Back to: Botany 200 Level
Hello, dear learner! I hope you’re having a fantastic day! Have you ever thought about how plants use sunlight to power their growth? Just like we need electricity to charge our phones, plants need energy to make food. This energy comes from the movement of electrons in a process called electron transport, which happens in the thylakoid membranes of the chloroplasts. Today, we’ll learn about the two types of electron transport in photosynthesis: non-cyclic and cyclic electron transport.
Non-cyclic and cyclic electron transport
Plants use electron transport to convert light energy into ATP and NADPH, which are essential for making glucose. These electrons don’t just move randomly; they follow specific pathways to ensure energy is efficiently produced.
Non-Cyclic Electron Transport (The Complete Energy-Making Process)
This is the main electron transport system used by plants to produce both ATP and NADPH, and it also releases oxygen. It involves Photosystem II (PSII) and Photosystem I (PSI) working together.
Steps of Non-Cyclic Electron Transport:
Light Absorption by PSII: Sunlight excites electrons in Photosystem II (PSII), causing them to leave the chlorophyll molecule.
Water Splitting (Photolysis): To replace the lost electrons, PSII splits water molecules (H₂O) into oxygen (O₂), protons (H⁺), and electrons (e⁻). This is why plants release oxygen into the air!
Electron Transport Chain: The excited electrons move through a series of proteins, transferring energy to pump protons into the thylakoid space, creating a proton gradient.
ATP Formation: The built-up protons flow through ATP synthase, generating ATP in a process called chemiosmosis.
Excitation in PSI: The electrons reach Photosystem I (PSI), where they get re-energised by sunlight.
NADPH Formation: The electrons are passed to NADP⁺, forming NADPH, which is later used in the Calvin cycle to make glucose.
End products of non-cyclic electron transport:
ATP (energy for cellular activities)
NADPH (used in glucose production)
Oxygen (O₂) (released into the air)
Cyclic Electron Transport (A Backup Energy Source)
Unlike non-cyclic transport, cyclic electron transport only involves Photosystem I (PSI) and does not produce NADPH or oxygen. It happens when a plant needs more ATP but already has enough NADPH.
Steps of Cyclic Electron Transport:
Light excites electrons in PSI, and they leave the chlorophyll molecule.
Instead of moving to NADP⁺, the electrons cycle back to the electron transport chain.
As electrons move through the chain, protons are pumped into the thylakoid space.
ATP is produced through chemiosmosis, but no NADPH or oxygen is formed.
Why Do Plants Need Both?
Non-cyclic transport provides ATP, NADPH, and oxygen for photosynthesis and survival.
Cyclic transport allows plants to make extra ATP when needed, especially when there is more NADPH than ATP.
Summary
Plants use non-cyclic electron transport to produce ATP, NADPH, and oxygen by moving electrons from PSII to PSI. However, when ATP is low, they switch to cyclic electron transport, which only makes ATP. These processes ensure that plants get the right balance of energy to grow and produce food.
Let’s Test Your Understanding:
- What is the main difference between cyclic and non-cyclic electron transport?
- Why do plants need both ATP and NADPH?
- Which type of electron transport produces oxygen?
Awesome work, champion! Keep going strong, and always remember—every green leaf around you is busy moving electrons to make energy, just like a mini solar power plant! See you in the next lesson!
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