Photosynthesis (Light-Dependent Reactions)

Photosynthesis

Light-Dependent Reactions

Light-Dependent Reactions

• In photosystem II, solar energy excites electrons and water molecules are split into hydrogen ions, oxygen molecules, and free electrons

• The free electrons travel through the electron transport chain along the thylakoid membrane

Light-Dependent Reactions

• As the electrons travel, some energy is used to actively transport hydrogen ions against their concentration gradient from the stroma into the inner thylakoid space

• The hydrogen ions then move along their concentration gradient back into the stroma through specific channels. These channels contain enzymes that create ATP as the hydrogen atoms flow

Light-Dependent Reactions

• The electrons continue on the electron transport chain (ETC) until they reach photosystem I, where electron carriers are charged

• Think of photosystem I as a charging outlet

• At this photosystem, chlorophyll molecules absorb photons of sunlight energy and electrons pass the energy along another electron transport chain

• At the end of this chain, the electrons, NADP+, and hydrogen ions react to form NADPH, another energy carrier molecule

Multiple Choice

What part of the water molecule that splits travel through the ETC (electron transport chain) along the thylakoid membrane?

• Hydrogen Ions

• Free Electrons

• Oxygen Molecules

Multiple Select

Check all of the following that apply for the creation of ATP.

• Energy is used to actively transport hydrogen ions

• The hydrogen ions are moved against their concentration gradient from the stroma into the inner thylakoid space

• Then move along their concentration gradient back into the stroma through specific channels

• The channels contain enzymes that create ATP as the hydrogen atoms flow

• The electrons continue down the chain to create ATP

Multiple Choice

True or False: Electrons are charged in photosystem I.

• True

• False

Open Ended

What happens at photosystem I?

Answer to Last Question (what happens at photosystem I?)

At this photosystem, chlorophyll molecules absorb photons of sunlight energy and electrons pass the energy along another electron transport chain

Multiple Select

What three things react to form NADPH?

• Electrons

• ATP

• Hydrogen Ions

• NADP+

• Enzymes