Homeostasis, Transport
& The Cell Membrane
Chapter 4-2 (pg 73 – 75)
Chapter 5
Unit 5:
Lecture 1

Topic:
◦ The Cell Membrane

Covers:
◦ Chapter 5, pages 95 - 96
◦ Chapter 4, pages 73 - 75
The Cell Membrane
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
The chemistry of living organisms involves the study of
solutions.
◦ A large portion of our body is water, and the
chemical reactions of life occur in aqueous (watery)
solutions.
◦ Nutrients move through the watery matrix of your
blood to deliver the nutrients to cells.
Cell membranes help organisms by controlling what
substances may enter or leave the cells.
◦ Known as Selectively Permeable or Semipermeable
◦ Some substances can cross the cell membrane
without any input of energy, whereas other materials
The Cell Membrane
It’s Selectively Permeable…
HOW DOES IT DO THAT?
◦ Because of the membrane’s structure
◦ Cell membrane is a PHOSPHOLIPID BILAYER
 BILAYER - 2 LAYERS
 PHOSPHOLIPID - 2 PARTS
 1. Phosphate head
 2. Lipid tail


1. Phosphate head - Outer part of the bilayer
◦ HYDROPHILIC - "Water loving”

2. Lipid Tail - Middle part of the bilayer
◦ HYDROPHOBIC - "Water hating"



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The phospholipids are not attached to one another,
enabling the membrane to have “fluid” like properties
Because of the lipid bilayer’s chemical properties, not all
types of molecules can cross through the membrane
Some substances can cross through on their own
◦ Small, uncharged particles can squeeze between
phospholipids and can cross though the lipid layer
Some substances need assistance to cross through the
membrane
◦ Large molecules cannot fit between phospholipids
◦ Charged particles (ions) cannot cross through the lipid
layer
Other Parts of
the Cell Membrane

1. CHOLESTEROL (type of lipid)
◦ Function: Helps to make the membrane "fluid", not rigid
◦ Location: Part of the the bilayer

2. PERIPHERAL PROTEINS
◦ Function: Helps to keep the shape of the cell
◦ Location: Inner layer of cell membrane, connected to
fibers of the cytoskeleton
Other Parts of
the Cell Membrane

3. INTEGRAL PROTEINS
◦ Function: Channel for molecules to come into the cell
◦ Location: Embedded in the membrane (goes through
membrane, from one side to the other)
◦ Some integral proteins have carbohydrates attached
 Known as Glycoprotein
Other Parts of
the Cell Membrane

4. GLYCOPROTEINS
◦ Location: Integral protein with a carbohydrate attached
 Carbohydrate (glycogen) sticks out of the cell, on
outside of cell membrane
◦ Functions:
 Used in cell recognition
 Different cell types have different shaped
glycoproteins attached
 Used as a cell receptor
 Glycoprotein accepts proteins/substances meant
for that specific cell type
End Lecture 1
Unit 5:
Lecture 2

Topics:
◦ Transport across membranes
◦ Passive Transport (Diffusion, Osmosis)

Covers:
◦ Chapter 5, pages 95 – 99
Transport Across
Cell Membrane



Many materials cross through the cell membrane
(enter cell or leave cell)
The types of transport are grouped into two categories:
◦ Passive Transport
◦ Active Transport
The type of transport used to move the material
depends on the concentration gradient as well as the
type of molecule being transported



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CONCENTRATION GRADIENT – when the solutions on
either side of the membrane do not have the same
concentration of solutes (one more concentrated than
the other)
When the concentration is equal throughout the
space/solution, the solution is said to be in EQUILIBRIUM
Due to kinetic energy, molecules are in constant motion,
even when the solution is in a state of equilibrium
In the cell, molecules will diffuse in & out of the cell even
when the cell is in equilibrium with its surroundings
Types of Transport:
Passive

Passive Transport occurs naturally due to kinetic
energy, so it does not require any additional energy
from the cell.
◦ In passive transport, the molecules are said to be
moving "down the concentration gradient" because
the molecules are moving to an area with a lower
concentration.

Types of Passive Transport:
◦ Diffusion
◦ Osmosis
◦ Facilitated Diffusion
◦ Ion Channel

DIFFUSION: Movement of molecules from an area of
high concentration to an area of lower concentration

EXAMPLES: Food coloring in water, Solute added to a solvent
 Types of Passive Transport:
◦ Diffusion
◦ Osmosis
◦ Facilitated Diffusion
◦ Ion Channel
OSMOSIS
 Type of Passive Transport driven by kinetic energy
 OSMOSIS is the diffusion of water!
◦ Water molecules are moving from an area of high
concentration (of water) to an area of low
concentration (of water)
◦ If water is diffusing into or out of a cell, the water
molecules will be crossing through the cell membrane
 Cell is trying to reach EQULIBRIUM with its
surrounding environment
HYPOTONIC SOLUTION

External solution has higher
concentration of water than
inside the cell

Water moves into the cell

Cell can burst!
HYPERTONIC SOLUTION

External solution has a lower
concentration of water than
inside the cell

Water moves out of the cell

Cell shrivels up!
ISOTONIC SOLUTION

Concentration of water inside and
outside the cell is and inside the
cell are equal

Cell is in equilibrium with its
surrounding environment!

