cell membrane and transport

Question 1

cell membrane contents

Answer 1

made up of entirely proteins and phosolipids
Membrane contains glycoproteins, glycolipids and sterols

Question 2

Phospholipids in membrane

Answer 2

Forms by layers, one sheet of phospholipid molecules opposite another
Inside layer - hydrophilic, heads pointing in towards cell, intercat w water in cytoplasm
Outer layer - hydrophyllic head pointing outwards interacting with water surrounding cell
Hydrophobic tails of both layers point towards each other to centre of membrane
Phospholipid component of membrane allows lipid soluble molecules across but non water soluble molecules are not

Question 3

Proteins in membrane

Answer 3

Scattered throughout bilayer of membrane

Question 4

Extrinsic proteins

Answer 4

On either surface of Bilayer, provide structural support and form recognition sites by identifying cells and receptor sites for hormone attachment

Question 5

Intrinsic proteins

Answer 5

Extend across both layers of Bilayer. The transport proteins, which use active or passive transport to move molecules and ions across cell membrane

Question 6

fluid mosaic model of membrane structure

Answer 6

Introduced by singer and Nicholson in 1972

Question 7

Why is it called fluid mosaic

Answer 7

Individual phospholipid can move within a layer relative to one another (fluid)
Proteins embedded in bilayer vary in shape and size among phospholipid (mosiac)

Question 8

Cholesterol in animal cell membrane

occurs between

Answer 8

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

Question 9

Glycocalyx

Answer 9

Carbohydrate layer around cell
Some molecules in this have roles as hormone receptors, in cell to cell recognition and in cell to cell cohesion

Question 10

Permeability of membranE
Eg O and CO2

Answer 10

Small molecules move between phospholipid molecules and diffuse across the membrane
Eg. Oxygen and carbon dioxide

Question 11

Lipid soluble substances

Answer 11

Dissolve in phospholipid and diffuse across membrane
Phospholipid layer is hydrophobic so liquid soluble molecules move through the cell membrane more easily than water soluble substances
Eg. Vitamin A
DIFFUSION

Question 12

water soluble substances

Answer 12

Cannot readily diffuse across membrane through phospholipids and must pass through intrinsic protein molecules which form water filled channels across membrane
Therefore cell surface membrane is selectively permeable to water and some solutes
FACILITATED DIFFUSION

Question 13

Diffusion

Answer 13

Simple diffusion - passive transport
Movement of molecules from a region of high concentration to a region of low concentration eg. Down a concentration gradient until equally distributed

Question 14

Rates of diffusion is affected by
Concentration gradient

Answer 14

The greater difference in concentration of molecules in two areas, the more molecules diffuse in given time

Question 15

Rates of diffusion is affected by
Thickness of exchange surface/ Distance of travel over which diffusion takes place

Answer 15

The thin of the membrane or the shorter the distance, the more molecules diffuse in a given time

Question 16

Rate of diffusion is affected by
Surface area of the membrane

Answer 16

The larger the area, the more molecules have room to diffuse across in a given time

Question 17

Rate of diffusion equation

Answer 17

SA x diff in conc/ length of diffusion pass

Question 18

Other factors affecting rate

Answer 18

• Size of the diffusing molecule: smaller molecules diffuse faster than larger, higher KE o pass thru PP molecules
• Nature of diffusing molecule: fat soluble molecules diffuse faster than water soluble and non polar molecules diffuse faster than polar

Temperature: increase temperature increases rate, as molecules have more KE

Question 19

Facilitated Diffusion

Answer 19

‘made easier’
- Allows movement of insoluble molecules across membrane
- Passive transfer of molecules or ions down a concentration gradient, across a membrane, by channel or carrier protein molecules in the membrane

Question 20

Channel proteins

Answer 20

Molecules with pores lined with polar groups
As the channel are hydrophilic, ions are water soluble so can pass through
Channels open and close according to needs of the cell

Question 21

Carrier proteins

Answer 21

Allows the fusion of larger polar molecules across membrane
Eg. Sugars and amino acids
Molecule attaches to binding site on carrier protein
Carrier protein changes shape and releases molecule on the other side of membrane before changing back to its original shape

Question 22

Active transport

Answer 22

Movement of molecules across a membrane against the concentration gradient using energy from the hydrolysis of ATP

Question 23

Features of active transport

Answer 23

• Ions and molecules are moved from a lower to higher concentration eh. Against concentration gradient
• Process requires energy from ATP. Anything that affects respiration will affect active transport
• Process occurs through intrinsic carrier proteins spanning membrane
• Rate is limited by number and availability of carrier proteins

Question 24

Active uptake of single molecule
1

Answer 24

• molecule/ion combines with specific carrier protein on outside of membrane

Question 25

Active uptake of single molecule
2

Answer 25

• ATP transfers phosphate group to carry a protein on outside of membrane

Question 26

Active uptake of single molecule
3

Answer 26

• Carrier protein changes shape and carries molecule across the membrane to the inside of cells
• Molecule released into cytoplasm

Question 27

Active uptake of single molecule
4

Answer 27

Phosphate ion released from carrier molecule back to cytoplasm and recombines with ADP to form ATP
Carrier protein returns to original shape

