1. *
2.1 Cell theory

2. * Each will receive a section of text. Read it and
study it for a few minutes.
* Find other students with different sections of
text and get together in groups
* Explain your section to the other members of
the group to learn and understand the main
concepts.
* As a group prepare an oral presentation of the
topic. You will be randomly chosen.
*

3. *
*The cell theory has 3 basic principles:
*ALL LIVING THINGS ARE MADE FROM CELLS
*CELLS ARE THE SMALLEST UNITS OF LIFE
*CELLS COME ONLY FROM OTHER CELLS
*Exceptions? Muscle cells, fungal cells,
protoctista, virus

4. *
* Robert Hooke (1635 – 1703)
* Pioneer microscopist, optics enthusiast, coiner of
the term “cell”
* Famous drawings of cork section in a microscope
* Antonie van Leeuwenhoek (1632 – 1723)
* “Father of microbiology”
* Master lens-maker
* He discovered „animalcules‟ in water and became
known as the discoverer of many cells

5. *
* Early microscopes
* Light microscopes
* Transmission Electron Microscope
* Scanning Electron Microscope

6. *
* “All living things consist of cells”
* Since Hooke and van Leeuwenhoek, huge
numbers of tissue samples from many different
organisms have been examined using microscopes
and have been found to be made of cells.

7. * “Cells are the smallest unit of life”
* Based on the idea that nothing smaller than a
cell can survive independently
* Experiments can be done to separate the cell‟s
subunits, and these do not survive by
themselves.
* A cell is the smallest unit that can show all the
characteristics of living processes.

8. *
* “Cells come from pre-existing cells”
* Spontaneous generation: by preventing
entry of airborne particles to a nutrient
Pasteur‟s Experiment for broth, Pasteur stopped the growth of the
spontaneous generation culture.
* Robert Remak discovered cellular division

9. *
* Magnification = size of image
actual size of specimen
• Often calculations are needed to convert from the size of the image
to the real size of the specimen
• It is important to use the same metric prefixes: micrometers or
millimeters for all
• Scale bars are often used on drawings and pictures

13. *
* 1. molecules (1nm). 2. cell membrane thickness
(10nm). 3. virus (100nm). 4. bacteria (1um). 5.
organelles (less 10um). 6. cells (<100 um). 7. generally
plant cells are larger than animal cells.

14. *

15. *
* A. Calculate magnification
Magnification= measured length
scale bar label
B. Actual size
Actual size = measured length
magnification
Remember: To answer questions “calculate the magnification”
the image is irrelevant as long as you have the scale bar.

16. *
* A student looks at an image of a cell magnified 350 times. The
image is 250mm long. Calculate the actual length of the sample
in the image

17. *
* A sperm cell has a tail 50μm long. A student draws it 75mm long.
What is the magnification?

18. *
* Why are most cells so small?
* Because of the surface area-to-volume ratio.
* Doubling the diameter of a cell increases its volume by 8 times,
but increases the its surface area only by 4 times.
* The significance of this relationship is that the volume of a cell
determines the chemical activity that can take place within it,
whereas the surface area determines the amount of substances
that can be exchanged between the inside and the outside of
the cell.

19. *

20. *
* The rate of heat production, the rate of waste production and the
rate of resource consumption of a cell are functions of its volume
* The rate of exchange of materials and energy (heat) is a function
of its surface area.
* A large SA:vol ratio benefits by:
* Diffusion pathways are shorter, therefore more efficient
* Concentration gradients are easier to generate (it takes less solute to
make a 10% solution in a beaker than in a bucket!)

21. *
* Cells are small because: (oxygen example)
* A big cell needs more oxygen to diffuse across the membrane
* A big cell has a relatively small surface area compared to its volume
* The rate of diffusion across the membrane limits the amount of
oxygen that enters the cell.
* Two cells are more efficient than one large cell.
* This also leads to cell differentiation, specialized functions and
more complex multicellular life.

22. * Emergent properties arise from the interaction of component
parts: the whole is greater than the sum of its parts.
* TOK: The concept of emergent properties has many
implications in biology. Life itself can be viewed as an
emergent property, and the nature of life could be discussed in
the light of this, including differences between living and non-
living things and problems about defining death in medical
decisions.

23. *
* As a model consider the electric light bulb. The bulb is the
system and is composed of a filament made of tungsten, a
metal cup, and a glass container. We can study the parts
individually how they function and the properties they posses.
These would be the properties of :
* Tungsten
* Metal cup
* Glass container.
* When studied individually they do not allow the prediction of
the properties of the light bulb. Only when we combine them
to form the bulb can these properties be determined. There is
nothing supernatural about the emergent properties rather it is
simply the combination of the parts that results in new
properties emerging.

24. *
* Emergence is the occurrence of unexpected characteristics or
properties in a complex system. These properties emerge from
the interaction of the „parts‟ of the system. Remember that
biology insists on a population thinking so that we know the
interacting „parts‟ vary in themselves and therefore their
„emerging‟ properties can only be generalised. On a biological
scale consider the current debate about the nature of human
consciousness or the origin of life itself.
* Mayr, E (2004) What Makes Biology Unique? Cambridge University Press:
Cambridge
*A relatively new field in biology, Systems Biology, looks at
the way different parts of a whole organism interact with
each other to give emergent properties.
*Think about the human brain, for example.

25. *
* Remember: When we studied genes and DNA we saw how cells
acquire a specific function: differentiation.
* As a general principle then we find that the larger a
multicellular organisms become the more diversity and
differentiated specialisms there are within the organism.
* Rather than all cells carrying out all functions, tissues and
organs specialise to particular functions. These organs and
systems are then integrated to give the whole organism (with its
emergent properties).

26. *
* Specialised cells have switched on particular genes (expressed)
that correlate to these specialist functions.
* These specific gene expressions produce particular shapes,
functions and adaptations within a cell.
* Therefore a muscle cell will express muscle genes but not those
genes which are for nerve cells.
* What is the benefit of differentiation and specialisation of tissues
rather than all tissues carrying out all functions?

27. *

28. *
* Embryonic stem cells
* Potential: promising
source for treating
many diseases
* Considerations: Needs
drugs to suppress
immune system
* Ethically: When
isolating hES (human)
in the lab, embryos are
destroyed
Genetic Science Learning Center (1969,
December 31) Stem Cell Quick Reference.
Learn.Genetics. Retrieved February 26,
2012, from
http://learn.genetics.utah.edu/content/t
ech/stemcells/quickref/

29. *
* Somatic stem cells
* Potential: Routinely
used for blood-related
diseases, but not for
producing an
unrelated cell type.
* Considerations: Most
types of somatic stem
cells are present in
low abundance and
are difficult to isolate
and grow in culture.
* Ethically: Not
controversial

30. * Induced pluripotent
*
stem cells
* Potential: Mouse iPS
cells can become any
cell in the body.
Although more analysis
is needed, the same
appears to be true for
human iPS cells.
* Considerations: much
less expensive to
create than ES cells
generated through
therapeutic cloning
* Ethically: subject to
the same ethical
considerations that
apply to all medical
procedures.

31. * Therapeutic cloning *
* Potential: can, in
theory, generate ES
cells with the potential
to become any type of
cell in the body.
* Considerations: made
from a patient's own
DNA, there is no danger
of rejection by the
immune system. the
cloning process has
been time consuming,
inefficient, and
expensive
* Ethically: involves
creating a clone of a
human being and
destroying the cloned
embryo, and it requires
a human egg donor.

32. *

33. *
* Learn Genetics web page: http://learn.genetics.utah.edu
* Membranes
* Inside the cell
* Transport inside the cell