How cells deal with osmosis...
HYPOTONIC SOLUTION
 In plants - vacuole fills with water creating turgor pressure
◦ Helps to support plant cell
 In unicellular freshwater organisms - water constantly entering cell,
these organisms must continuously pump the water out of the cell
◦ Contractile Vacuole - Organelle that removes water
 In Red Blood Cells – water fills up the RBC & the cell can burst!
◦ Known as CYTOLYSIS
HYPERTONIC SOLUTION
 In plants - when water leaves cell, turgor pressure reduced and
plants become wilted, Known as PLASMOLYSIS
 In Red Blood Cells - cells can't compensate for extreme changes in
concentration, so cells would shrivel
◦ Known as CRENATION
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
ISOTONIC SOLUTION
End Lecture 2
Unit 5
Lecture 3

Topics:
◦ Transport across membranes
 Passive Transport (Facilitated Diffusion, Ion Channel)
 Active Transport

Covers:
◦ Chapter 5, pages 99 – 104

Types of Passive Transport:
◦ Diffusion
◦ Osmosis
◦ Facilitated Diffusion
◦ Ion Channel
FACILITATED DIFFUSION
 Type of passive transport that is driven by kinetic energy
◦ Moving molecules from high to low concentration (“Down
the gradient”)
 Transports molecules that can not diffuse on their own
◦ EX. - too big, not soluble in lipids, glucose, polysaccharides
 These molecules are assisted across the membrane by a type
of integral protein known as a CARRIER PROTEIN
 Many types of carrier proteins because each carrier protein
can only assist ONE type of molecule
 * REMEMBER - Form Fits Function! *

Types of Passive Transport:
◦ Diffusion
◦ Osmosis
◦ Facilitated Diffusion
◦ Ion Channel
ION CHANNEL
* REMEMBER - An ION is an atom or molecule with a charge
 Type of passive transport that is driven by kinetic energy
◦ Moving molecules from high to low concentration (“Down
the gradient”)
 Ions are not soluble in lipids, so ions cannot cross through the
lipid bilayer (cell membrane) on their own
 Ions cross through the cell membrane by traveling through a
type of integral protein known as an ION CHANNEL
 Many types of ion channels because each ion channel can only
assist ONE kind of ion across the membrane
 Sodium (Na+)
- Potassium (K+)
 Calcium (Ca++)
- Chlorine (Cl-)
ACTIVE TRANSPORT
 Unlike passive transport, ACTIVE TRANSPORT
requires the cell to use energy to move the molecules
across the membrane
◦ Energy supplied by the cell's mitochondria in the form
of ATP
 Active transport moves molecules from an area of lower
concentration to an area of higher concentration
◦ Molecules moving "up the gradient” or “against the
gradient”, solution moving away from equilibrium

Types of Active Transport:
◦ Membrane Pumps
(Sodium-Potassium)
◦ Endocytosis
◦ Exocytosis
SODIUM - POTASSIUM PUMP
 Type of Active Transport, requires ATP to occur
 Membrane Pumps require a special type of carrier
proteins (a type of integral protein)
 Membrane Pumps transport molecules from an area of
low concentration to an area of high concentration
 In the Sodium-Potassium Pump, sodium ions (Na+) are
pumped out of the cell and potassium ions (K+) are
pumped into the cell
◦ 3 sodium leave cell for every 2 potassium that enter
 Cell needs to have a high concentration of Na+ outside
the cell and a high concentration of K+ inside the cell

Types of Active Transport:
◦ Membrane Pumps
◦ Endocytosis
◦ Exocytosis
ENDOCYTOSIS
 Type of Active Transport, requires ATP to occur
◦ Requires additional energy because the cell is making
major structural changes
 Endocytosis is how:
◦ Cells ingest large particles
◦ Unicellular organisms ingest their food
◦ Our body begins to get rid of bacteria and viruses
 2 Types of Endocytosis:
◦ PINOCYTOSIS - transport of fluids
◦ PHAGOCYTOSIS - movement of large particles or
whole cells
Endocytosis:
The Process
1. Cell membrane folds in and begins to form a pouch
 2. Cell membrane encloses the external materials in a
pouch
 3. Pouch pinches off to form a VESICLE
◦ Vesicle - membrane bound organelle used to transport
molecules. Often combines with lysosomes to break
down ingested materials

 Types of Active Transport:
◦ Membrane Pumps
◦ Endocytosis
◦ Exocytosis
EXOCYTOSIS
 Type of Active Transport, requires ATP to occur
◦ Requires additional energy because the cell is
making major structural changes
 Exocytosis is how:
◦ Cells release proteins after protein leaves the Golgi
◦ Cells release waste products
Exocytosis:
The Process
1.Vesicle moves to the cell membrane
 2. Vesicle fuses with the cell membrane
 3. Contents gets released to the outside of the cell

End Lecture 3