root pressurethat water can be forced out of leaves on humidnights.

Transport within roots

Apoplastic movement (passive):Hydrophilic cellulose in the cell walls of the epidermis (root hairs are epidermal cells) absorb water & the minerals dissolved in it.Minerals & water move from one cell wall to another toward the xylem, but the Casparian strip forces a detour into the cytoplasm.

(water insoluble materialblocks flow through cell wall.)

Transport within roots

Symplastic movement:

Once within a cell’s cytoplasm, minerals move to adjacent cells by diffusion, passing from one cell to another through plasmodes-mata – tunnels in the cell walls – moving toward the xylem.

Types of edible plant roots

Roots store energy; some are food sources.

sweet potato

Variety of plant leaves

Venusfly trap

Pitcherplant

Cactus (leavesare the needles)

Specialized leaves

Diagram of a dicot plant leaf

Leaves photosynthesize, making food for the plant.

Be able to draw this.

Functions of leaf tissuesCuticle: waxy covering to prevent loss of

moistureEpidermis: layer of protective cells (no

chloro-plasts)

Functions of leaf tissuesMesophyll: 2 layers, both contain

chloroplasts for photosynthesisSpongy parenchyma: air spaces for gas exchange

Functions of leaf tissuesVascular tissue: xylem moves water from

roots; phloem moves photosynthate away from the leaf.

Functions of leaf tissuesStoma (pl. stomata): an opening in the epider-mis through which H2O, O2 and CO2 may pass.

Guard cells: regulate gas exchange by expanding and contracting using ion pumps and osmosis to open and close the stoma.

Functions of leaf tissuesStoma (pl. stomata): an opening in the epider-mis through which H2O, O2 and CO2 may pass.

Guard cells: regulate gas exchange by expanding and contracting using ion pumps and osmosis to open and close the stoma.

Dicot flower structure

Draw and label all:

Male partsStamen

Holds pollen

Female parts Carpel (= pistil)

OvulationFertilization

Pollination

Pollination – placement of pollen onto the stigma of a carpel (pistil) by

wind or animal carriers.

Pollen is a haploid (1n) spore that carries the genes

of the male plant.

Pollination

Pollination – placement of pollen onto the stigma of a carpel (pistil) by wind or animal carriers.

Fertilization

Fertilization – union of haploid gametes to produce a diploid zygote.

After the pollen germinates on the stigma, the pollen

tube must grow down the style to

deliver the sperm to the

egg.FemaleGametophyte 1n

Sporophytetissue 2n

Seed dispersal

Seed dispersal – Process of moving seeds

away from the parent plant.

Adaptations for: Wind (feathery)Water (flotation) Animal (barbs, food source (fruit, nut)

Seed dispersal

Seed dispersal – Process of moving seeds away

from the parent plant.

Seed dispersal

Why disperse seeds?Colonize new areasGet away from the parent plant:

Excess shadeFew nutrientsPlant toxins

Control of plant growthPlants are rooted in the ground, yet

they can still move. They bend one way or the other.

Geotropism – movement due to gravityPhototropism – movement due to light

PositivePhototropism

NegativeGeotropism

Control of plant growth

Phototropism results from stimulation of plant cells by the hormone auxin. Hormones are made in one place but act

elsewhere.Auxin is made in shoot meristems.

It stimulates growth (elongation) of cells.

Cells on the shaded side grow larger,causing a bending of the plant shoot.

Control of plant growth

Phototropism results from stimulation of plant cells by the hormone auxin.

Auxin, made in shoot meristems, causes cells on the dark side to elongate by loosening their cell walls; internal water pressure causes cells to expand.

Giuseppe Arcimboldo’s painting, Vertumnus