Leaves

Leaves

Leaf Structure and Function

Stems to Leaves

Leaves are the primary photosynthetic organs of the plant.
Leaves are held to the stems by a petiole.
Plants are diverse and some plants lack the petiole altogether. These leaves
are called sessile leaves and attach directly to the stem. Sessile leaves are common in grasses and succulents.

Leaf Structure

​The leave is attached to the stem by a petiole.

​

The edge of the leaf is called the margin.

​

​The apex is the tip of the leaf and the base is the bottom that attached to the petiole.

Multiple Choice

What is the main body of the leaf called?

• Blade

• Petiole

• Vein

• Margin

Multiple Choice

thin stalk that connects the blade of the leaf to the plant's stem

• blade

• cuticle

• petiole

• epidermis

Leaves and Water Loss

Leaves are mostly broad (widened) to
maximize their surface area to
expose their chloroplasts to sunlight and perform photosynthesis. Unfortunately, by increasing their exposure they also increase their water
loss. To combat this, leaves
have a waxy coating of lipid (fatty)
material known as the cuticle.

Leaves and Water Loss

On the underside of each leaf, there are tiny openings called stomata which regulate the exchange of gases including carbon dioxide, oxygen, and water vapor.

The stomata are opened and closed
by specialized cells called guard
cells. Guard cells fill with
water and swell shut or release
water to close.

Cuticle - ​Thick, waxy covering that protects plants from drying out

​

​Epidermis - Single, protective layer of cells

​

​Mesophyll - Conducts photosynthesis, has chloroplasts 

​

​Stomata - Allow gases into and out of the leaf for photosynthesis

Layers of a Leaf

​A leaf consists of the following layers:

​1. Cuticle

​2. Upper epidermis

​3. Palisade mesophyll

​4. Spongy mesophyll

​5. Lower epidermis

​6. Pores (openings) also known as stomata

Multiple Choice

____________­lines the lower area of the leaf.

• blade

• cuticle

• petiole

• epidermis

Multiple Choice

_________is where photosynethesis actually occurs

• mesothelioma

• mesophyll

• metophyll

Multiple Choice

What is the function of a cuticle?

• Water Transport

• Sugar Transport

• Reduce Water Loss

• Increase Water Loss

Simple or Compound Leaves

A simple leaf is a single, undivided
leaf blade while compound leaves are
divided into leaflets.
In compound leaves, the leaflets attach to the same petiole and are arranged in palm or feather shapes.

​Leaves can either be simple or compound.

​

​

​Compound leaves have leaflets attached to the midrib by their own stalks.

Multiple Select

Which of the following is a simple leaf? There may be more than one answer.

Multiple Select

Which of the following is NOT a compound leaf? There may be more than one answer.

Multiple Choice

If there are 2 or more leaflets attached to the petiole, it is called

• compound leaves

• palmate leaves

• pinnate leaves

• simple leaves

Leaf Shape

Leaf shape often has everything to do with location and climate. Leaves are shaped differently according to temperature, light level, water availability, and weather (especially wind).
For example, the pine tree
combats wind by producing small, stiff leaves that do not drag in high wind. Deciduous trees shed their leaves altogether in winter months to avoid weather damage.

Leaf Shape

Leaf Edges or Margins: Entire
(straight, smooth), Undulate
(smooth, wavy), serrate
(toothed), crenate, lobed, or
parted.

Shape: lanceolate (long,
narrow), triangular, ovate,
cordate (heart-shaped),
elliptical, linear, or oblong

Leaf Margins

​Entire - a smooth edge

​

​Serrate - forward pointing like a saw or knife

​

​Lobed- smooth, round bumps

​

​Parted- big indentations in the leaf edge

Multiple Choice

Leaf margin?

• Lobed

• Serrated

• Entire

• Undulate

Multiple Choice

How do you call the part that is the edge of the leaf?

• Vein

• Petiole

• Leaf margin

• Mid vein

• Leaf blade

Multiple Choice

A leaf margin that DOES NOT contain teeth is called ______________.

• entire

• serrate

• lobed

Leaf Veins

Vascular bundles carrying water and nutrients are diverted from the stem at the node into the petiole and onto the leaf as veins. Venation can be either parallel or netted. Parallel venation is primarily seen in monocots while netted venation is found mostly in dicots. Netted venation can be palmate, pinnate, or reticulate.

​Leaf Venation

Parallel - Veins run along side each other along the length of the leaf.

​

​Palmate - Veins radiate out from the base

​

​Pinnate- Branching off from one main vein

Multiple Choice

The pattern of veins on the leaf.

• Design

• Lamination

• Venation

• Pollination

Multiple Choice

When the veins runs parallel to each other from the base to the tip of the leaf is called________ venation

• parallel

• Reticulate

• straight

• linear

Specialized Leaves

Spines are modified
stipules from the base
of leaves that protect
the base of the petiole.

Prickles are projections from the dermal tissue that can appear on leaves or stems.

Neither of these projections is considered thorns.

Specialized Leaves

Bracts are modified
leaves that appear
to be petals of a
flower but are not
flower parts.
Examples are
poinsettias and the
dogwood tree.

Multiple Choice

This is a close up of a flower from a dogwood tree. You can see the flowers in yellow. What is shown in white in the photo?

• Bracts

• Inflorescence

• Petals

• Leaves

Multiple Choice

What is shown in the photo?

• Prickles

• Spines

• Thorns

• Plant knives