Transport across cell membranes

Question 1

What are carrier proteins?

Answer 1

They bind to ions or molecules (glucose or amino acids) and change shape to move across the membrane and allow active transport

Question 2

How does cholesterol reduce lateral movements of phospholipids?

Answer 2

Pull together fatty acid tails of phospholipids

Question 3

How does cholesterol prevent leakage of water and dissolved ions?

Answer 3

Very hydrophobic

Question 4

How do phospholipids remain rigid at high temperatures?

Answer 4

Cholesterol add strength to the membranes

Question 5

How are glycolipids made?

Answer 5

Carbohydrate chain covalently bonded with a lipid

Question 6

How do glycoproteins act as recognition sites?

Answer 6

Carbohydrate chain extend into watery environment outside the cell, where it acts as a receptor for specific cells

Question 7

What are the components of the cell-surface membrane?

Answer 7

Phospholipids, proteins (carrier and channel), cholesterol, glycolipids and glycoproteins

Question 8

How thick is the cell-surface membrane?

Answer 8

7nm

Question 9

Why are cell-surface membranes described as fluid?

Answer 9

Individual phospholipids can move relative to one another, giving the membrane a flexible structure that is constantly changing shape

Question 10

Why are cell-surface membranes described as mosaic?

Answer 10

The embedded proteins vary in shape, size and pattern that create a mosaic-looking image

Question 11

What is diffusion defined as?

Answer 11

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed

Question 12

What molecules can diffuse easily across plasma membranes?

Answer 12

Small, non-polar molecules such as oxygen

Question 13

What is facilitated diffusion?

Answer 13

Diffusion using transmembrane channels and carriers that span the membrane, e.g. carrier proteins and channel proteins

Question 14

How do proteins channel select ions to move through?

Answer 14

Ions bind with the protein causing it to change shape in a way that closes one side and opens another

Question 15

How do carrier proteins release molecules into membrane?

Answer 15

Specific molecules (glucose) will bind with different proteins that then change shape and release molecules

Question 16

What is osmosis?

Answer 16

The passage of water from a region of high water potential to a region of low water potential through a selectively permeable membrane

Question 17

What is water potential represented and what are the units?

Answer 17

The greek letter Psi
Kilopascals (kPa)

Question 18

When is water potential 0?

Answer 18

Pure water at standard temperature and pressure (25C, 100kPa)

Question 19

How do concentration and water potential link?

Answer 19

Higher concentrations lower the water potential

Question 20

What is cotransport?

Answer 20

The coupled movement of substances across a cell membrane, by combining facilitated diffusion and active transport

Question 21

How is active transport different from passive transport?

Answer 21

ATP is needed, against a concentration gradient, carrier protein molecules and highly selective

Question 22

What are the functions of the phospholipid?

Answer 22

Allow lipid-soluble substances to cross, prevent water-soluble substances crossing and flexible and self-healing

Question 23

What are the functions of glycolipids?

Answer 23

Act as recognition sites, maintain stability and help cells attach to form tissues

Question 24

What are the functions of glycoproteins?

Answer 24

Recognition sites (hormones and neurotransmitters), help cells to form tissues and allows cells to recognise one another (lymphocytes)

Question 25

What is active transport?

Answer 25

Movement of molecules or ions into or out of a cell from a region of low concentration to higher concentration using ATP and carrier proteins

Question 26

What do the proteins on the surface of the membrane do?

Answer 26

Mechanical support and cell receptors (hormone)

Question 27

What are protein channels for?

Answer 27

Form water-filled tubes to allow water soluble ions to diffuse across the membrane

Question 28

What are the features of the cells specialised for absorption?

Answer 28

Microvilli, large number of co-transporters/ protein channels/ carrier proteins and many mitochondria

Question 29

How does the membrane structure affect movement of substances across membrane?

Answer 29

Phospholipid bilayer allows non-polar and inhibits polar movement
Carrier allow active transport
Channel/ carrier allow facilitated diffusion
Membrane surface area
Cholesterol rigidity

Question 30

What happens to membranes when temp increases to more than 80C?

Answer 30

Damage cell-surface membrane
Proteins denature
Increased fluidity

Question 31

How do inorganic ions enter cells?

Answer 31

Move down the concentration gradient, through protein channels and can move against the concentration gradient by active transport