Chapter 10 Study ?’s (part 2): The Light Reactions
**NOTE: Read ALL of the figure captions!!!
1a) What is the electromagnetic spectrum? THE ENTIRE RANGE OF RADIATION FROM THE
SUN
1b) Which segment of the spectrum is most important to life? VISIBLE SPECTRUM (380nm – 750 nm)
Why? VISIBLE LIGHT DRIVES PHOTOSYNTHESIS (EXCITES ELECTRONS IN
CHLOROPYHLL-a
2) A student performs an experiment in which she places 3 plants under 3 different colored lamps: blue, red,
and green. Which color(s) of light will be best for the plant? Which color(s) will be the worst? Explain.
BLUE & RED WILL BE BEST BECAUSE CHLOROPHYLL ABSORBS THESE WAVELENGTHS BEST;
GREEN IS THE WORST BECAUSE CHLORO. DOESN’T ABSORB GREEN, IT TRANSMITS OR REFLECTS
GREEN; THERE IS MORE CHLORO. THAN ANY OTHER PIGMENT
3) Explain the significance of the accessory pigments:
-chlorophyll b: ALMOST IDENTICAL TO CHLORO-a, BUT THE SLIGHT DIFFERENCE IN
STRUCTURE ALLOWS IT TO ABSORB SLIGHTLY DIFFERENT WAVELENGTHS; CHLOR-b PASSES
ENERGY IT ABSORBS TO CHLOR-a
-carotenoids: 1) MAY BROADEN THE SPECTRUM OF ABSORBED WAVELENGTHS
2) PHOTOPROTECTION: ABSORB & DISSIPATE EXCESSIVE LIGHT ENERGY THAT
WOULD DAMAGE CHLORPHYLL
4a) What does it mean when a pigment molecule is described as being in its “ground state” versus its
“excited state”? GROUND STATE: ELECTRON IN NORMAL ORBITAL
EXCITED STATE: ABSORPTIONOF PHOTON BOOSTS AN ELECTRON TO AN
ORBITAL OF HIGHER ENERGY
4b) Generally, how long will pigments remain in their excited state? BILLIONTH OF A SECOND
(UNSTABLE THERE)
What happens to the excited electrons? THEY WILL DROP BACK TO THEIR GROUND STATE
5) Compare and contrast chlorophyll solutions that are illuminated with light in the lab versus chlorophyll
in an intact chloroplast. How and why is there a
difference?
CHLOROPHYLL SOLUTIONS IN A LAB WILL
FLOURESCE BECAUSE THIS CHLOROPHYLL IS NOT
LOCATED IN A REACTION CENTER NEXT TO AN
ELECTRON ACCEPTOR. THEREFORE, THE EXCITED
ELECTRON FALLS BACK TO ITS GROUND STATE AND
GIVES OFF THE ENERGY AS LIGHT
CHLOROPHYLL IN A CHLOROPLAST WILL LOSE ITS
ELECTRON TO THE ELECTRON ACCEPTOR (ENERGY
GIVEN AWAY), SO NO FLOURESENCE (LIGHT)
6a) Describe what makes up the “reaction center” of a photosystem. CHLORPHYLL-a AND PRIMARY
ELECTRON ACCEPTOR
6b) Explain how a photosystem harvests light energy. You may include a sketch of a photosystem to
illustrate the process.
 CHLOR-a, CHLOR-b, & OTHER PIGMENTS ABSORB LIGHT ENERGY (ALL PASS ENERGY TO
CHLOR-a)

THAT ENERGY EXCITES AN ELECTRON FROM GROUND STATE TO AN EXCITED STATE

PRIMARY ELECTRON ACCEPTOR CAPTURES ELECTRONS

PRIMARY ELECTRON ACCEPTOR SENDS ELECTRONS DOWN ETC (REDOX REACTIONS)
7) Create a chart in which you compare noncyclic electron flow with cyclic electron flow. Include in your
chart: the components used; the inputs and outputs of each.
COMPONENTS USED
INPUTS
OUTPUTS
NONCYCLIC
PSII, PSI, BOTH ETC’S
WATER,LIGHT,
ATP, NADPH,
ELECTRON FLOW
NADP+, ADP, Pi
OXYGEN, H+
CYCLIC ELECTRON
PSI, AND ETC
LIGHT, ADP, Pi
ATP
FLOW
BETWEEN PSII & PSI
8a) Which energy molecules are produced in noncyclic electron flow? ATP & NADPH
In cyclic electron flow? ATP ONLY
8b) Why is there a difference? CYCLIC ELECTRON FLOW MAKES UP THE DIFFERENCE IN ATP USED
IN THE CALVIN CYCLE (LIGHT INDEPENDENT REACTIONS); CALVIN CYCLE USES MORE ATP
THAN NADPH; ELECTRONS BACK UP IN THE ETC THAT SENDS ELECTRONS TO NADP+
REDUCTASE SO 1ST PROTEIN IN THAT ETC CYCLES BACK AND SENDS EXCIRTED ELECTRONS
DOWN ETC BETWEEN PHOTOSYSTEM II AND PHOTOSYSTEM I (GENERATES ATP)
8c) How is NADPH concentration involved in feedback inhibition of noncyclic electron flow?
AS NADPH CONCENTRATION INCREASES OVER ATP, IT BEGINS TO ACCUMULATE IN THE
STROMA; THIS TEMPORARILY SHIFTS THE MODE OF ELECTRON CONVERSION FROM NONCYCLIC
TO CYCLIC (NOT ENOUGH NADP+ TO TAKE ANY MORE ELECTRONS AND THE ELECTRONS BACK
UP IN THAT ETC)