THE CELL MEMBRANE AND SURFACE AREA DEMOS
The typical cell membrane is actually made up of two very different types of membranes. The passive biphospholipid part (75-95%) and the active protein part (5-25%). Those cells that have to do more exchanging of materials, such as glandular cells, have more of the protein membrane. Those cells that have minimal exchange of materials, such as fat cells, have less protein membrane. The protein part of the cell membrane provides: communication, "I.D." tags, anchors to microtubules, gates of exchange for large molecules and pumps for maintaining ionic balance.
The cell membrane represents the "DOORS, WINDOWS, SEWER LINES, PHONE LINES, MAIL BOX, GAS LINES, ELECTRIC LINES and CHIMNEY" of the cell. The more cell membrane per unit of protoplasm that a cell has, the easier it is for that cell to maintain that special physiological balance called "HOMEOSTASIS". As a general rule, the smaller something is, the more membrane or "SURFACE AREA" it has.
The shapes of cells can also effect the amount of surface area that a cell has. Spherical cells have the least membrane per unit of volume, while flat or long cells have the most. If cells get too big, they will get sick and die. As they become bigger they have less surface per unit of volume of protoplasm. This makes it much more difficult to exchange materials with the environment. If this condition is not changed (cell division?), the cell will not be able to maintain its homeostasis and it will die. Cells must maintain a large "S.A.", surface area, to maintain good health.
The following demonstrations will illustrate the many different effects that surface area can have.
- Time how long it takes for a lightly crumpled piece of paper to burn Vs a tightly folded piece of paper. Size or shape?
- Time how long it takes for half of a piece (not crushed) of an Alka Seltzer tablet to blow the lid off of a Fuji Film canister half full of water Vs how long it takes for half of a piece (crushed) of an Alka Seltzer tablet to blow the lid off of a Fuji Film canister half full of water. Size or shape?
- Take four different flasks of the same shape but different sizes and pour each one them full of boiling water. Measure the rate that the temperature drops in each of the flasks. Which drops the fastest? Size or shape?
- Take a solid steel rod and try to burn it. Next take steel wool and try to burn it. What happens? Size or shape?
- Suck on a solid piece of candy and time how long it takes to dissolve in your mouth. Next take another piece of the same kind and amount of candy and time how long it takes to dissolve in your mouth if you chew and suck. Size or shape?
- You and a partner have a race in trying dissolve five grams of salt in 200ml of tap water. One partner will use granulated salt and the other will use rock salt. Who do you think will win? Size or shape?
- (A.) If you have a solid block of Styrofoam one foot by one foot by one foot, what is your total volume? What is your total surface area? What is the ratio of volume to surface area?
(B.) If you have twelve pieces of Styrofoam one inch by one foot by one foot, what is your total volume? What is your total surface area? What is the ratio of volume to surface area? How much more surface area do you have with the twelve pieces?
- Pour 100 ml of water through a column holding 500 grams of fine sand and measure
how much water passed through the sand column. Next do the same thing except this time use 500 grams of coarse sand. Explain what happened.