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Lesson: Chapter 6 — The Structure and Function of Plant and Animal Cells

6.4. Cell organelles and structures 5 of 8

Mitochondria and ribosomes

These two organelles could hardly be less alike in size or in structure. But a cell needs both to work at all: one supplies the energy, the other supplies the place where protein gets made.

The mitochondrion

Figure to be added

Figure 6.11 — a mitochondrion, with its double membrane and inner folds.

A mitochondrion is an oval or rod-shaped membranous cell organelle. Because aerobic respiration reactions take place inside mitochondria and release energy, they are known as the power plants of the cell. The energy produced in them is used for the metabolic reactions that go on within the cell.

The ribosome

Figure to be added

Figure 6.13 — a ribosome, with its large and small sub-units.

A ribosome is a very small cell organelle that carries no membrane. It is made of two sub-units, one large and one small. Ribosomes occur both freely in the cytoplasm and attached to the rough endoplasmic reticulum.

The two functions

  • Mitochondrion — releasing energy through aerobic respiration.
  • Ribosome — providing the sites for protein synthesis.

Having a membrane, and not having one

The mitochondrion is enclosed by a membrane; the ribosome is not. Assuming that every organelle is membrane-bound is a common slip — and the ribosome is the counter-example that settles it.