Bio Unit 1.3 - Cell Membranes and Transport

Question 1

Why are the hydrophilic heads pointing in important in the phospholipid bilayer?

Answer 1

Interacts with water in the cytoplasm

Question 2

Why are the hydrophilic heads pointing out important in the phospholipid bilayer?

Answer 2

Interacts with water surrounding the cell

Question 3

Which way do hydrophobic tails point?

Answer 3

Toward each other, to centre of membrane

Question 4

What does the phospholipid component of the bilayer allow to cross?

Answer 4

Allows lipid soluble molecules across but not water soluble molecules

Question 5

Extrinsic Proteins (on surface of bilayer)

Answer 5

Provide structural support and form recognition sites (by identifying cells) and receptor sites hormone attachment

Question 6

Intrinsic Protein (extends across both layers)

Answer 6

Include transport proteins which use active/passive transport to move molecules/ions across cell membrane

Question 7

2 reasons why phospholipid bilayer is known as ‘fluid-mosaic’ model

Answer 7

1. Fluid - individual phospholipid molecules can move within layer relative to one another
2. Mosaic - proteins embedded in bilayer vary in shape and size and in their distribution

Question 8

What do both plant and animal cells contain in their cell membrane?

Answer 8

Sterols, glycoproteins, glycolipids

Question 9

What is the sterol in animal membrane?

Answer 9

Cholesterol

Question 10

What does cholesterol do?

Answer 10

Occurs between phospholipid molecules, making membrane more stable to high temperatures and more fluid at low temperatures

Question 11

What is the carbohydrate layer around animal cells and what does it do?

Answer 11

Glycocalyx - works as hormone receptors

Question 12

How can small molecules travel across the membrane? (O2 and Co2)

Answer 12

Move between phospholipid molecules and diffuse across membrane

Question 13

How do lipid soluble molecules (vitamin A) move across?

Answer 13

Dissolve in phospholipid and diffuses across membrane. The phospholipid layer is hydrophobic so lipid soluble molecules move through easier.

Question 14

How do water soluble molecules pass through the membrane?

Answer 14

Must pass through intrinsic proteins forming water filled channels across the membrane (why cell surface is selectively permeable)

Question 15

Where do glycoproteins connect to?

Answer 15

Extrinsic Proteins

Question 16

Diffusion

Answer 16

The passive movement of a molecule/ion down a concentration gradient from a region of high concentration to a region of low concentration until they are equally distributed

Question 17

How does concentration gradient affect rate of diffusion?

Answer 17

Greater difference in concentration of molecules in two areas - more molecules diffuse in given time

Question 18

What affects rate of diffusion?

Answer 18

Concentration gradient, thickness of exchange surface, surface area of membrane

Question 19

Other irregular factors that might affect rate of diffusion?

Answer 19

Size of molecule, nature of diffusing molecules, temperature

Question 20

Facilitated Diffusion

Answer 20

Passive transfer of molecules down a concentration gradient across a membrane by channel or carrier protein molecules in the membrane

Question 21

Where does facilitated diffusion occur?

Answer 21

Sites on membrane where transport proteins are present (numbers limit rate of facilitated diffusion.)

Question 22

2 types of facilitated diffusion?

Answer 22

Channels proteins and Carrier Proteins

Question 23

Channel Protein facilitated diffusion

Answer 23

Molecules with pores lined with polar groups, channels are hydrophilic so water soluble ions can pass through

Question 24

Carrier Protein facilitated diffusion

Answer 24

Allows diffusion of larger polar molecules (sugars and amino acids)

Question 25

How does carrier protein f.d work?

Answer 25

Molecules attaches to its binding site, protein changes shape and releases molecule on the other side of membrane before resuming original shape

Question 26

Do carrier proteins allow active transport?

Answer 26

Yes

Question 27

What different molecules do channel and carrier proteins transport?

Answer 27

Channel-water soluble Carrier - soluble and insoluble

Question 28

Active Transport

Answer 28

Movement of molecules against a concentration gradient using energy from hydolysis of ATP made by cell respiration

Question 29

Features of active transport

Answer 29

1. Low to high concentration 2. Requires energy from ATP 3. Occurs through intrinsic carrier proteins 4. Rate is limited by availability of carrier proteins

Question 30

Process of Active Transport through Carrier Protein

Answer 30

1. molecule combines with specific carrier protein outside the membrane 2. ATP transfers phosphate group to the carrier protein on inside of membrane 3. Carrier protein changes shape and takes molecule across membrane 4. Molecule released into cytoplasm 5. Phosphate ion is released from carrier molecule back to cytoplasm and forms ATP 6. Carrier protein returns to original shape

Question 31

Effect of cyanide?

