1. Cell Theory

3. Large Cells!
ostrich egg

4. Assessment Statements (objectives)
2.1.1 Outline the cell theory Discuss the evidence for the cell theory State that 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 a factor limiting cell size State that multicellular organisms show emergent properties Explain that cells in multicellular organisms differentiate to carry our 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.

5. Cell Theory All organisms are composed of one or more cells.
Cells are the smallest units of life.
All cells come from pre-existing cells.

6. Cell Theory Cont. Theory:
A hypothesis that has been extensively tested over time and that explains a broad range of scientific facts with a high degree of reliability
Scientific question → Hypothesis → Data → Theory
Cell theory has taken several hundred years to formulate
Many scientists contributed to its development
Microscope has given the theory credibility

7. Scientists and Cell Theory
Robert Hooke
1st described cells in 1665 looking at cork with a homemade microscope

8. Scientists and Cell Theory
Leeuwenhoek
Observed first living cells a few years later and called them “animalcules”
Meaning little animals

9. Scientists and Cell Theory
Matthias Schleiden
In 1838, stated plants are made of “independent, separate beings” called cells
Theodor Schwann
Made same statement about animal cells

10. Cell Theory Cont.
We have not been able to find any living entity that is not made of at least one cell.
Louis Pasteur
Sterilized chicken broth by boiling, and showed that living organisms would not “spontaneously” reappear.
Pre-existing cells were needed to re-establish life

11. Pasteurization
Heat food at specific temperature for a certain length of time and then cooling it immediately
Reduces the number of pathogens and bacteria in food

12. Life is Everywhere!

13. Functions of Life
All organisms exist in either a unicellular or multicellular form.
All organisms carry out all the functions of life.
Functions of life:
Metabolism
Growth/development
Reproduction
Response
Homeostasis
Nutrition
Order
Adaptation
Unicellular
Multicellular

14. Function of life Metabolism: Growth and development:
All chemical reactions that occur within an organism
Growth and development:
Heritable programs in the form of DNA direct the pattern of growth and development
Produces an organism that is characteristic of its species

15. Function of life Reproduction: Response to environment:
Involves hereditary molecules that can be passed to offspring
Organisms reproduce their own kind
Life comes only from life
Response to environment:
Imperative to survival
Plants growing towards sunlight

16. Function of life Homeostasis: Nutrition:
Maintaining a constant internal environment (e.g. temperature, acid base levels) even though external environment may fluctuate
Nutrition:
Organisms take in energy and transform it to do many kinds of work
Providing source of compounds with many chemical bonds which can be broken down to provide energy and nutrients necessary to maintain life

17. Function of life Order: Adaptation:
Characteristics of life emerge from organisms highly ordered structure
Adaptation:
Life evolves as a result of interaction between organisms and their environments
Adaptation of organisms to their environment

18. Cells and Sizes Cells are made up of a number of different subunits
Subunits are microscopically small
Most cases, microscopes are needed to see cells and their subunits

19. Microscopes Magnification Resolution
Enlarging the physical appearance or image of something
Resolution
The closest proximity of two objects that can be seen as two distinct regions of the image (like pixels)
Refers to the clarity of viewed object

20. Light Microscopes
Use light to pass through the living or dead specimen to form an image
Stains may be used to improve viewing

21. Electron Microscopes
Provide greatest magnification (over 100,000x) and resolution
Electrons pass through a specimen to form an image
Pollen

22. 1 micrometer = 1µm = 1 x 10-6
1 nanometer = 1nm = 1 x 10-9
Relative Size
Cells (up to 100µm) are relatively large, and then in decreasing size order are:
Organelles (up to 10µm)
Bacteria (up to 1µm)
Viruses (up to 100nm)
Membranes (up to 10nm)
Molecules (near 1nm)

23. Scale Bars
100nm
Mitochondria
0.5µm

24. Calculating Specimen Size
In order to calculate actual specimen size:
Magnification may be stated (x400, x10) or
Scale bars may be used to first calculate magnification and then specimen size
This is considered the image size. Size from magnification
Specimen size is its true size in nature. Usually too small to be seen without aid.

25. Calculating Specimen Size given Magnification
Specimen Size = (Image Size) / (Magnification)
Ex: Onion cells under 400x magnification
Step 1
Measure image of one onion cell (pay attention to length vs. height)
Step 2 (not to actual scale it’s for example purpose)
Calculate
(10 cm) / (400)
Specimen size = cm
Image Size
( 10 cm)

26. Calculating Specimen Size given Scale Bar
Specimen Size = (Image Size) / (Magnification)
Ex: Onion cells with scale bar
Step 1 (not to actual scale it’s for example purpose)
Measure length of scale bar (scale bar image size) with ruler
Step 2
Convert scale bar image size to µm
(1.5cm) x (1m/100cm) x (1µm/(1x10-6m) = 1.5 x 104 µm
Calculate magnification=
(Image size)/(specimen size)
(1.5 x 104 µm)/ (10 µm)= 1.5 x 105
Step 3
Calculate specimen size of cell using magnification
Measure cell and divide by magnification (units matter!)
(9.5cm)=(9.5x104µm)/(1.5x105) = 0.63 µm
10 µm
Image Size
( 1.5 cm)

27. All cells have at least on feature in common… they are small in one or more dimensions
Why do cells stay so small?
and
Why don’t they grow to a larger size?

