1. Topic 1.1 Introduction to the Cell & Cell Theory
IB Biology
S.Dosman

2. Cell Biology
4/17/2017
Cells are Us
A person contains about 100 trillion cells. That’s 100,000,000,000,000 or 1 x 1014 cells.
There are about 200 different cell types in mammals (one of us).
nerve cell
Cells are teeny, tiny, measuring on average about cm (20 um) across. That’s about 1250 cells, “shoulder-to-shoulder” per inch.
G. Podgorski, Biol 1010 2

3. Why Study Cell Biology?
The key to every biological problem must finally be sought in the cell, for every living organism is, or at some time has been, a cell. E.B. Wilson, 1925

4. All organisms are composed of one or more cells
1.1 (U1) According to the cell theory, living organisms are composed of cells
The Cell Theory (proposed independently in 1838 and 1839) is a cornerstone of biology.
All organisms are composed of one or more cells
Cells are the basic/smallest unit of life
All cells arise from previously existing cells
Evidence? Many scientists through research formed the theory. Microscope evidence is key. When cells are removed from tissue they can survive for periods of time. No unit smaller than a cell could survive on its own.

5. Cells come in a variety of types

6. Evidence to support the cell theory.
Through the process of scientific investigation much evidence has been collected to support the cell theory. Living things have been examined and all have been found to consist of cells thus far.
However, like much of science there are some exceptions to the rule and while they do not disprove the cell theory they do not fit into our idea of cells as small box-like structures with the same organelles inside each cell.

7. 1.1 (A1) Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
The following examples do not disprove the cell theory but do not fit into our typical idea of cells
Striated Muscle
skeletal muscle fibers are larger (can be 300mm long)
have one plasma membrane but many nuclei
is not the typical view of one nuclei per cell

8. 1.1 (A1) Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
Giant Algae (ex. Acetabularia)
Is a single celled organism that challenges the idea that cells must be small in size and simple in structure
It has a complex structure made up of three anatomical parts
Huge in size (5-100mm)

9. Aceptate fungal hyphae
1.1 (A1) Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
Aceptate fungal hyphae
Challenges idea that a cell is a single unit
Hyphae are large, many nucleus
Continuous cytoplasm
Cell walls made of chitin

10. Homework Assignment
Research the main contributions of the following scientists to the evidence for the cell theory.
Robert Hooke
Anton van Leewenhoek
Mathias Schleiden
Theordor Schwann
Louis Pasteur

11. Evidence to support the cell theory.
Despite these exceptions most living tissues are composed of cells. Cells can be removed from an organism and survive whereas smaller parts cannot so this is evidence that supports the theory that cells are the smallest unit of life.
The evidence for support of the last statement of the cell theory has shown up in biology experiments that disprove the idea of spontaneous generation. The only exception to this would be when life first appeared on the Earth’s surface.

12. 1.1 (U2) Organisms consisting of only one cell carry out all functions of life in that cell.
Unicellular organisms consist of only one cell and that one cell must carry out all life functions for that organism.
This includes nutrition, metabolism,, growth, response, excretion, homeostasis, and reproduction.

13. 1.1 (U2) Organisms consisting of one cell carry out all functions of that one cell
Nutrition: source of compounds to provide energy, either absorption or materials or photosynthesis
Metabolism: all chemical reactions, ex. respiration
Growth: grow or change size, may be limited but evident
Response: react to the environment or stimuli
Excretion: removal of metabolic waste
Homeostasis: constant internal environment, ie. Temperature, pH, water balance
Reproduction: hereditary molecules that can be passed on either sexually or asexually

19. Cell Size
Once cells reach a certain size they stop growing and divide.
If a cell grew too large it would have many problems because its surface area to volume ratio would become too small.
As the size of an object increases the ratio between surface are and volume decreases.

20. Relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells.
Eukaryotic cell
10 – 100 µm
= 10 – 100 x 10-6 m
Prokaryotic cell
1 – 5 µm
= 1 – 5 x 10-6 m
Nucleus
10 – 20 µm
= 10 – 20 x 10-6 m
Chloroplast
2 – 10 µm
= 2 – 10 x 10-6 m
Mitochondrion
0.5 – 5 µm
= 0.5 – 5 x 10-6 m
Bacteria
1 – 4 µm
= 1 x 10-6 m
Large virus (HIV)
100 nm
= 100 x m
Ribosome
25 nm
= 25 x m
Cell membrane
7.5 nm thick
= 7.5 x m
DNA double helix
2 nm diameter
= 2 x m
Hydrogen atom
0.1 nm
= 0.1 x 10-9 m

21. Cell Size Relative order
Organelles
Bacteria
Viruses
Membranes
molecules

22. 1.1 U3 Surface area to volume ratio is important in the limitation of cell size

23. The connection between surface area of a cell and its ability to exchange materials with its outside environment.
In cells, the rate at which materials can enter or leave a cell depends on the surface area of that cell while the rate at which those materials can be used or produced depends on the volume of that cell.
If cells become too large it becomes inefficient at exchanging materials with its environment.

24. Also, the cell’s nucleus (the brain) can only control a certain amount of living active cytoplasm
How was this picture taken?

25. Shrew-high SA/vol ratio How might this be a disadvantage?
- Warm blooded, lose heat constantly
-need to eat constantly
Cactus- thin needle like leaves
Decrease SA/vol ratio and alter metabolism
Need to conserve water

26. Organisms try to optimize the SA/vol ratio to suit their environments
Ex. Intestinal villi Ex. Surface area of lungs

27. Homework Challenge
Research an unusually large cell and find out how it has overcome its large size.

28. 1.1 (U4) Multicellular organisms have properties that emerge from the interaction of their cellular components.
Emergent properties can be defined as properties where the whole is more than the sum of their parts.
In other words, multicellular organisms can achieve more than the sum of what each cell could accomplish individually.

29. Emergent Properties
Multicellular organisms show emergent properties when the cells work together to achieve more than what one cell on its own can achieve (unicellular).
A good example of emergent properties in a multicellular organism would be the human brain. On their own, individual neurons (nerve cells) are not capable of thought but it is the interactions of all neurons that allow the brain to think.

32. Define differentiation.
Differentiation is a process that occurs in the cells of multicellular organisms where cells develop in different ways and become specialized for one particular function.

34. To summarize……..
The process of differentiation is directed by the genes of the cells. All the cells contain the same genes but the cell only uses the ones it needs to follow its path of development. In other words all cells have genes they turn on and others they leave inactive.
For example, the cells in your toes contain the genetic information in the form of genes to make the pigment colors for your eyes but the cell does not express those genes.

35. Define stem cells.
Stem cells are unspecialized cells that have the ability to divide or self renew by cell division and to differentiate.
Sources of stem cells are human embryos, umbilical cord of a new born baby, and some can be found in the adult body mostly in the bone marrow.

36. 1.1 U7 The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses
(glowing mice)

37. 1.1 A3 Use of stem cells to treat Stargardt’s disease and one other named condition
-See assignment

38. Review research

46. Comparison