Answer 31

Respiratory inhibitor, will prevent aerobic respiration and without production of ATP active transport cannot take place

Question 32

Co transport

Answer 32

A transport mechanism in which facilitated diffusion brings molecules and ions (glucose and Na+ ions) across cell membrane together (on the same transport protein molecule) into cell

Question 33

Why is glucose and sodium co transport important?

Answer 33

Significant for absorbing these substances across cell membranes and into the blood in the ileum and kidney nephron

Question 34

Process of co-transport

Answer 34

1. Glucose/Sodium ions bind to carrier protein in cell membrane 2. Carrier changes shape and deposits both inside the cell (facilitated diffusion) 3. Both substances separately diffuse through cytoplasm to the opposite membrane 4. Glucose passes into blood by facilitated diffusion 5. Sodium ions carried out of epithelial cell via active transport by same carrier that moves potassium in

Question 35

Why is sodium level low in epithelial cell?

Answer 35

S0 more sodium ions can move in and bring in more glucose (so facilitated diffusion can continue)

Question 36

Water Potential

Answer 36

measure of free energy of water molecules and the tendency of water to move (kPa)

Question 37

Osmosis

Answer 37

The net passive diffusion of water molecules across a selectively permeable membrane from a region of higher water potential to a region of lower water potential

Question 38

What is water potential of pure water?

Answer 38

Zero

Question 39

What does addition of solute to pure water do to water potential?

Answer 39

Lowers it into a negative value

Question 40

Higher concentration impact on water potential

Answer 40

More concentrated, fewer water molecules free to move, pull on water molecules greater, water potential more negative

Question 41

Solute Potential

Answer 41

Measure of osmotic strength of a solution. The reduction of water potential due to the presence of solute molecules

Question 42

More solute impact of solute potential?

Answer 42

more solute, more tightly water molecules are held, lower tendency of water to move out therefore higher concentration has more negative solute potential

Question 43

Pressure potential

Answer 43

Pressure of when water enters cell by osmosis and expands the vacuole, pushing against the cell wall. Cell wall can only expand a little so pressure outwards builds up, resisting entry of more water (cell becomes turgid)

Question 44

What does pressure potential increase?

Answer 44

Increases tendency of water to move out

Question 45

Potential Equation

Answer 45

Solute potential + Pressure potential = Water potential

Question 46

If water potential of external solution is less negative than inside solution?

Answer 46

External solution is hypotonic to cell and water flows in.

Question 47

If water potential externally is more negative than inside then?

Answer 47

External solution is hypertonic to cell and water flows out

Question 48

Same water potentials externally and internally?

Answer 48

External solution and cell are isotonic

Question 49

Plasmolysis

Answer 49

Retraction of cytoplasm and cell membrane from cell wall as cell loses water by osmosis

Question 50

Incipient Plasmolysis

Answer 50

Cell membrane and cytoplasm are partially detached from cell wall due to insufficient water to make cell turgid

Question 51

After playmolysis...

Answer 51

Flaccid

Question 52

Turgid

Answer 52

Cytoplasm pushes against cell wall

Question 53

Why is pressure potential not considered in animal cells?

Answer 53

No cell wall to be pushed against

Question 54

Hameolysis

Answer 54

Bursting of (eg. red blood cells) without a cell wall after water enters through osmosis

Question 55

When will red blood cell burst?

Answer 55

In pure water (too much water moves in)

Question 56

When will cell shrink?

Answer 56

In concentrated solution (too much water moves out)

Question 57

Endocytosis

Answer 57

active process of cell membrane engulfing material, bringing it into cell in a vesicle

Question 58

Exocytosis

Answer 58

active process of vesicle fusing with cell membrane , releasing the molecule it contains

Question 59

2 types of endocytosis

Answer 59

Phagocytosis and Pinocytosis

Question 60

Phagocytosis

Answer 60

Uptake of solid material too large to be taken in by diffusion Granulocytes engulf bacteria, a lysosome fuses with vesicle formed and enzymes digest cells, products absorbed into cytoplasm

Question 61

What does the cell membrane have to do when exocytosis and endocotosis take place?

Answer 61

Change shape and requires energy (uses ATP produced by respiration)

Question 62

Pinocytosis

Answer 62

Uptake of liquid by the same mechanism (vesicles are smaller though)