a)A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism.

b)All cells are surrounded by aplasma membrane. Themembraneis composed of a phospholipid bilayer arranged back-to-back. Themembraneis also covered in places with cholesterol molecules and proteins. Theplasma membraneis selectively permeable and regulates which molecules are allowed to enter and exit thecell.

c)The mitochondrion is a double-membrane-bound organelle found in most eukaryotic organisms. Some cells in some multicellular organisms may, however, lack them.

d)In cell biology a centriole is a cylindrical cellular organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells. A bound pair of centrioles, surrounded by a shapeless mass of dense material, called the pericentriolar material, makes up a structure called a centrosome.

e)Lysosomes are specialized vesicles within cells that digest large molecules through the use of hydrolytic enzymes. Vesicles are small spheres of fluid surrounded by a lipid bilayer membrane, and they have roles in transporting molecules within the cell