Unit 1: CELLS
2.1 Cell Theory (p9-14)
The Cell Theory
1. All living organisms are composed of one or more
cells
2. Cells are the smallest units of life
3. Cells only come from pre-existing cells
Functions of Life
• All organisms exist in either a unicellular or a
multicellular form. All organisms carry out all the
functions of life. These functions include;
•
•
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•
•
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Metabolism
Growth
Reproduction
Response to the environment
Homeostasis
Nutrition (excretion)
Functions together produce living things
• Metabolism includes all chemical reactions that occur in
the body
• Growth may be limited but is always evident in one way
or another
• Reproduction involves hereditary molecules that can be
passed to offspring
• Response to the environment is imperative to the survival
of the organism
• Homeostasis is maintaining a constant internal
environment (e.g. temperature).
• Nutrition is providing a source of compounds with many
chemical bonds that can be broken down to provide
energy and nutrients.
Functions of paramecium
• Movement- hair like structures (cilia) on the outside beat
rhythmically, and propel the cell through liquid.
• Nutrients-They consume small algae and plants, which
they ingest through sweeping the food into mouth-like
structures called buccal cavities( lined with cilia).
Photosynthetic can make own food from the sun’s energy.
• Reproduction- can sexually reproduce and can asexually
make exact copies of themselves.
• Response: has some sense of movement because it
responds when it bumps into something. It also can sense
certain chemicals
• Growth: evident up to a certain size.
• Homeostasis: the paramecium has a regulated internal
environment aided by it membrane
Viruses: the exception
• Viruses are non-cellular structures consisting of DNA
or RNA surrounded by a protein coat. Viruses are not
considered as living cells!
• They do not reproduce on their own, they do not
produce waste.
• Giant Algae:
• Aseptate fungal hyphae:
The discovery of the cell is due to the
development and advancements in
technology
• 1590- Zaharias Janzen:
Invents the compound microscope.
• 1665- Robert Hooke:
Studies cork and coins “cells”. Observed honeycomb
compartments in cork he named cells.
• Antoine van Leeuwenhoek:
Discovers unicellular organisms. Termed organisms
'animalcules‘ (little animals).
• 1838- Mathias Schlieden:
Observed plant tissues. Proposed all plants are composed of
separate cells & proposed that nucleus controls cell
development. “All plants are made of cells”
• 1839- Theodor Schwann:
“All animals are made of cells”
• 1855- Rudolf Virchow:
Noticed cell division. “All cells come from pre-existing cells”
• 1860s- Louis Pasteur
Designed sterilization experiments to test the above theory
Spontaneous Generation
• spontaneous generation, the hypothetical process by
which living organisms develop from nonliving matter;
• Currently an obsolete theory to explain the origin of life
Pasteur Experiment
Findings
• If spontaneous generation had been a real phenomenon,
Pasteur argued, the broth in the curved-neck flask would
have eventually become re-infected because the germs
would have spontaneously generated.
• The curved-neck flask never became infected, indicating
that the germs could only come from other germs and
spontaneous generation does NOT occur
• Pasteurization is the process of removing harmful
pathogens from various types of food. Still used today for
milk production
• http://science.howstuffworks.com/life/cellular-microscopic/pasteurization.htm
Unicellular Organisms
• Some organisms are unicellular meaning they are made of
only a single cell.
(Examples: Amoeba, Chlorella, Scenedesmus)
• This single cell has to carry out all the functions of life
Multicellular Organisms
• Organisms comprised of more than one cell.
• The cells in a multicellular organism work together to
carry out the various functions of life.
Emergent Properties
• Multicellular organisms show emergent properties.
• This means that the organism can achieve more than the sum of
what each cell could achieve individually, because of cell
interaction.
• Ex: anthill, human brain
Differentiation and Specialized
Functions
• In multicellular organisms such as humans, the DNA in
every somatic cell is identical.
• ie, your stomach cells have the exact same DNA as your
heart cells
• Differentiated cells may contain identical DNA, but
they differ in which genes are activated.
• Differentiation is when cells become specialized to
perform one task, which is reflected in their structure and
function.
• Organisms can use differentiation as they grow from a
single cell to create all the necessary types of cells
STEM CELLS(plants-meristematic cells)
• Unspecialized cells These cells can become any
type of cell or tissue(“pluripotent”).
• Embryo’s, the umbilical cord and bone marrow
are sources of stem cells
• Adult stem cells are “multipotent”. For example,
stem cells in the bone marrow can only give rise
to all the various types of blood cells.
• A stem cells ability to replicate and differentiate
along different pathways is necessary for
embryonic development and therapeutic uses.
Utilization
• Adults still have some stem cells in their bone marrow
which can be used to treat diseases such as leukemia
• Stems cells can differentiate into specialized cells when
given a certain chemical signal. Therefore, the potential
to grow a new organ in vitro exists.
• Potential uses in the future include treatments for
Diabetes, heart disease, Multiple Sclerosis, Parkinson’s
etc.
• Induced pluripotent stem (iPS) cells, discovered in 2007,
are ”man-made”, reprogrammed, stem cells that share ES
cells' ability to become other cell types.
Therapeutic use of Stem
Cells
• CELL THERAPY: non-functioning cells are replaced
with healthy, functioning cells
• Ex: Bone Marrow Transplants for leukemia patients.
