Cell Transport Essential Questions: How do we experience the effects of cell transport in our everyday lives? How does the plasma membrane help maintain homeostasis?

All life processes – metabolism, muscle movement, breathing, etc All life processes – metabolism, muscle movement, breathing, etc. happens on the cellular level. Explore: What happens when you exercise? What do you experience? How do you feel?

Is Gatorade better than water while you are exercising? http://vimeo.com/8569574 What do YOU think? What makes Gatorade so FIERCE? Make a prediction before our discussion today. Now let’s look closer at what Gatorade does on the cellular level… To start, we have to get to know the plasma membrane, the “bouncer of the cell,” a little bit better… What do we already know about cell membranes?

The Bouncer of the cell The Plasma Membrane provides a barrier between the inside of the cell (the cytoplasm) and the external environment. The plasma membrane is Selectively Permeable. This means that, like entry into a club, not all molecules can enter the cell through the plasma membrane. Some molecules are allowed into the cell, while others are kept out or only allowed in under certain conditions

The bouncer’s job description What does the Plasma Membrane (Bouncer) do? Allows Water, sodium ions and calcium ions to enter the cell (club), but under different conditions The Bouncer gives preference to the owner of the club (water), but also allows a safe number of paying customers (sodium ions and calcium ions) in. Allows a steady supply of nutrients to come into the cell People employed at a club (servers, etc) Keeps out harmful ions Dangerous people or people who do not pay for the club’s services! Removes excess nutrients in the cell if levels get too high A Bouncer will cut servers or move them if they are doing nothing or not busy. Gets waste products out of the cell A Bouncer removes anyone resembling a waste product from the club.  Recall: What is the process of maintaining a balanced cellular environment called?

Plasma Membrane

Structure of the Plasma Membrane Made of Lipids Why are lipids a good choice? Lipids… Insulate against temperature change Protect against shock damage Are Flexible against direct damage Phospholipid: Hydrophilic phosphate group head Hydrophobic lipid tails Why is the plasma membrane arranged as a phospholipid bilayer? Why will one row of phospholipids not do the job?

“The Fluid Mosaic Model” Fluid because the membrane is flexible (like currents on a lake) A mosaic because the membrane is embedded and dotted on the surface with different proteins, cholesterols, and carbohydrates.

“The Fluid Mosaic Model” Cholesterol : Stabilizes the membrane by keeping the fatty acids from sticking together. Transport Proteins Regulate which larger molecules can enter the cell (nutrients) and which can leave (wastes). Proteins embedded in the membrane move among the phospholipids like boats with their “decks above water” and their “hulls below water.” Carbohydrates: Aid in cell-cell recognition.

We know the plasma membrane is selective – So who gets into the club? Substances can enter the cell via Passive or Active Transport

Simple Diffusion Diffusion – net movement of particles down a concentration gradient (from an area of higher concentration to an area of lower concentration) Caused by random movement Is a relatively slow process because it relies on the random molecular motion of atoms

Rate of Diffusion Three key factors affect the rate of diffusion: Concentration: The most important factor. The more the concentrated the substances, the faster diffusion occurs. Temperature: Increased temperature can speed diffusion because of more rapid molecular movement Pressure: Increased pressure will accelerate molecular movement and speed up diffusion.

The Result of Diffusion Eventually, the molecules will be distributed evenly, and the solutions will be in dynamic equilibrium We know that equilibrium means balance. Why is it dynamic?

Osmosis Osmosis – the diffusion of water across a selectively permeable membrane (like the cell membrane!)

What controls Osmosis? If two solutions are separated by a selectively permeable membrane that freely allows water through but does not allow the solute through… Water will flow “down” the concentration gradient to the side of the membrane where the water concentration is lower dynamic equilibrium

Your Turn! Which way will the water go? 1. Predict whether water will flow into the red blood cells or out into the surrounding solution. 2. Draw what you think each red blood cell will look like after the water moves. Draw arrows to indicate which direction the water is flowing in (Red blood cells with about 5% salt in their cytoplasm) RB Cells in 40% Salt Solution RB Cells in 5% Salt Solution RB Cells in 0% Salt Solution (pure water)

Check your work!

How Osmosis affects cells: Isotonic Solution All cells are subject to osmosis since they are surrounded by water. In an Isotonic Solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell. There is equal flow and water goes in both directions. Therefore, cells retain their original shape since the water concentrations are equal.

How Osmosis affects cells: Hypotonic Solution In an Hypotonic Solution, the concentration of dissolved substances in the solution is lower than the concentration of dissolved substances inside the cell. Therefore, there is more water outside the cell than inside & water flows in! How might a hypotonic solution affect an animal cell? How might a hypotonic solution affect a plant cell? Consider the different structures of plant and animal cells

How Osmosis affects cells: Hypertonic Solution In a Hypertonic Solution, the concentration of dissolved substances in the solution is higher than as the concentration of dissolved substances inside the cell. Therefore, there is less water outside the cell than inside & water flows out! How might a hypertonic solution affect an animal cell? How might a hypertonic solution affect a plant cell?

How osmosis affects cells If people represent salt ions, and which “cells” are in a hypotonic, hypertonic, and isotonic outside environment? ______________ _______________ ______________

How osmosis affects cells If people represent salt ions, which clubs are in a hypotonic, hypertonic, and isotonic outside environment? Hypotonic Hypertonic Isotonic

Facilitated Diffusion Type of Passive Transport with the aid of Transport Proteins Fast and specific, but does not use energy! Driven by a concentration gradient Includes Sugars and Amino Acids – molecules that need special escorts (transport proteins) to enter the cell Why can they not pass through on their own?

Then there are molecules that are SUCH a BIG deal that the club will actually pay for them to come in! What is the cell’s currency? ATP Energy!

Active Transport Active Transport is the movement of materials through a membrane against (or “up”) a concentration gradient. Special transport proteins like calcium pumps, potassium pumps, and sodium pumps change shape to allow these ions through the plasma membrane (either in or out of the cell) Requires ENERGY from the cell Which organelle supplies this energy? MITOCHONDRIA

So, is Gatorade better than water when you’re exercising? What do you lose when you exercise? When you lose salts and other electrolytes from your blood stream, what happens to your cells? What does Gatorade provide for your body? Why is this important for maintaining homeostasis? Health note: Is Gatorade better than water if you are not rigorously exercising? Why?

Let’s see for ourselves! With your neighbor, tie a string tightly around two baby carrots (individually, do not tie them together) place one baby carrot in a cup of tap water. Place the other baby carrot in a cup of salt water. Make predictions on your notes about what you think will happen to the carrot We will observe the results on Friday