The document discusses cell membranes and transport across membranes. It begins by explaining the structure of membranes, noting they are composed of a phospholipid bilayer with hydrophobic and hydrophilic regions. Membrane proteins embedded in the bilayer perform various functions and transport roles. The document then describes six types of transport across membranes: diffusion, osmosis, facilitated diffusion, active transport, endocytosis, and exocytosis. It explains the differences between passive and active transport, and provides examples of protein transporters involved in each.

1. 2.4 MEMBRANES
2.4.1 Draw and label a diagram to show the structure of a membrane
2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of
cell membranes
2.4.3 List the functions of membrane proteins
2.4.4 Define diffusion and osmosis
2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion
2.4.6 explain the role of protein pumps and ATP in active transport across membranes
2.4.7 explain how vesicles are used to transport materials within a cell between the rough E.R., G.A., and plasma
membrane
2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis
and exocytosis
Membrane Structure: p.21-30
See Fig 2.13 p. 50
Polar Hydrophilic Region
(water loving)
Non-Polar Hydrophobic Region
(water hating)
See Cross-Sectional View of the Phospholipids bilayer Fig 1.19 p. 21. What is the functional
implication of having a double layer of phospholipids?
GO TO YOUR WORKBOOK P. 93 AND USE FIG. 1.17 P. 21 TO ANNOTATE THE DIAGRAM
BELOW
A: glycoprotein (carbohydrate attached) to
extrinsic protein
B: carbohydrate (attached to lipid – glycolipid)
C: intrinsic protein
D: carbohydrate (glycolipid)
E: cholesterol
F: phospholipid
inside cells - cytoskeleton

2. Proteins: - embedded into Fluid Matrix
- Integral Proteins: all the way through
- Peripheral Proteins: surface only
Basic Structure: chain of amino acids = Proteins
There are 20 different amino acids
http://www.teachersparadise.com/ency/en/media/c/c5/amino_acids_2.png
Their 6 general functions are:
 Hormone binding sites – exterior fits the shape of specific hormones  change of protein shape 
message into cell
 Enzymatic action – catalyze chemical reactions
 Cell adhesion – hook together  permanent & temporary connections
 Cell-to-cell communication – have carbohydrates attached / labels type & species of cell
 Channels for passive transport – passageway for substances to pass through
 Pumps for active transport – shuttles substances across the membrane by changing shape

3. Carbohydrate (sugar) attached to proteins act as distinctive antigens by which cells can recognize
each other
- glycoprotein -when attached to a protein, the complex is called a glycoprotein
- glycolipids -also exist in the cell membrane, a carbohydrate portion attached to a lipid molecule
Cholesterol is also present in the plasma membrane. Cholesterol is a LIPID (fat-like molecule)
that gives rigidity and strength to the plasma membrane, and is found in the hydrophobic area
Transport Across the Membrane: (IB learning Outcomes 2.4.4 2.4.8 p. 22-30)
- The structure of the cell surface membrane, the nuclear membrane and the membranes of the
organelles allow them to be selectively permeable, and provide for a variety of transport
mechanisms.
- Control of the exchange across membranes depends on the physical and chemical properties of
the membrane and the molecules moving through them.
Passive Transport Active Transport
VS
Movement = down the concentration gradient Movement =against the concentration gradient
High  Low Low  High
NRG not required – KMT provides all req. nrg NRG required = ATP from cell metabolism

4. Biology 11 IB Earland
Transport Types
1. Diffusion (passive transport – no energy required)
- the movement of molecules from an area of high concentration to low (down a
concentration gradient
- caused by random movement of molecules (Brownian motion) – dependent on
temperature, size of the molecules, and size of the gradient
- in cells, diffusion is limited to small molecules and ions that freely move across the
membrane: water, oxygen and carbon dioxide, lipid soluble molecules
- Recall: the rate of diffusion is instrumental in determining cell size
2. Osmosis (passive transport)
- the movement of water from an area of high concentration of water (low concentration
of solute) to low concentration of water (high concentration of solute) through a
SELECTIVELY permeable membrane
- described in terms of tonicity of the solution with respect to the cell
- hypertonic solution: has a higher
concentration of solute
- hypotonic solution: has a lower concentration of solute
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5. Biology 11 IB Earland
- isotonic solution: has the same concentration of solute
3. Facilitated Diffusion
- involves the use of transport proteins
that are specific to certain solutes –
with specific binding sites
- it is believed that the protein changes
shape to allow the transport of a solute
down a concentration gradient
4. Active Transport (active – requires an energy input from the cell)
- involves the use of transport proteins, but takes place against a concentration gradient
- ex: the Na+/K+ pump
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6. Biology 11 IB Earland
5. Endocytosis (active)
- used to transport larger molecules across the membrane and INTO the cell
- there are two types of endocytosis (both consume cell membrane)
- pinocytosis – the cell gulps in extracellular fluid into small vesicles
- phagocytosis – the cell extends pseudopodia and wraps the particles into a vacuole,
which will later fuse with a lysosome for digestion
6. Exocytosis (active)
- used to transport large molecules out of the cell – usually vesicles budded from the
ER or GA
- a vesicle will move towards and fuse with the cell membrane, spilling its contents into the
extracellular fluid
- exocytosis and endocytosis generally balance each other resulting in no change in the size
of the cell
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