Unit 2 - Diffusion/osmosis/active transport Flashcards
Define diffusion
The net movement of particles from an region of higher concentration to a region of lower concentration
Is diffusion active or passive?
Passive
Define passive transport
Movement of substances that does not require energy
Define osmosis
The movement of water from a region of high water potential to a region of low water potential across a partially permeable membrane
Define facilitated diffusion
Diffusion across a plasma membrane through protein channels
Is facilitated diffusion passive?
Yes
Is osmosis passive or active?
Passive
Define active transport
The movement of molecules from an area of low concentration of that molecule to an area of high concentration of that molecule. This movement requires ATP
What sort of molecules tend to move via diffusion across a membrane?
-small molecules (e.g. gases)
-lipid soluble molecules
-non-polar molecules
Which 2 factors affect the rate of diffusion?
Temperature
Concentration difference
What effect does an increase in temperature have on the rate of diffusion?
It increases the rate of diffusion
What effect does a greater difference in concentration of two regions have on the rate of diffusion?
It increases the rate of diffusion
Why does a higher temperature increase rate of diffusion?
-higher temperature means particles have more kinetic energy and move at higher speeds
Why is it easier for oxygen to diffuse across a membrane than water?
-oxygen molecules are small and non-polar whereas water molecules are polar
-the hydrophobic interior of the phospholipid bilayer repels the charged molecules
-water is only partially charged so is still able to diffuse through the membrane, though only slowly
What 4 factors affect the rate of diffusion across a membrane?
-temperature
-concentration gradient
-surface area
-thickness of membrane
Why are membranes containing protein channels selectively permeable?
-Most protein channels are specific to one molecule or ion
-Therefore only these specific molecules/ions are able to move across the membrane
What does facilitated diffusion allow to move across a membrane?
-larger molecules
-lipid insoluble molecules
-small charged particles
What does active transport require to occur?
ATP
Carrier proteins
Define endocytosis
the bulk transport of material into cells
Define pinocytosis
the bulk transport of liquids into cells
Define phagocytosis
the bulk transport of solids into cells, most commonly the process by which white blood cells engulf pathogens
Define exocytosis
the bulk transport of materials out of a cell
Does bulk transport require ATP?
Yes
Why would a molecule be moved by bulk transport?
It is too big for channel or carrier proteins
Outline how exocytosis occurs
-vesicles are usually formed by the golgi apparatus
-vesicles move towards and fuse with the cell surface membrane
-contents of the vesicle are then released outside of a cell
How can the effect of surface area on the rate of diffusion be investigated?
-agar made with phenolpthalein and NaOH is pink as NaOH is alkai
-cubes of different sizes are placed in HCl
-In HCl the cubes will go colourless
-Leave for 5 minutes
-measure the volume of cube that is still pink
-calculate % diffusion
How can the effect of temperature on the rate of diffusion be investigated?
-an artificial cell is made from dialysis tubing
-solution is placed in cell
-cell is placed in water bath at different temperatures
-indicators can be used to see the rate of diffusion (e.g. iodine for starch or benedict’s solution for glucose)
What is the effect of a higher surface area to volume ratio on the rate of diffusion?
It increases the rate of diffusion
What is a hypertonic solution?
having a higher concentration of solute relative to another solution
What is an isotonic solution?
having the same concentration of solute relative to another solution
What is a hypotonic solution?
having a lower concentration of solute relative to another solution
What would be the effect of placing a red blood cell in a hypotonic solution?
-net movement of water into the cell
-cell swells and bursts
-causing haemolysis
-cell contents lost, haemoglobin released
What would be the effect of placing a red blood cell in a hypertonic solution?
-net movement of water out of the cell
-cell shrinks and shrivels
-becomes darker in colour as haemoglobin is more concentrated
-crenation
What would be the effect of placing a plant cell in a hypotonic solution?
-net movement of water into cell
-cell becomes turgid
-protoplast pushed against cell wall
What would be the effect of placing a plant cell in a hypertonic solution?
-net movement of water out of cell
-contents shrink
-cell plasmolysed
-protoplast completely pulled away
