B2 : Movement across membranes

Question 1

membrane is a …. and is a ….

Answer 1

• selective barrier

- highly flexible barrier to stop the cell contents from escaping and control which substances enter and leave the cell.

Question 2

define diffusion

Answer 2

Diffusion is the net movement of molecules and ions
from a region of their higher concentration to a region of their lower concentration
down a concentration gradient,
as a result of their random movement.
This continues until there is no net movement.

Question 3

factors affecting diffusion - conc gradient

Answer 3

greater the difference in the concentration of particles between two locations,
the faster the rate of diffusion.
The particles move due to the transfer of kinetic energy to and from the water molecules.

Question 4

factors affecting diffusion - temp

Answer 4

if a system is hot, the particles have more kinetic energy so they move faster.

Question 5

factors affecting diffusion - distance

Answer 5

further the particles have to travel,

the longer it takes the molecules to diffuse.

Question 6

factors affecting diffusion - size

Answer 6

smaller particles

faster diffusion

Question 7

factors affecting diffusion - sf area

Answer 7

larger sf area

faster diffusion

Question 8

define osmosis

Answer 8

movement of water f
rom a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane.

Question 9

what happens if a plant cell is placed into pure water

Answer 9

large difference in water potential outside cell(higher) + inside cell( lower)
water will flow across membrane into cell

Question 10

what happens inside cell if plant cell placed into pure water

Answer 10

sap vacuole fills up
exerts pressure on cytoplasm, pressing against cell wall
cell becomes turgid - cell wall prevents cell bursting

Question 11

what happens when animal cell placed in pure water

Answer 11

osmosis causes water to enter cell
volume of cytoplasm increases.
cell membrane stretches
membrane bursts

Question 12

what happens when plant cells placed in conc solution

Answer 12

p cell becomes flaccid
volume of fluid in cell sap decreases
pressure reduces
resulting in cell membrane + cytoplasm shrinking away from cell wall

Question 13

what happens when animal cell placed in conc solution

Answer 13

becomes crenated - RBC

volume of cytoplasm decreases

Question 14

define active transport

Answer 14

movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration
using the energy from respiration.