Function of leaves:

Leaf Structures: Wide variety of shapes and sizes- important feature in plant identification

• Blade: Broad, flat portion of leaf

•Primary site of photosynthesis

•Site of transpiration

•Site of gas exchange

- Site of most photosynthesis

• Petiole: Stalk like region on leaf where it is attached to stem

Three Tissue Layers:

1. Epidermis layer: usually 1 cell layer thick

- On top and bottom of leaf

- impermeable cuticle (top & bottom)

- H2O, O2, & CO2 enter & exit through stomata (bottom)

Upper

Epidermis

Lower

EpidermisCO2 O2

LEAF CS

**Label Your Leaf CS**

2. Mesophyll Layer: Organized into two layersa. Palisade Mesophyll

- Lays directly beneath upper epidermis- Site of most photosynthesis

- Made up of columnar cells & are tightly packed into one or two layers

LEAF CSPalisade Mesophyll

Mesophyll

b. Spongy Mesophyll:- Beneath palisade layer

- Irregularly shaped cells (balloons)

LEAF CS

MesophyllSpongy Mesophyll

All the Black Space is AIR!!!

-surrounded by large air spaces for diffusion: O2, CO2, and H2O

3. Vascular Layer:

- Consists of vascular bundles called veins (circular)

- Continuous with vascular bundles in stem & petiole

- Veins branch repeatedly so each cell is less than 1mm from a vein. Xylem

(top)

Phloem

LEAF CS

• Venation in Monocots and Dictos: Arrangements of veins in a leaf

- Monocots: Parallel venation

- Ex: grasses

- Dicots: Net Venation

- Ex: maple

Leaf Processes:1. Transpiration: Evaporation of water in plant

through stomata which increases absorption at roots

2. Gas Exchange: Exchange of CO2 and O2 through stomata

•Stomata: Bordered by 2 kidney shaped guard cells

-Modified epidermis cells that regulate H2O and gas exchange

- Contain chloroplasts - Open during day, closed during night

- Found in lower epidermis

**Write Small!!!**

Stomata in monocot and dicot leaves:

Monocots: ParallelDicots: RandomLEAF CS

Stomata

3. Photosynthesis: Process by which chlorophyll and enzymes in leaves convert certain wave lengths of light to chemical energy

Simple equation of photosynthesis:Sunlight + CO2 + H2O Carbohydrates + O2

Chloroplasts: Sacks that contain photosynthetic pigments

- Site of photosynthesis

Thylakoids: Series of flattened sacks

- Acts like solar panels to collect sun energy

Grana: Stacks of thylakoids

Stroma: Liquid solution which contains 4 pigments

- Surrounds grana

Carotenes ORANGES

Spring/Summer: only green is reflected = SEE

all other colors hidden

Fall Colors: Chlorophyll is all used up, see other reflected pigments

Chromatography: technique used to separate a mixture into its different components

2 Other Pigments: Xanthophylls YELLOWS

Chlorophyll: 1) Chlorophyll A = 95%

2) Chlorophyll B = 5%

ROYGBIV

700nm 400nm

= White Light (prism)

ed

range

el

low

reen

lue

ndigo

iolet

Uses of Leaves in Plant Identification

1. Arrangement of leaves on stem 2. Divisions in a leaf 3. Shape 4. Character of leaf margin 5. Veins