IG6.2 & 6.3 Leaves and Factors of Photosynthesis

Leaf Anatomy

Leaf Structure

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

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The edge of the leaf is called the margin.

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

​Leaves can either be simple or compound.

​

​

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

Leaf Margins

​Entire - a smooth edge

​

​Serrate - forward pointing like a saw or knife

​

​Lobed- smooth, round bumps

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​Parted- big indentations in the leaf edge

​Leaf Venation

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

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​Palmate - Veins radiate out from the base

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​Pinnate- Branching off from one main vein

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

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.

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.

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

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

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.

Factors Affecting Photosynthesis

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