Leaves | DAT
Structure of a Leaf
• Layers of a leaf (from top to
bottom) include:
o Cuticle – waxy exterior
which protects the leaf
and prevents water loss
o Upper epidermis – also
protects the leaf and
minimizes water loss
o Palisade layer – packed
with chloroplasts
Primary location
of photosynthesis
o Spongy layer – Looselypacked layer whose air
pockets are conducive to
transporting gases
A leaf’s veins are
vascular bundles
found in this layer
o Lower epidermis – offers
protection
Contains pores
call stomata,
which allow the
exchange of gas
or water
The opening and
closing of stomata
is regulated by
guard cells
o Cuticle – like the top
cuticle, this protects the
leaf and minimizes water
loss
Typically
narrower than the
top cuticle
Layers of a Leaf
Layers of a leaf include the cuticle (red arrow),
upper epidermis (orange arrow), palisade layer
(yellow arrow), spongy layer (green arrow),
lower epidermis (blue arrow), and another cuticle
(purple arrow). The lower epidermis contains
pores (white arrow) called stomata. Stomata
facilitate the exchange of gases and water, and
they are opened/closed by neighboring guard
cells (gray arrow).
Transpiration
• Transpiration – the regulated
release of water through the
stomata of leaves
• Transpiration is responsible for
providing the upwards force that
carries water up through a plant’s
xylem
• Water leaving the leaves creates
a cohesive pull on water
throughout the plant’s xylem,
thereby pulling it upwards
o Thus, a plant expends no
energy transporting water
upwards, against gravity!
Transpiration
Water departing the leaves via transpiration
exerts a cohesive pull on water in the plant’s
xylem. The water is thereby channeled up the
plant without the expenditure of energy.
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© 2016 J Co Review, Inc., Accessed by Guest on 09-29-2016