1. Unit 3B Cell Membrane & Transport

2. What is Cell Transport? Transport- the movement of materials between an organism and its environment Cellular Transport- movement of materials into and out of a cell Materials move from the water based solution outside the cell (its environment) to the water based solution inside the cell (the cytoplasm/cytosol), or vice versa Movement occurs across the cell membrane

3. Solutions Solution- a type of mixture in which all components are evenly distributed Made of a – Solvent- the substance that does the dissolving (ex: water is an excellent solvent) – Solute- the substance that is dissolved Cells are surrounded by aqueous (water based) solutions and contain an aqueous solution called cytoplasm

4. Cell Membranes Found surrounding all cells Made of a lipid bilayer Protects and supports the cell Regulates what comes in and out of the cell

5. The Lipid Bilayer Has 2 layers of lipids (“Bi” means two) The layers are made up of molecules called phospholipids Each phospholipid has a HYDROPHOBIC fatty acid tail region and a HYDROPHILIC head region HYDRO = means water PHOBIC = means afraid PHILIC = means loving Hydrophilic head region Hydrophobic tail region

6. Lipid Bilayer (Continued) Because the fatty acid tails are “afraid” of water (hydrophobic), they turn towards each other so they won’t be exposed to the cytoplasm, or the outside of the cell (both of which contain water)

7. The Fluid Mosaic Model “Fluid” means moving “Mosaic” means many different things put together – The Cell membrane contains different types of molecules that can move around through the phospholipids Carbohydrates attached to proteins and act as signals for molecules to attach (NOT AS MANY) Proteins in Membrane- allow for transport of molecules across the membrane (ABUNDANT)

8. The Cell Membrane is Selectively Permeable (semipermeable) Some substances can pass through the membrane and some cannot. The structure of the membrane and the proteins in it decide which molecules can enter and which can leave.

9. How does a cell membrane help a cell maintain homeostasis? – By transporting substances across the membrane to achieve equilibrium (the correct amount of each material inside and outside each cell) Build a Cell Membrane Activity

10. 2 Main Types of Transport – passive -no energy needed from the cell – active -energy from cell needed

11. 1. Passive Transport Diffusion- particles move from an area of high concentration to an area of low concentration to maintain equilibrium – This is called movement “down the concentration gradient” – A concentration gradient occurs where there are two different concentrations of a particle on either side of the membrane – Particles move straight through the lipid bilayer and no energy is required. Ex: O 2 and CO 2

12. Dynamic Equilibrium Once diffusion has occurred and the cell has reached equilibrium, will the solutes stop moving entirely? No- they still continue to move across the membrane but with equal amounts going in and out (no “net Movement”) This is called dynamic equilibrium (dynamic means movement)

13. What happens if a molecule/solute is too large and/or not dissolvable in lipids? Facilitated Diffusion -the molecule/solute will go through a carrier protein specific for that molecule. -still goes from high to low concentration; so no energy needed.

14. Facilitated Diffusion

15. Water Can Use a Channel to get through the Cell Membrane Although possible, water has difficulty dissolving through the cell membrane by regular diffusion. Why do you think this is? The inside of the cell membrane is hydrophobic Water needs the aquaporin protein channel to get through quickly! This is an example of facilitated diffusion

16. Osmosis The simple or facilitated diffusion of water molecules across a cell membrane From where there is more water (less solute) to where there is less water (more solute) Depends upon the solvent/solute ratio

17. Solutions can be classified by the amount of solutes they contain compared to other solutions: HYPERTONIC: A solution with a greater solute [concentration] – (Ex: a solution with 20% sugar and 80% water is hypertonic to a solution of 10% sugar and 90% water) HYPOTONIC: a solution with a lower solute concentration – (Ex: a solution of 5% NaCl and 95% water is hypotonic to a solution of 20% NaCl and 80% water) ISOTONIC: a solution with equal solute concentration with another solution – (Ex: outside of a cell has 10% NaCl and the cytoplasm inside the cell also has 10% NaCl)

18. What happens to our cells if they are placed into a/an… HypErtonic Solution- Since the [solute] is higher and the [water] is lower outside the cell, the cell attempts to correct this by rushing water out (osmotic pressure) Result= cell shrinks and dies E for water exiting the cell

19. HypOtonic Solution- Since the [solute] is lower and [water] is higher outside the cell, water rushes into the cell (osmotic pressure) Result= cell enlarges, can burst and die O for the cell “opens the door” to let water in

20. Isotonic Solution- Since the solution has a similar [solute] and [water] as the cytoplasm, water moves in/out at equal rates Dynamic equilibrium In addition to osmosis, solutes can also be moving at the same time by diffusion or facilitated diffusion  Passive transport animations Passive transport animations

21. Osmosis in Plant and Animal Cells What is different about the plant and animal cells during the process of osmosis? _______________________________________________________ Plant cells have cell walls which help them keep their shape. The central vacuole in each plant cell stores the water.

22. Practice What is the solvent concentration of a solution with a 3% concentration of solute? __________ What is the solvent concentration of a solution with a 15% concentration of glucose? __________ What is the solute concentration of a solution with 98% solvent? _________________________ What is the solute concentration of a solution with 75% water? _________________________ 97% 85% 2% 25%

23. Practice Conditions Water will… (move in, out, or both?) Environment is… (Hypotonic, hypertonic, or isotonic?) Solute concentration in the environment is equal to that in the cell Solute concentration in the environment is greater than the cell Solute concentration in the environment is less than the cell Predict how water will move in each of the following conditions. Name each environment with the correct solution type.

24. Fill in… ConditionsWater will…Environment is... Solute concentration in the environment is equal to that in the cell Solute concentration in the environment is greater than the cell Solute concentration in the environment is less than the cell

25. Practice

27. 13 Draw the following cells if placed in each type of environment: Hypertonic Hypotonic Isotonic Cell stays the same Cell swells and possibly bursts Cell shrinks

28. 2. Active Transport Cells move substances from low concentrations to high concentrations This is also called moving substances “UP their concentration gradient” Energy is needed in the form of ATP

29. A. Molecular Active Transport Uses a protein in the cell membrane to carry the substance across Allows for a cell to purposely concentrate a molecule in a particular location even when the forces of diffusion will want the molecule to move in the other direction Example: Sodium-Potassium Pump

30. B. Bulk Transport (for large Molecules) 1.Some substances are too large to pass through any of the pores, channels, and pumps in the cell membrane 2.Or large quantities need to be transported into/out of the cell 3.Vesicles are produced by the membrane: pouches that are extensions of the cell membrane that pinch off and surround the substance

31. Bulk Transport: a. Endocytosis Bring in large particles (ingestion) 2 Types: Pinocytosis- transports large amounts of small solutes or liquids Phagocytosis- transport of large molecules or whole cells (ex. white blood cells “eat” damaged cells) Cell membrane surrounds the particles and pinches inward to bring the materials into the cell using a vesicle.

32. Bulk Transport: b. Exocytosis Reverse of endocytosis Materials to be released from the cell are taken into a vesicle The vesicle fuses with the cell membrane and releases the materials from the cell (ex: releasing proteins) This is how wastes are removed from many cells