IB BIOLOGY
TOPIC 2: CELLS
I. CELL THEORY
A. What It Says
1. All living things are made of one or more cells
2. The cell is the basic unit of life/the smallest unit that shows all the
characteristics of life
3. All cells come from pre-existing cells
B. History of Cell Discovery and Evidence for the Cell Theory
1. History of Cell Discovery
Table 1. Some significant events in the development of the cell theory.
DATE
NAME(S)
1590’ Zaccharias
s
and Hans
Janssen
~166 Robert
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Hooke*
1674
Anton(y) van
Leeuwenhoek
*
1683
~183
8
1839
1833
1858
1859
Matthias
Schleiden
Theodor
Schwann
Schleiden
and Schwann
Robert Brown
Rudolph
Virchow
Louis Pasteur
SIGNIFICANT EVENT/DISCOVERY
Invention of microscope
Invented compound microscope and iris diaphragm
Observed plant tissues, specifically cork, and found repeated
units he called cells described in Micrographia, published in
1965
Also accomplished in a number of other areas including
physics (Hooke’s Law)
First observed unicellular organisms (protists) in pond water
Discovered bacteria
Improved the microscope
Found cells in all plants
Found cells in all animals
Proposed the cell theory (they were incorrect in stating that
cells form spontaneously)
Discovered the nucleus
“Cells come from pre-existing cells.”
Disproved the “spontaneous generation” hypothesis
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His experiment is described here:
http://bcs.whfreeman.com/thelifewire/content/chp03/0302003
.html
*Were contemporaries and aware of each other’s work. Van Leeuwenhoek may have
read Hooke’s Micrographia and Hooke was given the job of confirming
Leeuwenhoek’s discovery of “little animals” or “animalcules” by the Royal Society of
London.
2. Evidence For Each Part of the Cell Theory
a. All living things are made of one or more cells.
i. Schleiden and Schwann: plants and animals are made of cells
ii. observations of living things continue to support that they are made
of one (unicellular organisms such as Monerans and Protists) or
more (multicellular organisms such as Fungi, Plants and Animals)
smaller units called cells
a. Debatable: Viruses…are they alive? They are not cells!
b. The cell is the basic unit of life/smallest unit that shows all the
characteristics of living things.
i. structures within cells cannot survive on their own
ii. cells isolated from tissues can survive in culture
c. All cells come from pre-existing cells.
i. binary fission, mitosis and meiosis are the processes used for one
cell to produce more cells
a. Debatable: Where did the first cell come from? The first cell(s)
provide an exception to this part of the cell theory. Scientists
have yet to produce cells from non-living precursors in the
laboratory.
A discussion of “The Evolution of the Cell” can be found here:
http://learn.genetics.utah.edu/content/begin/cells/organelles/
II. Relative Sizes of Things
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Figure 1: The relative sizes of chemical and biological structures.
http://www.mhhe.com//biosci/genbio/bio_prep/bioA1.html
III. Unicellular or Multicellular?
A. Emergent Properties: multicellular organisms are able to carry out certain
functions because they are multicellular and their cells interact with each
other; these properties make the whole more than “the sum of its parts”
B. Limits to Cell Size-will be discussed in the Membrane Section
IV. Types of Cells
A. Prokaryotic: cells that do not have a nucleus
B. Eukaryotic: cell that do have a nucleus
V. Structures Found in All Cells
A. Cell or Plasma Membrane
Figure 2: Diagram of the cell/plasma membrane.
http://micro.magnet.fsu.edu/cells/plasmamembrane/plasmamembrane.html
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Integral protein
Figure 3. Diagram of the cell/plasma membrane.
http://kentsimmons.uwinnipeg.ca/cm1504/plasmamembrane.htm
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1. Structure:
a. most common model is called the “fluid mosaic model”
i. “fluid” because the component parts can move past each other much
like the molecules in a fluid
ii. mosaic because there are many different components to the cell
membrane
b. components:
i. phospholipids: the main component, have a phosphate “head” region
(hydrophilic or polar)* and 2 fatty acid “tails” (hydrophobic or polar)*
*more on the definitions of these terms when we study Topic 3 The Chemistry
of Life
Figure 4. The structure of phospholipids.