• Ex: Skin grafts for burn victims
• Ex. Replenished brain cells for Parkinson’s and
Alzheimers
• Ex. Replace Insulin secreting pancreatic cells in diabetics
• Ex. Help stop and reverse vision in people with
Stargardt’s disease
•
http://www.technologyreview.com/news/526591/stem-cell-treatment-for-blindness-movingthrough-patient-testing/
Ethical Implications
• Internationally there has been much sharing of data
involving stem cell research.
• Most stem cells are generated in the lab, using in-vitro
fertilization (IVF) techniques.
• National governments are influenced by local, cultural
and religious traditions that impact the work of scientists
and the use of stem cells in therapy.
• Research is restricted and regulated.
• Gathering stem cells requires the death of the embryo and
opponents argue this is taking human life.
• WHAT DO YOU THINK?
Cells and Sizes
• Microscopes with high magnification and resolution (clarity)
are required to often visualize microorganisms and organelles
• An electron microscope (100 000x magnification) is used to
study the internal structure of a cell (the organelles).
• Because these structures are very small, special units are used
to measure them:
• Micrometre (μm) = 10-6 m
• Nanometer (nm) = 10-9 m
Some typical sizes….
•
Limiting Cell Size…
Cell Size: Cells never get too large because:
Surface area-to-volume ratio puts limits on diffusion
The following have functions dependent on size and diffusion
• Heat production and distribution
• Waste removal and resource use (The bigger the cell, the more
waste produced and resources required)
• Movement of materials through membrane
• Communication between cells and throughout cytoplasm (smaller
cells have less volume, so less distance for molecules to travel)
• As a cell grows, its volume and surface area increase, however,
the volume increases more rapidly than its surface area.
• To deal with this, cells increase their surface area with
protruding extensions or by flattening the cell.
• Seen in the lining of the small intestine and with the alveoli in
the lungs
Sm. Intestine
Human lung
Compound Microscope
10X
Low 4x,
medium10x and
high power
(100x)
To find total
magnification
multiply your ocular
lens magnification
with your
magnification from
the objective lens
http://carlyperrymicroscopy.weebly.com/mic
roscope-instructions.html
Measuring
Calculate FOV (low power)
• Place a clear plastic ruler with mm markings on top of the
stage of your microscope. Looking through the lowest
power objective, focus your image. Count how many
divisions of the ruler fit across the diameter of the field of
view. Multiply the number of divisions by 1000 to obtain
the field of view in micrometers (µm). Record this in µm
(1mm = 1000 µm ).
Estimating Actual Size…
Estimating the Actual Size of Microorganisms
2. Record the FOV Diameter for each of the 3 lenses in a safe place for
later use. Record the diameters both in mm (millimeters) and in µm
(micrometers).
3. On low power, find an object to view. You could estimate its size at this
power, or center the object and switch to medium power.
4. If we use the medium power lens shown above, we know its FOV
Diameter is 1.3 mm.
5. Estimate how many of the objects viewed with this lens can fit
across the circular area at its widest.
• 6. Approximately 3.5 creatures may fit lengthwise across
the middle of the field of view.
• 7. Divide the FOV Diameter for medium power (1.3 µm)
by 3.5.
• 8. The organism is estimated to be 0.37 mm long, or
about 370 µm.
Calculating the Magnification
of Drawings
• Example: Calculate the drawing magnification of the
drawing shown below right. The actual size can be
estimated at left below.
What is the
FOV?
What is the
approx size
of object?
What is the
measured
size?
Notice the
use of cm
heremultiply by
10000
ANSWER
• a. The size of the beastie at lower left is estimated to
be 200 µm (half of the FOV)
• b. The drawing at lower right is measured to be about
6 cm long. Convert this to µm, which is about 60000
µm long.
• c. Divide the drawing length by the actual size of the
organism
• In this case: 60000 µm / 200 µm = 300 X
• The drawing is 300 times larger than the actual
organism!
Calculating magnification using the scale
bar
• Diagrams and photographs can be shown larger or
smaller than reality
• The magnification or a scale bar is given to indicate
the real size of the object
• A scale bar is a line that shows the actual size of an
image in relative proportion to its scale
• The following formulas will help you determine the real size of
the image:
Real size = magnified size
magnification
* Magnified size is measured with your ruler
What is the real size of the amobea?
• Step 1- convert units to be the same  convert to mm by
multiplying by 10
• Step 2- find magnification
• magnification = measured scale bar/ scale bar value
= 14mm/0.2mm
= 70x
• Step 3 – find the real size
• Real size = magnified size (ruler)/ magnification
= 30mm/70
= 0.42mm or 420 µm
Electron Microscope
• Microscopes that use electrons to increase magnification
and resolution of very small objects.
• can reveal the structure of smaller objects because
electrons have wavelengths about 100,000 times shorter
than visible light photons.
Transmission electron
microscope…
• Electrons pass through ultra thin specimens. Images are
seen with great clarity.
• An image is formed from the interaction of the electrons
transmitted through the specimen; the image is magnified
and focused onto an imaging device, such as a fluorescent
screen
Scanning Electron
Microscope…
• Electrons bounced of surface of object viewed. Outer
surfaces seen in clear view with great depth of field
TO sum it up…
• http://www.biologycorner.com/quiz/qz_cell_theory.html
• http://www.pbs.org/wgbh/nova/sciencenow/0305/03.html
• (stem cell documentary)