Question 28

Active transport and respiration

Answer 28

At a higher concentration difference across a membrane, the rates of uptake increases and reaches a plateau at which the carrier proteins are saturated and all solute binding sites are occupied
Rate of uptake is reduced with an addition of respiratory inhibitor implying process requires ATP and so active transport must be taking place

Question 29

Cyanide

Answer 29

A respiratory inhibitor which prevents aerobic respiration and production of atp in the mitochondria
Without ATP, active transport cannot occur so cyanide reduces active transport

Question 30

Active transport and respiration - experiments in oxygen

Answer 30

Experiments shown an increase in active transport if more oxygen is available to the cells, When it was previously limiting
Indicates active transport as the oxygen would have increased the production of ATP by aerobic respiration

Question 31

Co transport

Answer 31

Transport mechanism in which facilitated diffusion brings molecules and ions across the cell membrane together into the cell

Question 32

Difference between active transport and facilated diffusion

Answer 32

AT:
Uses membrane proteins
Pumps against a concentration gradient.
Requires energy
Occurs in living cells

FD:
Use membrane proteins
Passively moves particles down a concentration gradient.
No need of energy
cell doesn’t need to be alive

Question 33

Osmosis

Answer 33

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 34

Water potential

Answer 34

Tendency for water to move into a system, water moons from a solution with high water potential (less neg) to one with a lower water potential (more neg)
what the potential is decreased by addition of solute
Pure water has a water potential of zero as there’s no tendency for water molecules to move into pure water

Question 35

Solute potential

Answer 35

Measure of osmotic strength of a solution
Reduction in water potential due to presence of solute molecules
The more solid presence, the more tightly water molecules are held, the lower the tendency of water to move out. So a higher concentration solution has a lower, more negative solid potential

Question 36

turgid

Answer 36

A plant cell that holds as much water as possible. feather entry of waters prevented as the cell wall cannot expand further

Question 37

Pressure potential explain

Answer 37

Water entering a plant cell by osmosis expands the vacuum and pushes cytoplasm against the cell wall. Pressure outwards builds up, resisting entry of more water- turgid
Prussia is a pressure potential, and as it is a push outwards= positive sign

Question 38

Water potential equation

Answer 38

water potential of cell= pressure P + solute P

Question 39

Pressure potential definition

Answer 39

The hydrostatic pressure exerted by the cell contents on the cell wall. it is equal and opposite to the pressure exerted by the cell Wall on the cell

Question 40

plasmosysis

Answer 40

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

Question 41

incipient plasmosysis

Answer 41

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

Question 42

hypotonic

Answer 42

if the water potential of external solution is LESS negative ( higher) than solution in cell, external solution is HYPOTONIC to the cell and water flows into the cell

Question 43

hypertonic

Answer 43

if the water potential of external solution is MORE negative ( lower) than solution inside cell, external solution is HYPERTONIC to the cell and water flows out of the cell

Question 44

isotonic

Answer 44

if the cell has the same water potential as the surrounding solution, the external solution and cell are isotonic and there is no net movement

Question 45

plasmosyis process

Answer 45

Plant cells in a hypertonic solution lose water by osmosis. Process is plasmolysis and when complete the cell is flaccid - floppy
Plant wilts- cells can’t provide support

Question 46

Incipient plasmolysis process

Answer 46

If the external concentration is high enough that the South has lost just enough water that its membrane begins to be pulled away from the cell wall, the cell is at incipient plasmolysis
Salworld does not exert any pressure on the cytoplasm so there is no pressure potential= 0

Question 47

A plant cell in a hypotonic solution

Answer 47

Takes in water until prevented by the opposing pressure from cell wall
As water enters the cells, The contents expand and push out more on the cell wall, increasing the pressure potential.
The pressure potential rises until it is equal and opposite to the pull inwards of solute potential. No more water can enter and as there is no tendency for the cell to absorb water- water potential is 0
Pp= -Sp

Question 48

significant of turgor to plants

Answer 48

Provide support, maintains their shape and holds them upright

Question 49

Osmosis and animal cells

Answer 49

An animal cell has no cell wall and so pressure potential isnt considered
Water potential= solute potential

Question 50

Haemolysis

Answer 50

if red blood cells are in distilled water, water enters by osmosis and without a cell wall they burst

Question 51

Red blood cells in concentrated salt solution

Answer 51

Water leaves the cells and they shrink becoming crenated

Question 52

Endocytosis

Answer 52

Active process of the cell membrane engulfing material, bringing it into the cell in a vesicle
Two types: phagocytosis and pinocytosis

Question 53

Exocytosis

Answer 53

Active process of a vesicle fusing with the cell membrane, releasing the molecules it contains

Question 54

Phagocytosis

Answer 54

Active process of the cell membrane engulf in large particles, bringing them into the cell in a vesicle

Question 55

pinocytosis

Answer 55

Active process of the sound membrane engulfing droplets of fluid, bringing them into the cell of a vesicle

Question 56

When endocytosis and exocytosis occur

Answer 56

Cell membrane has to change shape this requires energy. Processes are therefore active, using ATP, generated by the cells respiration.
In both cases the cell membrane flows. The property of fluidity of the cell membrane is essential for these processes to occur