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Understanding the Light-Dependent Reactions and Calvin Cycle in Photosynthesis, Study notes of Cellular and Molecular Biology

Information on the light-dependent reactions and the calvin cycle in photosynthesis. It includes true or false questions, explanations, and a diagram. The light-dependent reactions involve the absorption of light by photosystems, the generation of atp and nadph, and the electron transport chain. The calvin cycle, or light-independent reactions, uses atp and nadph to produce sugars from carbon dioxide.

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Name KEY
8.3 The Process of Photosynthesis
The Light-Dependent Reactions: Generating ATP and NADPH
For Questions 15, 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
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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

across the membrane, provides the energy to make ATP.

The Light-Independent Reactions: Producing Sugars

10. What does the Calvin cycle use to produce high-energy sugars?

The Calvin cycle uses carbon dioxide molecules as well as ATP and NADPH from the

light-dependent reactions to make sugars.

11. Why are the reactions of the Calvin cycle called light-independent reactions?

The reactions of the Calvin cycle use ATP and NADPH as energy sources. They do not

directly require light.

12. What makes the Calvin cycle a cycle?

The compound (RUBP) with which CO2 from the air combines is a product of the cycle, which

enables the series of reactions to occur over and over.