Cell Membrane - structure AND passive transport

Question 1

What is the cell membrane and function

Answer 1

Made of:
- Phospholipid bilayer with
embedded proteins
Function:
- Protects the inside of the cell
from exterior factors
- Controls the movement of
substances into and out of the
cell

Question 2

What is the phospholipid bilayer

Answer 2

• Made of glycerol, two fatty acid
  tails, and a phosphate-linked head
  group
• Made of hydrophilic head and
  hydrophobic tail

Question 3

What is a hydrophilic head

Answer 3

Hydrophilic heads are “water
loving” and attract water
molecules into the membrane

Question 4

What is a hydrophobic tail

Answer 4

Hydrophobic tails are “water
fearing” and push the water
molecules away to the second
hydrophilic head

Question 5

Is the cell membrane semi-permeable, and if so, what does that mean

Answer 5

Yes, the cell membrane is semi-permeable, meaning only some substances
can pass through

Small, uncharged molecules (ex. O2, CO2, and H2O) are soluble in the
lipid bilayer and can pass through the cell membrane via the
phospholipid tails

Question 6

Can large, charged molecules pass through

Answer 6

No, large, charged molecules (ex. glucose, ions; Ca2+ and Cl-) cannot pass
through the phospholipid bilayer as the charges are repelled by the
uncharged hydrophobic tails

• Instead, large, charged molecules must use proteins embedded in the
  bilayer to move across the cell membrane

Question 7

What is passive transport

Answer 7

Does not require energy

• Particles move down/along the
  concentration gradient*
• Examples: simple diffusion, facilitated
  diffusion, osmosis

Question 8

What is active transport

Answer 8

• Requires energy
• Particles move against the
  concentration gradient
• Examples: active transport,
  cytosis

Question 9

What is the concentration gradient

Answer 9

Concentration gradient 🡪 a measure of
how the concentration of a solution changes
from one place to another (ex. inside vs
outside the cell)

Question 10

What will happen when one area has a higher concentration of particles in the concentration gradient

Answer 10

When one area has a larger
number of particles (higher
concentration) than another
area, the particles will move
from an area of high
concentration to low
concentration until the
concentrations reach an
equilibrium (equal
concentrations)

Question 11

What is equilibrium

Answer 11

When the concentration in both areas are equal,
this is called equilibrium

• The particles then resume random movement
  once equilibrium is reached

Question 12

What is facilitated diffusion

Answer 12

Facilitated diffusion is the movement of a substance from an area of high
concentration to an area of low concentration along/down a concentration
gradient. It is a passive process and uses a transport protein
- Large substances can still diffuse through the cell membrane but need a
protein channel to do so
- Ex. glucose and ions

Question 13

Define what surface area to volume ratio is and how it is a factor affecting diffusion

Answer 13

• As cells increase in size, the volume increases faster than the surface
  area
• Volume (V) 🡪 what is inside the cell
• Surface area (SA) 🡪 cell membrane
• Nutrients such as oxygen and waste such as carbon dioxide take longer
  to diffuse out of the cell when they have a longer distance to travel
  (large cell volume = larger distance for molecules to travel out of the
  cell)
• Nutrients and waste can enter and exit the cell faster with more
  ‘openings/doors’ (increased surface area = increased openings/doors)
• For an optimal rate of diffusion, cells want increased SA and less

Question 14

Describe how concentration is a factor affecting diffusion

Answer 14

The bigger the difference in concentration between two areas = the
steeper the gradient = the faster the rate of diffusion

Question 15

Describe how distance is a factor affecting diffusion

Answer 15

The less distance that molecules
need to travel, the faster the rate of
diffusion because the molecules do
not have as far to travel

Question 16

Describe how temperature is a factor affecting diffusion

Answer 16

• Particles move faster at high temperatures than low temperatures
• The higher the temperature, the faster the rate of diffusion

Question 17

What is osmosis

Answer 17

Diffusion of water

Movement of water from an
area of high concentration to
an area of low concentration
along/down a concentration
gradient. It is a passive
process, so does not require
energy and it occurs through
a semipermeable membrane

Question 18

What is the aim of osmosis

Answer 18

Osmosis is an attempt to “balance” the salt/solute concentrations by
diluting the more concentrated salt side with water

Question 19

What is the movement of water in a hypertonic solution

Answer 19

Has a higher
concentration of
solutes than the inside
of cell

Water moves OUT of
the cell (low salt conc.
🡪 high salt conc.)

Question 20

What is the movement of water in a hypotonic solution

Answer 20

• Has a lower
  concentration of
  solutes than the inside
  of cell
• Water moves INTO
  the cell

Question 21

What is the movement of water in an isotonic solution

Answer 21

• Has an equal solute
  and water
  concentration both
  inside and outside of
  cell
• Water moves equally
  IN AND OUT of cell,
  therefore, no net
  movement

Question 22

What are the effects of plant cells in different situations

Answer 22

• The cell wall (only found in plants) is a rigid/stiff structure located
  outside the cell membrane
• The rigidity protects the plant cell from bursting and gives support to
  the plant to stand upright via turgor pressure/water pressure
• Plants use tonicity to provide increased structural support by keeping
  plant cells in a turgid/swollen state with water (hypotonic solution)
• In plant cells, hypotonic solution is normal, whereas in animal cells,
  an isotonic solution is normal