Activity 4: Cellular Transport Mechanisms Flashcards
types of diffusion
passive diffusion
facilitated transport
facilitated diffusion
- Molecules and ions dissolved in water are in constant motion, moving about randomly
- This random motion causes a net movement of these substances from regions where their concentration is high to regions where their concentration is lower, a process called ____________
- This movement leads to a uniform or equal concentration of molecules in both regions.
- A net movement driven by diffusion will continue until the concentrations in all regions are the same.
passive diffusion
diffusion
- Like glucose and other energy sources, some are polar and cannot pass through the nonpolar interior of the phospholipid bilayer.
- These molecules enter through specific channels in the plasma membrane. The inside of the cell is polar and thus “friendly” to the polar molecules, facilitating their transport across the membrane.
facilitated transport
________, another class of membrane protein (the first one being channels), transport ions and other solutes like ____ and ________ (the building blocks of proteins) across the membrane.
- Unlike channels, however, they facilitate the movement of solutes across the membrane by physically binding them on one side of the membrane and releasing them to another.
- Again, the movement depends on which area has a higher or lower solute concentration.
FACILITATED DIFFUSION
carriers
sugars and amino acids
If the solute concentration in the cytoplasm is greater, the solutes will move from the cell to the extracellular space (area outside the cell).
However, if the solute concentration is higher in the extracellular space, the solutes will move from the extracellular space to the cell.
FACILITATED DIFFUSION
When the concentration of the transported substance rises high enough, all of the carriers will be in use, and the capacity of the transport system will be ______________.
- substances that move across the membrane by simple diffusion (diffusion through channels in the bilayer without the assistance of carriers) do not show saturation
FACILITATED DIFFUSION
saturated
provides the cell with a ready way to prevent the buildup of unwanted molecules within the cell or to take up needed molecules, such as sugars, that may be present outside the cell in high concentrations.
Facilitated diffusion
3 essential characteristics of facilitated diffusion
specific
passive
saturates
Any given carrier transports only certain molecules or ions.
specific
The direction of net movement is determined by the relative concentrations of the transported substance inside and outside the cell.
passive
If all relevant protein carriers are in use, increases in the concentration gradient do not increase -the absorption rate.
saturates
contains ions and molecules, such as sugars and amino acids, dissolved in water.
The mixture of these substances and water is called an ________________
cytoplasm
aqueous solution
Most solutes, including ____ and _____, are not lipid-soluble and, therefore, cannot cross the membrane’s lipid bilayer.
ions and sugars
Water flows through _________, which are specialized channels for water.
aquaporins
when there is an imbalance in the solute or solvent concentration and two regions containing water are separated with a semipermeable membrane, water will move from an area of lower to higher solute concentration or higher to lower solvent concentration to achieve uniformity or equilibrium.
osmosis
_____________ in a solution determines the osmotic concentration of the solution.
concentration of all solutes
If two solutions have unequal osmotic concentrations, the solution with the higher concentration is _________ (Greek hyper, “more than”), and the solution with the lower concentration is __________ (Greek hypo, “less than”).
hyperosmotic
hypoosmotic
If the osmotic concentrations of two solutions are equal, the solutions are ___________ (Greek iso, “the same”).
isosmotic
While diffusion, facilitated diffusion, and osmosis are ________ transport processes that move materials _____ their concentration gradients, cells can also move substances across the membrane up their concentration gradients.
passive
down
cells can also move substances across the membrane up their concentration gradients
This process requires the expenditure of energy, typically ATP, and is therefore called ____________
active transport
- process by which cells absorb molecules (such as proteins) by engulfing them
- It is used by all body cells because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane.
endocytosis
2 categories
phagocytosis (cell-eating)
pinocytosis (cell drinking)
used by many protists (eg, amoeba) to acquire nutrients.
In humans and other multicellular animals, it is an important defense mechanism against infection
phagocytosis
process of taking fluid together with its contents into the cell by forming narrow channels through its membrane that pinch off into vesicles, and fuse with ________ that hydrolyze or break down contents.
pinocytosis
lysosomes
- process by which a cell directs the contents of secretory vesicles out of the cell membrane.
- These membrane-bound vesicles contain soluble proteins to be secreted to the extracellular environment, as well as membrane proteins and lipids that are sent to become components of the cell membrane.
exocytosis
also requires energy, but the energy does not come directly from ATP; instead, mechanical pressure.
Water and dissolved materials are forced through a membrane from an area of higher pressure to lower pressure.
filtration
