1. Cell Transport How things move in and out of the cell General Biology (Chapter 7) Honors Biology (Chapter 5)

2. Cell Transport Overview Homeostasis Understanding concentrations Structure of the cell membrane Types of Transport Types of Passive Transport Types of Active Transport Regulating Transport in Cells

3. Homeostasis Homeostasis – maintaining a stable internal environment Applies to organisms as a whole Also applies to individual cells Transport is an important part of a cell’s ability to maintain homeostasis

4. Concentration of Solutions Solution - a homogenous mixture throughout which two or more substances are uniformly dispersed solute - substance that is being dissolved in a solution, Example: Kool-Aid, sugar solvent - the substance that is being dissolved, Example: water

5. Concentration of Solutions Concentration gradient - the difference in concentration of molecules across a distance Concentration - refers to the amount of solute that is present in a certain amount of solvent Particles naturally move from areas of high concentration to areas of low concentration

6. Concentration of Solutions Particles that move from areas of HIGH TO LOW concentrations are said to move WITH the concentration gradient Particles that move in the opposite directions, from areas of LOW TO HIGH concentration, are said to move AGAINST the concentration gradient

7. The cell membrane The cell membrane controls what enters and leaves the cell (cell transport) The unique combination of molecules that make up the cell membrane allow it to “choose” what enters and leaves the cell

8. Cell membrane – con’t The fluid mosaic model of the cell membrane – says that all of the different molecules in the cell membrane work together to do one function (regulate transport), just as the different tiles in a mosaic come together to make a picture.

9. Cell membrane – con’t The cell membrane is primarily made up of a double layer of phospholipids For this reason it is often called a lipid bilayer

10. Cell membrane – con’t A phospholipid is a molecule that is made up of two regions. The “head” of the phospholipid is polar and, therefore, hydrophilic (water-loving) The “tails” of the phospholipid are nonpolar and, therefore, hydrophobic (water-fearing)

11. Cell membrane – con’t Water is found in the cytoplasm inside the cell and in the extracellular fluid outside the cell So phospholipids arrange themselves so that the hydrophilic heads are touching the water and the hydrophobic tails are tucked safely inside away from the water

12. Cell membrane – con’t Only small, charged particles can move through the lipid bilayer Examples include oxygen and carbon dioxide Nonpolar and large molecules must enter or leave the cell through proteins.

13. Cell membrane – con’t The proteins in the cell serve as “doorways” for substances that cannot enter through the lipid bilayer. They can be used for facilitated diffusion or active transport

14. Cell membrane – con’t Transport proteins have a certain shape and only bind with molecules that fit their shape. Therefore, if a molecule cannot enter or leave the cell through the lipid bilayer and it doesn’t fit any of the transport proteins, it cannot pass through the membrane This is what makes the cell membrane semi- permeable, or selectively permeable; allowing some things to pass, put not others.

15. Cell membrane – con’t Cholesterol molecules in animal cells help stabilize the cell membrane by anchoring the phospholipids in place, which keeps the cell membrane from falling apart ( the cell wall does this in bacterial, plant, and fungal cells) Cholesterol also keeps phospholipids away from one another enough to keep them from solidifying when temperatures get cold.

16. Cell membrane – con’t Carbohydrate chains that are attached to different phospholipids and proteins in the cell membrane act as identification molecules. This allows molecules that need to enter the cell to find their “doorways” (proteins) into the cell

17. Types of Cell Transport  Passive transport - transport of substances across the cell membrane that does not require energy (moves with the concentration gradient)  Active Transport - transport of substances across the cell membrane that does require energy (moves against the concentration gradient)

18. 3 Types of Passive Transport Diffusion - the movement of molecules/atoms from areas of high concentration to low concentrations Osmosis - the diffusion of water across a membrane Facilitated diffusion - diffusion of large or charged molecules through the cell membrane by transport proteins

19. Diffusion Occurs naturally without energy Example: If you place a drop of food coloring in a glass of water, the molecules of food coloring will naturally move away from each other to other parts of the glass where there is no food coloring (they are moving from areas of high concentration of food coloring to areas of low concentration)

20. Osmosis Water moves from where there is a more water to where there is less water. Requires no energy (passive transport) Movement of water has to do with concentrations of solutions involved Concentration terms are relative (two or more solutions must be compared to say which one is more or less concentrated

21. Types of Solutions involved in Osmosis Hypotonic Hypertonic Isotonic

22. Hypotonic Solution A solution that has less solute than the cell When a cell is placed in a hypotonic solution, water moves into the cell lysis - when a cell takes in water until it bursts

23. Hypertonic Solution A solution that has more solute than the cell When a cell is placed in a hypertonic solution, water moves out of the cell crenation - the cell shrinks and becomes prickly as it loses water

24. Isotonic Solution A solution that has the same amount of solute as the cell When a cell is placed in an istonic solution, water moves in and out of the cell at the same rate there is no net movement of water

25. Facilitated Diffusion Particles move from high to low concentration they are too large to squeeze between phospholipids, so they must go through carrier (transport, or channel) proteins the proteins are very specific. Only one type of molecule can enter each kind therefore, there are hundreds of different carrier proteins

26. Types of Active Transport Active transport sodium-potassium pump endocytosis (pinocytosis and phagocytosis) exocytosis

27. Steps of Active Transport A molecule/atom approaches the cell membrane the molecule enters a carrier protein as far as it can go the carrier protein changes shape around the molecule and pushes it into the cell the carrier protein returns to its original shape in order to repeat the process again with another molecule

28. Sodium-Potassium Pump A common example of an active transport pump 3 sodium ions are pumped out of the cell, 2 potassium ions are pumped into the cell Next of Kin (mnemonic to help you remember)

29. Endocytosis When the cell takes in large molecules from outside the cell by moving the cell membrane around the particle and forming a vessicle around the particle as it brings it into the cell phagocytosis - endocytosis of a solid pinocytosis - endocytosis of a liquid

30. Exocytosis When the cell expels a molecule from inside the cell by moving a vessicle that contains the molecule to the edge of the cell membrane Then, the membrane of the vessicle joins the cell membrane and pushes the particle out of the cell