Pyrenoids are present mostly in green algae. Its central core is made up of protein which is surrounded by starch sheath. pyrenoids act as a starch formation

Explanation:
The pyrenoids are specialized structures found in certain algae, particularly in the Chlorophyta (green algae) and the Haptophyta (a group of marine algae). These structures are involved in the process of carbon fixation, which is the conversion of carbon dioxide into organic compounds through photosynthesis. The correct answer to the given question is option B, i.e., the pyrenoids are composed of a proteinaceous center and a starchy sheath.

Structure of Pyrenoids:
Pyrenoids are typically located within the chloroplasts of algae and are surrounded by a membrane-like structure called the pyrenoid envelope. They are often embedded within a matrix of thylakoid membranes, which are responsible for capturing light energy during photosynthesis.

Proteinaceous Center:
The proteinaceous center of the pyrenoid is where the actual enzymatic reactions of carbon fixation take place. It consists of various enzymes, including ribulose bisphosphate carboxylase-oxygenase (Rubisco), which is the key enzyme in the Calvin cycle, the biochemical pathway responsible for carbon fixation.

Starchy Sheath:
The starchy sheath surrounding the proteinaceous center serves as a storage site for the fixed carbon compounds produced during photosynthesis. It is composed of starch granules, which are large, insoluble polysaccharides made up of glucose molecules. Starch acts as a reserve energy source for the algae, allowing them to store excess carbon for later use.

Function of Pyrenoids:
Pyrenoids play a crucial role in the efficient functioning of algae. They help to concentrate carbon dioxide around the Rubisco enzyme, enhancing its efficiency in fixing carbon. The starchy sheath surrounding the proteinaceous center acts as a buffer, regulating the availability of carbon dioxide and ensuring a steady supply of substrates for carbon fixation.

Conclusion:
In summary, pyrenoids are specialized structures found in certain algae that are involved in the process of carbon fixation. They consist of a proteinaceous center where carbon fixation occurs and a starchy sheath that serves as a storage site for fixed carbon compounds. Option B, which states that pyrenoids are composed of a proteinaceous center and a starchy sheath, is the correct answer.