Cell Membranes

Question 1

What is the fluid mosaic model?

Answer 1

-Phospholipid molecules form a bilayer
-Channel proteins and carrier proteins=allow large molecules and ions to pass through the membrane
-Receptor proteins=allow the cell to detect chemicals released from other cells
-Glycoproteins and glycolipids
-Cholesterol

Question 2

Why is cholesterol important in the cell-surface membrane?

Answer 2

-Stability
-Binds to hydrophobic tails, causing them to pack more closely towards each other
-Restrict movement of phospholipids
-Hydrophobic regions=further barrier to polar substances

Question 3

How does the membrane act in temperatures below 0 degrees?

Answer 3

-Not much energy
-Phospholipids packed closely together and membrane is rigid
-Channel proteins and carrier proteins denature, increasing permeability of membrane
-Ice crystals may form, making membrane more permeable

Question 4

How does the membrane act in temperatures between 0 and 45 degrees?

Answer 4

-Phospholipids can move around and aren’t packed as tightly together
-Partially permeable

Question 5

How does the membrane act in temperatures higher than 45 degrees?

Answer 5

-Bilayer starts to melt
-More permeable
-Water inside cell expands, putting pressure on the membrane
-Channel proteins and carrier proteins denature
-Permeability increases

Question 6

What is diffusion?

Answer 6

-The net movement of particles from an area of higher concentration to an area of lower concentration

Question 7

What are the factors affecting the rate of diffusion?

Answer 7

-Concentration gradient
-Thickness of exchange surface
-Surface area

Question 8

How do carrier proteins work?

Answer 8

-Large molecule attaches to a carrier protein in the membrane
-Protein changes shape
-Releases the molecule on the opposite side of the membrane

Question 9

What do channel proteins do?

Answer 9

-Pores in the membrane that charged particles diffuse through

Question 10

What factors affect facilitated diffusion?

Answer 10

-Concentration gradient
-Number of channel or carrier proteins

Question 11

What is osmosis?

Answer 11

-The diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential

Question 12

What is water potential?

Answer 12

-The potential of water molecules to diffuse out of or into a solution

Question 13

What is an isotonic solution?

Answer 13

-No net movement of water in or out of a cell

Question 14

What is a hypertonic solution?

Answer 14

-Net movement of water out of a cell

Question 15

What is a hypotonic solution?

Answer 15

-Net movement of water into a cell

Question 16

What factors affect the rate of osmosis?

Answer 16

-Water potential gradient
-Thickness of exchange surface
-Surface area

Question 17

Describe co-transport and the absorption of glucose

Answer 17

-Sodium ions are actively transported out of the epithelium cells in the ileum, into the blood, by the sodium-potassium pump
-Creates a concentration gradient
-Causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell, down the concentration gradient
-Via the sodium-glucose co-transporter
-Concentration of glucose inside cell increases
-Glucose diffuses out of cell, into blood through a protein channel, by facilitated diffusion

Question 18

What factors affect the rate of active transport?

Answer 18

-Speed of individual carrier proteins
-Number of carrier proteins present
-Rate of respiration in the cell and availability of ATP