Diffusion + Osmosis + Passive and Active Transport + Endocytosis + Exocytosis Flashcards
What is passive transport?
The movement of materials in and out of a cell from an area of high concentration to an area of low concentration without any energy input. This moves with/along/down the gradient and basically naturally goes with the flow
What are the two types of passive transport?
osmosis and diffusion
What is simple diffusion?
(1)the movement of SOLUTE particles (2) from an area of high concentration to an area of low concentration (3) without energy input (4) until an equilibrium is reached
What condition of the concentration gradient allows diffusion and osmosis to occur?
diffusion and osmosis can only occur along a concentration gradient where a solute is more concentrated in one area than another. So there has to be a high concentration place and a low concentration place
What is osmosis?
(1) a type of diffusion (2) the net movement of SOLVENT (base) molecules across a semipermeable membrane (3) from a place of higher solvent concentration to low solvent concentration
When is equilibrium reached in diffusion?
when there is equal movement of molecules in either direction. The particle STILL MOVES. It’s just that there is the same amount of molecules moving in as moving out.
Describe simply how diffusion works with an example (non-scientifically)
if someone sprayed a burst of perfume (which is the solute in the solvent of air) in the back corner of a room, the people closest to the corner where the perfume was sprayed (and where it is the most concentrated) will smell it quickly. People at the front won’t smell anything yet. The perfume molecules will gradually move from the highest concentration in the back to the lowest concentration in the front. Basically, it will spread across the room until the concentration is even (EQUILIBRIUM). So, the perfume has diffused across the library with no energy
What is movement along a concentration gradient?
movement from high concentration to low concentration
Describe simply how movement along a concentration gradient works with an example (non-scientifically)
Molecules moving down or along a concentration gradient are like rocks rolling down a hill. They need no energy input to keep moving
What factors can change the rate of diffusion?
- the difference in the concentration of substances
- mass of the molecule diffusing
- the temperature
How does the temperature change the rate of diffusion?
more heat means more kinetic energy → more kinetic energy means faster movement of the particles
How does the difference in the concentration of substances affect the diffusion rate?
a greater difference in the concentration of solvent and solute means the concentration gradient will be steeper and diffusion will occur faster. The greater the difference in concentration, the more rapid the diffusion. The closer the distribution of the material gets to equilibrium, the slower the rate of diffusion becomes
What is active transport?
the movement of particles in and out of the cell from an area of low concentration to an area of high concentration with the energy needed to push through. This goes against the flow
Does passive transport go along/down or against/up the concentration gradient?
along the concentration gradient
Does active transport go along/down or against/up the concentration gradient?
against
What are the two types of active transport?
exocytosis and endocytosis
What solvent is commonly used in osmosis?
water as the solvent
What is osmosis (in terms of water)?
the process through which water moves through a cell membrane
What type of particles can move through a cell membrane using diffusion?
small and uncharged or very minimally charged molecules
Why do charged molecules of any size struggle to passively cross a cell membrane?
The hydrophilic heads of the cell membrane (fluid mosaic) are charged (negatively) and the middle hydrophobic layer of tails is uncharged. Like oil and water, charged molecules are repelled by uncharged molecules. So a charged molecule can pass through the hydrophilic heads but are stopped when it tries to push through the uncharged tail area in the middle
Why do large polar molecules struggle to passively cross a cell membrane?
Polar molecules have one slightly positive side and one slightly negative side and are hydrophilic. The hydrophobic inside tails are uncharged (non-polar) and repel water and charged molecules. Because of their charge, polar molecules can get through the hydrophilic heads but are repelled by the hydrophobic, non-polar heads inside tails. Small polar molecules may get through if their charge is not too significant.
What two substances will never reach equilibrium with diffusion in the body and why?
Oxygen and carbon dioxide, because cells rapidly use up oxygen during metabolism so there will usually be less oxygen inside the cells than outside. Carbon dioxide is produced in the metabolism process, so the carbon dioxide concentrations will have more inside the cells
What are some substances that can diffuse passively through the cell membrane and why?
