Chapter 4: Transport across cell membranes

Question 1

Cell-surface membranes

Answer 1

Outermost membrane of a cell
Barrier between cell and surrounding environment
Controls what enters and leaves cell
Partially permeable

Question 2

Membranes around organelles

Answer 2

Barrier between organelle and cytoplasm
Controls what enters and leaves the organelle
e.g. nuclear membrane

Question 3

What are the 3 ways in which substances move across the cell-surface membrane?

Answer 3

Diffusion or facilitated diffusion

Active transport or co-transport

Osmosis

Question 4

Cholesterol

Answer 4

Gives membranes stability
Found in all cell membranes except for bacteria
Between phospholipids
Bind to hydrophobic tails
Causes the phospholipids to pack more closely together
Makes the membrane less fluid and more rigid
Helps maintain cell’s shape in animals because animal cells don’t have cell walls

Question 5

Cholesterol is especially important in the membranes of red blood cells. Why?

Answer 5

Blood cells float free in the blood. They are unsupported by other cells being around them.
They need cholesterol

Question 6

Cell membranes

Answer 6

Fluid-mosaic structure
Made up of: lipids (phospholipids) proteins and carbohydrates
Cholesterol can also be found in the bilayer
Phospholipid bilayer
Lipids: phospholipids, cholesterol and glycolipids
Proteins: channel proteins, carrier proteins, receptor proteins
Carbohydrates: glycoproteins
Glycolipids: lipids in the bilayer with a polysaccharide attached
Glycoproteins: proteins in the bilayer with a polysaccharide attached