5.2 The Plasma Membrane And Cell Wall Flashcards
plasma membrane
phospholipids with embedded proteins make up the membrane surrounding all cells
what is the defining feature of all cells? why?
the plasma membrane because it actively maintains intracellular conditions compatible with life.
cell wall
a defining boundary in many organism, external to the cell membrane, that helps maintain the shape and internal composition of the cell
homeostasis
the active regulation and maintenance, in animals, organs, or cells, of a stable internal physiological state in the face of a changing external environment
how does the plasma membrane maintain homeostasis?
it is selectively permeable
selectively permeable
lets some molecules in and out freely, lets other in and out under certain conditions, prevents other molecules from passing through at all
the plasma membrane’s ability to act as a selective barrier is the result of:
the combination of lipids and embedded proteins of which it is composed
the hydrophobic interior of the lipid bilayer prevents:
ions and charged/polar molecules from diffusing freely across the plasma membrane
many macromolecules (proteins/polysaccharides) can’t cross the plasma membrane because:
they’re too large
gases, lipids, and small polar molecules can move across the lipid bilayer because:
they are small
what allows the export and import of certain molecules that can’t cross the cell membrane on their own?
protein transporters
diffusion
the random motion of individual molecules, with net movement occurring where there are areas of higher and lower concentration of the molecules
the simplest form of movement into and out of cells is:
passive transport which works by diffusion
the frequency with which molecules collide have important consequences for:
chemical reactions which depend on the interaction of molecules
diffusion leads to a net movement of:
the substance from one region to another when there is a concentration gradient (areas of higher concentration to lower)
some molecules diffuse freely across the plasma membrane as a result of:
difference in concentrations between the inside and outside of a cell
some molecules that cannot move across the lipid bilayer directly can move passively toward:
a region of lower concentration through protein transporters
facilitated diffusion
diffusion through a membrane protein, bypassing the lipid bilayer
diffusion and facilitated diffusion both result from:
the random motion of molecules
net movement of the substance occurs when:
there are concentration differences
in facilitated diffusion, the molecules moves through a ______. in simple diffusion, the molecules moves directly though the _____.
membrane transporter; lipid bilayer
what are the two types of membrane transporters?
channel and carrier
channel
a transporter with a passage that allows the movement of molecules through it (depends on their shape and charge)
some membrane channels are gated which means:
they open in response to some sort of signal (ex. chemical or electrical)
carrier
a transporter that facilitates movement of specific molecules
membrane carriers exist in two conformations:
one that is open to one side of the cell, and another that is open to the other side of the cell
binding of the transported molecule induces a conformation change in the membrane protein, allowing:
the molecule to be transported across the lipid bilayer
even though the plasma membrane is hydrophobic:
water molecules are small enough to move passively through to a limited extent by simple diffusion
aquaporin
a protein channel that allows water to flow through the plasma membrane more readily by facilitated diffusion
osmosis
the net movement of a solvent, such as water, across a selectively permeable membrane toward the side of higher solute concentration
high solute concentration equals:
low water concentration
low solute concentration equals:
high water concentration
during osmosis, the net movement of water is:
toward the side of the membrane with higher solute concentration until it is opposed by another force
passive transport works to the cell’s advantage only if:
the concentration gradient is in the right direction
active transport
the “uphill” movement of substances against a concentration gradient requiring an input of energy
during active transport, cells move substances through:
transport proteins embedded in the cell membrane
most of the energy used by a cell goes towards:
keeping the inside of the cell different from the outside, a function carried out by proteins in the plasma membrane
protein pumps
use energy directly to move a substance into or out of a cell (ex. sodium-potassium pump)
primary active transport
active transport that uses the energy of ATP directly
antiporters
transporters that move molecules/ions in opposite directions (ex. sodium-potassium pump)
symporters/cotransporters
transporters that move two molecules in the same direction
a concentration gradient stores:
potential energy that can be harnessed to drive the movement of other substances across the membrane against their concentration gradient
protons (and other ions) move from areas of:
like charge to areas of unlike charge, driven by an electrical gradient
electrochemical gradient
a gradient that combines the charge gradient and the chemical gradient of protons and other ions
secondary active transport
active transport that uses the energy of an electrochemical gradient to drive the movement of molecules
what do many cells use to maintain their size?
active transport
hypertonic solution
one with a higher solute concentration that that inside the cell: water leaves cell and cell shrinks
hypotonic solution
one with a lower solute concentration that that inside the cell, water moves into the cell and cell lyses or bursts
isotonic
at the same solute concentration
animals solve the problems of osmosis by keeping the intracellular fluid:
isotonic with extracellular fluid
cells use active transport of ions to maintain:
equal concentrations inside and out; sodium-potassium pump plays an important role in keeping the inside of the cell isotonic with the extracellular fluid
contractile vacuole
a type of cellular compartment that takes up excess water and waste products from inside the cell and expels them into the external environment
how do organisms such as plants, fungi, and bacteria maintain cell size and shape?
cell wall surrounding the plasma membrane (provides structural support and protection to the cell)
the cell wall resists expansion and allows pressure to:
build up in a cell when it absorbs water; this pressure resists further expansion and opposes the driving force for the water to enter
turgor pressure/hydrostatic pressure
pressure within a cell resulting from the movement of water into the cell by osmosis and the tendency of the cell wall to resist deformation
vacuole
a cell structure that absorbs water and contributes to turgor pressure (different from contractile vacuole)
why do plants wilt when dehydrated?
loss of water from the vacuoles reduces turgor pressure and the cells can no longer maintain their shape within the cell wall
plant cell wall is composed of:
polysaccharides (cellulose)
the cell wall is composed of different components including:
carbohydrates and proteins
