Chapter 7: Cell Membrane (Test 2)

Question 1

Phospholipids are the most abundant lipid in the plasma membrane​

Phospholipids are ___ molecules, containing hydrophobic and hydrophilic regions​

The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it

Answer 1

amphipathic

Question 2

___ studies of the plasma membrane supported the fluid mosaic model​

​

Freeze-fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer

Answer 2

Freeze-fracture

Question 3

Phospholipids in the plasma membrane can move within the bilayer​

Most of the phospholipids drift laterally, but rarely does a molecule flip-flop transversely across the membrane​

Some proteins drift within the phospholipid bilayer​

Other proteins never move and are anchored to the cytoskeleton below

Question 4

As temperatures cool, membranes switch from a fluid state to a solid state​

Components of membrane types of lipids​

Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids

Answer 4

Question 5

Cholesterol acts as a “temperature buffer” for the membrane​
​

At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids​

At cool temperatures, it maintains fluidity by preventing tight packing

Question 6

___ proteins penetrate the hydrophobic core ​

___ proteins are bound to the surface of the membrane

Answer 6

Integral

Peripheral

Question 7

Six major functions of membrane proteins:​

• Transport​
• Enzymatic activity​
• Signal transduction​
• Cell-cell recognition​
• Intercellular joining​
• Attachment to the cytoskeleton and extracellular matrix (ECM)

Question 8

___ molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly​

___ molecules, such as sugars and ions do not cross the membrane easily

Answer 8

Hydrophobic (nonpolar)

Hydrophilic (polar)

Question 9

___ is the tendency for molecules to spread out evenly. (molecules move from areas of higher to lower concentration)​

Although each molecule moves randomly, diffusion of a population of molecules may exhibit a net movement in one direction​

At ___ , as many molecules cross one way as cross in the other direction

Answer 9

Diffusion

dynamic equilibrium

Question 10

Substances diffuse down their ___, the difference in concentration of a substance from one area to another​

No work must be done to move substances down the concentration gradient​

The diffusion of a substance across a biological membrane is ___ because it requires no energy from the cell to make it happen

Answer 10

concentration gradient

passive transport

Question 11

___ is the diffusion of water across a selectively permeable membrane​

Water diffuses across a membrane from the region of lower solute(higher water molecules) concentration to the region of higher solute (lower water molecules) concentration

Answer 11

Osmosis

Question 12

___ is the ability of a solution to cause a cell to gain or lose water

Answer 12

Tonicity

Question 13

___: Solute concentration is less than that inside the cell; cell gains water

Answer 13

Hypotonic solution

Question 14

___: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane

Answer 14

Isotonic solution

Question 15

___: Solute concentration is greater than that inside the cell; cell loses water

Answer 15

Hypertonic solution

Question 16

Hypertonic or hypotonic environments create challenges for organisms​

___, the control of water balance, is a necessary adaptation for life in such environments

Answer 16

Osmoregulation

Question 17

In ___, transport proteins speed the passive movement of molecules across the plasma membrane

Answer 17

facilitated diffusion

Question 18

___ allow passage of hydrophilic substances across the membrane​

___ provide corridors that allow a specific molecule or ion to cross the membrane​

• Aquaporins- for facilitated diffusion of water​
• Ion channels- open or close in response to a stimulus (gated channels)

Answer 18

Transport proteins

Channel proteins

Question 19

___ undergo a subtle change in shape that translocates the solute-binding site across the membrane

Answer 19

Carrier proteins

Question 20

___ moves substances against their concentration gradient​

Active transport requires energy, usually in the form of ATP​

Active transport is performed by specific proteins embedded in the membranes

Answer 20

Active transport

Question 21

Active transport allows cells to maintain concentration gradients that differ from their surroundings​

The ___ is one type of active transport system

Answer 21

sodium-potassium pump

Question 22

Large molecules, such as polysaccharides and proteins cross the membrane in bulk via packaging in vesicles​

​

​

Bulk transport requires energy

Question 23

In ___, transport vesicles migrate to the membrane, fuse with it, and release their contents out of cell​

Many secretory cells (like those in the pancreas secreting insulin) use exocytosis to export their products

Answer 23

exocytosis

Question 24

In ___, the cell takes in macromolecules by forming vesicles from the plasma membrane​

Endocytosis is a reversal of exocytosis, involving different proteins​

There are three types of endocytosis:​

Phagocytosis (“cellular eating”)​

Pinocytosis (“cellular drinking”)​

Receptor-mediated endocytosis

Answer 24

endocytosis

Question 25

In ___ a cell engulfs a particle in a food vacuole​

The vacuole fuses with a lysosome to digest the particle

Answer 25

phagocytosis

Question 26

In ___, molecules are taken up when extracellular fluid is “gulped” into tiny vesicles

Answer 26

pinocytosis

Question 27

In receptor-mediated endocytosis, vesicle formation is triggered by signals from outside the cell that bind to receptors on plasma membrane

Answer 27