What is Granum? - Definition & Function

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  • 0:01 Plant Cell Review
  • 0:31 What is Granum?
  • 1:31 Importance of Granum
  • 2:25 Lesson Summary
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Lesson Transcript
Instructor: Jeremy Battista
Deep inside the chloroplasts of plant cells we find granum, or the stacks of membranes that play an important role in photosynthesis. In this lesson, we'll do a quick review of plant cells before exploring the structure and function of granum.

Review of Plant Cells

Before we start learning about granum, let's do a quick review of plant cells. Plant cells are eukaryotic cells, or cells with membrane-bound organelles and a nucleus. Their most important features include the chloroplasts, which are found inside the cells of the green or leafy portions of the plant and contain granum. Photosynthesis occurs in the chloroplasts. Remember, photosynthesis is the mechanism by which plants use carbon dioxide, a chemical compound, and water to make their own food.

What Is Granum?

The term granum refers to a stack of coin-shaped thylakoids in the chloroplasts of plant cells. There can be as few as 2 or as many as 100 thylakoids in grana, or groups of granum, and between 40 and 60 grana in a plant cell. Thylakoids are membranous pockets or structures found inside the chloroplasts of plant cells.

Thylakoids contain chlorophyll, the pigment used by plants for photosynthesis. Within the thylakoid membrane we find two photosystems, or protein complexes. Photosystems are responsible for absorbing the sunlight to be used in the creation of sugars.

The membranous granum is typically found in more complex plants rather than simplistic ones. The grana in the chloroplast act together as a unit and are interconnected through small tunnels in the lower part of thylakoid stacks called stromal thylakoids. Grana help contribute to the chloroplast's large surface area. They help add more surface area to the thylakoids because they are organized and stacked.

Here is an example of granum
Here is an example of granum

Importance of Granum

Granum act to increase the surface area of the thylakoids, which results in more light being absorbed into the chlorophyll. When you increase the surface area, you allow more materials to attach to the surface, or in this case, react in the different photosystems in the thylakoid membrane. This allows the plant to take in more sunlight and increase production of sugars through photosynthesis.

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