5.2 The Plasma Membrane And Cell Wall Flashcards Preview

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Flashcards in 5.2 The Plasma Membrane And Cell Wall Deck (59)
1

plasma membrane

phospholipids with embedded proteins make up the membrane surrounding all cells

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what is the defining feature of all cells? why?

the plasma membrane because it actively maintains intracellular conditions compatible with life.

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cell wall

a defining boundary in many organism, external to the cell membrane, that helps maintain the shape and internal composition of the cell

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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

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how does the plasma membrane maintain homeostasis?

it is selectively permeable

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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

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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

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the hydrophobic interior of the lipid bilayer prevents:

ions and charged/polar molecules from diffusing freely across the plasma membrane

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many macromolecules (proteins/polysaccharides) can't cross the plasma membrane because:

they're too large

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gases, lipids, and small polar molecules can move across the lipid bilayer because:

they are small

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what allows the export and import of certain molecules that can't cross the cell membrane on their own?

protein transporters

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diffusion

the random motion of individual molecules, with net movement occurring where there are areas of higher and lower concentration of the molecules

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the simplest form of movement into and out of cells is:

passive transport which works by diffusion

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the frequency with which molecules collide have important consequences for:

chemical reactions which depend on the interaction of molecules

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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)

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some molecules diffuse freely across the plasma membrane as a result of:

difference in concentrations between the inside and outside of a cell

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some molecules that cannot move across the lipid bilayer directly can move passively toward:

a region of lower concentration through protein transporters

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facilitated diffusion

diffusion through a membrane protein, bypassing the lipid bilayer

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diffusion and facilitated diffusion both result from:

the random motion of molecules

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net movement of the substance occurs when:

there are concentration differences

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in facilitated diffusion, the molecules moves through a ______. in simple diffusion, the molecules moves directly though the _____.

membrane transporter; lipid bilayer

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what are the two types of membrane transporters?

channel and carrier

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channel

a transporter with a passage that allows the movement of molecules through it (depends on their shape and charge)

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some membrane channels are gated which means:

they open in response to some sort of signal (ex. chemical or electrical)

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carrier

a transporter that facilitates movement of specific molecules

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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

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binding of the transported molecule induces a conformation change in the membrane protein, allowing:

the molecule to be transported across the lipid bilayer

28

even though the plasma membrane is hydrophobic:

water molecules are small enough to move passively through to a limited extent by simple diffusion

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aquaporin

a protein channel that allows water to flow through the plasma membrane more readily by facilitated diffusion

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osmosis

the net movement of a solvent, such as water, across a selectively permeable membrane toward the side of higher solute concentration

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high solute concentration equals:

low water concentration

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low solute concentration equals:

high water concentration

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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

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passive transport works to the cell's advantage only if:

the concentration gradient is in the right direction

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active transport

the "uphill" movement of substances against a concentration gradient requiring an input of energy

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during active transport, cells move substances through:

transport proteins embedded in the cell membrane

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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

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protein pumps

use energy directly to move a substance into or out of a cell (ex. sodium-potassium pump)

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primary active transport

active transport that uses the energy of ATP directly

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antiporters

transporters that move molecules/ions in opposite directions (ex. sodium-potassium pump)

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symporters/cotransporters

transporters that move two molecules in the same direction

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a concentration gradient stores:

potential energy that can be harnessed to drive the movement of other substances across the membrane against their concentration gradient

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protons (and other ions) move from areas of:

like charge to areas of unlike charge, driven by an electrical gradient

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electrochemical gradient

a gradient that combines the charge gradient and the chemical gradient of protons and other ions

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secondary active transport

active transport that uses the energy of an electrochemical gradient to drive the movement of molecules

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what do many cells use to maintain their size?

active transport

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hypertonic solution

one with a higher solute concentration that that inside the cell: water leaves cell and cell shrinks

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hypotonic solution

one with a lower solute concentration that that inside the cell, water moves into the cell and cell lyses or bursts

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isotonic

at the same solute concentration

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animals solve the problems of osmosis by keeping the intracellular fluid:

isotonic with extracellular fluid

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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

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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

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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)

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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

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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

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vacuole

a cell structure that absorbs water and contributes to turgor pressure (different from contractile vacuole)

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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

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plant cell wall is composed of:

polysaccharides (cellulose)

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the cell wall is composed of different components including:

carbohydrates and proteins