CELL TRANSPORT and THE PLASMA MEMBRANE. SB1d. Explain the impact of water on life processes (i.e., osmosis, diffusion).

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1 CELL TRANSPORT and THE PLASMA MEMBRANE SB1d. Explain the impact of water on life processes (i.e., osmosis, diffusion).

2 What if What would happen if an organism could not get energy or get rid of wastes? An organism s cells perform all of these functions. Cells must exchange materials with their environments. The cell membrane (also called the plasma membrane) allows this exchange to take place.

3 FUNCTIONS OF THE PLASMA (CELL) MEMBRANE Surrounds and protects the cell Controls flow in and out of the cell SELECTIVELY PERMEABLE: allows some molecules in, others are kept out Maintains homeostasis (balance within cells)

4 Plasma Membrane Structure Fluid-Mosaic Model: molecules are free to move Outside of cell Cell membrane Proteins Carbohydrate chains Inside of cell (cytoplasm) Protein channel Lipid bilayer

5 Plasma Membrane Structure Phospholipid bilayer: Hydrophilic heads Hydrophobic tails Proteins embedded in the membrane help transport substances across the membrane and determine which particles can pass through.

6 Tonicity of Solutions Tonicity refers to the force exerted across the membrane as differing concentrations of solutes travel in and out of the cell. Isotonic solutions Hypotonic solutions Hypertonic solutions

7 Isotonic solutions This is a solution where the concentration of the dissolved substances outside of the cell is the same as the inside of the cell. Movement of molecules into the cell=movement of molecule outside of the cell The concentration of water is the same inside and outside of the cell.

8 Hypotonic solutions The concentration of dissolved substances is lower outside of the cell than inside of the cell Water will move in to equalize Osmotic pressure increases Cell expands; animal cells may burst (cytolysis) Plant cells don t burst due to cell wall

9 Hypertonic solutions The concentration of dissolved substances is higher outside the cell than inside of the cell Water rushes out of the cell and causes it to shrivel This can result in plasmolysis: water goes out of plant cells causing the plant to wilt

10 Cytolysis & Plasmolysis Cytolysis Plasmolysis

11 View Tonicity Animations

12 Moving Across Membranes There are two types of transport across the cell membrane Active Transport requires the cell to use energy Passive Transport no energy is used

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14 Types of Passive Transport DIFFUSION molecules move from high concentration to low concentration OSMOSIS diffusion of water FACILITATED DIFFUSION uses carrier proteins to move large molecules The difference in the concentrations is called a gradient

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17 Osmosis Section 7-3 Figure 7-17 Osmosis Higher Concentration of Water Water molecules Cell membrane Lower Concentration of Water Sugar molecules Go to Section:

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19 Active Transport Uses energy Moves molecules from low concentration to high concentration against the concentration gradient Imagine pushing clothes into a hamper that is already full ATP energy

20 Example of Active Transport Sodium-Potassium Pump moves 3 potassium (K + ) ions into and 2 sodium (NA + ) ions out of a cell requires energy and a transport protein

21 Active vs Passive Transport

22 Moving Very Large Particles Some molecules can t use the carrier proteins Carbohydrates, Starches, etc. They must enter and leave the cell using endocytosis and exocytosis. This requires energy.

23 Endocytosis-entering the cell 1. Molecule touches cell. 2. Cell membrane surrounds molecule. 3. Vesicle forms and enters cell.

24 Exocytosis-leaving the cell 1. Molecule packaged in vesicle. 2. Vesicle fuses with cell membrane. 3. Molecule is released to outside of cell.

25 Cell Transport Review 1. What term refers to the diffusion of water? 2. What type of transport is used when moving from low to high concentration? 3. What structures allow molecules to cross the cell membrane in facilitated diffusion? 4. Give three examples of passive transport. 5. What structure is formed when the cell membrane surrounds a large molecule?