Understanding Light-Dependent Reactions

Light-Dependent Reaction

The goal of the _____ of photosynthesis is to convert light energy from the sun into chemical energy.

Thylakoid

Where does light-dependent happen?

Chloroplast

Where does thylakoid located?

Light-Dependent Reaction

Tracing the path of a single electron.

ATP, NADPH

What does light-dependent reaction produce?

ATP and NADPH

It is batteries in the plant cell

Adenosine Triphosphate (energy molecule)

What is the meaning of ATP acronym?

Nicotinamide adenine dinucleotide phosphate

What is the meaning of the acronym NADPH?

NADPH

Reduced electron camer

Light-Dependent Reaction.

Plants trap light to make chemical energy.

Photosystems

It is called antennas

Photosystems

• Pigment clusters acting like energy funnels.

• Accessory pigments catch light.

• Energy bounces down to Chlorophyll-a.

Resonance energy transfer

Scientific name of photosystems

Photosystems

proteins and pigments that absorb light

1. P680

2. P700

   
   

Reaction Center

Photosystem II:

Photosystem I:

1. 680 nm

2. 700 nm

   
   

Best Light Wavelength

Photosystem II:

Photosystem I:

1. Stacked region

2. Unstacked region

Location in Grana

Photosystem II:

Photosystem I:

1. Absorption of light energy

2. Splitting of water molecules

3. Release of oxygen

4. Formation of ATP and NADPH

Stages:

• Light Hits PSIl & Splitting Water

• Sunlight excites an electron in PSIl.

• The electron leaves its home.l

• To replace it, water is split (Photolysis).

• Oxygen is released into the air!

Step 1

Photolysis

The process of splitting water.

H2o = H+, e-, O2

Formula of Photolysis

The Electron Transport Chain

• The excited electron travels down a conveyor belt.

• It loses energy as it moves.

• This energy pumps
  Hydrogen ions (H+) into the lumen.

• Pressure builds up inside!

Step 2:

Making ATP (Chemiosmosis)

• H+ ions want to escape the crowded lumen.

• They rush out through a turbine (ATP Synthase),

• The spinning turbine charges ADP into ATP.

Step 3

ATP synthase

H* will Fuel the synthase and transforms ADP → ATP

Re-energizing at PSI

• The electron arrives at

• Photosystem I exhausted.

• More sunlight hits the
  P700 reaction center.

• The electron gets a second massive energy boost!

Step 4

Charging the Final Battery

• The high-energy electron leaves PSI.

• It is caught by an empty
  NADP+ molecule.

• This creates NADPH (our second battery).

Step 5

NADP+ + e-

Formula for NADPH:

1. PSI

2. PSI and PSII

Photosystems Used

Cyclic Flow:

Non-Cyclic Flow:

1. No

2. Yes

Is water split?

Cyclic Flow:

Non-Cyclic Flow:

1. ATP

2. ATP and NADPH

Final products

Cyclic Flow:

Non-Cyclic Flow:

• The light reaction does NOT make food/sugar.

• It only makes the batteries (ATP & NADPH).

• These batteries power the Dark Reaction to finally build glucose.

Why Did We Do All This?