Summary BOT161 leaf lecture

PLANT STRUCTURE AND FUNCTIONS OF STEMS
Theme C


Leaves and adaptations
What is a leaf?

Any usually flattened green outgrowth from the stem of a vascular plant.

• Photosynthesis

• Transpiration

• Storage of water and nutrients.

• Defence or protection

The structural parts of a leaf are:

1. Midrib 2. Veins

3. Margin 4. Leaf base

5. Petiole 6. Lamina (the leaf blade)

7. Stipules (small pair of leaf-like structures at the base of the petiole)

Structure: Function:

• Leaf morphology • Photosynthesis • Pollination

• Leaf arrangement • Transpiration • Waste disposal

• Leaf anatomy • Protection

Tissue Organization of Leaves

• The epidermal barrier: Has stomata – gaseous exchange and transpiration, Coated by a waxy cuticle – why?

• The ground tissue – mesophyll: Is sandwiched between the adaxial and abaxial epidermis

• The vascular tissue: Is continuous with the vascular tissue of the stem

, Leaf arrangement

• Leaf arrangement on a stem may be

- Alternate (one leaf at each node)

- Opposite (two leaves at each node)

- Whorled (three or more leaves at each node)

• In classifying angiosperms - Taxonomists may use leaf morphology as a criterion




Leaf Venation

• Monocots and dicots (Differ in the arrangement of veins, the vascular tissue of leaves)

• Most monocots (Have parallel veins)

• Most dicots (Have branching veins (net veined)) (Pinnate / Palmate)

Modified leaves