151 Plant Structure and Function Cvs.pptx - Plant Structure...

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Plant Structure & Function
BIO 151

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desiccation , excessive water loss, is a
constant challenge for land plants

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Sister group of
green algae
Liverworts
Mosses
Hornworts
Lycophytes
Ferns and
horsetails
Gymnosperms
Angiosperms
Vascular plants
Bryophytes
Green algae
Land
plants
Phylogeny of Plants

Reproductive
organs
Leaf
Stem
Roots
S
h
o
o
t
Anatomy of a Vascular Plant
Evidence of
adaptation to a
terrestrial
environment

The Leaf
Cuticle
Upper
epidermis
_______
_cells
Lower
epidermis
Cuticle
Guard cell
Stoma
Vein
H
2
O
CO
2
Mesophyll cells near the upper
surface of the leaf have a
columnar arrangement that
maximizes light interception.
Mesophyll cells near the upper
surface of the leaf have a
columnar arrangement that
maximizes light interception.
Mesophyll cells close to the stomata have
a honeycomb-like arrangement to allow
CO
2
to spread easily throughout the leaf.
Mesophyll cells close to the stomata have
a honeycomb-like arrangement to allow
CO
2
to spread easily throughout the leaf.

Stomata
Small openings in the surface of the leaf that allow for
gas exchange (e.g. H
2
O, CO
2
); flanked by guard cells

The Leaf
Cuticle
Upper
epidermis
_______
cells
Lower
epidermis
Cuticle
Guard cell
Stoma
Vein
H
2
O
~400
ppm
~20,000
ppm
CO
2
~200 ppm ~40,000 ppm
CO
2
gradient
Water vapor gradient
The concentration difference driving the diffusion of
CO
2
into the leaf is typically 100 times smaller than
the concentration difference driving the diffusion of
water vapor out of the leaf.
The concentration difference driving the diffusion of
CO
2
into the leaf is typically 100 times smaller than
the concentration difference driving the diffusion of
water vapor out of the leaf.
Action of guard cells is important to control the
amount of gas exchange that can occur; admit
carbon dioxide, but control water loss
Action of guard cells is important to control the
amount of gas exchange that can occur; admit
carbon dioxide, but control water loss

Stomata and Guard Cells
Solutes
H
2
O
Solutes
H
2
O
Guard
cell
Radially
oriented
cellulose
microfibrils
Guard cells
shrink.
Guard cells
swell.
Open, high-volume
state
Closed, low-volume
state (default)
Uptake of solutes by guard cells causes
water to be drawn in by osmosis. As the
guard cells swell, they bow apart, opening
the stoma.
Uptake of solutes by guard cells causes
water to be drawn in by osmosis. As the
guard cells swell, they bow apart, opening
the stoma.
Release of solutes
causes water to flow
out of the guard cells,
closing the stoma.
Release of solutes
causes water to flow
out of the guard cells,
closing the stoma.

Slightly inflated balloon
Tied end
Add turgor
pressure (air)
“Stoma”
“balloon analogy” of guard cell action

Open stoma:
turgid guard cells
K
+
Cl
–