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.The Calvin cycle involves the fixation of carbon dioxide and results in the creation of sugar. It utilizes the light energy from the sun to excite electrons, which in turn give off energy by traveling the electron transport chain.
It replaces an electron and gives off more energy. Remember, this all occurs not in the thylakoid itself but in the thylakoid membrane. In a sense, the membrane acts as the power plant for the next part of photosynthesis.
Here are the important things about the thylakoid membrane in the photosynthetic process:
- The thylakoid membrane is the layer that encloses the thylakoid
- The thylakoid membrane is the site of the first part (the light dependent part) of photosynthesis
- In the thylakoid membrane, there are two photosystems that collect light energy
- The photosystems collect energy and excite electrons, creating energy
- Two energy molecules are the products here: ATP (or adenosine triphosphate, which is an energy molecule) and NADPH
- This energy is used in the Calvin cycle, which involves the fixation of carbon dioxide and results in the creation of sugar
Facts to Memorize
- Eukaryotic: plant cells have a nucleus and membrane-bound organelles
- Thylakoid: membrane-bound compartments inside of the chloroplasts
- Thylakoid Membrane: the layer that surrounds the thylakoid
- Adenosine Triphosphate (ATP): an energy molecule
- Calvin Cycle: carbon fixation process that creates sugars and starches
After this lesson ends, ensure your ability to easily:
- Detail what the thylakoid membrane does in photosynthesis
- Describe the light-dependency of the membrane
- Recall the way in which photosynthesis creates energy and oxygen