Transcript Cells

Cells
Structure and Function
Section 1: Introduction to the Cell:
Cell Theory
Cool Cell Facts
The average human being is
composed of around 100 Trillion
individual cells!
 It would take as many as 50 cells to
cover the area of a dot on the letter
“i”

WOW!!!
Discovery of Cells
The cell was first named by:
Robert Hooke (1665): He observed
a thin slice of cork (dead plant
cells) with a microscope. He
described what he observed as
“little boxes” (cells).
 He said it looked strangely
similar to ‘cells’ or small rooms
which monks inhabited.
Discovery of Cells

Anton van Leeuwenhoek
was the first person to
observe living cells
Anton van Leuwenhoek



1674- Used a handmade microscope to observe
pond scum & discovered single-celled organisms
He called them “animalcules”
(little animals)
He also observed blood cells from fish, birds,
frogs, dogs, and humans
150-200 Year Gap??

Between the Hooke/Leuwenhoek
discoveries and the mid 19th century, very
little cell advancements were made.
 This is probably due to the widely
accepted, traditional belief in
Spontaneous Generation.
 Examples:
-Mice from dirty clothes/corn husks
-Maggots from rotting meat
th
19
Century Advancement


Much doubt existed around
Spontaneous Generation
Conclusively disproved by Louis
Pasteur (boiled broth and showed
that living things didn’t appear)
Pasteur: (Ummm,
I don’t think so!!!)
+
?
=
Pasteur’s experiment: He made nutrient broth with yeast and sugar
in various-shaped flasks and boiled them. Microorganisms only
grew once the broth had been exposed to the air. The ‘swan’ necks
on some flasks prevented organisms from getting in the broth and
so it remained sterile.
He showed that no organisms spontaneously generate.
“Spontaneous Generation”:
Also disproved by Francesco Redi.
He put meat in 8 jars and closed 4 jars
with lids. As time went on, maggots
and flies appeared in the open jars but
none showed up in the closed jar. This
experiment proved that life was
coming to the non-living object, not
from it.
Development of Cell Theory


1838- German Botanist, M. Schleiden,
said that all plants are made of cells
1839- German physiologist, T. Schwann, who
was a close friend of Schleiden, stated that all
animal tissues are also composed of cells.
Development of Cell Theory

1858- Rudolf Virchow, a German physician,
after extensive study of cellular pathology,
concluded that:
all cells must arise from pre-existing cells.
All of this led to….
The Cell Theory

1. All living things are composed of one or
more cells. (Schleiden & Schwann)(1838-39)

2. The cell is the basic unit of life in all living
things. (Schleiden & Schwann)(1838-39)

3. All cells are produced by the division of
preexisting cells. (Virchow)(1858)
All cells carry out all the
functions of life, even
the unicellular ones!
Smallest Cells:
Cell Diversity- Size
Biggest Cells:
Longest Cells:
6 inches long, 5 inches wide, 3 pounds
Ostrich Egg
Functions of Life
Functions of Life
Discrepancies in the Cell Theory
Fungal hyphae:
can be aseptate!
(holes in the
dividing cells so
they share
cytoplasm!)
Acetabularia (algae): grows
up to 100mm; single-celled
organism with only one
nucleus!
The Metric System
Must know how to convert from one unit to another
Kilo1000
Units
Divide
Hecto100
units
Deka10
units
Multiply
Basic
Unit
Deci0.1
units
Centi0.01
units
Milli0.001
units

um, nm
What units are used to measure cells?
Units for Size Measurements
Most S.I. units differ from each other by a factor of
1000 (when measuring sizes of cells and structures)
– One millimeter is 1000x smaller than 1 meter
– One micrometer is 1000x smaller than 1 millimeter
– One nanometer is 1000x smaller than 1 micrometer
Summary:
1000 mm = 1 m
1000 um = 1 mm
1000 nm = 1 um
Size of various cells
and structures:







Molecules: 1 nm
Membranes (on organelles):
10 nm
Viruses: 100 nm
Bacteria: 1 um
Organelles: up to 10 um
Most cells: up to 100 um
Measurements above in 2d,
remember all structures have
3d shape.
Calculating Linear Magnification
(Photographs or drawings of structures
seen under a microscope show them
larger
than they really are – they magnify
them)
Drawings of cells and cell structures
should always include:
A scale bar: |------| = 1 µm
Magnification: ×250
Calculating Linear Magnification
To calculate magnification:
1.
Choose an obvious length, for ex. the maximum
diameter of the cell. Measure it on the drawing.
2.
Measure the same length on the actual specimen.
3.
Convert one of them so that they are in the same
units.
4.
Divide the length on the drawing by the length of the
actual specimen. The result is magnification.
Magnification = size of image
size of specimen
Calculating Linear Magnification
Example: the diameter of a cell is 40 um.
Calculate the magnification of the drawing.
note: With a ruler, you measured it to be 5.6 cm.
5.6 cm = 56 mm = 56000 um
56000/40 = ? (1400) so 1400x magnification
Magnification
x5



What is the actual size of this
specimen in um?
60mm/5 = 12mm
12mm x 1000 um =
12,000 um
60 mm
Measuring
picture
Limits on Cell Size
Why don’t cells get larger?
(Cells reach a maximum size
and then may divide, but
they don’t grow
Hint: Its because of the problem
indefinitely)
of the surface area / volume ratio

2.1.6
Surface Area to Volume Ratio
SA = 6lw
V = lwh
SA = 6 mm2
V = 1 mm3
SA/V = 6:1
SA = 24 mm2
V = 8 mm3
SA/V = 3:1
V increases faster than SA
SA = 96 mm2
V = 64 mm3
SA/V = 1.5:1
Surface area/volume ratio limits cell size

Metabolic rates increase faster than the surface area’s ability to
exchange nutrients, therefore a maximum size is reached.
*Plasma membrane must be large
enough relative to cell volume to regulate
passage of materials
**As cell size increases, the surface
area to volume ratio decreases. Rates
of chemical exchange may then be
inadequate for cell size.
Therefore, cells remains small.
(english version): Advantages of being small: large surface to volume ratio, so things
can be moved in and out efficiently. Also, diffusion time to center of cell is faster
Differentiation of Cells

Differentiation: Cells within a
multicellular organism develop in
different ways and can therefore
carry out different functions.

