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Cell
Membranes:
Osmosis and
Diffusion
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Membrane Functions
1. Protect cell
2. Guard incoming and outgoing
substances
3. Maintain ion concentrations of
various substances
4. Selectively permeable
a.
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b.
Allows some molecules in
Others are kept out
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Phospholipid Bilayer
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Fluid Mosaic Model
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Solutions
 Solutions
are made of solute and
a solvent
 Solvent - the liquid into which
the solute is poured and dissolved
 Solute - substance that is
dissolved or put into the solvent.
Salt and sucrose are solutes
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Membrane Transport
1.
Diffusion
a.
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b.
2.
Osmosis
a.
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Passive transport
No energy expended
b.
Passive transport
Water across membrane
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Diffusion
 Movement
of molecules from one
side of a membrane to the other
 Occurs
from a region of high
concentration of substance to a
region of lower concentration
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Osmosis
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Membrane Transport
3.
Facilitated Diffusion
a.
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b.
4.
Passive transport
Use of proteins to carry polar
molecules or ions across
Active Transport
a.
b.
Requires energy to transport
molecules against a concentration
gradient
Energy is in the form of ATP
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Tonicity
 Hypotonic
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Inside has higher salt concentration
 Hypertonic
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Solution
Inside has lower salt concentration
 Isotonic
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Solution
Solution
Both solutions have same
concentrations of solute
Plant and Animal Cells in Various Solutions
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Active Transport
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Movement against a
concentration gradient (from
low to high concentration)
Requires added energy (ATP)
and a specific membrane carrier
(“pump”)
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Endocytosis
 Ingestion
of large molecules or
particles
 Cell surrounds and envelops
substance forming a vesicle which
fuses with lysosome
– Phagocytosis
Endocytosis
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–
of organism
Pinocytosis
Endocytosis
of large, soluble molecules
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Exocytosis
Cell secretes material
Package in a vesicle
Moves in vesicle to cell surface
Vesicle membrane fuses with cell
membrane
Contents are secreted out
Specialized animal cells produce
and secrete digestive enzymes and
hormones
Cell
Structure
and
Function
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Early Discoveries

Mid 1600s - Robert Hooke observed and
described cells in cork
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observed sperm, microorganisms
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Late 1600s - Antony van Leeuwenhoek
1820s - Robert Brown observed and
named nucleus in plant cells
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Cell Theory
 Matthias
Schleiden
 Theodor
Schwann
 Rudolf
Virchow
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Cell Theory
1) Every organism is composed of one or
more cells
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2) Cell is smallest unit having properties of
life
3) Continuity of life arises from growth and
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division of single cells
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Cell
 Smallest
 Can
survive on its own or has
potential to do so
 Is
highly organized for metabolism
 Senses
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unit of life
 Has
and responds to environment
potential to reproduce
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Cells are Microscopic
 Why
aren’t cells larger?
 Animal cells range from 7-50 μm,
some are much larger:
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Nerve cells
Algae
Eggs
Plant cells are generally larger
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Why aren’t Cells Larger?
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As cells grow larger, volume increases
faster than surface area
Large cells do not have sufficient
surface area for efficient diffusion of
nutrients and wastes
Nuclei control activities of smaller
cells more easily
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Structure of Cells
Must Have:
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Two types:
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Plasma membrane
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Prokaryotic
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DNA Region
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Eukaryotic
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Cytoplasm
Structure of Cells
The plasma membrane
and internal cell
membranes consist of
lipids and proteins. The
lipids are organized as
two adjacent layers—as
bi-layer.
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Lipid Bilayer

Main component of
cell membranes

Gives the membrane
its fluid properties
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Two layers of
phospholipids
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Fluid Mosaic Model
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Membrane is a mosaic of
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Phospholipids
Glycolipids
Sterols
Proteins
Most phospholipids and some proteins
can drift through membrane
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Membrane Proteins

Transport proteins

Receptor proteins

Recognition proteins

Adhesion proteins
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Why Are Cells So Small?

