Diffusion, Osmosis & Active Transport Flashcards
Define diffusion.
Movement of molecules from an area of higher concentration to an area of lower concentration (down the concentration gradient).
What does diffusion do in unicellular organisms?
Obtain the oxygen and nutrients needed for survival, removes their waste.
Why is diffusion alone not enough for multicellular organisms?
The SA:V ratio is too low, so organ systems are required (otherwise processes are too slow).
What does concentration gradient mean?
The change in concentration of a substance from one area to another.
Define equilibrium.
Equal distribution of molecules throughout the space (a result of diffusion)
Why is it important to maximise the SA:V ratio?
Higher efficiency of material exchange, as cells have a larger area to absorb nutrients and remove waste.
Relationship between concentration gradient and diffusion rate.
The greater the concentration gradient, the more rapid the diffusion rate (and vice versa).
What are the six main factors that affect diffusion rate?
Size of molecules, size of pores in membrane, temperature, pressure, concentration, surface area
Why do growing cells tend to divide when they reach a certain size?
To maintain a higher SA:V ratio, necessary to sustain metabolism
What is the difference between passive and active diffusion?
Passive = no energy input (with the concentration gradient), Active = energy is required (against the concentration gradient)
Which types of transport (4) are passive, and which are active?
Passive: simple diffusion, facilitated diffusion, osmosis. Active: active transport
Compare osmosis and diffusion.
Osmosis: water molecules go through a semipermeable membrane. Diffusion: molecules (all but water) spread out over a large area. In both, molecules move around to create equilibrium
Why do water molecules diffuse through aquaporins (water-specific integral proteins)?
Because water is hydrophilic, so its diffusion across the hydrophobic lipid bilayer is too slow to sustain life processes
What area does tonicity refer to?
The extracellular space
State the characteristics of the three types of tonicity.
Isotonic: equal solute concentration on both sides, cell volume remains the same.
Hypotonic: extracellular solute concentration is lower, more water diffuses into cell.
Hypertonic: extracellular solute concentration is higher, less water diffuses into cell.
What are the dangers of hypo or hypertonicity?
Hypotonicity: too much water in the cell, swells and could burst. Hypertonicity: not enough water in the cell, shrinks and cannot support life processes
Simple vs facilitated diffusion.
Simple: molecules pass through lipid bilayer. Facilitated: molecules pass through integral proteins (generally used for large/hydrophilic solutions)
Which proteins are used in facilitated diffusion and active transport?
Facilitated: channel and carrier proteins, Active: carrier proteins
How do carrier proteins diffuse substances?
Carrier proteins selectively bind to substrates in the cell or extracellular environment. Shape or position of the carrier protein changes to release the substrate on the opposite side of the membrane.
Where does the energy required for active transport come from?
The breakdown of ATP (adenosine triphosphate)
Describe the two types of bulk active transport.
Endocytosis: transports materials (mostly food) into a cell, materials become enveloped in the membrane to form a vesicle that is transported into the cell.
Exocytosis: transports materials (mostly waste) out of a cell, golgi apparatus packages materials into vesicles that fuse with the membrane and are excreted from the cell
Does osmosis move with or against the concentration gradient?
Osmosis diffuses water molecules with the water concentration gradient, but against the solute concentration gradient (eg. water molecules will diffuse from an area of higher water & lower solute concentration, to an area of lower water & higher solute concentration to dilute the solutes)
Why might active transport be necessary?
The amount of substance available in the cell must be regulated, or the substance needs to be used in the external environment and the concentration gradient is not favourable.
Two examples where active transport would be necessary.
- Cells need to pump out carbon dioxide into the surrounding blood vessels, but blood vessels already have a higher concentration of carbon dioxide.
- Glucose will diffuse into villi, but once the concentration gradient is not favourable then energy must be used to continue to store the glucose, otherwise it will be excreted as waste.
