1. Homeostasis and Cell Transport
Chapter 5
Section 1

2. 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

3. 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

4. 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!!!

5. 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

6. 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

7. 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

8. 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

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

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

11. 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

12. 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

13. 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

14. 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