Cells they contain many chloroplasts and their

cells. They contain many chloroplasts, and their location below the epidermis and their
shape give them maximum exposure to light. Most photosynthesis takes place in the
palisade mesophyll.
Below the palisade mesophyll layer is the
spongy mesophyll.
In this layer, the
parenchyma cells are irregularly shaped and loosely packed. The open air spaces
between the cells in the spongy mesophyll allow oxygen, carbon dioxide, and water
vapour to move easily around the cells. Cells in the spongy mesophyll also contain
chloroplasts, but there are fewer of these per cell than in the palisade mesophyll layer.
palisade
-
mesophyll cell
1
epidermis
556 MHR
· Unit 5 Plants: Anatomy, Growth, and Function

. . .
Identifying Leaves
The diferences in the size, shape, and texture of leaves are all clues that can help to
identif a plant species.
Table 1 3.5
shows some of the characteristics used to describe
and identify leaves. The blade of a simple leaf is not divided into smaller parts. Te
blades of compound leaves are divided into smaller leaflets.
A leaf 's venation is the pattern of the veins in the leaf. Monocots, such as grasses
and irises, usually have parallel venation, in which the veins in the leaf run parallel
to the main, or central, vein and each other. Dicots usually have palmate or pinnate
leaves like those shown in
Table 1 3.5 .
Palmate leaves have veins that branch of from a
common point. Pinnate leaves have veins that branch of along the central vein.
Te arrangement of leaves on the stem, which is also shown in
Table 1 3.5 ,
is another
characteristic that can be used to identif plants. Leaf growth is
opposite
if two leaves
are attached to the stem directly opposite each other at the same level.
Alternate
growth
describes leaves arranged in a step-like pattern on either side of the stem, with each leaf
at a diferent level. In a
whorled
arrangement, three or more leaves are evenly spaced
around a stem at the same level.
Table 1 3.5 Characteristics Used to Identify Leaves
Leaf Type
Simple Palmate
Opposite
Alternate
Pinnate
Compound
Learning Check
venation the pattern
of veins in a leaf
19.
Describe a herbaceous stem.
20. You are serving potatoes for dinner, and your friend
comments on how much she enjoys eating root
vegetables. How is her statement inaccurate?
23. Provide a possible explanation for the fact that there
are fewer chloroplasts in the spongy mesophyll layer
of a leaf than in the palisade mesophyll layer.
21.
What is the function of the cuticle?
22. Predict why the air spaces in the spongy mesophyll
are particularly large near the epidermis, as
illustrated in
Figure 1 3
24. Trees have woody stems, whereas annuals (plants
that complete their life cycle in one growing
season or less) have herbaceous stems. Provide
an explanation for this diference.
. 1 9 .