Homeostasis and Cell Transport Chapter 5 Section 1

Movement of substances across the cell membrane without any input of energy by the cell. Remember: The cell membrane’s function is to help organisms maintain homeostasis by controlling what substances enter or leave the cell. Passive Transport

Diffusion Simplest type of passive transport. Movement of molecules from an area of higher concentration to an area of lower concentration. Concentration Gradient: the difference in the concentration of molecules across a distance. Equilibrium: the same throughout Diffusion

Keep in mind that molecules are constantly moving even if they appear to be still. The many movements of all molecules in all directions balances each other out so equilibrium is maintained. Why does sugar dissolve faster in hot tea than in cold tea? Important!!!

Simple Diffusion Diffusion of molecules across a membrane. Depends on size, type, and chemical charge. of molecule Small molecules, molecules that can dissolve in lipids, and non-polar molecules may pass through the membrane. Non soluble lipids may diffuse across the membrane through pores in the membrane. Simple Diffusion

Solution, solute, & solvent Solution: composed of a solute dissolved in a solvent. Solvent: Part of the solution that most abundant: Water Solute: the “stuff” dissolved in the solvent. Ex. Salt Solution, solute, & solvent

The process by which water molecules diffuse across an area of higher concentration to an are of lower concentration. No energy is used for this process therefore it is still passive transport. Osmosis

HIGH CONCENTRATION OF WATER TO LOW CONCENTRATION OF WATER Hypotonic: external concentration has lower concentration of solute (higher water) than then internal concentration Direction of Osmosis

Hypertonic: concentration of solute molecules outside the cell is higher (water lower) than inside the cell. Direction of Osmosis

Isotonic: concentration of solutes on inside and outside of the cell are equal. NO NET MOVEMENT! Direction of Osmosis

Most cells are typically exposed to an isotonic external environment. Freshwater fish are examples of an organism in a hypotonic solution. Why? Contractile vacuoles: a structure in some organisms that remove excess water from the organism. NOT PASSIVE TRANSPORT!! Cells and Osmosis

Plant roots are typically always in a hypotonic environment Plant roots are typically always in a hypotonic environment. This is important to the survival of the organism. Water moves into the roots by osmosis and the cells swell (where is the water stored?) When it fills with water, the cell membrane swells and pushes up against the cell wall; this pressure is called turgor pressure. The condition when pressure is lost is called Plasmolysis Plant Cells

Facilitated Diffussion Another type of passive transport Used for the molecules that cannot readily diffuse through cell membranes even if there is a concentration gradient. Travel through proteins called carrier proteins These molecules may not be soluble in lipids or too large to pass through pores. Facilitated Diffussion

Facilitate in movement down the concentration across the membrane. Does not require energy!!! Molecules bind to carrier protein and once bound, the protein changes shape to allow molecule to enter the cell. Ex. Glucose transfer. Carrier Proteins