Why Are Plants Green?
and how does color work?
Electromagnetic Spectrum
● Humans only see a small section of the
electromagnetic spectrum.
● Spectrum range: 1nm-1Mm
● Visible light: 380-760 nm
Color
Electromagnetic Spectrum
● The shorter the wavelength, the faster the
frequency of the wave.
● Waves with a shorter wavelength have more
energy.
Color
● Visible light appears in the spectrum in the
order of ROYGBIV
○ red, orange, yellow, green, blue, indigo,
violet
○ Red has a larger wavelength than blue
Color
Color
● We see color because light is
absorbed and reflected by
pigments
● A red object absorbs all light
except for red, which is reflected
to our eyes
Why Plants Are Green
● Plants have 2 types of chlorophyll
○ chlorophyll a- absorbs blue/violet and
red/orange light
○ peak absorption at 425 and 675 nm
Why Plants Are Green
● chlorophyll b- absorbs blue/violet and
red/orange light
○ peak absorption at 465 and 665 nm
● Both reflect yellow and green wavelengths
Why Plants Are Green
Why Plants Are Green
● Why do plants have 2
types of chlorophyll?
○ The different
ranges maximize
energy absorption
Other Plant Pigments
● Carotenoids absorb
violet, blue and green
○ reflect orange,
yellow, and red
Other Plant Pigments
● During fall, chlorophyll
breaks down, becomes
clear, and is saved until
spring
● Carotenoids are left, leaves
turn orange