Carbon dioxide and oxygen because they are both small with no charge and will not interfere with the non-polar hydrophobic tails. Carbon dioxide also has a higher concentration inside and diffuses outside while oxygen has a higher concentration outside and diffuses inside
What are some substances that would have trouble getting through the cell membrane and why?
charged molecules like potassium ions, sodium ions and chloride ions or large molecules like glucose and amino acids. Because both are positively charged, they would be attracted to the negative hydrophilic heads, and then be too attached to continue moving through the hydrophilic tails that have no charge to entice them with .
How does water passively move through the cell membrane?
First, because of the hydrophilic heads that attract water molecules. Also because water molecules are small and can diffuse slowly through
What should potentially stop water from moving through the cell membrane but doesn’t;t?
The hydrogen in water is positively charged. However, the charge is not strong enough that it will completely stop them. Not all, but a lot of them will passively diffuse through.
What is facilitated diffusion?
a process that uses membrane proteins to transport polar or charged molecules through the hydrophobic tail areas by “covering” their charge and “protecting” them from being repelled.
What are the two forms of membrane proteins?
membrane proteins can be either channel proteins or carrier proteins
Is facilitated diffusion along or against the gradient?
It is still along the gradient. The carrier proteins will always pick up and deposit molecules from a high concentration area to a low concentration area
How do carrier proteins help with facilitated diffusion?
They pick up the particles on one side of the cell membrane, change shape to hold them in and release the substance on the other side
What is an example of a molecule that would need a carrier protein?
glucose
How do channel proteins help with facilitated diffusion?
Channel proteins work like tunnels, opening to allow the molecules to move through and closing after
Why can water not diffuse directly through the lipid bilayer?
Because water is not lipid soluble
How does water typically move through the cell membrane?
through special tiny channel proteins called aquaporins (water pores)
What is the name of the channel proteins water uses to pass through the cell membrane in osmosis?
aquaporins or water pores
What happens to the cell during osmosis if the water concentration is higher outside?
water will move by osmosis into the cell and the cell may swell up
What happens to the cell during osmosis if the water concentration is higher inside?
water will move out of the cell by osmosis and the cell may shrink
What is osmotic pressure?
The pressure created by water moving across the semipermeable membrane due to osmosis
What increases osmotic pressure?
The more water that moves across the membrane, the higher the osmotic pressure
What does isotonic mean?
the same concentration. When the fluids inside and outside a cell are of equal solute concentration, the external solution is isotonic to the inside solution
What does the prefix “iso” mean?
same
What does hypotonic mean?
when cells have a higher solute concentration inside and a lower solute concentration outside
How is water movement when the internal and external cell fluids are isotonic?
water moves inside and outside equally because the solute concentration is perfect
How is water movement when the external cell fluids are hypotonic to the internal cell fluids?
hypo means lower → so the outside cell fluids are lower in solute concentration → more water will be moving from the outside to the inside of the cell, to dilute the higher outside solute concentration and reach balanced, isotonic state
What does the prefix hypo mean?
lower
What does hypertonic mean?
when cells have a lower solute concentration inside and a higher solute concentration outside
What does the prefix hyper mean?
higher
How is water movement when the external cell fluids are hypertonic to the internal cell fluids?
hyper means higher → the external cell fluids are higher in concentration → more water will be moving from the inside of cell to the outside to dilute the higher outside concentration and reach a balanced, isotonic state
Will water move (1) from hypotonic to hypertonic or (2) from hypertonic to hypotonic?
What are the 2 main rules for the direction of water movement in osmosis?
(1) Water will always move more from a place with a low concentration of solute to a place with a high concentration to balance out the concentrations
(2) Water will still move in BOTH directions, just MORE towards the place of high concentration
Equilibrium is reached for a hypertonic, hypotonic or isotonic solution?
isotonic
Is osmosis passive or active transport?
osmosis requires no energy input, so it is passive
What is the issue of a cell’s inside fluids being hypotonic for a unicellular eukaryotic organism?
because unicellular eukaryotes are surrounded only by a cell membrane if a cell’s inside fluid is hypotonic to the outside fluid, water will continue to flow in until the concentration is equal. However, too much water flowing in can cause the cell to swell and eventually burst.
How do cells in animals prevent bursting when internal cell fluids are isotonic?
Animal cells are not directly exposed to the external environment → Their external cell fluid is isotonic → so water can diffuse equally in both direction
Why do animal cells need to have isotonic internal cell fluids?
to coordinate biochemical reactions
What is turgor pressure?
internal pressure
