1. Mr. Chapman Biology 30

2.  Cells require protection, nutrients, water, elimination of waste, and response to stimuli.  The cell membrane performs all these functions for the cell.  The cell membrane acts as a barrier between the outside environment and the cell.

3.  Cells must keep the proper concentration of nutrients and water and eliminate wastes.  The plasma membrane is selectively permeable – it will allow some things to pass through, while blocking other things.

4.  The cell membrane consists of a double layer of phospholipids. This is also called a phospholipid bilayer.  Remember that a phospholipid consists of a phosphate group, glycerol, and two fatty acid chains.

5. Remember that hydrophilic means water loving, and hydrophobic means water hating.

7.  The cell membrane is oriented in such a way that the two layers of phospholipids sandwich themselves.  The heads will touch the outside environment as well as the cytoplasm inside the cell. The fatty acid chains are attracted to each other.

8.  The heads of the phospholipids are like the bread of the sandwich and the chains are the fillings in the sandwich.

9.  The cell membrane is responsible for allowing substances into and out of the cell.  This is important because the cell needs to maintain equilibrium.  The cell will need to take in nutrients and expel waste, or excess amount of substances.

11. 1. Cholesterol – helps to strengthen the membrane. 2. Proteins – help transport some molecules across the membrane, or act as receptors. 3. Carbohydrates – act as simple ID tags on the surface of the cells, to identify cell type. 4. Phospholipids – make up the majority of the cell membrane.

12.  Scientists have developed the fluid mosaic model, which describes the cell membrane in two different ways: 1.The cell membrane is flexible not rigid. Phospholipids can move from side to side and pass each other. The membrane acts as a fluid. 2.The numerous proteins and molecules that line the membrane and are embedded make the membrane colourful and display a mosaic of shapes and textures.

13.  The cell membrane is selectively permeable, meaning that it allows some substances to cross but not others. The membrane is also called semi- permeable.  Being selectively permeable allows the cell to maintain homeostasis, which is the ability to maintain equilibrium.  Cells need to have specific conditions to carry out certain functions; therefore they must be able to control what comes in and out of them.

14.  Molecules cross the membrane in several ways, which will be the topic of the next section.  Some of these methods require the cell to expend energy; others do not.  Several factors affect whether energy is required to move a particle. These include: 1. Size 2. Polarity 3. Concentration inside and outside of the cell

15.  There is more to learn about the cell membrane, but I would like you to complete this task on your own.  Assignment:  Read Section 3.3 of the textbook. Some of this you will find to be review of what we just talked about, and some will be new.  Complete Section 3.3 of the Study Guide. This time, I am going to take this in and grade your responses, so make sure to be thorough and do a good job. Cell membranes are very important to understand.