The Function of Leaves

Leaf Types and Patterns

• Five different types of leaf patterns– Needlelike or scalelike– Opposite compound leaves– Opposite simple leaves– Alternate compound leaves– Alternate simple leaves

Leaf Types and Patterns

• Trees with needlelike or scalelike leaves.

• Conifers cone bearing trees

• Gymnosperms: trees whose seeds are exposed (this is opposed to angiosperms whose seeds are enclosed in an ovary that ripens into a fruit.

Leaves opposite (compound and simple)

Leaf Types and Patterns

• Leaves Opposite and compound

• Compound leaves contain leaflet which lack buds at their base

• Leaves line up opposite or across from each other on the stem.

Leaf Types and Patterns

• Leaves Opposite and simple

• Buds at the base of the leaf.

• Twig is woody• Leaves align across

form each other

Alternate leaves (compound and simple)

Leaf Types and Patterns

• Alternate simple leaves

• Single leaf which contains a bud at the base of the leaf stalk.

• Leaves alternate along twig.

Leaf Types and Patterns

• Alternate compound leaves

• Compound leaves contain leaflet which lack buds at their base

• Leaflets alternate along the woody twig.

Adapted for Photosynthesis

• Leaves are usually thin – High surface area-to-volume ratio

– Promotes diffusion of carbon dioxide in, oxygen out

• Leaves are arranged to capture sunlight– Are held perpendicular to rays of sun

– Arrange so they don’t shade one another

Leaf Structure

UPPEREPIDERMIS

PALISADEMESOPHYLL

SPONGYMESOPHYLL

LOWEREPIDERMIS

one stoma

cuticle

O2CO2

xylem

phloem

Mesophyll:Photosynthetic Tissue

• Mesophyll Cells have

chloroplasts

• Chloroplasts are the

Organelles which capture

energy from the sun to

drive photosynthesis.

• Photosynthesis converts

CO2 into sugars and

starch

in-text, p. 95

sunlight water uptake carbon dioxide uptake

ATP

ADP + Pi

NADPH

NADP+

glucoseP

oxygen release

LIGHT INDEPENDENT-

REACTIONS

LIGHT DEPENDENT-REACTIONS

new water

Fig. 6.3a, p. 94

leaf’s upper surface photosynthetic cells

two outer layers of membrane

inner membrane system (thylakoids, all interconnecting bychannels) stroma

(see next slide)

Fig. 6.9, p. 98

reaction center (a specialized chlorophyll a molecule)

sunlight

PHOTOSYSTEM

excitationenergy

The Rainbow catchers

• Pigment Molecules absorb wavelengths of light

• Most pigments can absorb only certain incoming wavelengths

• Chlorophylls are the main photosynthetic pigment

Fig. 6.6a, p. 97

Wav

elen

gth

ab

sorp

tio

n (

%)

Wavelength (nanometers)Wavelength (nanometers)

chlorophyll b

chlorophyll a

beta-carotene

phycoerythrin (a phycobilin)

Wav

elen

gth

ab

sorp

tio

n (

%)

in-text, p. 95

sunlight water uptake carbon dioxide uptake

ATP

ADP + Pi

NADPH

NADP+

glucoseP

oxygen release

LIGHT INDEPENDENT-

REACTIONS

LIGHT DEPENDENT-REACTIONS

new water

Carotenoids

• The Carotenoids are accessory pigments that absorb light of blue-violet and blue-green wavelengths and reflect yellow, orange, and red ones.

• Carotenoids color many flowers, vegetables and fruits.

• They are less abundant than chlorophylls in green leaves but in many plant species, they are visible in autumn

Autumn Foliage

• In late summer , leaves begin to forming layers of cells at the leafstalk base to help the leaf detach and heal the resulting scar

• As the these cells continue to grow they begin to clog the leave vains

• The dominant pigment, Chlorophyll is no longer renewed and disintegrates quickly, revealing the yellow and orange pigments of the carotenoids

Autumn Foliage

• Because these red pigments require high light intensity and elevated sugar content for their formation, the colors appear after a period of bright autumn days and cool night, which prevent accumulated sugar from leaving the ding leaf