2. Simple and Facilitated Diffusion 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
temperature
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;
Facilitated diffusion
Uses carrier or channel proteins
Particles travel down a
concentration gradient
Passive process
Useful for larger molecules such as glucose and amino acids and charged, water soluble particles such as ions
Carrier proteins vs Channel proteins
Carrier proteins - Move large molecules
Molecule attaches to carrier
Carrier protein changes shape releasing molecule on other side of membrane
Channel proteins - Form pores for charged particles to diffuse down
Different channel proteins are needed for different molecules
Describe and explain the graph
Glucose uptake by simple diffusion is much slower (non existent really) than its uptake by facilitated diffusion. Initially as the external concentration of glucose increases so does the uptake of glucose by facilitated diffusion. As equilibrium is reached increasing the external glucose concentration has no effect on the uptake of glucose. This is because most of the carrier proteins are in use.
Describe the adaptations of the epithelial cell from the small intestine.
- Microvilli- increase surface area for absorption
2. Mitochondria- provide energy for active transport
