3.2.3 Transport Across Membranes

Question 1

Functions of cell membranes?

Answer 1

Define the boundary of the call
Control in and out of substances in the cell
Plays a role in cell recognition
Allows cell to change shape
Helps cells stick together
Provides receptor sites for hormones and enzymes

Question 2

Function of internal membranes?

Answer 2

Compartmentalisation: isolating organelles from the rest of the cytoplasm allowing cellular processes to occur separately

A site for biochemical reactions

Controls which substances go in and out of

Question 3

What are the main molecular components of a membrane?

Answer 3

Phospholipids
Proteins
Glycoproteins
Glycolipids
Cholesterol

Question 4

What does the fluid mosaic mean?

Answer 4

Fluid: individual phospholipids and move laterally and change places with each other

Mosaic: when seen from above the membrane is like a mosaic of phospholipids with proteins of different shapes and sizes embedded in it

Question 5

What organelles have a double membrane?

Answer 5

Mitochondria and nucleus

Question 6

In terms of transport what are the 2 types?

Answer 6

Passive- no energy needed

Active- energy needed using ATP

Question 7

What are the 5 ways substances can cross a membrane and is it passive or active ?

Answer 7

Passive:
Diffusion- simple
Diffusion - facilitated
Osmosis

Active:
Active transport and Co-transport

Question 8

Explain simple diffusion

Answer 8

High conc—> low conc

Question 9

What is NET movement?

Answer 9

Overall/total particles mived

Question 10

What is Ficks law?

Answer 10

Rate Of Diffusion=
Surface Area x Difference in conc.
•/•
Thickness Of Exchange Surface

(ROD= SAD •/• TOES)

Question 11

What affects Ficks law?

Answer 11

SA- increase in SA means faster rate
Diffrence in conc-greater the difference the faster the rate
Thickness- the thicker the slower the rate

Question 12

What affects rate of diffusion?

Answer 12

Temp-inc means inc in rate
Conc gradient- inc means inc in rate
Stirring- inc in rate
SA- larger SA=inc in rate
Diffusion distance- thicker= slower
Size-smaller increases the rate of

Question 13

What can diffuse through the cell membrane

Answer 13

Lipid soluble, small water ions (hydrophobic molecules)

Question 14

What is osmosis?

Answer 14

Osmosis is the passage of water molecules from a high water potential to a low water potential through a selectively permeable membrane

Question 15

What is a more concentrated solution called?

Answer 15

Hypertonic

Question 16

What is a less concentrated solution are called?

Answer 16

hypotonic

Question 17

Solutions with the same concentration are called?

Answer 17

isotonic

Question 18

What is a solute and solvent ?

Answer 18

Solute- what you are dissolving
Solvent-liquid

Question 19

What is water potential and what is it measured in?

Answer 19

Water potential is the pressure created by water molecules trying to diffuse out of a solution down the conc. gradient (high-low)
Measured in kilopascals (kPa)

Question 20

What is the water potential of pure water?

Answer 20

0

Question 21

What has a higher water potential -35kPa or -65kPa and what is the movement of water molecules?

Answer 21

-35kPa is higher and moves from -35 to -65 until they are both -50

Question 22

What would happen in a cell with high water potential, equal and low
(Animal cells)

Answer 22

High- net movement in and cell bursts

Equal-nothing happens

Low- net movements out and cell shrinks

Question 23

What is incipient plasmolysis?

Answer 23

Cytoplasm has shrunk away and water left away via osmosis

Question 24

What would happens in a plant cell with a high, equal and low water potential

Answer 24

High- net movement in and cell become turgid

Equal- not net movement (incipient plamolysis-vacuole shrinks a little)

Low- water leave the cell and cell shrinks. It is flaccid and plasmolysed

Question 25

What substances use facilitated diffusion?

Answer 25

Hydrophilic polar molecules Ions(sodium ions) Large molecules (glucose)

Question 26

What is required in facilitated diffusion

Answer 26

Conc. gradient Channel proteins or protein carriers

Question 27

What type of particles are transported by channel proteins?

Answer 27

Ions and small polar molecules

Question 28

What type of molecules are transported by carrier proteins?

Answer 28

Larger polar molecules such as amino acids

Question 29

How do channel proteins work?

Answer 29

Water filled pores lined with polar groups so the channel is hydrophilic Most channels are gated so control entry and exit of ions

Question 30

How do carrier proteins work?

Answer 30

They are able to bind with a specific shaped molecule l. The binding site is alternately open to both sides of the membrane The carrier changes shape to release the molecules to the other side of the membrane

Question 31

What happened to a graph of simple and facilitated diffusion with rate and concentration?

Answer 31

Simple-keeps going in a straight line from the origin (positive correlation) Facilitated- starts the same as simple but at a certain point the proteins can only move a specific number of particles per minute so the graph levels of as rate reaches a constant

Question 32

What is active transport?

Answer 32

Low conc. -> high conc. using ATP and a carrier protein

Question 33

What does ATP do in active transport?

Answer 33

Directly move molecules Use co-transport to indirectly move molecules

Question 34

How does active transport work?

Answer 34

Carrier protein spans plasma membrane and binds to molecule being transported. Molecule bing to regular site. ATP hydrolyses with carrier protein splitting into ADP and Pi. Pi binds to carrier protein (phoshorylating it). Carrier protein changes shape. Opens opposite side and molecule is released. Carrier protein returns to original shape. Pi binds with ADP to form ATP again

Question 35

What is uniport, symport and antiport in co-transport

Answer 35

Uniport- 1 ion in/out in one go Symport- 2 ions in/out in one go Antiport- 1 in and 1 out at the same time

Question 36

How are cells that line the ileum adapted for absorption(small intestine)?

Answer 36

High SA Larger no. Of transport proteins One cell thick

Question 37

How does a sodium potassium pump work?

Answer 37

Na+ in K+ out ATP hydrolyses with carrier protein Pi changes its shape so it allows Na+ out the other side and K+ in