Topic 2.1 Cell Theory
Assessment Statements
2.1.1 Outline the cell theory.
2.1.2 Discuss the evidence for the cell theory.
Watch this:
Try this:
Cell Theory Jigsaw activity
1. Split into two groups A and B.
2. Each group has a different version of a text with
some key words missing.
3. Read through your text and write a list of
questions you could ask to identify the missing
words.
4. Pair up with a student in the other group and take
it in turns to read out the text and ask questions.
2.1.1 The Cell Theory
Schleiden and Schwann (1838)
All living things are made of cells
Cells are the smallest unit of life
All cells come from preexisting cells
2.1.2 Evidence for Cell Theory
All living things are made of cells…
When we look at living things under a
microscope they appear to be made of cells
All living things are made of cells
We can see them when we look down the
microscope:. Can you identify these cells?
Exceptions
What’s wrong with this?
Muscle cells: have
more than one
nucleus per cell.
Surrounded by a single
cell membrane but
are multinucleated
(many nuclei).
This does not conform
to the standard view
of a small single
nuclei within a cell
Fungal Hyphae: very large
with many nuclei and a
continuous cytoplasm
A tubular system of hyphae
form dense networks
called mycelium.
Multinucleated
Have cell walls made of
chitin
Cytoplasm is continuous
along the hyphae with no
end cell wall or
membrane
What is it?
Amoeba: a single cell capable of all life processes.
In more complex organisms cells are specialised i.e. one cell per function.
Amoeba are much larger than other cells and some
biologist consider them 'acellular' (non-cellular).
The cell is the basic unit of life
There are many single
celled organisms:
The cell is the smallest unit of organisation that
can show all the characteristics of living things.
Organelles often require the cooperation of other
organelles for their successful function.
Read
this:http://learn.genetics.utah.edu/content/begin
/cells/organelles/
to learn about how cells evolved.
All cells come from preexisting cells
We can see this in these
processes.
Can you name them?
Evidence
Eukaryotic (plant, animal and fungal cells)
undergo mitosis
Prokaryotes (bacteria) reproduce by binary
fission.
Louis Pasteur carried out a famous experiment
to prove that spontaneous generation did not
occur.
But when Pasteur broke the swan neck off the
bottle microorganisms soon grew in the broth.
Watch this:
Check this out:
2.1.3 State that unicellular organisms
carry out all the functions of life.
Reproduction
Usually a form of asexual
reproduction called binary
fission which produces a
clone.
Yeast cells
reproduce by
budding.
Nutrition
The synthesis or
absorption of
organic matter.
Often in the form of
phagocytosis, e.g.
this amoeba.
Many bacteria are
parasitic whilst
others can
photosynthesise.
Metabolism includes the process of respiration
which produces energy in the form of ATP.
In yeast anaerobic respiration produces alcohol
as a waste product!
Response to a change
in the environment.
This can be seen when
bacteria such as this
E. coli demonstrate
chemotaxis (respond
to chemicals in their
environment).
Homeostasis is the maintenance of internal
cell conditions. Single celled organisms can
withstand large changes in environmental
conditions as a result of their ability to carry
out all of the life processes.
Growth in unicellular
organisms is an
increase in cell size
and volume.
Assessment Statement
2.1.4 Compare the relative sizes of molecules,
cell membrane thickness, viruses, bacteria,
organelles and cells, using the appropriate SI
unit.
Relative Sizes of Cells
Assessment Statement:
2.1.5 Calculate the linear magnification of
drawings and the actual size of specimens in
images of known magnification.
Magnification
The number of times bigger than the actual size.
Biological diagrams and photographs usually
indicate magnification.
As a scale bar
As a number (x500)
Calculating Magnification
magnification = image size
actual size
Rules for magnification calculations
1. Convert all units to make them the same
(where appropriate).
You will often be working with mm, um and nm.
