What is a stack of thylakoids called?

A stack of thylakoids is called a granum.

Understanding Grana in Chloroplasts

Thylakoids are flattened, sac-like structures within chloroplasts, the organelles responsible for photosynthesis in plant cells. These thylakoids are not randomly distributed; they are organized into stacks. Here's a closer look at what that means:

• Thylakoids: These membrane-bound compartments contain chlorophyll and other pigments necessary for light-dependent reactions of photosynthesis.
• Granum (plural: grana): A stack of thylakoids. This arrangement is crucial for maximizing the surface area available for photosynthesis, much like folded paper creates more usable space than a flat sheet.
• Importance of Increased Surface Area: The increased surface area provided by the grana allows chloroplasts to capture more light energy efficiently. The light-dependent reactions occur in thylakoid membranes, hence more membrane means more opportunity for photosynthesis.

Granum Functionality

* **Light Capture:** The chlorophyll within the thylakoids captures photons of light.
* **Electron Transport:** Light energy drives the electron transport chain, a series of reactions within the thylakoid membrane.
* **ATP and NADPH Production:** The final result of these reactions are molecules of ATP and NADPH, the energy currency and reducing agent used in the light-independent reactions.

Key Takeaway

The granum is essential for the efficient operation of photosynthesis because it organizes the thylakoids in a way that increases the surface area, thereby maximizing light capture and overall photosynthetic output. A single granum can contain anywhere from a few to over 100 thylakoids.