4. Cell Membranes and Transport

Question 1

Draw and label a cell surface membrane (11)

Answer 1

glycoprotein, glycolipid, glycocalyx, phosphate head, fatty acid tail, phospholipid (bilayer), hydrophobic core, carrier protein, channel protein, cholesterol, glycoprotein

Question 2

What is the fluid mosaic model?

Answer 2

fluid: phospholipids and proteins can move about by diffusion; phospholipids can move sideways in their layers, and proteins can move within the bilayer

mosaic: scattered protein molecules when viewed from above

Question 3

What affects fluidity?

Answer 3

1) fatty acid tails: the more saturated, the less fluid

2) presence of cholesterol

3) length of fatty acid tails: longer = less fluid

4) temperature: lower temp. = less fluid

Question 4

What are the functions of cholesterol in the cell surface membrane? (3)

Answer 4

1) responsible for mechanical stability and strengthens the membrane

2) hydrophobic regions prevent ions or polar molecules from passing through

3) maintains fluidity by preventing phospholipid tails from packing too closely together at low temperatures, so that cells can withstand colder pressures

Question 5

What are the functions of carbohydrate chains glycolipid and glycoprotein? (2)

Answer 5

1) act as receptor molecules
– bind with particular substances at the cell surface

2) cell to cell recognition
– bind to complementary sites on other cells

Question 6

What are the functions of protein in the cell surface membrane? (2)

Answer 6

1) act as enzymes

2) some proteins on the inside are attached to a system of protein filaments – cytoskeleton: helps to maintain and decide the shape of the cell

3) act as transport proteins: carrier or channel

Question 7

5 types of movement of substances across membranes

Answer 7

1) diffusion
2) osmosis
3) bulk transport
4) active transport
5) facilitated diffusion

Question 8

List 3 points about water potential

Answer 8

1) high water potential to low water potential

2) highest water potential is 0, then it goes into the negatives

3) equal water potential on both sides = no net movement

Question 9

Unit for osmosis?

Answer 9

psi, trident shape

Question 10

What is a hypotonic solution?

Answer 10

water moves from solution into the cell

Question 11

What is a isotonic solution?

Answer 11

both solutions have a same water potential

Question 12

What is a hypertonic solution?

Answer 12

water moves from the cell to the solution

Question 13

What is it called when cells burst from osmosis?

Answer 13

lysis

Question 14

What is it called when cells shrivel from osmosis?

Answer 14

crenation

Question 15

What is incipient plasmolysis?

Answer 15

when 50% of the cells are plasmolysed, occurs when the surrounding solution has the same water potential as the plant cells

Question 16

The gaps caused by plasmolysis are filled with what?

Answer 16

the surrounding solution, NOT AIR

Question 17

What affects the rate of diffusion?

Answer 17

1) steepness of concentration gradient

2) temperature

3) nature of molecules or ions
– large molecules need more energy to move
– non-polar molecules diffuse easier through cell membranes than polar molecules

4) surface area where diffusion takes place

Question 18

Which 2 proteins are used in facilitated diffusion?

Answer 18

channel proteins and carrier proteins

Question 19

What are aquaporins?

Answer 19

a part of facilitated diffusion, proteins that increase water movement across the cell surface membrane

Question 20

Function of channel protein

Answer 20

has water-filled pores that allow hydrophilic ions or molecules to pass

Question 21

Function of carrier protein

Answer 21

have specific shape for a particular type of ion or molecule, opens to allow a passage in and out the cell

Question 22

What is active transport?

Answer 22

movement of molecules or ions through transport proteins against their concentration gradient, with the use of ATP

it requires intrinsic carrier proteins (pumps)

Question 23

What is the function of the receptor site on the pump?

Answer 23

it is a receptor site for ATP, and acts as an ATPase enzyme which hydrolyses ATP into ADP

Question 24

What is endocytosis?

Answer 24

engulfs material into cell

a form of bulk transport; by the infolding of the cell surface membrane to form vesicles containing the substance being transported

Question 25

What is exocytosis?

Answer 25

material removed from cell

a form of bulk transport; by the fusion of vesicles containing the substance being transported with the cell surface membrane

Question 26

What are phagocytosis and pinocytosis?

Answer 26

2 forms of endocytosis

phagocytosis: solid material

pinocytosis: liquid

Question 27

Which processes require ATP?

Answer 27

active transport, exocytosis, endocytosis