Download Diffusion and Membranes


4 methods by which substances (eg. Oxygen, Carbon Dioxide, Water, Amino acids, Fatty acids, Sugars, Vitamins,
Mineral ions, hormones etc) move across cell membranes
 DIFFUSION
 FACILITATED DIFFUSION
 OSMOSIS
 ACTIVE TRANSPORT

The cell membrane is selectively permeable
 some particles are small enough to fit through pores in the membrane
 some are helped through
 large molecules restricted
 molecules such as water, carbon dioxide, oxygen can pass through easily
 glucose and ions can move through channels with the assistance of transport proteins

Movement of particles from a region of HIGH CONCENTRATION to a region of LOW
CONCENTRATION

Aims to achieve equilibrium (will continue to occur whilst there is a CONCENTRATION GRADIENT)

DOES NOT require energy

In cells, it is driven by concentration differences across the membrane

Diffusion rate can be increased by
 increase in particle concentration (i.e. Concentration gradient made steeper)
 smaller solute size
 high temperatures

Molecule aided across a
membrane by attachment
to a specific carrier
molecule

Speeds up the rate of
diffusion of particular
molecules

Substances moved by
facilitated diffusion usually
cannot diffuse by
dissolving in the lipid
bilayer

Large polar and non-polar
molecules need carrier
proteins to move through
the membrane
(eg. Glucose)
Active Transport
EXAMPLES

Sodium – Potassium Pump
-Uses energy to exchange
Na+ for K+
- This then drives other
active transport
mechanisms
ENERGY REQUIRING (ENDERGONIC)
Proton Pumps
-Uses energy to move H+
ions from inside to outside
the cell
- The potential (charge)
difference is then used to
drive other reactions
Net movement of molecules against a concentration gradient
from region of LOW concentration to a region of HIGH
concentration

Allows cells to maintain stable internal conditions despite
outside conditions

Can select which molecules move into or out of the cell via
specific carrier molecules in the membrane

ATP transfers a phosphate molecule to a carrier protein
(ATP  ADP + Pi) ------ENERGY REQUIRED
- carrier protein changes shape
- allows substance bound to it to move across the
membrane
VIDEO –
OSMOSIS THE
BASICS

The net movement of WATER molecules from a low concentration solution
(high water content) to a high concentration solution (low water content)
through a semi-permeable membrane
 DOES NOT require energy
 Cells with maximum water = TURGID
 Cells with low water content = FLACCID
 PLASMOLYSIS is the process of water being
lost from plant cells
PROCESS
DEFINITION
PART OF THE
CELL INVOLVED
PASSIVE/
ACTIVE
EG. OF MATERIAL
MOVED
DIFFUSION
Movement of particles from a region of HIGH
concentration to a region of LOW
concentration
Cell Membrane, various
organelles
Passive
Carbon dioxide, Oxygen,
Ethanol, Glycerol
FACILITATED
DIFFUSION
Same as diffusion but aided by attachment to
a specific carrier molecule (IONOPHORE) to
pass across a membrane. May involve
transport proteins or channel proteins
Cell membrane (Carrier
proteins, Channel
proteins)
Passive or
Active
Simple sugars, amino acids,
nucleotides, charged ions
OSMOSIS
Net movement of WATER molecules from a
region of HIGH concentration to a LOW
concentration through a semi-permeable
membrane
Cell membrane, various
organelles
Passive
Water
ACTIVE
TRANSPORT
Movement of particles against a
concentration gradient from a region of LOW
concentration to a region of HIGH
concentration
Cell membrane (Carrier
proteins)
Active
Glucose, some ions
ENDOCYTOSIS
The movement of solids or liquids into the
cell
Cell membrane, vesicles
Mostly
passive
Various usually large
particles such as digestive
enzymes, hormones, toxins
EXOCYTOSIS
The movement of solids or liquids out of the
cell (usually via vesicles)
Cell membrane, vesicles
Mostly
passive
Various usually large
particles such as digestive
enzymes, hormones, toxins
PINOCYTOSIS
Endocytosis involving the movement of
LIQUIDS into the cell
Cell membrane, vesicles
Mostly
passive
Liquids
PHAGOCYTOSIS
Endocytosis involving the movement of
foreign material (mostly solids) into the cell
for diigestion
Cell membrane, vesicles
Mostly
passive
Solids (usually foreign
matter such as bacteria
BULK
TRANSPORT
VIDEO: CRASH
COURSE CELL
MEMBRANES &
TRANSPORT

FUNCTION:
Acts as a SELECTIVE BARRIER between the inside of the cell and external fluid
 Regulates the transfer of substances into and out of the cell. Supplying nutrients and removing
wastes
 Utilises the processes of DIFFUSION & ACTIVE TRANSPORT
 Width is usually 7 – 10 nm

