1. Topic 2 Cells

2. Assessment Statements
2.1 Cell Theory
Assessment Statements
Outline the Cell Theory
Discuss the evidence for the cell theory
State the unicellular organisms carry out all the functions of life.
Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit.
Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification.
Explain the importance of the surface area to volume ratio as factor limiting cell size.
State that multicellular organisms show emergent characteristics.
Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.
State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways.
Outline one therapeutic use of stem cells.

3. 2.1.1. and 2.1.2. Cell Theory Robert Hooke
Living organisms are composed of cells
Cells are the smallest unit of life
Cells come from pre-existing cells

4. 2.1.3: Unicellular Organisms
Euglena. sp
STATE: Unicellular organisms carry out all the functions of life
metabolism e.g. cellular respiration
response or sensitivity
homeostasis
growth
reproduction
nutrition

5. Functions of Life in Unicellular Organisms
A unicellular organism such as the Amoeba needs to metabolize organic materials in order to make the chemicals needed to sustain life.
It must be able to detect changes in its environment, so it can respond to conditions.
It must also be able to control its internal environment (homeostasis).
It must be able to obtain food, either make its own (photosynthesis) or ingested- nutrition.
If the species is to survive it must then reproduce.

6. One the function carried out by all living organisms is reproduction
Meaning, the first principle of the cell theory is that cells can only come from pre-existing cells.
They cannot be created from non-living
material.

7. Evidence for the Cell Theory
Can’t be proven “true”
Require us to examine every single cell….which is impossible!
Evidence for the cell theory comes from observation and experimentation. When observed with a light microscope, every kind of cell - from every kind of organism
Evidence comes form observations and experimentation.
The statement that all living cells come from pre-existing cells does not mean that life has always existed; biologists believe that self- replicating molecules gradually evolved into the earliest cells.

8. Onion Cell Stained with Iodine
x40 Magnification
How big is an onion cell?

9. Cell Size
One of the few cells that is large enough to be visible to the naked eye is the mature human ovum, which is about 150um.
Most cells are much smaller, can only be seen using a microscope. Light microscopes can magnify up to 1000 times, but can only reveal large internal structures such as the nucleus.
An electron microscope is needed to see smaller structures. It can magnify up to 500,00 times.

10. 1 meter (m)= 1m
1 millimeter (mm)=10-3m
1 micrometer (um)=10-6m
1 nanometer (nm)= 10-9m

11. 10 nm membrane thickness 100 nm virus 1 µm bacteria
1mm = 1,000 µm
1 µm = 1,000 nm
1 nm molecules
10 nm membrane thickness
100 nm virus
1 µm bacteria
(up to) 10 µm organelles
(up to) µm cells

12. Size Matters!
Size Matters!
Size Matters!

13. Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit.
A molecule
1nm

14. A molecule 10nm Glucose (1nm)

15. 100nm 10nm A virus – the T bacteriophage

16. Bacteriophage (virus) E.coli (bacteria cell)
100nm
0.1µm
1000nm1µm

17. Bacteria (1µm) Organelle (10µm) Eukaryote Cell (100µm)

18. 2.1.4: Relative sizes

19. In the last sequence of slides every thing increased by a magnitude of 10x each time. The IB requires you to remember the sizes.
Make up a mnemonic to help you to remember the order!
My Mom Visits Bieber Outside Concerts.
My Money Vanishes Beautifully On Cars.
My Most Valued subject is Bio, Obviously! Cool!

20. How to Figure out Cell Size
Calculate the linear magnification of drawings
How to Figure out Cell Size
Microscopes are used to see these really small cells.
Our microscopes have 3 lenses on them with magnification of x40, x100, x400.
In order to figure out the size of a cell we need to first figure out the field of view under the microscope.

21. Calculating Field of View
x40
Field of view is 4mm or 4,000um
4mm
To work out the field of view, under the x40 lens and using a ruler it’ll be about 40mm. However you need to do calculations under the higher magnifications.
High power/low power = low magnification/ high magnification
x/4,000um = 40/100 solve for x= 1,600um.

22. Field of View 4mm
Now that we have our filed of view we can calculate our cell size.
Field of view/ number of cells across
4,000um/2= 2,000um

23. To calculate the magnification of a drawing:
Drawing size/ Real Size
Using a ruler: 50mm/ 2,000um
Make sure the units our the same. Most cells should be measured in um. 50,000um/2,000= 25x magnification

24. Surface Area to Volume Ratio
Cells are very small, no matter what the size of the organism that they are part of.
Cells do not and cannot grow to be very large and this is important in the way living organisms are built and function.

