Thylakoid Membrane in Photosynthesis: Definition, Function & Structure

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  • 0:00 Plant Cell Structure
  • 0:16 Chloroplasts and Thylakoids
  • 0:40 Definition and Function
  • 2:24 Lesson Summary
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Lesson Transcript
Jeremy Battista

Jeremy has a master of science degree in education.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

Inside of plant cells, there are chloroplasts. Inside the chloroplasts are all of the structures that help plants capture and convert light into energy. The thylakoid membrane is where much of this occurs, and we will discuss its role here.

Plant Cell Structure

Plant cells are eukaryotic, meaning that they have a nucleus and membrane-bound organelles. Most of the organelles will resemble those found in other eukaryotic cells. There are some different organelles, though. One of those organelles is the chloroplast.

Chloroplasts and Thylakoids

Inside the chloroplasts of plant cells, you will find stacks of thylakoids called grana. In some plant cells, thylakoids will not always be stacked. As a brief reminder, thylakoids are membrane-bound compartments inside of the chloroplasts. Thylakoids are the epicenter for photosynthetic light-reactions. They contain the chlorophyll for the plant, which is the light-collecting pigment.

Definition and Function of Thylakoid Membrane

The thylakoids themselves contain the chlorophyll, but the thylakoid membrane, which is the layer that surrounds the thylakoid, is where the light reactions take place. Embedded in the thylakoid membrane are two photosystems, named photosystem I and photosystem II. In each photosystem, there are different proteins and slightly different chlorophyll pigments that allow for different kinds of light absorption.

Photosystem II absorbs the light energy, exciting (energizing) an electron that takes off into the electron transport chain. It moves along this chain (similar to respiration) and gives off energy as ATP (adenosine triphosphate, which is an energy molecule). It arrives at photosystem I and fills in a hole left by an electron that got excited as well.

The second electron will then shoot up and travel down a similar electron transport chain. When it gets to the end of the chain, it meets ferredoxin, which is just a protein that contains iron. It then goes through a redox, or oxidation/reduction, reaction where it bonds to NADP+, creating a different energy molecule, NADPH, to be used to help run the secondary part of photosynthesis, which is known as the Calvin cycle.

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Additional Activities

Thylakoid Membrane Word Search Activity

This activity will help you assess your knowledge of the definition, structure, and function of the thylakoid membrane in photosynthesis.


For this activity, print this page on a blank piece of paper. Search and highlight the word that will complete each of the given clues. Afterward, neatly write them on the appropriate blank space in the clues.


  1. The creation of _____ occurs from the fixation of carbon dioxide highlighted by a process known as the Calvin cycle.
  2. A _____ is an organelle found in the cells of green plants and in photosynthetic algae, where photosynthesis takes place.
  3. The process of photosynthesis is characterized by the absorption and conversion of _____ energy into chemical energy.
  4. The stack-like structure of thylakoids in plant chloroplasts that contain chlorophyll is referred to as _____.
  5. _____ are folded membrane compounds found within plant chloroplasts.
  6. _____ is a green pigment found in the chloroplasts of plants and other photosynthetic organisms such as cyanobacteria.
  7. ATP is an organic compound that provides _____ to drive many processes in living cells.
  8. The _____ part of photosynthesis is known as the Calvin cycle.
  9. As the light energy is absorbed by the Photosystem II, an electron is _____ and takes off into the electron transport chain.
  10. _____ is a protein found in green plants, that functions in electron transport and photosynthesis.

Answer Key

  1. SUGAR
  3. LIGHT
  4. GRANA

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