Download THE PLANT BODY AND PLANT CELLS

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
Dicots
Monocots
Seed leaves, Leaf venation
cotyledons
Two
Reticulate
One
Parallel
Bougainvilleas are dicots.
Secondary growth
Flower part multiples
Yes
Unusual
4s and 5s
3s
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
Collenchyma
cell
Summary
•Shoot system
•Root system
•Dicots vs monocots
•Basic plant cells and tissues
• Parenchyma
• Collenchyma
• Fibers and sclereids
•Osmosis and turgor