Cell Membranes - B6

Question 1

True or false: all cells are surrounded by a membrane.

Answer 1

true

Question 2

What is the cell membrane a barrier between? (for cell surface membranes)

Answer 2

It is a barrier between the cell and the environment

Question 3

Is the cell surface membrane partially permeable?

Answer 3

Yes

Question 4

What are the 3 transportation methods for cell surface membranes?

Answer 4

diffusion, osmosis, and active transport

Question 5

What does the organelle membrane do?

Answer 5

It divides the cell into different compartments. They act as a barrier between the organelle and the cytoplasm. It’s partially permeable

Question 6

What are the different parts of a phospholipid and are they hydrophilic or hydrophobic?

Answer 6

-phosphate head > hydrophilic > polar(charged)
-fatty acids> hydrophobic> not polar

Question 7

Are the phosphate heads on the outside or inside of the phospholipid blayer?

Answer 7

One is on the outside of the cell, one is on the inside, so the fatty acids are facing each other.

Question 8

Why are cell membranes described as being a fluid mosaic?

Answer 8

-mosaic: membrane is made up from a variety of different molecules arranged into a mosaic(these molecules vary between cell to cell)
-fluid: the position of these molecules within the membrane is fluid - they are able to move around within the cell

Question 9

What structures make up a cell membrane?

Answer 9

-phospholipid bilayer
-channel protein
-carrier protein
-glycolipids and glycoproteins
-cholesterol
-receptors
-enzymes

Question 10

What types of molecules go straight through the phospholipid bilayer?

Answer 10

small and non-carged molecules

Question 11

What type of molecules go through channel proteins?

Answer 11

-small or big water-soluble ions
-can’t get through the bilayer as they’re repelled by phosphates

Question 12

What type of molecule travels thorugh channel proteins?

Answer 12

glucose, amino acids

Question 13

How does a carrier protein work?

Answer 13

bind to substrate > change tertiary structure > allows molecule to pass through

Question 14

What is a glycolipid made from?

Answer 14

made of sugars and lipids

Question 15

What is a glycoprotein?

Answer 15

protein with sugars on

Question 16

How does cholesterol aid cell membranes?

Answer 16

-add rigidity/strength
-keeps molecules in place i.e. channel proteins

Question 17

What do enzymes do for cell membrane structures?

Answer 17

-hydrolyse disaccharides
-uses induced fit
-the disaccharides become monosaccharides and then go through the carrier protein

Question 18

How do the small, non-charged travel through the phospholipid bilayer?

Answer 18

-move by simple diffusion - doesn’t rely on proteins.
-high conc. on the outside of the cell and a low conc. on the inside of the cell
-simple diffusion is passive - rate increases as conc. difference increases

Question 19

How do molecules travel through channel and carrier proteins?

Answer 19

-facilitated diffusion(proteins help the diffusion)
-high to low > passive
-rate of diffusion is limited by the no. of proteins - channel or carrier
-some carrier proteins also carry out active transport - low to high, requires energy, have lots of mitochondria

Question 20

What is the definition of osmosis?

Answer 20

Osmosis is the movement of water molecules from a high water potential to a low water potential across a partially permeable membrane

Question 21

What is water potential?

Answer 21

the pressure of water on a membrane

Question 22

What is the water potential of pure water?

Answer 22

-PURE wp is 0(the biggest)
-solutions have a -ve wp (lower wp)

Question 23

What is the process of osmosis?

Answer 23

-water molecules in constant motion
-some hit the membrane as they move randomly
-the collision of the molecules with the membrane causes a pressure on it. This pressure is known as water potential and is measured in units.
-more water molecules = greater water potential

Question 24

What does it mean if a solution is isotonic?

Answer 24

no difference in wp - solutions of equal solute conc.

Question 25

What does it mean if a solution is hypertonic?

Answer 25

-lots of solutes in solution
-RBC shrinks
-osmosis from high to low

Question 26

What does it mean if a solution is hypotonic?

Answer 26

-solution has higher wp than molecule
-water diffuses via osmosis into molecule
-molecule swells and bursts

Question 27

Describe the process of facilitated diffusion.

Answer 27

-from high to low conc.
-through protein channel or using a specific carrier protein
-passive
-rate is limited by no. of proteins

Question 28

Describe the process of active transport.

Answer 28

-from low to high conc.
-uses a specific carrier protein
-requires ATP
-rate limited by ATP availability
-cells which actively transport require many mitochondria to produce ATP via cellular respiration