Surface-to-volume ratio

The bigger a cell is, the less surface area
there is per unit volume

Above a certain size, material cannot be
moved in or out of cell fast enough
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Microscopes
 Create
detailed images of something
that is otherwise too small to see
 Light
–
microscopes
Simple or compound
 Electron
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–
microscopes
Transmission EM or Scanning EM
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Light Microscope Limitations
 Wavelengths
of light are 400-750 nm
(nanometers)
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 If
a structure is less than one-half of a
wavelength long, it will not be visible
 Light
microscopes can resolve
objects down to about 200 nm in size
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Electron Microscopy
 Uses
streams of accelerated electrons
rather than light
 Electrons
are focused by magnets
rather than glass lenses
 Can
nm
resolve structures down to 0.5
Plant cell
Eukaryotic Cells
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Defined as a cell that starts
out life with a nucleus
Have a nucleus and other
organelles
Eukaryotic organisms
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Plants
Animals
Protista
Fungi
Animal cell
Animal Cell Features
Plasma membrane
 Cytoskeleton
 Nucleus
 Ribosomes
 Endoplasmic
reticulum
 Vesicle
 Mitochondria
 Golgi body
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Plant Cell Features
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Nucleus
 Plasma Membrane
 Ribosomes
 Endoplasmic
reticulum
 Golgi body
 Mitochondria
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Cell wall
 Chloroplast
 Central Vacuole
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Functions of Nucleus
 Keeps
the DNA molecules of
eukaryotic cells separated from
metabolic machinery of cytoplasm
 Makes
it easier to organize DNA and
to copy it before parent cells divide
into daughter cells
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Components of Nucleus
• Nuclear envelope - double membrane enclosing
the nucleus
• Nucleoplasm - fluid portion of the nucleus
• Nucleolus - where other organelles are
constructed
• Chromosome – made of chromatin
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• Chromatin - DNA with all associated protein
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Nuclear Envelope

Two outer membranes (lipid bi-layers)

Innermost surface has DNA attachment
sites
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Pores span bi-layer
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Nucleolus
 Dense
mass of material in nucleus
 May be one or more
 Cluster of DNA and proteins
 Puts together ribosomal subunits
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Chromatin
Cell’s collection of DNA and associated
proteins
 Chromosome is one DNA molecule and its
associated proteins
 Appearance changes as cell divides
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Cytomembrane System
 Group
of related organelles in which
lipids are assembled and new
polypeptide chains are modified
 Products
are sorted and shipped to
various destinations
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Cyto-membrane System
Endoplasmic reticulum
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Golgi bodies
Vesicles
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Endoplasmic Reticulum
 In
animal cells, continuous with
nuclear membrane
 Extends
 Two
throughout cytoplasm
regions - rough and smooth
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Rough ER

Arranged into flattened sacs
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Ribosomes on surface give it a rough
appearance
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Some polypeptide chains enter rough ER
and are modified

Cells that specialize in secreting proteins
have lots of rough ER
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Smooth ER
 A series
of interconnected tubules
 No ribosomes on surface
 Lipids assembled inside tubules
 Smooth ER of liver inactivates
wastes, drugs
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Golgi Bodies
 Put
finishing touches on proteins and
lipids that arrive from ER
 Package finished material for shipment
to final destinations
 Material arrives and leaves in vesicles
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Vesicles

Membranous sacs that move
through the cytoplasm
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Lysosomes
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Peroxisomes
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Mitochondria
 ATP-producing
powerhouses
 Double-membrane
 Carry
system
out most efficient energy-
releasing reactions that require
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oxygen
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Mitochondrial Structure
 Outer
membrane faces cytoplasm
 Inner
membrane folds back on itself
 Membranes
form two distinct
compartments
 ATP-making
machinery is embedded
in the inner mitochondrial membrane
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Mitochondrial Origins
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Mitochondria resemble bacteria
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Have own DNA, ribosomes
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Divide on their own
 May
have evolved from ancient
bacteria that were engulfed but not
digested
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Plant Organelles
 Plastids organelles
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that specialize in
photosynthesis
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Central Vacuole
store amino acids, sugars,
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ions and toxic wastes.
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Chloroplasts
Convert sunlight energy to ATP through
photosynthesis
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Photosynthesis

First stage
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Second stage
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Occurs at thylakoid membrane
Light energy is trapped by pigments and
stored as ATP
Inside stroma, ATP energy is used to make
sugars, then other carbohydrates
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Central Vacuole

Fluid-filled organelle

Stores amino acids, sugars, wastes
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As cell grows, expansion of vacuole as a
result of pressure that forces end cell
walls to expand
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In mature cell, central vacuole takes up
50-90 percent of cell interior
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Cytoskeleton
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 Basis
 Present
for cell shape and internal
organization
 Allows
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in all eukaryotic cells
organelle movement within
cells and, in some cases, cell motility
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Flagella and Cilia
 Structures
for
cell motility
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Cell Wall
Plasma membrane
 Structural
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component that
wraps around the
plasma membrane
 Occurs in plants,
some fungi, some
protista
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Prokaryotic Cells

