LEAF Flashcards
other plant organ that, along with stems, constitutes the shoot of the plant body. Its principal function is to act as the main site of photosynthesis in a plant.
leaf
The leaf consists of a flattened laminar portion called the
blade
The leaf consists of a stalk and which attaches the blade to the stem
petiole
If the blade is attached directly to the stem, the leaf is described as
sessile
Leaves arise from an apical or lateral bud that is often protected by
bud scales
are small leaf-like structures which develop in pairs on each side of the leaf during the growing season
Stipules
In monocots, the blades are usually narrow whose base, wholly or partly encloses the stem
sheath
Between the blade and the sheath, some monocot plants have appendages such as
auricles and ligules
persistent meristem at the base of the leaf that allows it to grow indefinitely in monocots
true
The most common shapes
linear (thin), lanceolate (like a spear), ovate (oval) and cordate (heart-shaped).
lined with the veins; the middle portion of the blade usually has a prominent central vein
blade or lamina
prominent central vein, while smaller veins radiate from this
midrib
veins are arranged differently in monocots and dicots, explain
Dicots display netted venation while monocots usually have parallel venation.
edge of the blade is called
margin
margin types
toothed, lobed or entire.
leaf tip
apex
part near the petiole is called
leaf base
There are two types of leaves
There are two types of leaves
a single blade or lamina and may have any of the above characteristics
They may be deeply lobed.
simple leaf
is composed of two or more separate leaflets.
compound leaf
There are two basic kinds of compound leaves:
There are two basic kinds of compound leaves:
the leaflets occur in a linear sequence lined up along both sides of a central axis
pinnately compound leaf
central axis
rachis
which three, five, seven or more leaflets are all attached at one point near the tip of the petiole and they radiate out from this tip.
palmate compound leaf
How do you tell if a leaf is compound?
Look at the base of the leaf or petiole where it is attached to the stem. If there is a bud in the angle formed by the petiole and stem, like an axillary bud, then the entire structure supported by the petiole is a leaf, regardless of the number of leaflets present. All the leaflets of a compound leaf occur in the same plane. Also, some very large pinnately compound leaves sometimes resemble an entire branch. The branch will have a terminal bud, but a compound leaf won’t have a terminal branch.
Leaf arrangement is referred to
phyllotaxy
one leaf occurs at each node
alternate or spiral arrangement
alternate and the leaves occur only on two rows
distichous
two leaves at a node facing each other
opposite
which two opposite leaves are perpendicular to the two opposite leaves below or above them
decussate
arrangement has three or more leaves at one node
whorled
outermost layer of cells
epidermis
These epidermal cells secrete a waxy substance which forms a covering over the outer dermal cells rendering these cells impermeable to water. The waxy covering is called
cuticle
There is an upper epidermis and a lower epidermis in a leaf with
dorsiventral
The openings in the epidermis are called
stomates
stomates which are formed between specialized epidermal cells called
guard cells
are found on the undersurface of the leaves and herbaceous stems
These help reduce evaporation of water from plants or protect young shoots from herbivores.
trichomes
with the exception of the vascular bundles, comprises all of the cells between the upper and lower epidermis and is usually divided into two parts.
mesophyll
The cells toward the upper epidermis, which are elongated, make up the
palisade layer
The zone below the palisade layer, composed of irregularly shaped cells
spongy layer
are found between mesophyll cells
Inter-cellular air spaces
In some monocots, there is no distinct palisade and spongy layers because the leaves are
all the parenchyma cells with chloroplast between the upper and lower epidermis comprise the mesophyll layer.
isobilateral
function both as supporting and conducting tissue.
vascular bundles
They are composed of two fundamental tissues:
xylem and phloem
These conducting tissues are surrounded by vascular bundle sheath cells and are collectively called
veins
