Photosynthesis Part 2Pages 112 to 113

Solar Energy to Chemical Energy – Vocab Review

Electromagnetic energy› Solar energy or radiation which travels in

space a rhythmic waves and can be measured in photons

Wavelength› The distance between crests of adjacent

waves such as those of the electromagnetic spectrum

Visible Light› The radiation our eyes see as different colors

UV

Fig. 10-6

Visible light

InfraredMicro-waves

RadiowavesX-raysGamma

rays

103 m1 m

(109 nm)106 nm103 nm1 nm10–3 nm10–5 nm

380 450 500 550 600 650 700 750 nm

Longer wavelengthLower energyHigher energy

Shorter wavelength

Vocab continued…

Pigments › Substances that absorb some wavelengths

of light and reflect others› Different pigments absorb/reflect different

wavelengths Photon

› A fixed quantity of light energy› The shorter the wavelength of light the

greater the energy of a photon

Fig. 10-7

Reflectedlight

Absorbedlight

Light

Chloroplast

Transmittedlight

Granum

Chlorophyll – primary pigment of photosynthesis

Which wavelengths are absorbed most?› Primarily blue and red

Why do plants appear green?› They reflect green light

What is the role of accessory pigments?› They allow the plant to absorb energy from

more the visible light spectrum – making the plant more efficient.

Fig. 10-9

Wavelength of light (nm)

(b) Action spectrum

(a) Absorption spectra

(c) Engelmann’s experiment

Aerobic bacteria

RESULTS

Rate

of

ph

oto

syn

thesis

(measu

red

by O

2 r

ele

ase)

Ab

sorp

tion

of

lig

ht

by

ch

loro

pla

st

pig

men

ts

Filamentof alga

Chloro- phyll a Chlorophyll b

Carotenoids

500400 600 700

700600500400

Excitation of chlorophyll by light

When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable

When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence

If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat

Photosystems capture solar power

Photosystem (1st part)› Light harvesting

complexes pigment molecules

bounded by proteins; absorb

transfer energy to chlorophyll a of reaction center

Photosystems capture solar power

Photosystem (2nd part)› Reaction Center

Chlorophyll a and a primary electron acceptor

Chlorophyll a uses energy from light harvesting complexes to pass a pair of electrons to the primary electron acceptor