Archaebacteria and Eubacteria

DNA is NOT enclosed in nucleus

Generally the smallest, simplest cells

No organelles
Prokaryotic Structure
pilus
cytoplasm
with ribosomes
DNA
flagellum
capsule
cell plasma
wall membrane
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Things to know:
The first cell seen under a microscope was
cork.
 One portion of the cell theory states that
all living organisms are made up of cells.
 The cell theory was proposed by Theodor
Schwann and Matthias Schleiden.
 The idea that all living cells come from
pre-existing living cells was proposed by
Rudolf Virchow.
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Things to know:
 The
phospholipid molecules of most
membranes have a hydrophilic head
and two hydrophobic tails.
 Hydrophobic reactions of
phospholipids may produce clusters
of their fatty acid tails, which form a
lipid bilayer.
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Things to know:
 The
relative impermeability of
membranes to water-soluble
molecules is a result of the presence
of phospholipids in the lipid bilayer.
 Membranes have holes due to proteins
that extend through the membrane.
 Some membranes have proteins with
channels or pores that allow for the
passage of hydrophilic substances.
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Things to know:
The current concept of a membrane can be
best summarized by the fluid mosaic model.
 The lipid bilayer serves as a hydrophobic
barrier between two fluid regions.
 Receptor proteins are responsible for
binding hormones that can switch on a cell.
 There are 1,000,000,000 nanometers in a
meter.
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Things to know:
The maximum power of magnification of
a light microscope is 4,000.
 The highest magnification generally used
to study cells is provided by the
transmission electron microscope.
 The transmission electron microscope has
the highest magnification.
 The ribosomes are made of two subunits
of RNA and protein.
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Things to know:
Organelles composed of a system of canals,
tubes and sacs that transport molecules
inside the cytoplasm are endoplasmic
reticula.
 Mitochondria are the primary cellular sites
for the recapture of energy from
carbohydrates.
 Golgi bodies are the primary structures for
the packaging of cellular secretions for
export from the cell.
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Things to know:
The cell part responsible for maintaining cell
shape, internal organization, and cell
movement is the cytoskeleton.
 The cell wall is found in plant cells but not in
animal cells.
 The nucleolus is found in the nucleus.
 The nuclear envelope has two lipid layers;
there are pores in the membrane; ribosomal
subunits can pass out of the nucleus; protein
filaments are attached to inner surface.
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Things to know:
Scientists use the word “chromosome” to
describe an individual DNA molecule.
 Endoplasmic reticula are sometimes
referred to as rough or smooth.
 Ribosomes are the primary cellular sites for
the production of protein.
 The Golgi body has been likened to a stack
of pancakes.
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Things to know:
The lysosomes contain enzymes and are the
main organelles of intracellular digestion.
 Animal cells dismantle and dispose of
waste materials by several lysosomes
fusing with a sac that encloses the wastes.
 A tadpole’s tail disappears when it changes
into an adult frog by action of lysosomes.
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Things to know:
The nuclei and mitochondria contain DNA.
 Mitochondria contain enzymes used in the
breakdown of glucose and generation of
ATP.
 Energy stored in carbon compounds is
converted by mitochondria to a form usable
by the cell.
 There are two membranes surrounding the
mitochondrion.
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Things to know:
The inner membranes of mitochondria are
called cristae.
 Fluid-filled sacs that may store food or
water in cells are called vacuoles.
 Plastids in plant cells function in
photosynthesis or storage.
 Stroma and grana are portions of
chloroplasts.
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Things to know:
Vacuoles dramatically increase the cell size
and surface area.
 Flagellum is compared to a whip and used
for mobility.
 Bacteria are examples of prokaryotes.
 Prokaryotic cells do NOT have membrane
bound nucleus.
 Prokaryotes have DNA regions; are
unicellular; have cell walls; and are bacteria.

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Bibliography
1.
2.
http://filebox.vt.edu/users/malsaghi/ 6 Dec
2004, Mohannad AL-Saghir, Biology
Department, Virginia Tech
http://pls.atu.edu/biology/, 6 Dec 2004,
Arkansas Tech University, Biology
Department, Beck,