ch 3 gaining admission: the cell membrane

Question 1

the cell membrane is like the

Answer 1

• gatekeeper
• guardian
• border guard

Question 2

despite being only 6 to 10 nanometers thick and visible only through an electron microscope, the cell membrane keeps the cell’s

Answer 2

cytoplasm in place and lets only select materials enter and depart the cell as needed

Question 3

this semipermeability or selective permeability is a result of a

Answer 3

double layer (bilayer) of phospholipid molecules interspersed with protein molecules

Question 4

the outer surface of each layer is made up of tighly packed

Answer 4

hydrophilic (or water-loving) polar heads

Question 5

inside between the two layers you find

Answer 5

hydrophobic (water-fearing) nonpolar tails consistinf of fatty acid chains

Question 6

since the phospholipids give the membrane a rather

Answer 6

• fluid structure
• cholesterol molecules are embedded to provide stability and make it less permeable to water-soluble substances

Question 7

both cytoplasm and the matrix, the environment outside of the cell, are primarily

Answer 7

water

Question 8

the polar heads electrostatically attract

Answer 8

polar water molecules

Question 9

the membrane’s interior made up of

Answer 9

non-polar fatty acid molecules (the phospholipid tails) creating a dry middle layer

Question 10

Lipid-soluble molecules can pass through this layer but water soluble molecules such as

Answer 10

• amino acids
• sugars
• many proteins
  cannot

these molecules must enter the cell through little tunnels created by channel proteins

Question 11

in addition to forming protein channels, other proteins do not span the membrane but stick out from the

Answer 11

outer surface, sometimes with a carbohydrate attached

Question 12

protein channels serve numerous purposes for example

Answer 12

• creating receptors for hormones
• binding site for other cells
• aiding in recognition of self versus non-self

Question 13

the cell membrane is designed to hold the cell

Answer 13

together and to isolate it as a distinct functional unit

Question 14

although the cell membrane can spontaneously

Answer 14

• repair minor tears
• severe damage to the membrane will cause the cell to disintegrate

Question 15

the membrane is picky about which molecules it

Answer 15

lets in or out

Question 16

the cell membrane allows movement across its barrier by

Answer 16

• diffusion
• osmosis
• active transport

Question 17

diffusion

atoms, ions, and molecules are in constant

Answer 17

motion, taking a straight-line path until they inevitably crash into another particle and bounce off with a new trajectory

as a result the molcules will naturally flot to areas of lower concentration (more collisions means more movement)

Question 18

diffusion