Name:  Peter Nelson       

Subject: Biology I (The Cell)

Period: 1st

Approximate Time: 50 minutes

Objectives:

The student will distinguish between active and passive transport (Biology 3.e)

The student will identify key words associated with active and passive transport        (Biology 3.e)

Materials:

Set:  Over the last couple of days we have been looking at the overall picture of organelles as they relate to the cell. Today we will look a little bit closer at one part of the cell, the cell membrane. What do we know about the cell membrane so far? Right, today we will get a chance to examine the meaning of “selectively permeable” as well as look closer at the structure of the cell membrane. By the end of the day today you should be able to identify some of the key words associated with active and passive transport as well as distinguish between active and passive transport.

Procedure:

1. On overhead, begin to draw and explain the structure of the cellular membrane. Write down vocabulary words as you go. Phospholipid bilayer, hydrophilic (head), hydrophobic (tails). Use the analogy of a phobia like  Arithmophobia- Fear of numbers. Also define peripheral (inside or outside of cell bound to membrane lipids or integral proteins) and integral proteins (imbedded in the bilayer, sometimes reaching both the outside and inside. Fluid Mosaic model (scientists first thought that the proteins were stood still but they actually move laterally to where they are needed).

2. So a cell membranes job is to maintain homeostasis, can anyone think of what homeostasis might mean? Homeostasis is basically maintaining a stable environment among many possibilities for change. In part, our cells do this using the cellular membrane. If our cells were not able to maintain homeostasis, we would be in serious trouble. Cells can control what goes in and out of them by passive and active transport.

3. Diffusion is an example of passive transport (write diffusion on the board). Diffusion is the movement of molecules from a high concentration to a low concentration. The concentration difference is referred to as the concentration gradient. Movement from a high concentration to a low concentration is considered to be with the concentration gradient. Sugar cube example. Sugar will diffuse until equilibrium is reached (concentration of molecules is the same throughout a space).

4. Relate to cell membranes. Whether or not molecules are able to diffuse across a cell membrane depends on the size and type of molecule. Is it lipid soluble? CO2 and O2 are so they can diffuse across if the their concentration is lower in the cell. Small particle can cross through pores. Ask for questions.

5. Osmosis is another form of passive transport. Osmosis is the movement of water molecules across a cell membrane from an area of high concentration to an area of low concentration. Is that with the concentration gradient? Explain hypotonic (solute molecules are lower outside the cell, water diffuses in). If solute molecules are low, what is the level of water? Hypertonic (so solute levels are higher outside the cell and water moves out). Isotonic, equal levels of solute.  Give a few examples.

6. After some examples of osmosis on the board (have them come up to draw the direction of water movement), cells in isotonic atmosphere don’t have any problems keeping movement of water in balance. However, many cells function in hypotonic environments. Some of the ways cells deal with this are

    contractile vacuoles: organelles that remove water by collecting it and then con        tracting to rid the cell of the water (think of a sponge)

    Some cells pump solute of the cell. (water is then less likely to diffuse in)

    Plant cells have walls to control cell shape (turgor pressure (cell pushes against         the cell wall) in hypotonic environment. Plasmolysis in a hypertonic environment         (cell shrinks away from cell wall. Plasmolysis is why plants shirvel up when they         don’t get enough water.

7. Some cells don’t have any way to control water if they are placed in a hypertonic or hypotonic environment. What do you think happens when a cell can’t deal with osmotic pressure? So they change shape, in hypotonic environments they can actually burst because of incoming water.

8. Another type of passive transport is facilitated diffusion. Used for molecules that are not lipid soluble or are too big to get into the cell. Uses specific proteins called carrier proteins. Carrier protein binds to molecule --> changes shape --> released on other side. The molecule is shielded from the membrane.

9. If you have enough time, talk about diffusion through ion channels. (Na+, K+, CL-).

10.  Discuss active transport. One means of active transport involves a carrier protein called the sodium potassium pump. This protein transports Na+ and K+ ions up their concentration gradients. Cells want to have a high concentration of Na+ ions outside the cell and a high concentration of K+ ions inside the cell. In order to do this, they must work against the concentration gradient. Explain that 3 Na+ ions are loaded into the protein and energy is used to push them against the concentration gradient. Once they are released, K+ ions are pushed into the cell.

11. Endocytosis -- exocytosis. (on overhead)

Closure: Like many of our other organelles, the cellular membrane is crucial for our survival. Why is that? There are many reasons, some of them relate to our cell’s ability to perform passive and active transport. Today we were able to state objectives. Tomorrow we will look closer at plant and animal cells and highlight some of their differences and similarities. Can anyone think of one difference that we talked about today in relation to osmosis?

Assessment/Evaluation:

Objective: The student will distinguish between active and passive transport (Biology 3.e)

Informal: The teacher will listen to the students as they identify the main concepts related to passive and active transport.

Formal: The teacher will collect and grade an osmosis worksheet. The grade will be entered into the grade book.

The student will identify key words associated with active and passive transport        (Biology 3.e)

Informal: The teacher will listen to the students as they identify the main concepts related to passive and active transport.

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