PHOSPHOLIPID BILAYER
HYDROPHOBIC tails form a non-polar hydrophobic interior
(VERY INSOLUBLE IN WATER – NON-POLAR)
HYDROPHILIC ends face the aqueous medium and are
polar
(VERY SOLUBLE IN WATER)

The hydrophobic head tends to dissolve in water and the hydrophobic tails are repelled and force inward forming
a PHOSPHOLIPID BILAYER

Phospholipids are capable of sideways movement

Specialised protein molecules are also embedded in a ‘mosaic’ pattern

Proteins and lipids can flip around in the membrane
- protein molecules in the membrane have particular functions and can carry a sugar molecule
(GLYCOPROTEIN)

Glycoproteins are often receptors/marker molecules important in cell recognition

The lipid structure gives it the property of being flexible and able to repair itself

Allows it to change shape and for vesicles to be pinched off from them or fuse to it
PERMEABLE SUBSTANCES
Small hydrophobic molecules
 Oxygen, Carbon Dioxide, Nitrogen
NON-PERMEABLE SUBSTANCES
Ions
 Na+, H+, K+, Mg+, Cl-, HCO3-
Small uncharged polar molecules
 Water, Glycerol, Ethanol
Larger uncharged molecules
 Amino acids, Nucleotides, Glucose
PHOSPHOLIPIDS:
The bilayer structure means the non-polar tails act as a barrier for
ions and watersoluble substances

CHOLESTEROL:
Help regulate the fluidity of the membrane preventing it from
becoming too rigid. Mechanical stability so membranes don’t
break easily

PROTEINS:
Transport Proteins: provide hydrophilic channels for ions & polar
molecules. Specific for the molecule being transported. Some are
enzymes which may catalyse reactions. Can be gated or nongated. Gated are important for Ca+, Na+ & K+ and muscle/nerve
operation

Cell Adhesion Proteins: attach adjacent cells to one another
Hormone Binding Proteins: allow hormones to bind to them
and a signal is transmitted to inside of the cell
Cell Recogniition Proteins: allows the cell to be recognised as
‘self’ or ‘foreign’ and act as markers
GLYCOLIPIDS & GLYCOPROTEINS:
Carbohydrate chains are often
attached to the lipids and proteins of the outer membrane. These are
known as glycolipids and glycoproteins. Project out into watery fluids
surrounding the cell where they form hydrogen bonds with water. They
help stabilise the membrane structure. Can act as receptor molecules for
hormones or neurotransmitters. Are the basis for cell ANTIGENS.

*may be called glycocalyx
CELL MEMBRANE
and PROTEINS

SOLVENT: a liquid in which a substance is dissolved in (H2O is the UNIVERSAL SOLVENT)

SOLUTE: particles/molecules that are dissolved in the solvent

SOLUTION: the mixture of dissolved particles in the solvent

HYPERTONIC: A highly concentrated solution (high solute)
- water molecules will diffuse OUT OF cells in a hypertonic solution

HYPOTONIC: A low concentrated solution (low solute)
- water molecules will diffuse INTO cells in hypotonic solution