28. Limiting Cell Size
There is a factor called the surface area to volume ratio that effectively limits the size of cells.
Surface area: total area of given surface
Ex. rectangular prism
Surface area = (height x width) + (height x width) + … of each side (six total)
Volume: the amount of space an object takes up
Height x width x length

29. Cell Volume The following are functions of (depend on) cell volume:
Rate of heat and waste production
Rate of resource consumption
Most chemical reactions occur inside the cell, so its size affects the rate of these reactions.

30. Cell Surface Area
On the surface of the cell, the membrane controls what materials move in and out of it
All raw materials, energy, and waste can enter or leave the cell only by crossing the plasma membrane
Microvilli

31. Surface Area to Volume Ratio
Cells with more surface area per unit volume are able to move more materials in and out
As width of cell increases, surface area also increases, but to a much slower rate than volume
Therefore, a large cell has less surface area to bring in needed materials and to rid the cell of waste
Cells are limited to a size they can carry out the functions of life

32. Large animals do not have larger cells, they have more cells

33. Cell Reproduction and Differentiation
Cells retain the ability to reproduce themselves
In multicellular organisms:
this allows the possibility of growth
and the replacement of damaged or dead cells
Live cells fluoresce green
Dead cells fluoresce red

34. Multicellular Organisms Show Emergent Properties
Emergent properties arise from the interaction of component parts:
the whole is greater than the sum of its parts
MacromoleculeOrganelleCellTissueOrgan SystemOrganism
When units of biological material are put together, the properties of the new material are not always additive, or equal to the sum of the properties of the components. Instead, at each level, new properties and rules emerge that cannot be predicted by observations and full knowledge of the lower levels. Such properties are called emergent properties (Novikoff, 1945).
As an example of why the reductionist approach fails, consider the function of one cell within a multicellular organism. Even if we understand the cell's function, that does not mean we fully understand the organism's physiology. After all, the activity of each cell is affected by the activity of other cells in the tissues, organs, and organ systems within the organism. The cell is thus no longer in isolation, and its integration into a system provides that system with emergent properties (Novikoff, 1945).

35. Multicellular Organisms
Start out as a single cell after sexual reproduction
This single cell has the ability to reproduce at a rapid rate
Resulting cells go through a differentiation process to produce all the required cell types for the well-being of the organism (staggered)

36. All of the cells in your adult body originated from a single cell (fertilized egg)…
And all of those cells (except those destine to become sperm or eggs) have exactly the same set of DNA,
Then why is your body composed of lots of different kinds of specialized cells?
If all your cells have the exact same set of genes, why don’t all your cells stay identical?

37. Differentiation
A cell becomes different from its parent or sister cell
At various developmental stages of life, cells differentiate because they begin to express different genes.

38. Cell Differentiation
Each cell contains all the genetic information for the production of the complete organism
However, each cell becomes a specific type of cell dependent on which DNA segment becomes active
Some cells have a greatly, or even completely, diminished ability to reproduce once they become specialized. Nerve and muscle cells are prime examples of this type of cell. Other cells, like epithelial cells like skin, retain the ability to rapidly reproduce throughout their life. The offspring of these rapidly reproducing cells then differentiate into the same cell type as the parent.

39. Stem Cells
Populations of cells within organisms that retain their ability to divide and differentiate into various cell types

40. Stem Cells Stem cells may be pluripotent or multipotent.
Pluripotent stem cells can give rise to any type of cell in the body except those needed to support and develop a fetus in the womb.
Can be isolated from human embryos
Stem cells that can give rise only to a small number of different cell types are called multipotent.

41. Stem Cells Plants contain stem cells in meristematic tissue
Occur near root and stem tips
Composed of rapidly reproducing cells that produce new cells capable of becoming various types of tissue
Gardeners take advantage of this by taking cuttings from stems or roots to produce new plants

42. Embryotic Stem Cells (ESC)
Ultimate stem cell is fertilized egg
All specialized cells of body originate from it
First 8 cells of human embryo are also stem cells b/c haven’t differentiated

43. Embryonic Stem Cells
In early 1800s, scientist found embryonic stem cells in mice
These cells retain the ability to:
Form any type of cell in an organism
Form a complete organism
“immortal”
Why researchers use them:
Easier to work with than adult cells b/c don’t adhere as tightly
Don’t usually provoke tissue rejection
Easier to administer to a patient
Can still become a specialized cell

44. ESC Research
Use stem cells to replace differentiated cells lost due to injury or disease:
Parkinson’s disease
Alzheimer’s disease
Both caused by loss of brain cells
Implanted stem cells could replace them
Diabetes
Help restore pancreas of essential cells that are depleted
Paralyzed victims
Nerve
Muscle

45. Other Stem Cell Research
Tissue specific stem cells
Ex. Blood cells to replace damaged bone marrow in leukemia patients
New research harvesting umbilical cord blood at birth
Keep vs. donate??
Induce Pluripotent Stem Cells (iPSC)

46. Therapeutic use of stem cells.
A retrovirus that has been rendered harmless is used to introduce a gene into a bone marrow stem cell of a patient that lacks it. The cell and its descendants will possess the gene.
Fig

47. Is Stem Cell Research Ethical?
Cells that come from embryos involves the death of the embryo
Does this represent the taking of a human life?
Others argue
That this research could result in the significant reduction of human suffering.