Transport across membranes

Question 1

What is the definition of diffusion?

Answer 1

The net movement of particles from a region of higher concentration to a region of lower concentration

Question 2

Is diffusion active or passive?

Answer 2

Passive, meaning it will occur without need for energy

Question 3

Why does diffusion occur?

Answer 3

Because particles have kinetic energy (are moving), and an unequal distribution of particles will eventually become an equal distribution (reach equilibrium)

Question 4

Once diffusion equilibrium is reached, what happens to the particles?

Answer 4

The particles continue to move, however the movement are equal in both directions resulting in no net change

Question 5

What is the trend between diffusion distance and rate of diffusion and why?

Answer 5

As diffusion distance increases, rate of diffusion will decrease, as the number of collisions between particles will increase

Question 6

How does temperature impact rate of diffusion and why?

Answer 6

As temperature increases, rate of diffusion also increases as particles have more kinetic energy so move more quickly

Question 7

How does concentration difference impact rate of diffusion and why?

Answer 7

The greater the difference in concentration between two regions the faster the rate of diffusion, as the overall movement from a higher to lower concentration will be larger

Question 8

What is simple diffusion?

Answer 8

Diffusion in the absence of barriers or membranes

Question 9

How does polarity affect ability to diffuse through membranes?

Answer 9

Non-polar molecules (such as O2) can diffuse freely through membranes, whereas charged/polar species struggle to diffuse freely

Question 10

Why do charged and polar species struggle to diffuse through membranes?

Answer 10

As the hydrophobic interior of the membrane repels charged/polar species

Question 11

Why are membranes described as partially permeable?

Answer 11

As some species diffuse freely, whereas others (like ions and polar molecules) cannot easily diffuse

Question 12

How does surface area of a membrane impact rate of diffusion?

Answer 12

The larger the surface area, the higher the rate of diffusion

Question 13

How does thickness of membrane impact rate of diffusion?

Answer 13

The thicker the membrane (the greater the diffusion distance), the slower the rate of diffusion

Question 14

What feature of membranes allow ions/polar molecules to pass through?

Answer 14

Membranes contain transport proteins, which polar/charge molecules can use to pass through the membrane

Question 15

What is diffusion across a membrane using transport proteins known as?

Answer 15

Facilitated diffusion

Question 16

Why are membranes with transport proteins known as selectively permeable?

Answer 16

As most transport proteins are specific to one molecule or ion

Question 17

What polar molecule can freely pass through membranes and why?

Answer 17

Water, despite being polar, can pass through the membrane without facilitated diffusion, as it is so small

Question 18

What are the two types of transport proteins?

Answer 18

Carrier and channel proteins

Question 19

How do channel proteins allow ions and polar molecules to pass through?

Answer 19

Channel proteins provide a hydrophilic channel that ions and polar molecules are able to transport through down a concentration gradient

Question 20

How do carrier proteins allow ions and polar molecules to pass through?

Answer 20

Carrier proteins change shape when a particular molecule binds to them, allowing the species to pass through

Question 21

Does facilitated diffusion require energy?

Answer 21

Both diffuse and facilitated diffusion are passive processes, meaning they do not require energy

Question 22

What is the definition of active transport?

Answer 22

The movement of particles from a region of lower concentration to a region of higher concentration

Question 23

What does active transport into a cell require?

Answer 23

Energy and carrier proteins

Question 24

What is the first step of active transport into a cell via carrier proteins?

Answer 24

The molecule/ion to be transported binds to receptors of the carrier protein on the outside of the cell

Question 25

What is the second step of active transport into a cell via carrier proteins, after the molecule has bound to the carrier protein?

Answer 25

On the inside of the cell, ATP binds to the carrier protein and is hydrolysed into ADP and a phosphate ion

Question 26

What is the third step of active transport into a cell via carrier proteins, after ATP has been hydrolysed?

Answer 26

The phosphate ion from the ATP binds to the carrier protein, causing the protein to change shape and open to allow the molecules to enter

Question 27

What is the fourth step of active transport into a cell via carrier proteins, after the molecules have entered the carrier protein?

Answer 27

The phosphate ion is released and recombines with ADP to form ATP, and consequently the protein returns to its original shape, allowing the molecules to enter

Question 28

What is the definition of osmosis?

Answer 28

The diffusion of water across a partially permeable membrane, from a region of higher water potential to lower water potential

Question 29

What is water potential?

Answer 29

The pressure exerted by water molecules as they collide with a membrane or container

Question 30

What is the highest water potential possible?

Answer 30

0kPa is the water potential of pure water, and so is the highest possible water potential. All other water potential values are negative

Question 31

What is crenation?

Answer 31

Where animal cells are placed in solutions of lower water potentials, they will lose water to the solution via osmosis, and will appear to shrink/shrivel

Question 32

What is cytolysis?

Answer 32

Where animal cells are placed in solutions of higher water potentials, they will gain water from the solution via osmosis. This will increase the hydrostatic pressure of the cell, causing the cell to stretch and eventually burst

Question 33

What is turgor pressure?

Answer 33

The pressure of plant cell surface membranes against the cell wall

Question 34

What happens to plants cells when they are placed in solutions of higher water potential?

Answer 34

Water will enter the cell until the turgor pressure is high enough so no more water can enter

Question 35

Why do plant cells tend to not burst?

Answer 35

As they have strong and rigid cell walls

Question 36

What is plasmolysis?

Answer 36

Where plant cells are placed in solutions of lower water potential, causing water to leave via osmosis and the cell surface membrane to peel away from the cell wall