Topic 1.1 Introduction to the Cell

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Topic 1.1 Introduction to the Cell Cell Theory

• IB Biology
• S.Dosman

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Cells are Us
A person contains about 100 trillion cells.
Thats 100,000,000,000,000 or 1 x 1014 cells.
There are about 200 different cell types in
mammals (one of us).
Cells are teeny, tiny, measuring on average about
0.002 cm (20 um) across. Thats about 1250 cells,
shoulder-to-shoulder per inch.
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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
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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.
https//www.youtube.com/watch?v4OpBylwH9DU
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Cells come in a variety of types
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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.

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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

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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)

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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

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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

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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 Earths surface.

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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.

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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
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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.

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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 10-9 m
Ribosome 25 nm 25 x 10-9 m
Cell membrane 7.5 nm thick 7.5 x 10-9 m
DNA double helix 2 nm diameter 2 x 10-9 m
Hydrogen atom 0.1 nm 0.1 x 10-9 m
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Cell SizeRelative order

• Organelles
• Bacteria
• Viruses
• Membranes
• molecules

http//www.cellsalive.com/howbig.htm http//micro.
magnet.fsu.edu/primer/java/scienceopticsu/powersof
10/
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1.1 U3 Surface area to volume ratio is important
in the limitation of cell size

http//vce-biology.blogspot.ca/2012/08/why-are-cel
ls-so-small-surface-area-to.html
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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.

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• Also, the cells nucleus (the brain) can only
  control a certain amount of living active
  cytoplasm

How was this picture taken?
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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
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Organisms try to optimize the SA/vol ratio to
suit their environments

• Ex. Intestinal villi Ex. Surface area of lungs

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Homework Challenge

• Research an unusually large cell and find out how
  it has overcome its large size.

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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.

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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.

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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.

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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.

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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.

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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
http//www.wired.com/wiredscience/2008/11/top-10-a
mazin-1/ (glowing mice)
https//www.youtube.com/watch?v2-3J6JGN-_Y
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1.1 A3 Use of stem cells to treat Stargardts
disease and one other named condition

• -See assignment

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Review research
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http//www.youtube.com/watch?vbvEtukFitdE
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Comparison

• http//www.biology.ualberta.ca/facilities/multimed
  ia/uploads/cell_biology/provseuk.html
• http//micro.magnet.fsu.edu/primer/java/electronmi
  croscopy/magnify1/index.html
• http//www.cellsalive.com/cells/3dcell.htm