The vacuole is a membrane bound space found in the cytoplasm. It contain water, sap, excretory product and other materials that are not seful for the cell. In plants osmosis vacuoles occupy $90 \%$ of the volume of the cell. They help in maintaining cell fluid balance, and shape of the cell by maintaining turger pressure against the cell well.

'S' refers to Svedbergs unit for sedimentation coefficient. Sedimentation coefficient depicts that how fast a cell organelle sediments during the ultracentrifugation. In cells heavier the structure, higher is the sedimentation coefficient. The value of $S$ is equal to $10^{-13}$ seconds ( $1 \mathrm{~s}=1 \times 1==^{-13}$ seconds).

Lysosomes are the membrane bound vesicular structures formed by Golgi apparatus. These vesicles on isolation have been found to be rich in all types of hydrolytic enzymes i.e., hydrolase, lipases, proteases and carbohydrases which digest carbohydrates proteins, lipids and nucleic acid at acidic pH .

Gas vacuoles are also known as pseudovacuoles or air vacuoles. Gas vacuoles are the characteristic feature of prokaryotes reported only in prokaryotes. Each gas vesicles are made of sub-microscopic hexagonal vesicles and are surrounded by a thin protein membrane. Gas vacuoles store metabolic gases and take part in buoyancy regulation.