Question

1. What happens if one solute can pass through the membrane, but another cannot?

2. How do semi-permeable membranes and the processes of diffusion and osmosis contribute to homeostasis in cells?

Answer 1

1) The important feature of the cell membrane is its selective permeability. Some substances, which can pass through it freely, but others cannot. Small and nonpolar molecules can freely pass through the membrane, but charged ions and large molecules such as proteins and sugars are cannot. The selective permeability of the cell membrane permits a cell to maintain its internal composition. Molecules, which can pass freely through the membrane, they follow concentration gradients, which move from the higher concentration area to the lower concentration area. These processes take no energy and they are known as passive transport. The molecules, which cannot pass freely across the phospholipid bilayer can be carried across the membrane in various processes, which need energy and so they are known as active transport.

2) Homeostasis is a form of balanced equilibrium, where everything is running smoothly. The plasma membrane maintains homeostasis by keeping cell contents in and foreign material out. Homeostasis maintains the internal states, which are essential for basic functioning. The plasma membrane is essential for maintenance of these conditions and functioning. This membrane separates the inside of the cell from the outside. It also maintains the process of homeostasis by making sure materials which can move in or out according to their requirements. Homeostasis depends on the maintenance of correct fluid levels within the cell and exchanging useable materials, such as oxygen, for waste products, such as carbon dioxide. Plasma membranes permit water, oxygen and carbon dioxide to pass through by the process of osmosis and diffusion. This is when molecules move through a semipermeable barrier along a concentration gradient, which is from an area of higher concentration to lower concentration.