Leaves

Goals

1. To understand how leaves are put together

2. To understand how leaves function

3. To understand how a leaf's structure is linked to its function

Outline

External morphology

parts of a leaf:

• blade
• petiole
• stipules

leaves may be:

• simple
• compound
  • pinnately compound
  • palmately compound

leaves may be:

• parallel-veined
• net-veined
  • pinnately veined
  • palmately veined

monocots vs. dicots

• monocots have parallel veins, usually w/o petiole
• dicots generally have netlike venation

Internal structure -- be sure to relate to function

Dermal tissue system: epidermis -- protection, prevention of water loss, gas exchange

• cuticle made of cutin
• trichomes
• guard cells flanking the stomata

Ground tissue system: mesophyll -- photosynthesis

• palisade mesophyll
• spongy mesophyll

Vascular tissue system: veins -- conduction

• composed of xylem and phloem
• surrounded by bundle sheath
• xylem is on top

Opening and closing of stomata

Guard cells: closed at rest, open when turgid

Turgor is produced by active transport of K⁺ into cells, and the resulting osmosis

Control: (normally open at day and closed at night in C₃ plants)

Opening triggered by:

1. an internal clock
2. light
3. low CO₂

Closing during day triggered by :

1. lack of water -- loss of turgor
2. high temperature, and accumulation of CO₂

Vocabulary

click here to go to leaf vocabulary