Lysosomes were discovered by Christian de Duve in 1955. These are small membrane bound cytoplasmic vesicles which are rich in hydrolytic enzymes. These help in digestion. They may arise from smooth endoplasmic reticulum or Golgi complex. Lysosomes are usually spherical vesicles bounded by a single unit membrane enclosing a dense matrix. The matrix of the lysosomes contain enzymes mainly hydrolytic enzymes like lipases, proteases which works at acidic pH. The lysosome helps in the digestion of proteins, carbohydrates and lipids. The lysosomes are sometimes known as suicide bags as they help in the digetion of damaged cell or its parts.
Receptor molecules are specific proteins in the cell's plasma membrane that receive chemical signals from outside the cell. When such chemical signals bind to a receptor, they cause some form of cellular response.