Transport Across Cell Membranes

Question 1

What are the functions of proteins in the membrane?

Answer 1

• Structural support
• Channels to transport water-soluble substances
• Allow active transport through carrier proteins
• Cell-surface receptors for identifying cells

Question 2

What are the functions of cholesterol in the membrane?

Answer 2

• Reduce lateral ( sideways ) movement of other molecules
• Make the membrane less fluid at high temperatures
• Prevent leakage of water and dissolved ions from the cell

Question 3

How does cholesterol reduce movement of the phospholipids in the membrane?

Answer 3

By pulling together their fatty acid tails

Question 4

What are the functions of glycolipids in the membrane?

Answer 4

• Act as recognition sites
• Help maintain stability
• Help cells attach to each other to form tissues

Question 5

What are extrinsic proteins?

Answer 5

Proteins on the surface of the cell-membrane

Question 6

What are intrinsic proteins?

Answer 6

Proteins that are embedded within the cell membrane

Question 7

What are the functions of glycoproteins in the membrane?

Answer 7

• Act as receptors and neurotransmitters
• Help cells attach to each other and form tissues
• Allows cells to recognise each other

Question 8

Why can some molecules not freely pass through the membrane?

Answer 8

• They are not soluble in lipids
• They are too large
• They are the same charge as the protein channels and so repel
• They are polar so cannot pass through the non-polar hydrophobic tails

Question 9

What does the fluid mosaic model mean?

Answer 9

• Fluid because the phospholipids can move which gives the membrane flexibility
• Mosaic because the proteins that are embedded within the membrane vary in shape, size, and pattern

Question 10

What is diffusion?

Answer 10

The net movement of non-polar molecules from an area of high concentration to an area of low concentration until they are evenly distributed

Question 11

What are the two proteins involved in facilitated diffusion?

Answer 11

• Protein channels
• Carrier proteins

Question 12

How do protein channels work?

Answer 12

• Allow polar molecules, charged and water soluble molecules to pass through
• They bind to the protein which causes it to change shape so that it closes on one side of the membrane and opens it on the other side

Question 13

How do carrier proteins work?

Answer 13

• Molecule that is specific to the protein binds to it
• Causes a change in shape where the molecule is released inside of the membrane

Question 14

What is osmosis?

Answer 14

Movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane

Question 15

How does co-transport of work in the ileum?

Answer 15

• Sodium ions are pumped out of the epithelial cell into the blood by active transport
• This creates a diffusion gradient
• Ions move into the epithelial cell by facilitated diffusion, carrying glucose and amino acids with it
• The glucose and amino acids then diffuse from high concentration in the epithelial cell to the low concentration in the blood

Question 16

What increases the rate of gas exchange by diffusion ?

Answer 16

• Increase in surface area
• Decrease in diffusion distance
• Steeper diffusion gradient
• Increase in temperature

Question 17

What is water potential?

Answer 17

• Pressure caused by water molecules
• The addition of a solute to pure water will lower its water potential