Cellular Transport

To discuss how nutrients get in and out of a cell, you’ll need to know these words. Solute: _____________________________________ Solvent: ____________________________________ The substance being dissolved The substance doing the dissolving solvent water saltwater solution salt solute In aqueous solutions, the solvent is always water. The cytoplasm in the cell is an aqueous solution.

Cell Membrane All cells are contained within the boundary of a cell membrane. Eukaryotic cells also have organelles on the inside which have their own plasma membranes. These membranes help control which molecules go in and out of the cell and its organelles.

Cell Membrane Membranes are made mostly out of a special lipid molecule known as a phospholipid. These phospholipids are arranged in a bilayer; this means that are two layers of lipids that make up a membrane.

Watch the short video over the membrane’s structure.

Genetic Science Learning Center, University of Utah, http://learn Membranes allow cells to communicate with other cells and the outside world. This allows the cells to respond to their environment and each other!

Cell Membrane Membranes also help maintain homeostasis by regulating which molecules come into and out of the cell. Helping to regulate the steady balance of nutrients in the cell is vital to the cell’s survival.

Passive Transport Systems Facilitated Diffusion Diffusion Osmosis There are also several processes for moving solutes into and out of the cell without using energy. Any process that allows molecules into and out of the cell without using energy is a form of passive transport.

Simple Diffusion Diffusion is the process of very small solutes moving directly through the membrane. During diffusion, molecules always travel from a higher concentration to a lower concentration.

Facilitated Diffusion Some molecules are too large or have an electrical charge and cannot go directly through the membrane. Protein channels and carrier proteins FACILITATE the diffusion of these solutes across the membrane.

Facilitated Diffusion Because this is still a form of diffusion, these solutes still travel from an area of high concentration to an area of low concentration. It also means that this does NOT require the cell to use any of its energy!

Watch the short video over Passive Transport.

Osmosis Water is one of the most important molecules in and around cells because of its ability to be a great solvent. The movement of water into and out of cells is known as osmosis. Because water is the solvent and not a solute, we have to think about it a bit differently.

Osmosis Water is able to move across the membrane via simple diffusion because it is so small, but we do NOT talk about solvents in the same way as solutes. Because of this, we say water travels from where it is purest to where it is least pure.

Osmosis When a cell is in a hypertonic solution, there is a higher concentration of solutes on the outside of the cell. So water travels out of the cell towards to the less pure solution and the cell shrinks and shrivels! Images by Zephyr

Osmosis When a cell is in a hypotonic solution, there is a lower concentration of solutes on the outside of the cell. So water travels into the cell towards to the less pure solution and the cell swells and can burst! Images by Zephyr

Osmosis When a cell is in a isotonic solution, there are the same concentrations of solutes on the inside and outside of the cell. So there is NO net movement of water, and the cell maintains the steady balance of water inside itself. Images by Zephyr

Sodium-Potassium Pump Active Transport Some ions and molecules must be forced across the cell membrane using the cell’s energy. This often involves pumping solutes into and out of the cell. Any process that requires energy to move solutes is known as active transport.

Sodium-Potassium Pump Active Transport Active transport is important for moving molecules against their concentration gradient. This means they travel from a low concentration to a high concentration. This is why it requires energy!

Watch the short video over Active Transport.

Endocytosis and Exocytosis Cells can also engulf molecules from the outside of the cell through the process of endocytosis. A small piece of the membrane is pinched off creating a vesicle with the solutes inside. Since this process requires energy, it is a form of active transport.

Endocytosis and Exocytosis Vesicles can also join to the membrane and expel their contents to the outside of the cell. This process is known as exocytosis. Endo- means inside of Exo- means outside of

Watch the short video over Exocytosis and Endocytosis.