Cell Membrane and
Tonicity Worksheet
Composition of the Cell Membrane
 The cell membrane is also called the
plasma membrane and is made of a
phospholipid bilayer.
Composition of the Cell Membrane
Composition of the Cell
Membrane
 The Phospholipids have a hydrophilic (water attracting)
head and two hydrophobic (water repelling) tails.
 The head of a phospholipid is made of an alcohol and
phosphate group, while the tails are chains of fatty
acids.
 Phospholipids can move apart and allow water and
other smaller molecules to pass through into or out of
the cell.
 This is known as simple diffusion or passive
transport because it does not require ATP (energy)
and the water or molecules are moving along the
concentration gradient.
Composition of the Cell Membrane
 Another type of lipid in the cell membrane is cholesterol that
makes the membrane more fluid.
 Embedded in the phospholipid bilayer are proteins that also
aid in diffusion and in cell recognition.
 Proteins called integral proteins go all the way through the
bilayer, while peripheral proteins are only on one side.
 Integral proteins are also called transport proteins. Large
molecules like starches or carbohydrates use proteins to
help move across cell membranes.
 Some of the membrane proteins have carbohydrate
receptors attached to help cells to recognize each other and
certain molecules.
Transport and Integral
 IT MEANS THE SAME THING!!!!!
Composition of the Cell Membrane
 List 4 functions of the cell or plasma
membrane:
 a. Regulate what may enter the cell
 b. Regulate what may leave the cell
 c. Maintain homeostasis within the cell
 d. Allows the cell to remain flexible.
 Define osmosis.
Osmosis
 is the movement of water molecules through a
selectively-permeable membrane up a concentration
gradient. NO ENERGY IS REQUIRED
 Define these 3 terms:
 a. isotonic- solutions that have equal osmotic
pressure
 b. hypertonic- a solution with a higher solute
concentration outside of the cell compared to
inside of the cell.
 c. hypotonic- a solution with a lower solute
concentration outside of the cell compared to the
inside of the cell.
What is Diffusion?
The process by which molecules of a substance
move from area of high concentration to areas
of low concentration
Diffusion occurs until EQUILIBRIUM is reached.
No ENERGY is required
Some examples of diffusion in humans include
GAS exchange in your LUNGS and the nutrients
absorbed by your SMALL INTESTINE
Hyper-, Hypo-, or Isotonic?
 Use arrows to show the direction of water
movement into or out of each cell. Color and
label the cell in an isotonic environment light
blue, the hypotonic environment yellow, and
the hypertonic environment light green.
Matching
A. Isotonic
B. Hypertonic
C. Hypotonic
 _____ solution with a lower solute
concentration
 _____ solution in which the solute
concentration is the same
 _____ condition plant cells require
 _____ condition that animal cells require
 _____ red blood cell bursts (cytolysis)
 _____ plant cell loses turgor pressure
(Plasmolysis)
 _____ solution with a higher solute
concentration
 _____ plant cell with good turgor pressure
 _____ solution with a high water
concentration
Label the Red Blood Cells
 What type of solution are they in?
Hypotonic
Isotonic
Hypertonic
Label the Plant Cell
 What type of solution are they in?
Hypotonic
Isotonic
Hypertonic
Transport Requiring
Energy
 What type of transport is represented by
the picture below?
 Hint the diagram shows that ATP is being used to transport the
molecule inside the cell.
 In what direction is the
movement occurring?
-against or along the concentration gradient?
Sodium-Potassium Pump
Sodium-Potassium Pump
 One type of active transport is called the
sodium potassium pump which helps muscle
cells contract. This pump uses ATP to move
ions against the concentration gradient. The
protein that is used to pump the ions through is
called a transport (carrier) protein and it
changes its shape to move the ions across the
cell membrane.
 Label and color the carrier proteins red and
the ions yellow.
Solutions
 Definition- when one or more solutes are
dissolved into a solvent.
 Solvent- any substance that can dissolve.
 Solute- any substance that can be
dissolved by a solvent.