Download Topic 2: Cells 2.1 Cell Theory 2.1.1 Outline the cell theory 2.1.2

Topic 2: Cells
2.1.1 Outline the cell theory
The cell theory states that:
1. All living organisms are
made of cells
2. Cells are the smallest unit of
life
3. Cells only come from preexisting cells
Modern additions to the cell theory
include:
1. Cells contain information for
growth, development and
behavior
2. Cells are the site for the
chemical reactions of life
(metabolism)
(Not yet in the IB curriculum)
bitesizebio.com/.../05/history-of-cell-biology/
2.1.2 Discuss the evidence for the cell theory
1.
All living things are made of cells:
When living things are observed under the microscope they consistently
appear to be composed of cells.
2.
Cells are the smallest unit of life.
The cell is the smallest unit of organization that can show all the
characteristics of living processes.
Organelles often require the cooperation of other organelles for their
successful function.
2.1.1 Outline the cell theory
2.1.2 Discuss the evidence for the cell theory
3.
Cells come only from other cells.
Where do cells come from?
Cells carry out a form of cell division to form new cells.
This process of cell replication in eukaryotes is called mitosis and in
prokaryotes is called binary fission.
The parental cell divides to produce identical daughter cells.
This aspect of cell theory suggests that all cells therefore have a common
ancestor, the original ancestral cell form which all other cells have arisen
by descent. (origin of cellular life).
This relationship of common ancestor suggest that all organisms came
from the very first cell.
2.1.3 State that unicellular organisms carryout all the
functions of life
One-celled organisms (unicellular
organisms) are able to carryout
all the functions of life
The functions of life include:
1. metabolism – respiration and
excretion
2. response – to a stimuli
3. growth – increase in cell size
4. reproduction – sexual or
asexual
5. homeostasis – maintain a
stable internal environment
6. nutrition – the source of food
http://www.micrographia.com/specbiol/protis/homamoeb/amoe0100/amoeba23.jpg
2.1.4 Compare the relative size of molecules, cell membrane
thickness, viruses, bacteria, organelles and cells using
appropriate SI units
• A micrometer (μm) is one millionth of a meter 10-6 m
1000μm = 1mm or
• A nanometer (nm) is a billionth of a meter 10-9 m
click4biology.info
2.1.4 Compare the relative size of molecules, cell membrane
thickness, viruses, bacteria, organelles and cells using
appropriate SI units
Take this cool little interactive
journey to get an idea for how small
things really are.
And this interesting video,
narrated by Morgan
Freeman, gives us a real
feel for the scale of the
universe and “micro-verse”.
2.1.5 Calculate the linear magnification of drawings and the actual
size of specimens in images of known magnifications
Magnification – the number of times
larger the image (picture) is than the
specimen
If you are using a compound
microscope and the eye piece
magnification is 10x and the objective
lens is 10x, than the image is
magnified 100x
http://www.bio12.com/ch16/IBExcretion/table4.GIF
magnification = size of the image (measured) / real size (scale bar)
real size (scale bar) = size of image (measured) / magnification
2.1.5 Calculate the linear magnification of drawings and the actual
size of specimens in images of known magnifications
2.1.5 Calculate the linear magnification of drawings and the actual
size of specimens in images of known magnifications
2.1.5 Calculate the linear magnification of drawings and the actual
size of specimens in images of known magnifications
2.1.5 Calculate the linear magnification of drawings and the actual
size of specimens in images of known magnifications
2.1.6 Explain the importance of the surface area to volume ratio as
a factor limiting cell size
Why are cells so small?
1. Cells are small because it is easier to exchange materials between the
cytoplasm and the environment
2. If a cell is too large, diffusion becomes very difficult and inefficient
• Because the uptake of resources and the removal of waste must
pass through the cell membrane it is important that it doesn't have
to travel a long distance
2.1.6 Explain the importance of the surface area to volume ratio as
a factor limiting cell size
Organisms have different ways to
cope with surface area to
volume ratio problems
1.
Flat worms increase surface
area by being flat
2.
The villi in the intestines help
with absorbing nutrients
3.
The alveoli in the lungs help with
gas exchange by increasing the
surface are to volume ratio
Image of nudabranch: richard-seaman.com
2.1.7 State that multi-cellular organisms show emergent properties
Definition – the whole is more than
the sum of its parts
•
An organism can do more than
what each cell can do
individually
•
Example – the human brain
2.1.8 Explain that cells in multi-cellular organisms differentiate to
carry out specialized functions by expressing some of their genes
but not others
Every cell in your body contains the exact
same genetic information.
Why are the cells that make up your hair
very different from the cells that make
up your brain?
Some information is expressed
(turned on) and some is not
expressed (turned off)
In the nucleus the genetic information
exists in two forms (euchromatin and
heterochromatin)
a) euchromatin is the part of the genetic
information of the cell that is
expressed
b) heterochromatin is not expressed
2.1.8 Explain that cells in multi-cellular organisms differentiate to
carry out specialized functions by expressing some of their genes
but not others
•
Cells have an effect on their neighboring cells and determine what information will be
expressed and what kind of cell it will be (through chemical gradients and positioning)
•
www.ncbi.nlm.nih.gov
2.1.9 State that stem cells retain the capacity to divide and have
the ability to differentiate along different pathways
Stem cells are characterized in three
ways:
a)
b)
c)
they are unspecialized and can
be any type of cell
they are self replicating (renew)
They can continue to divide into
new cells for a long period of
time
Sources of stem cells include:
a)
b)
c)
Embryos
Umbilical cord
Bone marrow
2.1.9 State that stem cells retain the capacity to divide and have
the ability to differentiate along different pathways
2.1.9 State that stem cells retain the capacity to divide and have
the ability to differentiate along different pathways
Controversy
•
•
Against
Embryonic stem (ES) cells are
a source of controversy
because the cells are obtained
from fertilized embryos (for
example, fertility treatments
and the embryos are then
discarded)
For
Stem cells may be a way to
grow new cells and treat
diseases like Alzheimer's,
Parkinson's, Type I diabetes,
etc...
2.1.9 State that stem cells retain the capacity to divide and have
the ability to differentiate along different pathways
Some terms
•
Totipotent
– stem cells from embryos that can become any type of cell
•
Pluripotent
– stem cells that can be any type of tissue
•
Multipotent
– Stem cells (usually from the umbilical cord) that can become a limited type of different cells
www.prayersforthepeople.com/id70.html
2.1.10 Outline one therapeutic use of stem cells
Can be used for burn victims to “regrow” skin
a)
The nucleus of a blastocyst
cell is removed
b)
The nucleus of the patients
cell (in this case, skin cell) is
transplanted into the
blastocyst cell
c)
The cells are then grown in a
Petri dish and then
transplanted back to the
patient
In some cases, the embryonic cell
can be “genetically triggered”
to produce the desired cell