Core concept: Cell (plasma) membranes and transport

Question 1

what is the model of the plasma membrane, and why is it called this?

…. …. model

Answer 1

fluid mosaic model
Fluid – because the phospholipid molecules within a layer can move relative to each other.
Mosaic – because the proteins within the phospholipid layer are of different sizes and shapes and form different patterns.

Question 2

how permeable are plasma membranes ?
how can it be increased?

Answer 2

Cell membranes are selectively permeable. They only allow certain molecules through.
Permeability can be increased by:
* Temperature – increases above 40C increase vibrations of phospholipids, moving them further apart.
* Organic solvents – dissolve phospholipids.

Question 3

how do molecules move through the plasma membrane?

Answer 3

Lipid soluble substances (vit A) and small molecules (O2 and CO2) can dissolve and move directly through the phospholipid bilayer.
Water soluble substances (glucose, ions, all polar molecules) cannot pass through the hydrophobic fatty acid tails and so must use intrinsic proteins to pass though.

Question 4

components of the phospholipid bilayer and their propeties?

just the phospholipid bilayer not the plasma membrane

Answer 4

The hydrophilic phosphate heads of the phospholipids arrange themselves facing outwards forming the outer and
inner surface of the cell membrane.

hydrophobic fatty acid tails arrange themselvs pointing toward eachother inwards

Question 5

what are extrinsic proteins
what is their funtion
what group can they have added to them
the function of this product.

Answer 5

polar proteins that are on either surface of the bilayer and provide strucural support. they can have sugar groups attatched (glycoproteins) which form recognition sites for cell to cell recognition and receptor sites for hormone attatchment

Question 6

what is the carbohydrate layer around the plasma membrane called?

Answer 6

glycocalyx

Question 7

what is the role of cholesterol

Answer 7

improves the Stability and Rigidity of the cell

Question 8

what are intrinsic proteins
name the two types
and their mechanism

Answer 8

non polar proteins that extend across both layers of the bilayer and function for transport of molecules
channel proteins-pores lined with polar (hydrophilic) groups that allow charged ions through, e.g. Na+.
carrier proteins -allow larger polar molecules through, such as water-soluble sugars and amino acids. Binding of the molecules changes the shape of the protein moving the substance into or out of the cell. involved in active transport

Question 9

define water potential (ψ)

Answer 9

a measurement of the free energy of water molecules, measured in kilopascals (KPa)

Question 10

Define osmosis

Answer 10

The diffusion of water, from a region of high water potential to a region of lower water potential through a selectively permeable membrane.

Question 11

what is the name of the protein that allows osmosis ?

Answer 11

aquaporin

Question 12

define turgid

Answer 12

when the plant cell that holds as much water as possible. further entry of water is prevented as the cell wall cannot expand further.

Question 13

define pressure potential (ψp)
how does this affect the tendency of water molecules

move in or out

Answer 13

the pressure applied to the cell wall by the cells contents (increases the tendency of water to move out )

Question 14

define solute potential (ψs)
how does this affect the tendency of water molecules

move in or out ?

Answer 14

a measure of the osmotic strength of a solution. it is the reduction in water potential due to the presence of dissolved solute molecules. (higher less liklely water is to move out)

Question 15

water potential of a cell is equal to ?

Answer 15

pressure potential + solute potential

Question 16

define hypertonic

Answer 16

low water potential due to high concentration of solutes (water moves in)

Question 17

define hypotonic

Answer 17

high water potential due to low concentration of solutes ( water moves out)

Question 18

define isotonic

Answer 18

means the same concentration of solute and the same water potential, so no net movement of water between the two solutions.

