Cell Membrane - structure AND passive transport Flashcards
What is the cell membrane and function
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
What is the phospholipid bilayer
- Made of glycerol, two fatty acid
tails, and a phosphate-linked head
group - Made of hydrophilic head and
hydrophobic tail
What is a hydrophilic head
Hydrophilic heads are “water
loving” and attract water
molecules into the membrane
What is a hydrophobic tail
Hydrophobic tails are “water
fearing” and push the water
molecules away to the second
hydrophilic head
Is the cell membrane semi-permeable, and if so, what does that mean
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
Can large, charged molecules pass through
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
What is passive transport
Does not require energy
- Particles move down/along the
concentration gradient* - Examples: simple diffusion, facilitated
diffusion, osmosis
What is active transport
- Requires energy
- Particles move against the
concentration gradient - Examples: active transport,
cytosis
What is the concentration gradient
Concentration gradient 🡪 a measure of
how the concentration of a solution changes
from one place to another (ex. inside vs
outside the cell)
What will happen when one area has a higher concentration of particles in the concentration gradient
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)
What is equilibrium
When the concentration in both areas are equal,
this is called equilibrium
- The particles then resume random movement
once equilibrium is reached
What is facilitated diffusion
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
Define what surface area to volume ratio is and how it is a factor affecting diffusion
- 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
Describe how concentration is a factor affecting diffusion
The bigger the difference in concentration between two areas = the
steeper the gradient = the faster the rate of diffusion
Describe how distance is a factor affecting diffusion
The less distance that molecules
need to travel, the faster the rate of
diffusion because the molecules do
not have as far to travel
Describe how temperature is a factor affecting diffusion
- Particles move faster at high temperatures than low temperatures
- The higher the temperature, the faster the rate of diffusion
What is osmosis
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
What is the aim of osmosis
Osmosis is an attempt to “balance” the salt/solute concentrations by
diluting the more concentrated salt side with water
What is the movement of water in a hypertonic solution
Has a higher
concentration of
solutes than the inside
of cell
Water moves OUT of
the cell (low salt conc.
🡪 high salt conc.)
What is the movement of water in a hypotonic solution
- Has a lower
concentration of
solutes than the inside
of cell - Water moves INTO
the cell
What is the movement of water in an isotonic solution
- 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
What are the effects of plant cells in different situations
- 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
