Download AK/NATS 1870: Fall Leaf Colour

AK/NATS 1870: Fall Leaf Colour

leaves (in summer) are green because they contain the chlorophyll molecule
→ a pigment that absorbs red and blue wavelengths, and reflects green
wavelengths

role of chlorophyll is to absorb sunlight and drive photosynthesis reactions, to
provide energy for plant

in fall (shortened days, cool nights) → chlorophyll production declines →
green colour fades

if leave contains carotene pigment → they appear bright yellow
- carotene absorbs BG and B wavelengths
- more stable than chlorophyll molecule
 if concentration of sugar in leaf increases, sugar reacts to form anthocyanins
→ red pigment family
- absorb B, BG, G wavelengths
- colour sensitive to pH (acidity) of sap:
acidic – bright red (ripe apples)
less acidic – purple (ripe grapes)
- formed by reactions between sugars + certain proteins in cell sap
→ does not occur until sugar concentration high
→ requires sunlight
(note – tops of trees, side facing south → turn red first)

other leaf pigments: flavones – yellow; tannins – brown