Remember that homeostasis is a state of balance. All organisms need to maintain homeostasis. Unicellular organisms need to maintain homeostasis simply in order to stay alive. In a multicellular organism, each cell needs to maintain homeostasis so that the organism can survive. (Image: Homeostasis is just as important in a unicellular amoeba as a multicellular human)
Cells maintain homeostasis in three important ways. First, cells need to obtain energy and excrete waste products. This happens through a process known as diffusion. Second, cells need to maintain a balanced amount of water so that the chemical reactions that sustain life can occur. This happens through a process called osmosis. Both diffusion and osmosis are examples of passive transport, processes that maintain homeostasis but do not require energy. The third way cells maintain homeostasis is through active transport, processes that use energy to maintain homeostasis in a cell.
Section 1: Diffusion
Diffusion is the process of movement along a concentration gradient from a high concentration to a low concentration. In cells, diffusion occurs across the cell membrane. Diffusion across the cell membrane can happen in 2 ways--across the lipid bilayer (simple diffusion) or through the protein channels (facilitated diffusion) (Image: Diffusion across cell membrane/close up of cell membrane)
Diffusion allows cells to maintain homeostasis in two ways. First, as cellular “food” (small carbon-based molecules such as glucose, or oxygen which helps power chemical reactions in cells) gets used up inside the cell, additional “food” will diffuse into the cell. The addition of food allows the cell to continue to power the chemical reactions that sustain cellular life. (Image: oxygen diffusing into a cell)
Second, as waste products build up inside the cell, they will diffuse out of the cell. The removal of waste products allows the cell to stay healthy. (Image: The red waste molecules will diffuse out the cell)