Question 19

define plasmolysed
why does this happen

Answer 19

The retraction of the cell membrane and cytoplasm from the cell wall due to loss of water by osmosis

Question 20

define incipient plasmolysis
what is the pressure potential

Answer 20

when the cell membrane and cytoplasm are partially detatched from the cell wall due to insuffiecient water to make the cell turgid (the pressure potential is 0)

Question 21

explain what happens to plant cells when placed in different solutions.

hyptonic , isotonic and hypertonic

Answer 21

hypotonic solution- water moves into the cell by osmosis causeing the cell to become turgid
isotonic solution- no net movemtent of water cell becomes incipient plasmolysed
hypertonic solution- water moves out of the plant cell by osmosis cell becomes plasmolysed

Question 22

Explain how and why this is different in animal cells what would be observed

placing the cell in hypotonic isotonic and hypertonic solutions

Answer 22

In hypotonic solution water moves in by osmosis and animal cells burst due to the absence of a cell wall and the increased pressure cannot be withstood by the cell membrane
isontoic cell remains normal must be in an isotonic solution
hypertonic water moves out of the cell by osmosis and cell shrinks

Question 23

Define diffusion

Answer 23

the passive movement of a molecule or ion from an region of high concentration to a region of lower concentration, down a concentration gradient

Question 24

How can the rate of diffusion be increased

6 points

Answer 24

higher concentration gradient
increased surface area
short diffusion pathway
increase in temperature
smaller molecules
lipid soluble or non polar molecules

Question 25

Describe the graph for diffusion and the effect of a respiratory inhibitor(cyanide) on the rate

Answer 25

rate of diffusion is directly proportional to the concentration gradient, cyanide has no effect as difusion is a passive process requiring no ATP

Question 26

Define facilitated diffusion

Answer 26

The passive transfer of molecules or ions down a concentration gradient, across a membrane, by transport proteins in the membrane

Question 27

Describe the graph for facilitated diffusion and the effect of a respiratory inhibitor(cyanide) on the rate

Answer 27

increases until the maximum rate is reached as a result of number of open channels becoming the limiting factor so the graph Plateaus cyanide has no effect as it is a passivve process no ATP is required

Question 28

Define active transport

Answer 28

The movement of molecules or ions across a membrane against a concentration gradient, using energy from the hydrolysis of ATP

Question 29

What intrinsic protein is used for active transport

Answer 29

carrier protein

Question 30

Mechanism for active transport

Answer 30

The ATP activates carrier proteins to move molecules across the cell membrane. This changes its shape transporting the molecules

Question 31

Describe the graph for active transport and the effect of a respiratory inhibitor(cyanide) on the rate

Answer 31

increases until the maximum rate is reached as a result of number of open channels becoming the limiting factor so the graph Plateaus, cyanide prevents more ATP from being made so the graph then decreases

Question 32

What intrinsic protein is used for co-transport

Answer 32

carrier

Question 33

Define co-transport
Provide an example

Answer 33

A transport mechanism in which facilitated diffusion brings molecules and ions across the cell membrane together in the cell ( uses the same protein at the same time)
2Na+ and glucose

Question 34

The mechanism for co-transport

Answer 34

molecules attach to a carrier protein on the outer side of the membrane. This changes the shape of the protein sufficiently to flip them to the inside of the membrane

Question 35

name two mechanisms of bulk transport Bulk transport

Answer 35

endocytosis
exocytosis

Question 36

Describe the process of endocytosis

3 step

Answer 36

1. Plasma membrane folds inwards.
2. Plasma membrane engulfs the material.
3. Vesicle formed from plasma membrane enters the cell.

Question 37

Define phagocytosis

Answer 37

active process of the cell membrane englufing large particles bringing them into the cell in a vesicle

Question 38

Define pinocytosis

Answer 38

the active process of the cell membrane engulfing droplets of liquid bringing them into the cell in a vesicle

Question 39

Describe the process go exocytosis and is it
Is it passive or active

3 step.

Answer 39

vesicles are made and transported from the golgi body and
move across the cytoplasm to the memebrane
vesicle fuses with the membrane and contents are expelled out
active as ATP is used to transport the vesicle across the cytoplasm