3.2.3.2 - Transport across membranes (C4) Flashcards
Diffusion is an example of
passive transport - energy comes from natural, inbuilt motion of particles
In diffusion the motion of the particles is described as
random motion
In diffusion the direction of particle movement is
from an area of high concentration to an area of lower concentration - until equilibrium is reached
Molecules which can diffuse through the phospholipid bilayer include
non-polar, small molecules e.g. oxygen and carbon dioxide
Facilitated diffusion and diffusion differ because
facilitated diffusion requires a special protein molecules e.g. carrier or channel protein
Facilitated and diffusion are similar because
they are both passive and molecules move with their concentration gradient (high to low)
Molecules which do not diffuse easily across the phospholipid bilayer are
large, charged ions and polar molecules e.g. glucose
What prevents large, charged and polar molecules diffusing across the plasma membrane
the hydrophobic fatty acids tails of the phospholipid bilayer
Name the two types of protein molecules involved in facilitated diffusion
carrier and channel proteins
Carrier proteins transport
molecules like glucose
How do carrier proteins transport molecules like glucose?
glucose binds to the carrier specifically, carrier changes shape, releasing it onto the other side of the membrane
Channel proteins transport…
water soluble ions
How do channel proteins transport molecules like water soluble ions?
ion binds causing a change in the shape of the channel allowing the ion to enter the cell
State 3 factors that affect the rate of diffusion
surface area, concentration gradient and thickness of exchange surface
For maximum diffusion what adaptations does the exchange surface need
large surface area
Large concentration gradient
Thin - short diffusion distance
Name 2 exchange surfaces in living organisms (humans)
alveoli and villi
Where does diffusion take place in living organisms
- alveoli - exchanging oxygen and carbon dioxide
- Villi - exchange soluble molecules into the blood
- Leaf (stomata) - carbon dioxide and oxygen
- Roots - water
How would diffusion be affected if the alveoli surface area is doubled
doubles
How would diffusion be affected if the surface area is halved but the oxygen concentration gradient is doubled
no change
How would diffusion be affected if the oxygen concentration is halved and the total thickness of the exchange surface is doubled
decreases 4 fold/quarter
what is a protein channel filled with?
water
What do carrier proteins and channel proteins have in order to transport molecules across the membrane?
binding sites
How do substances move across the cell surface membrane by facilitated diffusion
- Carrier/channel protein;
- (Protein) specific/complementary to substance;
- Substance moves down concentration gradient;
The passive movement of water from an area of high water potential to an area of low water potential through a selectively permeable membrane is…
Osmosis
Osmosis involves the movement of
water ONLY
By adding more solute the a solution how does this affect the water potential
it lowers the WP - becomes more negative
Why does pure water have a higher water potential than a solution of sugar
there are more ‘free’ water particles in pure water
A potato has a WP of -200kPa was placed in pure water WP 0kPa, what happens?
Water ENTERS the potato by osmosis (water moved from a high WP to a lower WP)
water potential is represented by
psi (greek letter)
water potential is measured in units of pressure which are
kPa
Pure water has a WP of
0kPa
How can you determine the the WP of a potato
place potato in a series of solutions of different WP. Where there is no net gain of water by the potato is the WP of the potato.
What happens if a red blood cell is placed in pure water
it swells and bursts - water enters the cell
What happens if a red blood cell is placed in strong sugar solution
It shrinks - water leaves the cell
What happens if a plant cell is placed in pure water
It swells - water enters the cell - it becomes turgid
What happens if a plant cell is placed in strong salt solution
water leaves the cell - it shrinks - it plasmolysed
What is meant by selectively permeable
Membrane only allows certain molecules through; it is only permeable to water and other small molecules `
During an osmosis practical, how and why do you dry the potato chips?
with a paper towel. To remove surface water - This would add to the mass - which we do not want
You must control the temperature during your osmosis practical - HOW?
Using a water bath and check the temperature at regular intervals using a thermometer
give 2 similarities in the movement of substances by diffusion and osmosis
- down a gradient (High to Low)
2. passive not active (does not use energy)
The movement of molecules or ions AGAINST a concentration gradient using ATP and carrier proteins is describing…
Active transport
Difference between active transport and facilitated diffusion
- active transport uses ATP
- Active transport uses only carriers (FD uses channels and carriers)
- Active transport moves molecules against their concentration gradient
Differences between active transport and osmosis
- Active transport moves solutes or ions osmosis water moves
- Active transport uses a carrier to transport a molecule across the plasma membrane, osmosis water moves through the membrane directly
In active transport what does the molecule that is moving bind to on the carrier molecule?
A receptor/binding site
After the molecule has bound to the receptor on the carrier (in active transport), what happens next?
ATP binds to the carrier on the opposite side, it splits into ADP and Phosphate (P) (releasing energy) causing the carrier to change shape, allowing the entry of the molecule.
Why do some cells like root hair cells possess so many mitochondria?
Because they transport mineral ions against a concentration gradient. This requires energy
What is unique about the carrier proteins used in active transport?
they have a specific tertiary structure
Where is active transport used in humans?
Gut/Small intestine - Na+/K+ pump (absorption of glucose)
How is low levels of glucose absorbed in the small intestine?
Using Na co transporter - ATP used indirectly
Which form of cell transport requires energy?
active transport
Which type of protein are involved in active transport?
carrier proteins
rate of active transport is affected by..
- speed of carrier molecules
- number of carrier molecules
- rate of respiration - ATP availability
How does more carrier molecules affect active transport?
increases the rate
How does an inhibitor of respiration affect active transport?
Less or NO ATP produced to rate of active transport reduced
Where does the energy for active transport come from?
Hydrolysis of ATP (produced in respiration)
Explain the process for the co-transport of glucose
- Na/K moves Na+ out epithelial cell into blood (via active transport)
- Decrease in Na+ ions in epithelial cell sets up conc. gradient with lumen of ileum
- Na+ diffuse through co transport protein (faciliated diffusion)
- Whilte diffuse carry glucose against conc. gradient
- Increase conc. glucose in side cell - move faciliated diffusion into blood
- Carried away by blood plasma
ATP used indirectly establish Na+ gradient