25. Why are cells so small?
Nutrients and wastes move across a cell surface by diffusion.
The chemical reactions that take place is known as the cell’s metabolism
TOPIC 2: CELLS

26. Substances must be absorbed by the cell and waste products must be removed.
The rate at which this occurs is determined by the surface area of the cell.
As size of an object increases the ratio between the surface area and volume decreases.
Rate materials enter and leave the cell depends on surface area
Rate materials are used or produced depends on the volume

27. Why is this important?
The surface area relates to how much material can enter a cell at a time.
The bigger the area is the more material can enter in an amount of time

28. The volume relates to how much material is needed at a time.
The bigger the volume is the more material is
needed to maintain it for an amount of time.

29. Lets look at Surface areas and volumes………
Fill in the table below: a
Size of side (a)
Surface area of the box
(a x a x 6)
Volume of the box
(a x a x a)
Surface area to volume ratio 1 6
6 : 1 2 24 8 3 54 27 4 96 64 5
150
125
216 7
294
343
Size of side (a)
Surface area of the box
(a x a x 6)
Volume of the box
(a x a x a)
Surface area to volume ratio 1 6
6 : 1 2 3 4 5 7
Size of side (a)
Surface area of the box
(a x a x 6)
Volume of the box
(a x a x a)
Surface area to volume ratio 1 6
6 : 1 2 24 8
3 : 1 3 54 27
2 : 1 4 96 64
1.5 : 1 5
150
125
1.2 : 1
216
1 : 1 7
294
343
0.9 : 1 a a

30. What trend did you notice?
What happened to the area as side size increased?
The area increased much faster than the side size.
What happened to the volume?
The volume increased much faster than the side size
Which one (area or volume) increased the fastest?

31. Assume that a volume of 1 needs 1 lot of material to sustain it…
Assume that a volume of 1 needs 1 lot of material to sustain it….And an area of 1 can provide 1 lot of material: a a a
Look at cell size where a=1. Is it able to supply its needs?
Look at cell size where a=6. Is it able to supply its needs?
What about a=7?
Area = 6 Volume =1 ….It can provide 6x as much material than it needs
Area = 216 Volume =216 ….It can just provide as much material than it needs

32. If the cell gets too large and the ratio of Surface Area to Volume decreases it can’t take in the essential materials or excrete the waste fast enough….. So it must divide.

33. The same idea is relevant for heat and waste needing to be given out by an organism.

34. Can you think of some organisms that have to deal with this problem?
Elephant – a very big organism produces lots of heat. How does it get rid of all the heat with a relatively low SA : Vol ratio?
Find out about elephant ears.
The Shrew – A very small organism with a relatively large SA : Vol ratio. How does it manage to stay warm in winter?
Find out about changes in metabolism.

35. 2.1.6: Surface area:volume
As a cell grows it has less surface area to obtain materials and to dispose of waste.
The rate of exchange of materials across the membrane becomes limiting and cannot keep up with the cell’s requirements.

36. Becoming multicellular has enormous advantages.
An organism can grow in size and its cells can differentiate, meaning they can take on specific functions, so the organism can grow in complexity as well as size.

37. Example: Nerve cells for interaction and communication with the outside, and muscle cells for movement.
Differentiation allows for emergent properties in a multicellular organism.
This means that different cell types interact with each other to allow more complex functions to take place.
Never cells may interact with muscle cells to stimulate movement.

38. Emergent Properties
One person playing the piano can produce a simple, recognizable tune.
If several musicians with other instruments join in and play together as a group, they produce a wide variety of sounds and many different effects.
One cell can function on its own, but if it interacts with other cells in a group, the organism can carry out a range of more complicated functions.

39. 2.1.8: Multicellular Organisms
All cells in an individual contain the same genetic information
At an early stage of embryonic development, cells differentiate and become specialized to perform specific function.
Some genes are turned on while others are not turned on to produce specific cells e.g. in muscle cells, muscle genes get turned on while liver genes get turned off.

40. 2.1.9: Stem cells
STATE: Stem cells retain the capacity to divide and have the ability to differentiate along different pathways
Cells become specialized known as differentiation and form cells for specific purposes- muscle cells for contraction, liver cells for metabolism of toxins, etc.
Once differentiation has happened, it cannot be reversed.
Embryonic stem cells are said to be pluripotent meaning they can turn into a great many different cell types.

41. Embryonic stem cells are unique in their potential versatility to differentiate into all the body’s cell types.
Stems cells differ from most other cells in these ways:
They are unspecialized
They can divide repeatedly to make large number of new cells.
They can differentiate into several types of cell.

42. 2.1.10: Therapeutic Stem Cells

43. For more than 30 years, bone marrow stem cells have been used to treat cancer patients with conditions like leukemia and lymphoma. During chemotherapy, most of the leukemia cells are killed as are the bone marrow stem cells needed as a patient recovers. However, if stem cells are removed before chemotherapy, and then re-injected after treatment is completed, the stem cells in the bone marrow are able to produce large amounts of red and white blood cells, to keep the body healthy and to help fight infections.