Organelles That Store, Clean Up, and Support

What are the functions of vacuoles, lysosomes, and the cytoskeleton?

Many of the organelles outside the nucleus of a eukaryotic cell have specific functions, or roles. Among them are structures called vacuoles, lysosomes, and cytoskeleton. These organelles represent the cellular factory's storage space, cleanup crew, and support structures.

Vacuoles and Vesicles Every factory needs a place to store things, and so does every cell. Many cells contain large, saclike, membrane-enclosed structures called vacuoles. Vacuoles store materials like water, salts, proteins, and carbohydrates. In many plant cells, there is a single, large central vacuole filled with liquid. The pressure of the central vacuole in these cells increases their rigidity, making it possible for plants to support heavy structures, such as leaves and flowers. The image on the left in Figure 7–8 shows a typical plant cell's large central vacuole.

Vacuoles are also found in some unicellular organisms and in some animals. The paramecium on the right in Figure 7–8 contains an organelle called a contractile vacuole. By contracting rhythmically, this specialized vacuole pumps excess water out of the cell. In addition, nearly all eukaryotic cells contain smaller membrane-enclosed structures called vesicles. Vesicles store and move materials between cell organelles, as well as to and from the cell surface.

FIGURE 7–8 Vacuoles The central vacuole of plant cells stores salts, proteins, and carbohydrates. A paramecium's contractile vacuole controls the water content of the organism by pumping water out. Apply Concepts How do vacuoles help support plant structures?

Lysosomes Even the neatest, cleanest factory needs a cleanup crew, and that's where lysosomes come in. Lysosomes are small organelles filled with enzymes. Lysosomes break down lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell. They are also involved in breaking down organelles that have outlived their usefulness. Lysosomes perform the vital function of removing “junk” that might otherwise accumulate and clutter up the cell. A number of serious human diseases can be traced to lysosomes that fail to function properly. Biologists once thought that lysosomes were only found in animal cells, but it is now clear that lysosomes are also found in a few specialized types of plant cells as well.

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