1cm = 10mm = 10,000um
1mm = 1000um
1um = 1000nm
To convert from mm to um x 1000
To convert from um to mm /1000
2. Rearrange the magnification equation as
needed to find the value you want.
M = I/A
A = I/M
I=AxM
3. Convert your answer into appropriate SI
units using scientific notation where
necessary.
e.g. 0.03mm = 30um = 3 x 10-2um
x 1000
Example calculation
Measure the length
of the image in mm
using a ruler.
Magnification is x600.
Plug the data into the
equation: A= I/M
Give answer in SI units.
Paramecium caudatum
Magnification using scale bars
Scale bars give
an indication of
the true size of an
object viewed
under a microscope.
We need another
formula to calculate
this:
magnification = measured length
scale bar label
Assessment Statement
2.1.6 Explain the importance of the surface
area to volume ratio as a factor limiting cell
size.
Giant Squid and Colossal
Squid have nerve cells as
long as 12 m
.
In humans, the longest
nerve cells are about 1.5m
running from the base of
the spine to the toes
The smallest cell
belongs to a genus of
bacteria called
Mycoplasma with a size
of 0.3 to 0.5 um.
The smallest
human cell is the
sperm cell at
100 to 200um
Limit to Cell Size
Factors affected by of cell volume:
- rate of heat production
- waste production
- resource consumption
Factors are affected by surface area:
- exchange of materials
- exchange of heat
Assessment Statement:
2.1.7 State that multicellular organisms show
emergent properties.
Emergent Properties
The whole is greater
than the sum of its parts.
An analogy - a light bulb.
Made of a glass sphere, a
tungsten filament and a metal
screw cap.
Looking at the properties of their
individual parts, you couldn’t
predict the properties of the light
bulb.
Examples
•New properties that emerge with each step upward
in the hierarchy of life, owing to the arrangement
and interaction of parts as complexity increases.
•Na is a metal, Cl is a poisonous gas – together, they
are edible
•Do macromolecules behave like a composite of
monomers?
•If you put chlorophyll and all molecules from plant
cell into test tube, could they perform
photosynthesis?
•If you put functioning nerve cells together, will there
be thought?
•Cycling of nutrients in an ecosystem involves
complex interaction of all members.
Assessment Statements:
2.1.8 Explain that cells in multicellular organisms
differentiate to carry out specialized functions by
expressing some of their genes but not others.
2.1.9 State that stem cells retain the capacity to
divide and have the ability to differentiate along
different pathways.
2.1.10 Outline one therapeutic use of stem cells.
Differentiation and Specialisation
Stem Cells
Up to the eight-cell
stage, all cells in an
embryo are identical.
They are called
embryonic stem cells.
Embryonic stem cells
have the potential to
develop into any other
specialised type of cell .
All cells contain the same
set of instructions in the
form of DNA.
Cells become specialised
because the genes that
are not required are
switched off.
Only the genes needed
to make a particular
type of cell work are
switched on.
Watch these:
Stem Cell Debate
In your groups you will be given a character
profile.
Read the information and decide if your
character is for or against the use of stem
cells.
Produce a 3 minute speech by your character
in response to the task outlined on your brief.
What you need to be able to do:
2.1.1 Outline the cell theory.
2.1.2 Discuss the evidence for the cell theory.
2.1.3 State that unicellular organisms carry out all the functions of life.
2.1.4 Compare the relative sizes of molecules, cell membrane thickness,
viruses, bacteria, organelles and cells, using the appropriate SI unit.
2.1.5 Calculate the linear magnification of drawings and the actual size of
specimens in images of known magnification.
2.1.6 Explain the importance of the surface area to volume ratio as a factor
limiting cell size.
2.1.7 State that multicellular organisms show emergent properties.
2.1.8 Explain that cells in multicellular organisms differentiate to carry out
specialized functions by expressing some of their genes but not others.
2.1.9 State that stem cells retain the capacity to divide and have the ability to
differentiate along different pathways.
2.1.10 Outline one therapeutic use of stem cells.