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Cell Transport AP Bio Cheat Sheet by

An AP Bio Study Guide

Essential Knowledge

Cell membranes are selectively permeable due to their stx
Cell membranes are composed of phospholipid bylayer that is both hydrophobic and hydrophilic which allows for only desired substances to pass
Growth, reproduction, & dynamic homeostasis require that cells create and maintain internal environments that are different from their external environments
Without maintaining a balanced internal environment the cell may die from shriveling up or exploding
Growth & dynamic homeostasis are maintained by their constant movement of molecules across membranes
Cells communicate through membranes which may include receiving signals and materials, or sending off waste or signals of their own as hormones or electricity
Eukaryotic cells maintain internal membranes that partition the cell into specialized regions
Eukaryotic cells have organelles specialized for tasks made from the membrane such as the mitochondria and golgi body

Big Ideas

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeos­tasis (Energy).
Relates to Big Idea 1: Evolution
Processes such as diffusion, and commun­ication did not always exist and were selected as enviro­nme­ntally advant­ageous so organisms with the trait survived to pass down this genetic inform­ation
Relates to Big Idea 3: Infrom­ation
Cells share inform­ation through process of cell signal commun­ication seen as hormones, and proteins that can trigger or stop cell processes such as transc­ription and replic­ation. Observed in Cell Cycle commun­ication
Relates to Big Idea 4: Systems
Organism body systems use cell commun­ication to trigger specific events to occur, such as the electr­och­emical gradient associated with the nervous system's nerve cells and the uses of hormonal commun­ication among cells in the Endocrine System


water potent­ial(ψ)
cell wall
electr­och­emical gradient
cell junctions
fluid mosaic model
selective permea­bility
surface area
concen­tration gradient
channel protein
osmotic pressure
nuclear envelope
facili­tated diffusion
transm­embrane protein
active transport
carrier protein
golgi body
plasma membrane
passive transport

Related Labs

Investigation 4 Diffusion and Osmosis
What causes plants to wilt if they are not watered?
Investigation 11 Transpiration
What factors including enviro­nmental variables, affect the rate of transp­iration in plants?


All cells need to move materials in and out of the cell. There are two types of transport that cells carry out: PASSIVE and ACTIVE
When small particles move from a high to a low concen­tra­tion, it is called passive transport. This is the normal flow of materials.
When small particles move from a low to a high concen­tra­tion, it is called active transport. This is AGAINST the normal flow of materials
There are two types of passive transport. Osmosis is when water is moving high to low through a cell membrane, and diffusion is when all other small particles move from high to low concen­tra­tion.
This type of transport requires ATP or energy
This type of transport does NOT require ATP or energy
If large particles need to enter or leave the cell, they require special types of active transport called endocy­tosis and exocytosis
Cells getting rid of CO2
Endocy­tosis occurs when a cell needs to bring in large particles. Think about “endo” sounding like “in the” cell
Cells taking in O2 for cellular respir­ation
Exocytosis occurs when a cell needs to take out large particles. Think about “exo” sounding like “exiting” the cell. This is how the Golgi ships proteins out of the cell
Water moving across the cell membrane when needed or as a waste product
cells brining in large food particles, cells releasing waste, white blood cells “eating” pathogens

Cell Signaling

Direct Contact
Paracrine Signaling
Synaptic Signaling
Endocrine Signaling
Cell/cell junction, gap junctions
localized only
Occurs in neurons
Long distance and long term
example-growth factors


https:­//w­ww.s­li­des­har­e.n­et/­Ton­iFo­ley­/24­-ce­ll-­mem­bra­ne-­and­-tr­ansport by Toni Foley

Endocy­tosis Diagram


Answer Key

The fluid-­mosaic model is the univer­sally agreed upon model of the cell because it represents the fluidity of the phosph­olipid composed cell membrane
A hypertonic solution is one in which the solute concen­tration is higher and therefore due to a desire for an isotonic situation water will be drawn towards the high containing of solutes
Osmosis is the diffusion of water according to the concen­tration gradient
that does not require energy
The sodium­-po­tassium pump exchanges sodium ions for potassium ions across the plasma membrane of animal cells. It accomp­lishes the transport of three Na+ to the outside of the cell and the transport of two K+ ions to the inside with protein pumps that utilize ATP.
Solution X is salt water because the water in the cell was drawn out in attempts to balance with the exterior salt content. Remember that SALT SUCKS!
The protozoans lost water and shriveled up due to the fact that water was diffused out of the cell through osmosis in an attempt to maintain equal conditions


1. Cells transport substances across their membranes. Choose three of the following four types of cellular transport.
Active Transport
Facili­tated Diffusion
For each of the three transport types you choose,
a) Describe the transport process and explain how the organi­zation of cell membranes functions in
the movement of specific molecules across membranes; and
b) Explain the signif­icance of each type of transport to a specific cell (you may use different cell types as examples).


2. During micros­copic examin­ation of human tissue samples, a student
observed the following at different magnif­ica­tions. In some cases, individual
cells were clearly visible (A and B). In others, the magnif­ication was too low
to clearly visualize individual cells although the dark patches of nuclei are
visible in fig C.

a. Identify the image that contains a cell or cells with the lowest surface area to
volume ratio. Explain your reasoning and provide a sample calcul­ation to
illustrate this.
b. Identify an image that shows a tissue that is ideally suited for the exchange of
materials with the enviro­nment. Justify your response and suggest the role this
tissue may have in the organism.
c. Explain how surface area to volume ratio can place a limit on the maximum size
of a cell.
d. Describe how you could model that the rate of exchange of materials is affected
by surface area to volume ratio. (Option – support your written response with
clearly labeled diagrams).

FRQ 2 Figures

Multiple Choice Practice Questions

1 What is the current model of cell membranes?
A Extrac­ellular Model
B Phosph­olipid Model
C Cellular Model
D Fluid-­mosaic Model
2 If a solution outside a cell is more concen­trated so that the cell loses water to its enviro­nment, the external solution is said to be __________ to the cell contents.
A hypertonic
B in equilibrium
C isotonic
D hypertonic
3 Osmosis is a process that
A moves water molecules from an area of higher concen­tration to an area of lower concen­tra­tion, using energy
B involves the active transport of dissolved solids
C equalizes the concen­tration of particles by the movement of water molecules
D continues until the medium on each side of the membrane has become hypertonic
4 The sodium­-po­tassium pump usually pumps
A potassium out of the cell
B sodium into the cell
C potassium into the cell
D only a potassium and sugar molecule together
Use the inform­ation below and your knowledge of biology to answer questions 5 through 6 which follow the reading passage
Each student in a biology laboratory received two solutions. One solution was distilled water. The other was a salt solution with concen­tra­tions of salts slightly greater than that of a living cell. The solutions were labeled X and Y, respec­tively. The students were instructed to place some fresh-­water protozoans in each of the solutions and to identify the solutions on the basis of their observ­ations. The protozoans in solution X shriveled. Those in solution Y swelled up and burst.
5 These results indicate that
A solution X was salt water
B solution Y contained killer protozoans
C solution Y was salt water
D solution X was distilled water
6 The protozoans in solution X shriveled because
A golgi bodies in the test organisms lost their function
B their membranes were more permeable to the passage of water than the organisms in Y
C osmotic pressure failed to operate
D a dispro­por­tionate amount of water diffused from the protozoans
Key is on the last page


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