Difference Between Grana and Stroma

Main Difference – Grana vs Stroma

Grana and stroma are two structures of chloroplast. Chloroplast is the organ where reactions of photosynthesis take place. The main difference between grana and stroma is that grana are the disk-like plates embedded in the stroma whereas stroma is the homogeneous, jell-like matrix of the chloroplast. Grana are connected to each other by intergranal lamellae. They contain different pigments such as chlorophyll-a, chlorophyll-b, carotene, and xanthophyll. Light reaction of photosynthesis occurs in the grana. Stroma dissolves the enzymes required for photosynthesis, cytocrome system, DNA and RNA of the chloroplast. Dark reaction of photosynthesis occurs in the stroma.

Key Areas Covered

1. What are Grana
      – Definition, Structure, Function
2. What is Stroma
      – Definition, Structure, Function
3. What are the Similarities Between Grana and Stroma
      – Outline of Common Features
4. What is the Difference Between Grana and Stroma
      – Comparison of Common Features

Key Terms: Chloroplast, Dark Reaction, Grana, Light Reaction, Photosynthesis, Stroma, Thylakoid

What are Grana

Grana refer to the stacks of thylakoids embedded in the stroma of a chloroplast. A combination of 2 to 100 thylakoids may form a granum. A single chloroplast may contain 10 to 100 grana. Grana are connected with each other by stromal thylakoids. Therefore, all grana in a particular chloroplast may act as a single functional unit. Stromal thylakoids are also called intergranal thylakoids or lamellae. Both thylakoid and stromal thylakoid contain photosynthetic pigments on their surfaces. On that account, the light reaction of photosynthesis occurs on the surface of grana. A granum is shown in figure 1.

Figure 1: Granum

Thylakoid is a round pillow-shaped stack inside the chloroplast. The space between thylakoid membrane is called thylakoid lumen. Chlorophyll and other photosynthetic pigments are held by membrane proteins on the surface of the thylakoid. They are organized into photosystem 1 and 2 on the thylakoid membrane.

What is Stroma

Stroma refers to a colorless jell-like matrix of the chloroplast in which the dark reaction of photosynthesis takes place. Enzymes required for the dark reaction are embedded in the stroma. Stroma surrounds the grana. In the stroma, carbon dioxide and water are used in the production of simple carbohydrates by using the light energy trapped by light reaction. Stroma and grana of a chloroplast are shown in figure 2.

Figure 2: Structure of a Chloroplast

Dark reaction of photosynthesis is also called the Calvin cycle. The three stages of the Calvin cycle are carbon fixation, reduction reactions, and RuBP regeneration.

Similarities Between Grana and Stroma

Both grana and stroma are two structures of the chloroplast.
Reactions of photosynthesis occur in both grana and stroma.

Definition

Grana: Grana refers to the stacks of thylakoids embedded in the stroma of a chloroplast.

Stroma: Stroma refers to a colorless jell-like matrix of chloroplast in which the dark reaction of photosynthesis takes place.

Structure

Grana: Grana are the disk-like plates in the stroma.

Stroma: Stroma is the jell-like matrix of the chloroplast.

Components

Grana: Grana consist of different pigments such as chlorophyll-a, chlorophyll-b, carotene, and xanthophyll.

Stroma: Stroma consists of enzymes required for photosynthesis, cytochrome system, DNA, and RNA of the chloroplast.

Reactions of Photosynthesis

Grana: The light reaction of photosynthesis occurs in the grana.

Stroma: The dark reaction of the photosynthesis occurs in the stroma.

Role

Grana: Grana provide a large surface for the attachment of photosynthetic pigments.

Stroma: Stroma embeds enzymes required by the dark reaction of photosynthesis.

Conclusion

Grana and stroma are two structures of chloroplast. Grana are the stacks of thylakoids where light reaction of photosynthesis takes place. Stroma is the jell-like matrix of the chloroplast, which contains the enzymes for dark reaction of photosynthesis. The main difference between grana and stroma is their structure and function.

Reference:

1.“Granum.” Plant Biology, Available here.
2.“Stroma Function.” Plant Biology, Available here.

Image Courtesy:

1. “Granum” (CC BY-SA 3.0) via Commons Wikimedia
2. “Chloroplast-new” (Public Domain) via Commons Wikimedia