Vesicles, Lysosomes and Vacuoles

Vesicles and Lysosomes

Vesicles are small, membrane-bound spherical sacs which facilitate the metabolism, transport and storage of molecules. Many vesicles are made in the Golgi body and the endoplasmic reticulum, or are made from parts of the cell membrane. Vesicles can be classified according to their contents and function. Transport vesicles transport molecules within the cell.

Lysosomes are formed by the Golgi body and contain powerful digestive enzymes that can potentially digest the cell. Lysosomes are formed by the Golgi body or the endoplasmic reticulum. These powerful enzymes can digest cell structures and food molecules such as carbohydrates and proteins. Lysosomes are abundant in animal cells that ingest food through food vacuoles. When a cell dies, the lysosome releases its enzymes and digests the cell.

Vacuoles

Vacuoles are membrane-bound, fluid-filled organelles that occur in the cytoplasm of most plant cells, but are very small or completely absent from animal cells. Plant cells generally have one large vacuole that takes up most of the cell's volume. A selectively permeable membrane called the tonoplast, surround the vacuole. The vacuole contains cell sap which is a liquid consisting of water, mineral salts, sugars and amino acids.

Functions of the Vacuole

• The vacuole plays an important role in digestion and excretion of cellular waste and storage of water and organic and inorganic substances.
• The vacuole takes in and releases water by osmosis in response to changes in the cytoplasm, as well as in the environment around the cell.
• The vacuole is also responsible for maintaining the shape of plant cells. When the cell is full of water, the vacuole exerts pressure outwards, pushing the cell membrane against the cell wall. This pressure is called turgor pressure.
• If there is not sufficient water, pressure exerted by the vacuole is reduced and the cells become flaccid causing the plant to wilt.