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NATS 1870 (78)
Lecture 4

Lecture 4 AK/NATS 1870: Fall Leaf Colour AK/NATS 1870: Colour Contrast (following Itten) 1. Contrast of Hue – strongest given by Y R B 2. Light/dark Contrast – white/black gives most extreme contrast 3. Cold/warm Contrast

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York University
Natural Science
NATS 1870
Robin Kingsburgh

AKNATS 1870 Fall Leaf Colourleaves in summer are green because they contain the chlorophyll molecule a pigment that absorbs red and blue wavelengths and reflects green wavelengthsrole of chlorophyll is to absorb sunlight and drive photosynthesis reactions to provide energy for plantin fall shortened days cool nightschlorophyll production declinesgreen colour fadesif leave contains carotene pigmentthey appear bright yellow carotene absorbs BG and B wavelengthsmore stable than chlorophyll moleculeif concentration of sugar in leaf increases sugar reacts to form anthocyaninsred pigment family absorb B BG G wavelengths colour sensitive to pH acidity of sap acidicbright red ripe apples less acidicpurple ripe grapesformed by reactions between sugarscertain proteins in cell sap does not occur until sugar concentration high requires sunlightnotetops of trees side facing southturn red firstother leaf pigments
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