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Example Questions
Example Question #1 : Understand Light Dependent Reactions
What is the first step in photosynthesis?
Photons present in light strike and excite electrons in chlorophyll
Light causes oxygen to pair with hydrogen, forming water for the plant
Water is split by chlorophyll
Light reduces sugars present in the plant cells to energized derivatives
Nutrients from the soil are turned into carbohydrates when combined with water
Photons present in light strike and excite electrons in chlorophyll
Photosynthesis begins with energy from light being converted to chemical energy. The only answer explanation accurately explaining this process describes the conversion of light energy (photons) to chemical energy (excited electrons).
Photons present in light strike and excite electrons in chlorophyll.
The photons are highly energized light particles, which strike chlorophyll and excite and free electrons in the chlorophyll molecule. These excited electrons pass through the electron transport chain and their energy is collected to make ATP.
Example Question #2 : Understand Light Dependent Reactions
Which of the following is a by-product of the light reactions in photosynthesis?
Water
Oxygen
Carbon dioxide
Sugar
Oxygen
During the light reactions water is split and the by-product is oxygen. Oxygen is then released back into the atmosphere. Sugars are produced during the Calvin cycle and are not a direct product of the light reactions.
Example Question #3 : Understand Light Dependent Reactions
The light reactions of photosynthesis are responsible for the production of which of the following molecules?
Producing carbon dioxide
Producing water
Converting solar energy to chemical energy
Producing sugars
Converting solar energy to chemical energy
The light reactions are the steps of the photosynthesis that function to convert solar energy into chemical energy that can be used during the Calvin cycle. The light reactions use solar energy to reduce to and to convert to .
Example Question #4 : Understand Light Dependent Reactions
Where do the light reactions of photosynthesis occur?
In the stroma
In the cell wall
In the mitochondrial membrane
In the thylakoid membranes
In the phospholipid bilayer
In the thylakoid membranes
The light reactions of photosynthesis occur in the thylakoid membranes inside of chloroplasts in plant cells. Photosynthesis depends on the buildup of a proton gradient across a membrane to generate ATP. The thylakoid is an organelle present only in plants. The phospholipid bilayer and cell wall surround plant cells, and are not involved in photosynthesis.
Example Question #5 : Understand Light Dependent Reactions
When a molecule of NAD⁺ gains a hydrogen atom, the molecule becomes?
plasmolyzed
redoxed
reduced
hydrolyzed
oxidized
reduced
The molecule is reduced because when a molecule gains an electron, it is said to be reduced. The answer oxidized would have been chosen if the molecule lost an electron. Plasmolysis has nothing to do with the gain or loss of an electron, and the term redoxed does not fit into this question. Hydrolysis is when a bond is broken using water, so that is incorrect as well.
Example Question #15 : Photosynthesis
What is the purpose of the light dependent reaction?
To convert solar energy into electrical energy
To convert solar energy into chemical energy
To produce CO2 necessary for light independent reaction
To convert chemical energy to solar energy
To convert solar energy into chemical energy
The light dependent reaction converts solar energy to chemical energy, using the photosystem to capture light energy, and ultimately produce ATP and NADPH. Pigment molecules in the photosystem absorb photons of light, which then reach the chlorophyll, exciting electrons in the chlorophyll. The excited electron then is transferred to a primary electron acceptor of the electron transport chain (and is replaced by the splitting of water (to produce O2, H+ and e-)).
Example Question #16 : Photosynthesis
During the light dependent reaction, what is the purpose of creating a proton gradient in the thylakoid lumen?
To power ATP synthase
To generate
To create
To power ATP hydrolysis
To power ATP synthase
The ATP synthase protein is embedded in the thylakoid membrane. When sunlight is captured by photosystem II in the light dependent reaction, water is split, producing O2 and 2 H+ ions and 2 electrons. As the electrons flow down the electron transport chain, this energy is used to pump hydrogen ions from the stroma into the thylakoid space, producing a high concentration of hydrogen ions inside the thylakoid lumen. Eventually, the hydrogen ions then flow from the area of high concentration (in the thylakoid lumen) to an area of low concentration (in the stroma ), through the ATP synthase protein. The movement of the hydrogen ions through this structure combines ADP with phosphate, producing ATP.
Example Question #2 : Understand Light Dependent Reactions
Which does not occur during the light dependent reaction?
is split, producing H+ ions, oxygen, and electrons
NADPH is produced
ATP is produced
carbon fixation is aided by the enzyme Rubisco
carbon fixation is aided by the enzyme Rubisco
Carbon fixation, catalyzed by Rubisco, occurs during the first step of the light independent reaction.
Example Question #6 : Understand Light Dependent Reactions
What products of the light dependent reaction are necessary for the light independent reaction to occur?
ATP and NAPH
ADP and NADP+
ADP and NADP+
ATP and NADP+
ATP and NAPH
ATP and NADPH are produced during the light dependent reaction, and are reactants necessary for the light independent reaction (Calvin Cycle) to occur. During the light independent reaction, ATP and NADPH are used to convert phosphoglycerate molecules (PGA) to glyceraldehyde-3-phosphate molecules (G3P). G3P is then used to produce glucose.
Example Question #17 : Photosynthesis
Which is true of light dependent reactions?
ATP is a product
is a reactant
GTP is a reactant
NADP+ is a product
ATP is a product
Light dependent reactions convert solar energy to chemical energy (in the form of ATP and NADPH). Sunlight and H2O are the reactant of the light dependent reaction. The sunlight is captured by photosystem II, and is used to excite electrons. Splitting of H2O produces hydrogen ions used to establish the proton gradient, and electrons produced replace the electrons transferred to the primary electron acceptor.
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