Cell Transport Unit Outline
You should be reviewing every night. Cramming before a test or quiz does not work.
We/I am/are available before or after school to help you with any questions you may have.
Please stop for help if you need it!!
PowerPoint presentations we discussed in class are available on my website under “biology
handouts.”
Sources of information:







Notes that you filled in
Notes written on the board
Intro to Cell Membrane structure web
questions
Labeled cell membrane
Diffusion in Agar Cubes activity
Osmosis in Plant Cells activity
Osmosis Inquiry Egg activity







Transport organizers
PowerPoint (online)
Practice Worksheets
Homework
Quizzes
Study guide and practice questions
Textbook; chapter 7
Unit Outline
1. The Cell Membrane
o Function: the function of the cell membrane is to regulate what enters and leaves a cell
o This is done to maintain homeostasis, a set of constant internal conditions, within living
organisms
2. The Structure of the Cell Membrane
o Lipid bilayer
 Phospholipid structure
 Polar hydrophilic head & non-polar hydrophobic tail
 How these structural properties determine how the lipid bilayer in your
body forms
o The hydrophilic heads point towards the inside and outside of the
cell, which are water based environments
o The hydrophobic tails point towards each other and away from the
water
o Membrane Proteins & their functions
 Membrane proteins are proteins embedded in the phospholipid bilayer and
function in transport of molecules across the membrane (facilitated diffusion)
 Two types of membrane proteins we discussed:
 Channel proteins: involved in passive transport
o Molecules pass through a channel in the protein
 Transport proteins: involved in active transport
o Molecules go into the transport protein on one side of the
membrane and energy is used to change the transport proteins
shape, and molecules are “dropped off” on the other side of the
membrane
o Carbohydrates
 Carbohydrates stick out on the outside of the cell membrane and serve the
function of cellular recognition and signaling
o Glycoproteins (proteins with a carbohydrate [glyco- prefix] attached to it)
 Glycoproteins are embedded in the phospholipid bilayer and serve the function of
cellular recognition and signaling
o Cholesterol
 Cholesterol molecules are embedded in the phospholipid bilayer to give the
membrane some stiffness/rigidity and stability
o Why the model of cell membrane is called “Fluid Mosaic”
 Fluid: the cellular membrane is fluid and flexible; this structure allows the
membrane to perform its function and for cells to move around in the body
 The phospholipids are considered the “fluid” part of the fluid mosaic
model
 Mosaic: the membrane proteins embedded within the phospholipids give the look
of a mosaic
o Why the cell membrane is described as selectively permeable a.k.a. semipermeable
 Permeable: have pores or openings which allow the passage of molecules
 Some substances are let through, others are not – “selective”
 It is important that the membrane be selectively permeable, otherwise it wouldn’t
there would be no regulation of what goes in or out
3. Passive Transport:
o Passive transport does not require energy
o Molecules moves from high concentration to low concentration a.k.a. “down” or “with”
the concentration gradient
o Diffusion is passive transport
 There are two kinds of diffusion:
 Simple diffusion: molecules move directly through the cell membrane
 Facilitated diffusion: molecules move through specialized proteins
embedded in the cell membrane
o Osmosis is a ONE specific type of facilitated diffusion
o Osmosis occurs through special channel proteins called
aquaporins
o Diffusion: The natural movement of molecules from high concentration to
low concentration
 Concentration gradient: a change in concentration over an area or between two
areas, like the inside and outside of a cell
 The process of diffusion occurs until equilibrium is reached
o Factors which affect the rate of diffusion:
 Concentration gradient: the greater the difference in concentrations on the
opposite sides of the membrane, the quicker diffusion occurs
 Temperature: diffusion occurs faster at higher temperatures
 Cell size: surface area to volume ratio: molecules diffuse faster when there is a
small SA:V ratio; smaller cells are more efficient
o Osmosis: The diffusion of water from high concentration to low concentration
 Hypotonic solution
 Contains more solutes inside the cell; another way to say this is: solute
concentration is higher inside the cell
o Since solute concentration is higher inside the cell, water
concentration is lower inside the cell
 Water moves from outside the cell (high concentration) to
inside the cell (low concentration)




Hypertonic solution
 Contains more solute outside the cell; another way to say this is solute
concentration is higher outside the cell
o Since solute concentration is higher outside the cell, water
concentration is lower outside the cell
 Water moves from inside the cell (high concentration) to
outside the cell (low concentration)
Isotonic solution
 The concentration of solutes and water are equal on both sides of the cell
membrane
Difference in water balance b/w animal and plant cells in different environments
(hypo, iso, and hyper- tonic)
 What happens to each kind of cell in each environment
Turgor pressure: effects of osmosis (osmotic pressure, pressure caused by water)
keep plant cells stiff and provide shape to plants
4. Active transport
 Active transport requires energy
 Molecules and ions are moved from low to high concentration a.k.a. against
the concentration gradient
 3 Types of Active Transport:
 Protein pumps: use energy to pumps ions across the cell membrane
 Endocytosis (bulk transport) – think “ENDO” = enter cell
o All types of endocytosis involve the formation of a vesicle; this
vesicle is formed by the cell membrane surrounding the food
molecule, etc, and pinching off inside the cell
o Two types: Phagocytosis (solids) and Pinocytosis (liquids)
 Exocytosis (bulk transport) – think “EXO” = exit cell
o Molecules exit the cell through the process of exocytosis
o Vesicles filled with substances to be transported move towards the
cell membrane and fuse with it, releasing its contents to the outside
You should be able to apply the above information in the following ways:
1.
2.
3.
4.
5.
6.
7.
Label the cellular membrane and its components
Explain the structure and function of each part of the cell membrane
Compare and contrast passive and active transport
List, explain, identify the different types of diffusion and what is transported in each
List, explain, identify the different types of active transport and what is transported in each
Predict the movement of molecules in different situations
Predict the movement of water across the cell membrane in different solutions; remember,
when doing osmosis problems, WATER moves from high concentration to low concentration;
you assume the membrane is not permeable to any solutes, only water
8. Identify and explain the effects of osmosis on animal and plant cells
Textbook: 203-213