Each cell has all genes, but it only
uses the ones that it needs for its
particular function

Specialized cells have switched
on (expressed) particular genes
that correlate to these specialist
functions.
Examples of Cell differentiation
All animals begin with a union of sperm
and egg to form a zygote.
The zygote divides and divides to make
lots of cells. At some point, those
cells differentiate into about 200
different varieties. Examples:
* epithelial cells lining stomach
secrete hydrochloric acid.
* muscle cells which make long
fibers that stretch and contract
* taste bud cells
* bone cells, eye cells, nerve
cells, etc.
http://www.teachersdomain.org/resource/tdc02.sci.life.stru.different/
Stem cells : What they are and
therapeutic uses
Stem Cells
Stem cells have the ability to self-renew
by cell division and to differentiate.
Human embryos consist entirely of
stem cells in the early stages, but
gradually the cells in the embryo
commit themselves to a certain type.
A small number of stem cells remain in
the body in places like bone marrow,
skin, and liver.
There has been great interest in stem
cells because of their potential for
tissue repair and treatment of
diseases (ex. Multiple sclerosis,
Parkinson’s disease, strokes)
Therapeutic use of stem cells (example)


Placenta and umbilical cord of a baby is used as the
source of stem cells. These cells can divide and
differentiate into any type of blood cell.
Cord blood can be used to treat children with leukemia
(a cancer in which the cells in bone marrow divide uncontrollably,
producing too many white blood cells.)
Chemotherapy is given to the child to
kill the bone marrow cells.
Then cord blood is given to the patient.
The stem cells divide and replace
the bone marrow cells.

Where do you stand in the debate
about the nature of stem cell
research? How do you feel about the
source of pluripotent (embryonic)
stem cells?
Microscopes

Magnification: refers to the microscope’s
power to increase an object’s apparent size
(ratio of an object’s image size to its real size)

Resolution: refers to the microscope’s power
to show detail clearly
(minimum distance 2 points can be
separated and still be distinguished as 2
points)
(ex. Star in sky can actually be two twin stars but
your eye only sees one…)
(Compound) Light Microscope
Light Microscope
Elodea - Aquatic Plant
40X
400X
Advantages of Light Microscopes




Object: can be living
Real colors visible
Within range of High School- easy to
work with (portable)
Up to 1000x magnification
Disadvantages: low magnification,
low resolution compared to electron microscopes
Stereoscopic (dissecting) Microscope
(another type of light microscope)
Advantages
Great for living organisms because it shows
3-dimensional view
Organisms can be living or dead (such as in
dissections)
Easy to work with
Disadvantages
Relatively low magnification (2x-40x) and
low resolution when compared to EM’s
Fern spores
(seen with dissecting microscope)
15X --^
35X 
Transmission Electron Microscope (TEM)
Transmission Electron Microscope
(TEM)


Uses electrons (not light)
Electrons are passed through a
thin slice of the specimen for an
internal view
Advantages:
Very high magnification (up to
250,000x)!
Very high resolution
Disadvantages:
HUGE, expensive, specimens have to
be dead, no real color
Transmission Electron Microscope (TEM)
Herpes Virus
Plant Root Cell
Scanning Electron Microscope (SEM)
Scanning Electron Microscope (SEM)
Scanning Electron Microscope (SEM)



Uses electrons (not light)
Specimen is plated with thin layer of gold
Electrons are bounced off the surface and reflected back
onto a screen for a 3-dimensional view of the external
surface
Advantages:
Very high magnification (up to 250,000x)!
Very high resolution
Disadvantages:
HUGE, expensive, specimens have to be dead, not real color
Scanning Electron Microscope (SEM)
Mosquito Head
200X
2000X
Scanning Electron Microscope (SEM)
Fly Eye
Scanning Electron Microscope (SEM)
Surface of
Tongue
Neuron
Inside of
Stomach
Scanning Electron Microscope (SEM)
Pollen
Yeast
Red Blood
Cell,
Platelet,
and White
Blood Cell
TEM vs. SEM
Viruses
leaving a
cell
2.3.5
Plant Cells vs. Animal Cells

Animal cells are very similar to
plant cells except for the
following major differences:
– Animal cells do not contain
chloroplasts
– Animal cells are not
surrounded by cell walls
– The vacuoles in plants are
much larger than those of
animals
Microscope Pictures of a
Plant Cell and an Animal Cell
Elodea
Human Cheek Cells
Extracellular components
2.3.6
Cell Diversity- Shape
Cells differ widely in shape.
 Most cells are roughly
cuboidal or spherical.

Multi-cellular organisms show
emergent properties
Organelles
 Cells
 Tissues
 Organs
 Organ systems
 Organisms
2.1.7
State that multicellular
organisms show
emergent properties
Organelles
discrete structures
within a cell that
each have their own
specific function
Tissue

Tissue- a group of similar
cells working together to
perform a particular task.
Organ

Organ- a structural
unit made up of a
group of tissues
which work
together to perform
a function.
Organ System

Organ system- several organs working together to
perform a job.

Exs: respiratory system
Digestive system
Reproductive system


Hierarchy of Biological Order