A secondary lysosome is: a. a lysosome that provides a backup to the primary lysosomes. b. a lysosome that is smaller than a primary lysosome. c. a lysosome that will become a primary lysosome when it fuses with a phagosome. d. a primary lysosome that has fused with a phagosome. e. a lysosome that has exocytosed.
The correct answer and explanation is:
The correct answer is:
d. a primary lysosome that has fused with a phagosome.
Explanation:
Lysosomes are membrane-bound organelles containing digestive enzymes that break down various macromolecules, cellular debris, and foreign particles. They are essential for intracellular digestion and recycling processes.
- Primary lysosomes are newly formed lysosomes that contain inactive hydrolytic enzymes. They have not yet engaged in digestion.
- When a primary lysosome fuses with a phagosome (a vesicle containing material ingested by phagocytosis, such as bacteria, dead cells, or foreign particles), it forms a secondary lysosome (also called a phagolysosome).
The fusion activates the lysosomal enzymes because the environment inside the secondary lysosome becomes acidic, ideal for enzymatic activity. This allows the secondary lysosome to digest the engulfed material.
Here is a breakdown of the options:
- a. a lysosome that provides a backup to the primary lysosomes
This is incorrect because lysosomes do not function as backups; they work actively in digestion. - b. a lysosome that is smaller than a primary lysosome
Size difference is not a defining characteristic of secondary lysosomes. - c. a lysosome that will become a primary lysosome when it fuses with a phagosome
This is backwards. A primary lysosome becomes a secondary lysosome after fusion, not the other way around. - d. a primary lysosome that has fused with a phagosome
This is correct, as described above. - e. a lysosome that has exocytosed
Lysosomes do not exocytose their contents; instead, they digest material inside the cell. Exocytosis refers to the expulsion of contents outside the cell, which is not the role of lysosomes.
Summary:
A secondary lysosome is formed when a primary lysosome merges with a phagosome. This fusion activates the digestive enzymes in the lysosome, allowing it to break down the engulfed material efficiently. Secondary lysosomes are critical in cellular waste processing and immune defense, ensuring harmful materials are safely degraded inside the cell.