Homeostasis Living organisms use energy to stay alive

Homeostasis Living organisms maintain an internal environment that is different from the external environment. This takes energy.

What are some internal conditions that your body must work to maintain? 1.Temperature 2. Water Balance 3. pH Balance 4. Concentrations of salts and other minerals

Membranes are essential for maintaining homeostasis at the cellular level.

Functions of Membranes Maintain an internal environment in cells or organelles that is different from the surrounding environment Regulate the movement of molecules into and out of cells

Structure Bilayer of phospholipids (fat molecules) Membrane proteins, which may by as much as 50% of the membrane weight

Membrane Proteins Transfer Proteins – move large molecules and ions into and out of the cell Receptor proteins – receive messages from other cells or parts of the body Adhesion proteins – cause cells to stick together, forming tissues and organs

Selective Permeability To keep a stable internal environment, cells regulate the movement of molecules through the cell membrane. This process of regulation is called “selective permeability.” (meaning, that the cell membrane is permeable to some things, but not others)

Types of Movement Through a Cell Membrane

Passive Transport Passive Transport is the spontaneous movement of molecules along their concentration gradient.

Simple Diffusion – the flow of molecules from an area of high to low concentration Osmosis – the flow of water from an area of high water concentration to low water concentration Facilitated Diffusion – the flow of a molecule through a cell membrane that requires the assistance of a membrane protein.

Active transport always moves molecules against their concentration gradient (from lower concentration to higher), coupled to a source of energy. Active Transport

Endocytosis & Exocytosis These 2 processes move large quantities of molecules into or out of a cell

A membrane bubble (called a vesicle) surrounds a large quantity of material. This vesicle can capture molecules to bring into the cell, or open at the cell surface to release a large amount material into the surrounds

Endocytosis – brings material into the cell Exocytosis – releases material from the cell to the surroundings.

Homeostasis Remember, the point of all this is to maintain a stable environment in the cell. Molecules are moved into or removed from the cell to control the cell’s internal environment and to adapt to changes in the surrounding environment