Leaf Color Change:
● Chlorophyll a and b are expensive for plant to make
● As angle of sunlight changes with season, fewer photons are available and it is no
longer worth it to make chlorophyll
● B-carotene and xanthophylls are accessory pigments that help protect cells against
intense light - don’t break down in fall
● When chlorophylls disappear, colors or carotenoids are visible as yellows, orange, and
red wavelengths that are not absorbed, thus they reflect back to our eyes
Accessory Pigments:
● Protect plants against sunburn
● Pigments such as B-carotene / xanthophylls absorb light and extra e- to convert energy
into heat that radiates away from plant
● This prevents chlorophyll from being “overworked” - depleted of e- faster than molecules
can recover
● Pigments and perfumes are expensive molecules that plants use sparingly, which is why
they look colorful and smell nice, but not both
In too much light, P680 is giving up electrons faster than they can be replaced
Photosystems:
● Transport e- to make H+ gradient
● H2O broken to return e- to P680 chlorophyll molecule that donated e- to transport chain
● H+ and O2 are released
● PSII surrounded by Light Harvesting Complexes (LHC II) that move around based on
lighting conditions
Lot of contact with core
● Chlorophyll a and b are expensive for plant to make
● As angle of sunlight changes with season, fewer photons are available and it is no
longer worth it to make chlorophyll
● B-carotene and xanthophylls are accessory pigments that help protect cells against
intense light - don’t break down in fall
● When chlorophylls disappear, colors or carotenoids are visible as yellows, orange, and
red wavelengths that are not absorbed, thus they reflect back to our eyes
Accessory Pigments:
● Protect plants against sunburn
● Pigments such as B-carotene / xanthophylls absorb light and extra e- to convert energy
into heat that radiates away from plant
● This prevents chlorophyll from being “overworked” - depleted of e- faster than molecules
can recover
● Pigments and perfumes are expensive molecules that plants use sparingly, which is why
they look colorful and smell nice, but not both
In too much light, P680 is giving up electrons faster than they can be replaced
Photosystems:
● Transport e- to make H+ gradient
● H2O broken to return e- to P680 chlorophyll molecule that donated e- to transport chain
● H+ and O2 are released
● PSII surrounded by Light Harvesting Complexes (LHC II) that move around based on
lighting conditions
Lot of contact with core
