Transport across membranes

Question 1

What is the function of phospholipids?

Answer 1

Allow lipid-soluble substances to enter and leave the cell
Prevent water-soluble substances from entering and leaving the cell
Make the membrane flexible and self-sealing

Question 2

Describe the fluid mosaic mode

Answer 2

Membranes have a fluid structure because the phospholipid molecules are constantly moving around relative to one another
Membranes have a mosaic structure because the protein molecules are unevenly distributed throughout the membrane

Question 3

What is the function of the cell surface membrane?

Answer 3

Isolates cytoplasm from extracellular environment
Selectively permeable to regulate transport of substances
Involved in cell recognition

Question 4

What are the components of the cell surface plasma membrane?

Answer 4

Phospholipids, cholesterol, proteins, glycoproteins

Question 5

What is the function of phospholipids in plasma membranes?

Answer 5

Hydrophobic fatty acid tail
Hydrophilic phosphate head
Non-polar (lipid soluble) molecules pass through by simple diffusion
Polar (or ions) cannot pass through

Question 6

What is the function of cholesterol in plasma membranes?

Answer 6

Regulate membrane fluidity
More cholesterol = less fluidity
Different types of cells have different proportions of cholesterol

Question 7

What is the function of channel proteins in plasma membranes?

Answer 7

Allow charged ions and small molecules to pass through facilitated diffusion
Can be open or close and intrinsic
Have a specific tertiary structure so only transport molecules with complementary shape to the channel protein can pass through

Question 8

What are aquaporins?

Answer 8

Special type of channel proteins specific to water
A lot of aquaporins = very permeable = carry out osmosis easily

Question 9

What is the function of carrier proteins in plasma membranes?

Answer 9

Transport ions/polar and large molecules through facilitated diffusion
Can be open or close and intrinsic
Have a specific tertiary structure so only transport molecules with complementary shape to the channel protein can pass through

Question 10

What is the function of glycoproteins in plasma membranes?

Answer 10

Made of carbohydrates and proteins
Found on the outer surface of membranes
Important in cell recognition, often acting as antigens
Produced in Golgi body

Question 11

What is diffusion?

Answer 11

Net movement of particles from an area of higher concentration to an area of lower concentration across a partially permeable membrane
Passive process
Allows non-polar, small and lipid soluble molecules to pass

Question 12

When does diffusion stop?

Answer 12

When equilibrium is reached (no concentration gradient - same concentration particles inside and outside)

Question 13

What is facilitated diffusion?

Answer 13

Net movement of particles through a channel/carrier protein from an area of higher concentration to lower concentration across a partially permeable membrane
Water soluble, charge and large particles pass through
Passive process

Question 14

What is osmosis?

Answer 14

Net movement of water molecules from higher water potential to lower water potential through a partially permeable membrane

Question 15

What is water potential?

Answer 15

Pressure created by water molecules, measured in kPa
More solute = water potential more negative
pure water = highest water potential
more solute dissolved in water = lower water potential

Question 16

What is active transport?

Answer 16

Movement of molecules across a cell membrane against their concentration gradient
Requires hydrolysis of ATP to produce energy
Requires a specifically shaped carrier protein, with complementary binding site, that only complementary molecules bind to

Question 17

What is exocytosis?

Answer 17

Bulk movement of molecules, with the use of ATP, from the cytoplasm to extracellular environment
Vesicle fuses with plasma membrane to release contents

Question 18

What is endocytosis?

Answer 18

Bulk movement of molecules, with the use of ATP, from extracellular environment into the cell
Engulfing by cell surface membrane to form vesicle

Question 19

What are the factors affecting rate of diffusion?

Answer 19

Concentration gradient
Surface area
Temperature
Diffusion distance/pathway

Question 20

How does an increase in temperature affect the rate of diffusion?

Answer 20

Increased kinetic energy
Faster rate of diffusion of molecules

Question 21

How does an increase in surface area affect the rate of diffusion?

Answer 21

More ‘space’ for molecules to pass through
Faster rate of diffusion

Question 22

How does an increase in concentration difference affect the rate of diffusion?

Answer 22

Rate of diffusion increases

Question 23

How does a shorter diffusion distance affect the rate of diffusion?

Answer 23

Fewer membranes to cross
The faster the molecules will travel from one area to the next