Photosynthesis (Light Reactions)

Summary

The photosynthesis electron transport chain involves a series of protein complexes and mobile carriers that convert light energy into chemical energy. Photons excite chlorophyll in Photosystem II, releasing electrons which travel through various carriers like plastoquinone, cytochrome b6-f, and plastocyanin. This process generates a proton gradient, which powers ATP synthesis via ATP synthase. Electrons are ultimately transferred to NADP+ to form NADPH. Oxygen is produced as a byproduct when water molecules are split. ATP, NADPH, and oxygen are the essential products of this process, crucial for plant energy production and growth.

Takeaways

• 😀 Photosynthesis occurs in the chloroplasts of plants, algae, and some single-cell organisms like cyanobacteria, which lack chloroplasts.
• 😀 The photosynthesis electron transport chain involves multiple protein complexes and mobile carriers to transfer electrons and create ATP and NADPH.
• 😀 Light energy is absorbed by chlorophyll in Photosystem II, exciting electrons and initiating the electron transport chain.
• 😀 Plastoquinone Qb is the first mobile carrier that picks up two electrons and two protons, which are essential for subsequent steps.
• 😀 Water splitting occurs in Photosystem II to replace the electrons lost during excitation, also releasing hydrogen ions and producing oxygen.
• 😀 Cytochrome b6-f complex pumps hydrogen ions into the lumen, contributing to the formation of a hydrogen ion gradient.
• 😀 Plastoquinone transfers electrons to cytochrome b6-f, and these are later passed to plastocyanin, a second mobile carrier.
• 😀 In Photosystem I, electrons are re-energized by light and transferred to ferredoxin, which then passes them to ferredoxin-NADP-reductase (FNR).
• 😀 NADPH is synthesized by FNR through the transfer of two electrons and a proton to NADP+.
• 😀 The proton gradient generated by the electron transport chain powers ATP synthase to produce ATP, similar to mitochondrial ATP synthesis.
• 😀 The final products of photosynthesis are ATP, NADPH, and molecular oxygen, all crucial for plant energy and growth.

Q & A

What is the main function of the photosynthesis electron transport chain?

The main function of the photosynthesis electron transport chain is to transfer electrons through a series of protein complexes and mobile carriers, ultimately producing ATP and NADPH, which are vital for the process of photosynthesis.

Where does photosynthesis occur in plants and algae?

Photosynthesis occurs in the chloroplasts of plants and algae.

Which organisms besides plants and algae also undergo photosynthesis?

Single-celled organisms, such as cyanobacteria, also undergo photosynthesis, even though they do not have chloroplasts.

What happens when a photon of light hits a chlorophyll molecule in Photosystem II?

When a photon of light hits a chlorophyll molecule in Photosystem II, it creates resonance energy that is transferred to neighboring chlorophyll molecules, eventually exciting electrons in the reaction center.

What is the role of plastoquinone (Qb) in the electron transport chain?

Plastoquinone (Qb) accepts two excited electrons from Photosystem II and picks up two protons from the stroma. It then transfers the electrons to the cytochrome b6-f complex.

How are the electrons lost from Photosystem II replaced?

The electrons lost from Photosystem II are replaced by the splitting of water molecules, which also releases hydrogen ions into the lumen and contributes to the formation of molecular oxygen.

What is the significance of the hydrogen ion gradient in photosynthesis?

The hydrogen ion gradient created by the electron transport chain is crucial for ATP synthesis, as it powers ATP synthase, which generates ATP from ADP and inorganic phosphate (Pi).

How does NADPH get produced during photosynthesis?

NADPH is produced when two excited electrons are transferred from Photosystem I to ferredoxin, which then transfers them to ferredoxin-NADP-reductase (FNR). The two electrons and a hydrogen ion are added to NADP+ to form NADPH.

What is the function of cytochrome b6-f in the electron transport chain?

Cytochrome b6-f transfers electrons from plastoquinone to plastocyanin and helps pump hydrogen ions into the lumen, contributing to the hydrogen ion gradient necessary for ATP synthesis.

What are the final products of photosynthesis?

The final products of photosynthesis are ATP, NADPH, and molecular oxygen.