Lysosomes are sacs of the cell filled with digestive enzymes. These digestive enzymes are synthesized by

Correct — C, rough endoplasmic reticulum. Digestive enzymes are proteins, and proteins bound for an organelle or for export are made on ribosomes attached to the endoplasmic reticulum — the studding of ribosomes is what makes that stretch of membrane look rough. The newly made enzymes pass from the rough endoplasmic reticulum to the Golgi apparatus, which modifies and tags them, and lysosomes then bud off from the Golgi carrying the finished cargo. So the Golgi packages the enzymes and the lysosome holds them, but the place they are actually synthesised is the rough endoplasmic reticulum.

• (a)Golgi bodies — The Golgi modifies, sorts and packages the enzymes, and lysosomes pinch off from it — which is why this option feels right. Packaging is not synthesis, and the Golgi has no ribosomes of its own.
• (b)smooth endoplasmic reticulum — Smooth means no ribosomes, and no ribosomes means no protein synthesis. This part of the network makes lipids and steroids and handles detoxification, notably in liver cells.
• (d)lysosome itself — A lysosome is a membrane sac holding the finished enzymes. It carries no ribosomes and no machinery for making protein, so it cannot manufacture its own contents.

A cell's secretory route runs in one direction. Ribosomes on the rough endoplasmic reticulum build the protein and feed it into the lumen of the network; vesicles carry it to the Golgi apparatus, which trims, tags and sorts it; and vesicles leave the Golgi either for the cell surface or as lysosomes, the acidic sacs of hydrolytic enzymes that digest worn-out organelles and material taken in from outside.

The question separates three verbs that students often merge — synthesise, package and store. All three organelles in the wrong options do genuine work on lysosomal enzymes, and only one of them makes them. The clue is built into the names: rough endoplasmic reticulum is rough because ribosomes are stuck to it, and ribosomes are where every protein in a cell is assembled. The smooth network, having none, works on lipids instead. A second point worth carrying away is why the enzymes do not digest the cell that makes them — they work best in the acidic interior of the lysosome and are far less active at the near-neutral pH of the cytoplasm. Christian de Duve, who identified lysosomes, called them the cell's suicide bags because a ruptured lysosome can digest the cell from within.

• The rough endoplasmic reticulum is studded with ribosomes and is where proteins destined for organelles or for export are synthesised.
• The smooth endoplasmic reticulum has no ribosomes; it makes lipids and steroids and detoxifies, notably in liver cells.
• The Golgi apparatus modifies, tags and packages proteins, and lysosomes bud off from it.
• Lysosomes are membrane-bound sacs of hydrolytic enzymes that work best in an acidic interior.
• A ruptured lysosome can digest its own cell, which is why lysosomes are described as suicide bags.

• Choosing the Golgi because lysosomes bud from it, when the question asks where the enzymes are made.
• Forgetting that 'smooth' in this context means the absence of ribosomes.
• Assuming a lysosome can manufacture its own contents.

Asked as a one-step process question in which every wrong option is an organelle that genuinely handles the enzyme at some other stage.

• practice — not a real PYQ

  The endoplasmic reticulum appears rough because of the presence of

  • (a)lysosomes on its surface
  • (b)ribosomes on its surface
  • (c)vacuoles in its lumen
  • (d)mitochondria alongside it

  Answer(b) ribosomes on its surface — and they are what make it a site of protein synthesis.

• practice — not a real PYQ

  Which organelle is chiefly responsible for the modification and packaging of proteins in a cell?

  • (a)Golgi apparatus
  • (b)Smooth endoplasmic reticulum
  • (c)Nucleolus
  • (d)Peroxisome

  Answer(a) Golgi apparatus — it receives proteins from the rough endoplasmic reticulum and dispatches them in vesicles.