ISOTONIC: A solution with the same concentration as its surrounding
- water molecules will NEITHER move into or out of cells in an isotonic
solution
(concentration inside and outside the cell are equal)
Cellular Structure and Function
Which of the following factors does NOT affect the rate of diffusion
across a membrane?
A) the number of different types of particles in a solution
B) the temperature of a solution
C) the size of the diffusing particles
D) the concentration gradient across the cell membrane
Free to share, print, make copies and changes. Get yours at www.boundless.com
Cellular Structure and Function
Which of the following factors does NOT affect the rate of diffusion
across a membrane?
A) the number of different types of particles in a solution
B) the temperature of a solution
C) the size of the diffusing particles
D) the concentration gradient across the cell membrane
Free to share, print, make copies and changes. Get yours at www.boundless.com
Boundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/
Cellular Structure and Function
In a beaker separated by a membrane permeable only to water, one
area has a high solute concentration and the other has a low solute
concentration. What do you expect will happen in the beaker?
A) Water will move to the area of low solute concentration.
B) Water will move to the area of high solute concentration.
C) Water will move to the area of high water concentration.
D) The solute will move to the area of low solute concentration.
Free to share, print, make copies and changes. Get yours at www.boundless.com
Cellular Structure and Function
In a beaker separated by a membrane permeable only to water, one
area has a high solute concentration and the other has a low solute
concentration. What do you expect will happen in the beaker?
A) Water will move to the area of low solute concentration.
B) Water will move to the area of high solute concentration.
C) Water will move to the area of high water concentration.
D) The solute will move to the area of low solute concentration.
Free to share, print, make copies and changes. Get yours at www.boundless.com
Boundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/
Cellular Structure and Function
You take a sample of blood cells and place them in a solution. Fifteen
minutes later, you observe that they appear shriveled. What is the
tonicity of the solution they were placed in?
A) Hypotonic
B) Isotonic
C) Hypertonic
D) Equitonic
Free to share, print, make copies and changes. Get yours at www.boundless.com
Cellular Structure and Function
You take a sample of blood cells and place them in a solution. Fifteen
minutes later, you observe that they appear shriveled. What is the
tonicity of the solution they were placed in?
A) Hypotonic
B) Isotonic
C) Hypertonic
D) Equitonic
Free to share, print, make copies and changes. Get yours at www.boundless.com
Boundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/
Cellular Structure and Function
Which of the following characteristics distinguishes facilitated
transport from simple diffusion? Passive transport ______________.
A) uses membrane proteins and channels to move molecules down
concentration gradients.
B) requires the input of cellular energy to transport biomolecules.
C) describes the movement of biomolecules such as proteins, carbohydrates,
and fatty acids.
D) explains the movement of molecules or ions from high to low concentration.
Free to share, print, make copies and changes. Get yours at www.boundless.com
Cellular Structure and Function
Which of the following characteristics distinguishes facilitated
transport from simple diffusion? Passive transport ______________.
A) uses membrane proteins and channels to move molecules down
concentration gradients.
B) requires the input of cellular energy to transport biomolecules.
C) describes the movement of biomolecules such as proteins, carbohydrates,
and fatty acids.
D) explains the movement of molecules or ions from high to low concentration.
Free to share, print, make copies and changes. Get yours at www.boundless.com
OpenStax OER. "OpenStax College." CC BY 3.0 http://openstaxcollege.org/
Cellular Structure and Function
Which of the following statements about channel proteins is true?
A) They change shape as they move molecules across a membrane.
B) Polar compounds pass through them to avoid nonpolar regions.
C) All of them are open at all times to allow passage of materials.
D) all of these answers
Free to share, print, make copies and changes. Get yours at www.boundless.com
Cellular Structure and Function
Which of the following statements about channel proteins is true?
A) They change shape as they move molecules across a membrane.
B) Polar compounds pass through them to avoid nonpolar regions.
C) All of them are open at all times to allow passage of materials.
D) all of these answers
Free to share, print, make copies and changes. Get yours at www.boundless.com
Boundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/
Cellular Structure and Function
Which of the following statements about passive transport is true?
A) Membrane proteins are always needed in order for it to take place.
B) Substances move from areas of low concentration to areas of high
concentration.
C) The input of ATP is required in order to facilitate transportation.
D) Substances move from areas of high concentration to areas of low
concentration.
Free to share, print, make copies and changes. Get yours at www.boundless.com
Cellular Structure and Function
Which of the following statements about passive transport is true?
A) Membrane proteins are always needed in order for it to take place.
B) Substances move from areas of low concentration to areas of high
concentration.
C) The input of ATP is required in order to facilitate transportation.
D) Substances move from areas of high concentration to areas of low
concentration.
Free to share, print, make copies and changes. Get yours at www.boundless.com
Boundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/
Cellular Structure and Function
How does active transport move substances against the
electrochemical gradient?
A) Sodium and potassium help push substances across membranes.
B) ATP causes red blood cells to break down membranes.
C) With the help of ATP, pumps move substances across membranes
D) all of these answers
Free to share, print, make copies and changes. Get yours at www.boundless.com
Cellular Structure and Function
How does active transport move substances against the
electrochemical gradient?
A) Sodium and potassium help push substances across membranes.
B) ATP causes red blood cells to break down membranes.
C) With the help of ATP, pumps move substances across membranes
D) all of these answers
Free to share, print, make copies and changes. Get yours at www.boundless.com
Boundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/
Cellular Structure and Function
What is the difference between phagocytosis and pinocytosis?
A) Phagocytosis takes in large food particles, while pinocytosis takes in liquid
particles.
B) Phagocytosis takes in carbohydrates, while pinocytosis takes in lipids.
C) Phagocytosis takes in cations, while pinocytosis takes in anions
D) Phagocytosis takes in caveolin, while pinocytosis takes in clathrin.
Free to share, print, make copies and changes. Get yours at www.boundless.com
Cellular Structure and Function
What is the difference between phagocytosis and pinocytosis?
A) Phagocytosis takes in large food particles, while pinocytosis takes in liquid
particles.
B) Phagocytosis takes in carbohydrates, while pinocytosis takes in lipids.
C) Phagocytosis takes in cations, while pinocytosis takes in anions
D) Phagocytosis takes in caveolin, while pinocytosis takes in clathrin.
Free to share, print, make copies and changes. Get yours at www.boundless.com
Boundless - LO. "Boundless." CC BY-SA 3.0 http://www.boundless.com/