Cell Structure: Question 6
Syllabus 1.2
A white blood cell (phagocyte) engulfs a bacterium, enclosing it within a vacuole in its cytoplasm. Powerful digestive (hydrolytic) enzymes are then released into this vacuole, breaking the bacterium down.
Which organelle releases these digestive enzymes into the vacuole?
Show worked solution Hide worked solution
Worked solution
Step 1: Identify what is needed
The scenario describes a vacuole inside the cytoplasm receiving powerful digestive (hydrolytic) enzymes, which then break down an engulfed bacterium. This is intracellular digestion, so the organelle involved must be one that stores concentrated digestive enzymes and can release them into another compartment.
Step 2: Recall lysosome structure and function
A lysosome is a small, membrane-bound organelle that contains a concentrated mixture of hydrolytic (digestive) enzymes. When a phagocyte engulfs a bacterium, the bacterium is enclosed in a vacuole. One or more lysosomes then fuse with this vacuole, releasing their enzymes into it and digesting the bacterium’s contents.
Step 3: Why the other options are wrong
- B: the mitochondrion is the site of aerobic respiration, releasing ATP for the cell’s energy needs; it does not contain or release digestive enzymes.
- C: the Golgi body processes and packages proteins, and does produce lysosomes by budding off vesicles of enzymes, but it is the lysosome itself, not the Golgi body directly, that releases the enzymes into the vacuole.
- D: the smooth endoplasmic reticulum synthesises lipids and steroids; it plays no part in storing or releasing digestive enzymes.
Final answer
- The organelle that releases digestive enzymes into the vacuole is the lysosome, option A.