Cell Membrane

Cell Membrane Every cell has a cell membrane. Protects the cell and helps move substances and messages in and out of the cell. By regulating transport the membrane helps the cell maintain constancy and order.

Homeostatsis Homeostasis is the maintenance of stable internal conditions in a changing environment. Individual cells along with organisms, must maintain homeostasis in order to live. A cell maintains homeostasis by controlling the movement of substances across the cell membrane.

Structure Phospholipid Bilayer Membrane Proteins Carbohydrates Hydrophilic (Water-Loving) Heads Hydrophobic (Water-Fearing) Tails Membrane Proteins For transport through membrane Carbohydrates Attached carbohydrates can hold cells together Viruses and chemical messages can attach to carbs too.

Phospholipid Hydrophilic head Protein Hydrophobic tail

Movement of Molecules Passive Transport Active Transport All movement of molecules across a membrane is one of two types of transport. Passive Transport No energy required Molecules move from high to low concentration. Active Transport Energy required Molecules almost always move from low to high concentration

Which is more concentrated? B A

Passive Transport Diffusion Is the natural tendency of molecules to move from high to low concentration. Some molecules can pass through the openings in the cell membrane. Others cannot. They require a protein helper. This process is called facilitated diffusion. Osmosis is one example of facilitated diffusion. Osmosis is the diffusion of water.

Osmosis Water moves via osmosis from hypotonic to hypertonic solutions. Solute: a dissolvable substance (ex. Kool Aid) Solvent: liquid used to dissolve a substance (ex. water). Hypertonic A solution that has more solute than another. Isotonic A solution that has the same amount of solute as another. Hypotonic A solution that has less solute than another.

Diffusion of dye in water

OSMOSIS IN RED BLOOD CELLS

Plant Cell OSMOSIS

Practice What is the solute? What is the solvent? If water can move through the bag, but salt cannot, which way will the water move? 1% Saltwater 2% Saltwater

Practice What is the solute? What is the solvent? If water can move through the bag, but salt cannot, which way will the water move? 4% Saltwater 2% Saltwater

Practice What is the solute? What is the solvent? If water can move through the bag, but sugar cannot, which way will the water move? 1.5% Sugar water

Active Transport Require energy Cell Membrane Pumps Two types Proteins in membrane that push molecules from low concentration to high concentration. Example is the Sodium/Potassium Pump Moves sodium ions out and potassium ions in Two types Endocytosis Exocytosis

Active Transport Endocytosis Exocytosis Movement of molecules into the cell through a vesicle or vacuole, created by the cell membrane. Phagocytosis – movement of large molecules such as food; “cell eating”. Pinocytosis – movement of small molecules such as water; “cell drinking”. Exocytosis Movement of molecules out of the cell through a vesicle that fuses with the cell membrane.

Vesicle Fusing with Membrane