The Plasma Membrane Gateway to the Cell 1

The Plasma Membrane - Gateway to the Cell 1

Cell Membrane Helps Maintain Homeostasis • Balanced internal condition of cells • Also called equilibrium • Maintained by cell membrane controlling what enters & leaves the cell 2

Semipermeable Membrane Ions, molecules larger than water like glucose, and large molecules such as proteins do not move through the membrane on their own. Small molecules (O 2, CO 2, H 2 O) move through easily (diffusion/osmosis) 3

Functions of Plasma Membrane ü Protective barrier ü Regulate transport in & out of cell (selectively permeable) ü Allow cell recognition üReceptor proteins function in cell communication ü Contains the cytoplasm (fluid in cell) ü Provide a binding site for enzymes 4

Structure of the Cell Membrane 5

Phospholipids Make up the cell membrane 2 lipid chains are nonpolar hydrophobic Phosphate Head is polar hydrophilic 6

FLUID MOSAIC MODEL FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid. MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above. 7

Types of Transport Across Cell Membranes 8

Experiment Put cornstarch & water baggie into large beaker containing water and iodine NOTE: When Iodine mixes with starch it turns purple Measure life saver. Width and height write measurement on note sheet Place lifesaver into small beaker of water 9

Simple Diffusion Molecules move from area of HIGH to LOW concentration • Fill a plastic baggie with 1 teaspoon of corn starch and 30 ml water • Fill a 200 ml beaker halfway with water ad add 40 drops of iodine 10

DIFFUSION Diffusion is a PASSIVE process • no energy is used to make the molecules move. Trying to reach EQUILIBRIUM • Same amount of particles inside as outside 11

Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW) 12

Two types of diffusion Facilitated Diffusion Simple Diffusion 13

Simple Diffusion Doesn’t require energy Moves high to low concentration Example: Oxygen diffusing into a cell and carbon dioxide diffusing out. 14

Facilitated diffusion Doesn’t require energy Uses channel proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell. 15

Write a Hypothesis Create a data table Starting color Ending color Beaker Baggie Based on your observation which substance moved? How did you determine this? Did this process require energy?

Osmosis Diffusion across a membrane Diffusion of water across a membrane Moves from HIGH water potential (low solute) to LOW water potential (high solute) Semipermeable membrane • Measure the diameter and the height of the gummy lifesaver. • Fill a 100 ml beaker half filled with water and place the gummy lifesaver in 17 the beaker.

Osmosis H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential 18 High solute concentration

Cell in Isotonic Solution Equal salt inside and outside the cell 10% Na. CL 90% H 2 O ENVIRONMENT CELL 10% Na. CL 90% H 2 O What is the direction of water movement? equilibrium The cell is at ________. NO NET MOVEMENT 19

Cell in Hypotonic Solution Less salt outside the cell than inside the cell 10% Na. CL 90% H 2 O CELL 60% Na. CL 40% H 2 O What is the direction of water movement? 20

Cell in Hypertonic Solution more salt outside the cell than inside the cell 20% Na. CL 80% H 2 O ENVIRONMENT CELL 5% Na. CL 95% H 2 O What is the direction of water movement? 21

Isotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS Hypertonic Solution PLASMOLYSIS 22

Osmosis in Red Blood Cells Isotonic Equilibrium Hypotonic Cytolysis Hypertonic Plasmolysis 23

Write a Hypothesis Create a data table Before water After water Diameter Describe what happened to the diameter of your lifesaver? Describe what happened to the texture of the life saver after soaking? Is the water in the beaker hypertonic, hypotonic, or isotonic?

ACTIVE TRANSPORT 25

Active Transport Requires energy or ATP Moves materials from Low to High concentration EXAMPLE: Sodium/Potassium pump Pumping Na+ out & K+ in against strong concentration gradients. 26

Transport Proteins Some carrier proteins change shape to move materials across the cell membrane 27

Materials: Plastic grocery bag, a piece of string, a pair of scissors and two small pieces of candy. The grocery bag represents the cell membrane. Pretend the membrane is completely sealed. Problem: Get the candy into the bag without using the opening of the bag

Moving the “Big Stuff” Exocytosis - moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted. 29

Exocytosis Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell Outside the Cell 30

Moving the “Big Stuff” Large molecules move materials into the cell by one of two forms of endocytosis Phagocytosis Intake solid material Pinocytosis Intake particles suspended in water 31

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