Problem 224 - Objective Biology for NEET

Question

Assertion: Pyrenoids are storage bodies. Reason: Pyrenoids contains starch and proteins.

Step-by-Step Solution

Answer

The assertion is true and the reason is also true because pyrenoids are indeed involved in the synthesis and storage of starch and proteins, thereby classifying them as 'storage bodies' in the cell.

Step 1: Understanding Pyrenoids

Pyrenoids are bodies or organelles found in chloroplasts of certain algae and hornwort species. They are involved in the synthesis of starch and protein as well as in the production of oxygen.

Step 2: Confirming the Assertion

Given that pyrenoids are involved in the synthesis of starch and protein and considering the general term 'storage bodies' would typically refer to biological structures where substances are store, it can be verified that the assertion is correct.

Step 3: Analyzing the Reason

The reasoning states that pyrenoids contain starch and proteins, which is a factually correct statement. In addition to storing these substances, pyrenoids are also involved in their production.

Step 4: Final Conclusion

Given the roles pyrenoids play in the synthesis and storage of starch and proteins, it can be concluded that the assertion 'Pyrenoids are storage bodies.' is correct and the reasoning 'Pyrenoids contains starch and proteins.' is factually true, making it a valid reason.

Key Concepts

Cellular Organelles

Cellular organelles are specialized structures within cells that perform distinct processes essential for cellular function. Each organelle carries out a specific role attributing to the cell's life, much like how organs in the human body contribute to overall health.

For example, mitochondria are known as the powerhouses of the cell, generating energy through respiration, while the nucleus holds genetic information directing all cellular activities. Similarly, chloroplasts are the site of photosynthesis in plant cells and algae, where they convert light energy into chemical energy.

In the context of algae, pyrenoids are unique organelles that are not found in all plant cells. Pyrenoids are particularly interesting because they are associated with photosynthesis and the production of storage compounds such as starch within the chloroplasts. Understanding the structure and function of cellular organelles like pyrenoids provides insights into the life-sustaining processes of different organisms.

Photosynthesis in Algae

Photosynthesis in algae operates on the same basic principle as in higher plants—converting light energy into chemical energy that the organism can use. However, there are some differences in the structures involved.

In algae, photosynthesis occurs in chloroplasts, which are filled with pigments like chlorophyll that capture light energy. The energy is then used to synthesize glucose from carbon dioxide and water, which serves as a fuel for the algae's metabolic activities. Oxygen is released as a byproduct in this process, contributing to the oxygen in our atmosphere.

Role of Pyrenoids

Within the chloroplasts of many algae, pyrenoids play a crucial role. They are associated with the enzyme Rubisco, which is pivotal in the Calvin cycle for fixing carbon dioxide during photosynthesis. Interestingly, pyrenoids are not just sites for carbon fixation; they also act in the synthesis and accumulation of starch, which implies that they serve dual purposes in the photosynthetic apparatus of algae.

Starch and Protein Synthesis

Starch and protein synthesis are fundamental biochemical processes that occur within cells. Starch is a polysaccharide made up of glucose units and serves as a primary energy reserve in plants and algae. Protein synthesis, on the other hand, is the creation of proteins based on genetic instructions.

Starch Synthesis in Pyrenoids

In the context of algae, pyrenoids are directly involved in the synthesis of starch. The process begins with the sugar molecules produced during photosynthesis. These molecules are then polymerized into larger starch molecules and stored within the pyrenoid. This makes pyrenoids critical for energy storage in algae, effectively acting as starch production and storage centers.

Protein Synthesis Tied to Pyrenoids

Proteins are synthesized in the ribosomes, and in algae, this process is closely tied to the photosynthetic activity of chloroplasts where pyrenoids are housed. Pyrenoids contain and support the activity of Rubisco, the protein that catalyzes carbon fixation, making protein synthesis in the pyrenoid a key component of the photosynthetic machinery. Therefore, studying these processes helps in understanding both the production and storage capabilities of pyrenoids in photosynthetic organisms.