Name KEY
8.3 The Process of Photosynthesis
The Light-Dependent Reactions: Generating ATP and NADPH
For Questions 1–5, write True if the statement is true. If the statement is false, change the underlined word
or words to make the statement true.
TRUE 1. Photosystems are clusters of chlorophyll and proteins.
PHOTOSYSTEM II 2. The light-dependent reactions begin when photosystem I absorbs light.
TRUE 3. Electrons from water molecules replace the ones lost by photosystem II.
NADPH 4. ATP is the product of photosystem I.
ENERGY 5. ATP and NADPH are two types of protein carriers.
6. How does ATP synthase produce ATP?
ROTATION OF ATP SYNTHASE PROVIDES ENERGY NEEDED TO BIND A PHOSPHATE
GROUP TO ADP, CREATING ATP
7. When sunlight excites electrons in chlorophyll, how do the electrons change?
THEY MOVE TO A HIGHER ENERGY STATE, OR MOVE FARTHER AWAY FROM THE
NUCLEUS
8. Where do the light-dependent reactions take place? THYLAKOID MEMBRANES
9. Complete the table by summarizing what happens in each phase of the light-dependent reactions of
photosynthesis.
Light-Dependent
Reactions
Summary
Photosystem II
Photosystem II absorbs light and increases the electrons’
energy level. The electrons are passed to the electron transport chain.
Enzymes in the thylakoid
break up water molecules into 2 electrons, 2 H+ ions, and 1 oxygen atom. The
2 electrons replace
the high-energy electrons that
have been lost to the electron transport chain.
Electron Transport
Chain
Energy from the electrons is used by the proteins in the
chain to pump H+ ions from the stroma into the thylakoid space. At the end
of the electron
transport chain, the
electrons themselves pass to photosystem I.
Photosystem I
The electrons do not contain as much energy as they
used to. Pigments use energy from light to reenergize the electrons. At the end
of a short second
electron transport chain, NADP + molecules in the stroma pick up the high-
energy electrons, along
with H+ ions, at the outer surface
of the thylakoid membrane, to become NADPH.
Hydrogen Ion
Movement and
ATP Formation
Hydrogen ions began to accumulate within the thylakoid
space. The buildup of hydrogen ions makes the stroma negatively charged
relative to the space
within the thy- lakoids. This gradient, the difference in both charge and H+
ion concentration
