Light-dependent reaction

Where does the light-dependent reaction take place?

Thylakoid membranes of the chloroplast

What is the first step of the light-dependent reaction?

Photoionisation:

Chlorophyll absorbs light

Light excites electrons in chlorophyll to a higher energy level

Chlorophyll loses electrons - becomes positively charged - has been oxidised

Electrons are taken up by an electron carrier - has been reduced

What happens to the electrons that leave the chlorophyll?

They pass along the electron transport chain in a series of oxidation-reduction reactions

Electrons lose energy at each stages which is used to make ATP

What is chemiosmosis?

The process by which the movement of hydrogen ions across a biological membrane generates ATP

What are the steps of the chemiosmosis?

The energy released by the electrons moving through the ETC allows the active transport of H+ ions to pass from a low concentration in the stroma to a high concentration in the thylakoid lumen

The protons then diffuse back though the ATP synthase channels which causes the production pf ATP from ADP and Pi

What is the photolysis of water?

The electron lost when chlorophyll absorbs lightly needs to be replaces

These electrons come from water molecules that are split using light energy

What is the equation for the photolysis of water?

2H₂O → 4H⁺ + 4e^- + O₂

What happens to the protons that are produced from the photolysis of water?

Pass out of the thylakoid space though the ATP synthase channels and are taken up by electron carrier NADP

The NADP becomes reduced

(Excited electrons and hydrogen ions from photolysis of water combine with NADP to form NADPH)

What happens to the reduced NADP?

Enters the light-independent stage

How are chloroplasts adapted to their function for carrying out the light-dependent reaction?

Thylakoid membrane has a large surface area for attachment of chlorophyll, electron carriers and enzymes

Granal membranes gave ATP synthase channels to catalyses the production of ATP and selectively permeable for a patroon gradient

Chloroplasts contain DNA and ribosomes so they can quickly and easily manufacture the proteins needed

What are the products of the light-dependent reaction?

ATP and NADPH

Not all the light falling on plants is used in photosynthesis, why not?

light misses the chlorophyll

Light is reflected

Light is wrong wavelength