Hint: A cell wall is a non-living rigid structure. It provides an outer covering for the plasma membrane of fungi and plants. Cell wall in fungi is composed of chitin which is a polymer of N-acetyl glucosamine. In plants, the cell wall consists of cellulose, hemicellulose, pectins and proteins.
Complete step by step answer: A cell wall is tough, flexible or rigid. It provides structural support and protection and behaves as a filtering membrane. The plasma membrane is made up of lipids and proteins mainly. It is the living part. The plasma membrane has a quasi fluid nature. Some of the functions that the plasma membrane performs due to its fluid nature are: i. Cell growth. ii. Cell division. iii. Formation of intercellular junctions. iv. Endocytosis. v. Secretion. The main function of the plasma membrane is the transportation of molecules across it. The plasma membrane is also known as the selectively permeable membrane, because of its selective nature. Plasma membrane allows transport of only some selective substances across it. This nature of plasma membrane is very useful for a cell as it helps the cell to allow the entry of only useful substances across it. No harmful or un-useful substances could cross the barrier formed by the cell membrane, in this way cells remain safe from foreign particles that could cause harm to the cell. If the cell membrane is absent, there will be no barrier for any external/foreign particles and therefore, any substance will enter into the cell whether needed or not, this might result in in- i. Cell dysfunction. ii. Death of the cell. Thus, a cell wall, as well as a cell membrane both, are needed for a plant cell to function properly.
Additional information: There are three ways in which any substance that is needed by the cell could cross the plasma membrane barrier: a. Passive transport- Those substances that can pass without the use of energy opt for this method of transport. b. Diffusion- Neutral solutes move across the membrane through this method along the concentration gradient (higher to lower concentration) c. Active transport- Here the substances are transported against their concentration gradient and thus they require ATP/energy.
Note: The cell membrane has a very essential role in the efficient working of the cell, these functions were easy to discover after Singer and Nicolson gave the very famous Fluid mosaic model in 1972. This model says that the cell membrane has a lipid bilayer in which protein molecules are integrated. This lipid bilayer provides fluidity and elasticity to the membrane.