THE PLANT BODY AND PLANT CELLS

Plant body overview

Shoot system

--generally aerial

--stem: axis of shoot

--apex; apical bud: growing point

--cotyledons

--attached leaves at nodes (note internodes)

blade, petiole

arrangement on stem variable (opposite, alternate,

etc)

axil (with axillary bud)

--axillary buds: dormant or growing

--branch: from axillary bud

--flowers: apical or axillary

--apex; apical bud: growing point

--stem: axis of shoot

-- leaves: attached at nodes

internode

blade

petiole

axil (with axillary bud)

alternate arrangement

opposite arrangement

--cotyledons

--flowers: apical or axillary

--axillary buds: dormant or growing

b r a n ch from axillary bud

Root system

--generally underground

--highly branched (lateral roots, but no nodes)

--2 types: fibrous and tap root systems

--growth at apices of all branches

Note the two main types of flowering plants: dicots

and monocots

Seed leaves,

cotyledons

Leaf venation Secondary growth Flower part multiples

Dicots Two Reticulate Yes 4s and 5s

Monocots One Parallel Unusual 3s

Bougainvilleas are dicots. Orchids are monocots.

The bean seed is a dicot seed:two cotyledons

The rice seed is a monocot seed:one cotyledon

Dicots have reticulate venation Monocots have parallel venation

Types of plant cells (tissues)

Parenchymal cell (parenchyma)

--cell wall: cellulose fibrils, connected by shorter, more

random carbohydrate chains (pectin,

hemicellulose), strong, elastic

--plasma membrane

--vacuole, tonoplast

--nucleus, nucleolus, chromatin, nuclear envelope

--plastids: chloroplasts, chromoplasts, amyloplasts,

proplastids

--mitochondria

--endoplasmic reticulum

--Golgi, called dictyosomes

--ribosomes, polysomes

--"standard, non-specialized" plant cell; photosynthetic

(in green shoots); for storage (in shoots and roots);

grows, provides some structure (turgid, stiff)

Osmosis and turgor Because the plasma membrane is differentially permeable, allowing water to cross more easily than solutes, water moves from the side with the lowest solute concentration to the side with the highest concentration.

Osmosis and turgor: In a plant, turgor makes a

parenchymal cells able to provide structure.

Assume cells with p.m., cell wall,

solutes in cytoplasm,

external dilute solution

Solute concentrations unbalanced

Water concentrations (activities)

unbalanced

Water flows in along activity gradient

(osmosis)

Cell volume rises, membrane

pushes against wall

(turgor pressure)

Wall resists stretching, pushes back

elastically (wall pressure)

Equilibrium exists when water flow

due to osmosis = water flow due

to wall pressure

So pressure of wall on membrane keeps cell from

lysing in pure water or dilute solution;

but also, pressure of membrane on wall provides

structure (like air in tire);

also, pressure provides force for controlled growth (if

wall "gives")]

Epidermal cells (epidermis)

--thin, broad cells that form skin over leaves, primary stems, roots

--secretes cuticle on outer surface (very hydrophobic): cutin (long chain fatty acids bound to cell wall) and waxes (long-chain fatty acids esterified to long chain alcohols)

CH3-CH2-CH2-CH2-----CO-O-CH2-CH2-CH2---CH3 --produces secondary compounds, stores them in

vacuole: absorb UV light, resist insects, fungi, etc.

Collenchymal cells (collenchyma)

--extra primary cell walls

--support (e.g. leaf petioles [celery]), sometimes have

chloroplasts

Fibers, schlereids (schlerenchyma)

--secondary cell wall, containing cellulose + lignin

(highly crosslinked polyphenolic compound, very

hard, hydrophobic), in strands or sheets under

primary cell wall

--autolysis of cell contents when wall finished

--wall provides support against compression and

expansion (even in low water-potential

environment); resistance to grazing (seed coat)

--with larger lumen, can serve as water conduit

Collenchymacell

Summary

•Shoot system•Root system

•Dicots vs monocots

•Basic plant cells and tissues• Parenchyma• Collenchyma• Fibers and sclereids

•Osmosis and turgor