#LightDependentReaction

#Biology

#Photosynthesis

Introduction

• Light - Dependent Reaction is the first step Photosynthesis.

• Light-dependent reactions are a series of photochemical reactions that occur in the thylakoid membranes of chloroplasts during photosynthesis.

• Energy Conversion - The light-dependent reactions convert light energy into chemical energy in the form of ATP and NADPH. This process is crucial for photosynthesis.

• Oxygen Production - One of the byproducts of the light-dependent reactions is oxygen (O2), which is released into the atmosphere as a result of water splitting.

• Energy Storage - The ATP and NADPH produced are essential for the subsequent light-independent reactions, providing the energy needed for synthesizing glucose.

Steps

• There are 4 main Steps for Light - Dependent Reaction :

1. Light Absorption in PSII

2. ATP Synthesis

3. Light Absorption in PSI

4. Reduction of NADP

Light Absorption in PSII

• When light is absorbed by one of the many pigments in photosystem II, energy is passed inward from pigment to pigment until it reaches the reaction center.

• There, energy is transferred to P680, boosting an electron to a high energy level. The high-energy electron is passed to an acceptor molecule and replaced with an electron from water.

• This splitting of water releases the O2

  we breathe.

ATP Synthesis

• The high-energy electron travels down an electron transport chain, losing energy as it goes. Some of the released energy drives pumping of H+ ions from the stroma into the thylakoid interior, building a gradient.

• H+ ions from the splitting of water also add to the gradient.) As H+

  ions flow down their gradient and into the stroma, they pass through ATP synthase, driving ATP production in a process known as chemiosmosis.

Light Absorption in PSI

• The electron arrives at photosystem I and joins the P700 special pair of chlorophylls in the reaction center. When light energy is absorbed by pigments and passed inward to the reaction center, the electron in P700 is boosted to a very high energy level and transferred to an acceptor molecule.

• The special pair's missing electron is replaced by a new electron from PSII (arriving via the electron transport chain).

Reduction of NADP

• The high-energy electron travels down a short second leg of the electron transport chain. At the end of the chain, the electron is passed to NADP

  \[^+\] (along with a second electron from the same pathway) to make NADPH.

The Video