http://bioweb.wku.edu/courses/biol115/wyatt/biochem/Lipid/Lipid_2.asp
Non-polar region
ii. proteins: these are embedded amongst the phospholipid molecules
and may be found more on the internal surface (peripheral),
external surface (peripheral) or spanning the membrane (integral)
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iii. glycoproteins: these are proteins with carbohydrate chains attached
to them, found only on extracellular surface
iv. glycolipids: these are fatty acids with carbohydrate chains attached to
them rather than phosphate groups, found only on
extracellular surface
v. cholesterol: a steroid (a class of lipid) that is found amongst the lipid
tails and helps to stabilize the membrane and maintain
its flexibility
2. Function(s):
a. holds all the internal components of the cell together and separates
them from the external environment thus allowing the internal
environment to be different from the external environment
b. actively selects some materials to enter and exit the cell because it is
selectively permeable
i. selectively permeable: describes a membrane that is semi-permeable
and also actively changes in order to control which substances can
pass through it (and thus enter or exit the cell)
c. communicates with other cells and senses the external environment
d. sticks to or joins with adjacent cells
e. anchors enzymes in prokaryotes
Here is a basic review of cell membrane structure with a review activity at the end:
http://www.wisc-online.com/objects/ViewObject.aspx?ID=ap1101
B. Cytoplasm: the material inside the cell membrane and outside of other
membranes within the cell, other structures can be found in this
material
1. Structure
a. gel-like, mostly water, dissolved particles (small covalently bonded
molecules such as glucose) or dissociated particles (ions such as Na+,
Cl-, K+, H+, etc.) and some water-soluble larger molecules (e.g. certain
proteins)
*often used as if synonymous with the term cytosol but cytosol refers
specifically to the water of the cytoplasm
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2. Function
a. site of many chemical reactions
b. helps to give cell its shape
C. Ribosomes
1. Structure
a. made of ribonucleic acid (RNA) and many proteins
b. each ribosome is made of a smaller subunit and a larger subunit
c. size, measured in Svedberg units (based on rate of sedimentation in a
centrifuge), is different in prokaryotes and eukaryotes
i. in prokaryotes, smaller, 70S
ii. in eukaryotes, larger, 80S
2. Site of protein synthesis (more detail to come)
D. Deoxyribonucleic Acid (DNA)
1. Structure (more detail later)
a. made of smaller units called nucleotides
b. each nucleotide is made of the elements carbon, hydrogen, oxygen,
phosphorus and nitrogen
c. in prokaryotes, forms a ring-shaped chromosome and possibly one or
more ring-shaped plasmids
d. in eukaryotes, forms linear chromosomes
2. Function (more detail later)
a. often said to contain the “blueprint of life”
b. is the molecule that contains the genetic information of the cell
c. directs all of the chemical reactions that occur in the cell
3. Location
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a. in the cytoplasm of prokaryotes, in a region often referred to as the
nucleoid region
b. in the nucleus of eukaryotes, separated from the cytoplasm by the
nuclear membrane
V. Structure of Prokaryotic Cells
Figure 5. Shapes of Prokaryotic Cells
http://www.pc.maricopa.edu/Biology/rcotter/BIO%20205/LessonBuilders/Chapter%
204%20LB/Ch4Lessonbuilder_print.html
A. Overall Shape
1. Spherical (singular: coccus, plural: cocci)
2. Rod-shaped (singular: bacillus, plural: bacilli)
3. Spiral (singular: spirillum, plural: spirilla)
Figure 6. E. coli bacterium.
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Figure 7. E. coli showing flagella (F) and pili (P).
http://parts.mit.edu/igem07/index.php/Escherichia_coli
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Figure 8. Electron micrograph of E. coli.
http://www.ucmp.berkeley.edu/bacteria/bacteriamm.html
Figure 9. Electron micrograph of E. coli.
http://www.ibguides.com/biology/notes/2.2-prokaryotic-cells
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B. Plasmid: extra-chromosomal genetic material
1. Structure
a. DNA in the shape of a ring
2. Function
a. extra genetic material
b. can be transferred between individuals
C. Cell Wall
1. Structure
A. made of peptidoglycan, a molecule that is a glycoprotein
1. if Gram+: more peptidoglycan and less lipopolysaccharide and
appear more purple after the Gram staining process
2. if Gram-: less peptidoglycan and more lipopolysaccharide and
appear pink after the Gram staining process
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2. Function
a. gives the cell shape
b. protects the cell from external environment
c. anchors pili and flagella
d. prevents the cell from bursting in hypotonic environments
D. Flagella: long, whip-like structures, usually few in number
1. Structure
a. made of a protein called flagellin
2. Function
a. locomotion
Here is a movie of E. coli bacteria moving:
http://www.rowland.org/labs/bacteria/movies/fluo_fil_leave.mov
E. Pili
1. Structure
a. made of protein
b. short, straight structure that sticks out from the cell
2. Function
a. attach bacteria to each other and transfer DNA during a process called
conjugation
b. attachment to surfaces
c. protection from phagocytosis
F. Fimbriae: another name for pili
G. Glycocalyx
1. Slime Layer
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a. Structure
i. glycoproteins loosely associated with cell wall
b. Function
i. adhere to solid surfaces
ii. prevent drying out
2. Capsule
a. Structure
i. polysaccharides firmly attached to the cell wall
b. function
i. adhere to solid surfaces
ii. protects cell from phagocytosis by host immune system
H. Cytoskeleton
1. Structure
a. made of proteins, thought to be the evolutionary precursors of the
cytoskeleton proteins in eukaryotic cells
2. Function
a. contribute to cell shape
I. Endospores
1. Structure
a. protective covering enclosing cell wall, cell membrane, cytoplasm and
nucleoid
2. Function
a. maintain cell during stressful environmental conditions
i. resistant to radiation, drying out, extreme temperatures, starvation,
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chemicals and lysozyme
Here is a basic summary and an interactive labelling exercise:
http://www.mhhe.com//biosci/genbio/bio_prep/bioA2.html
Another one:
http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/interactivemedia/a
ctivities/load.html?6&B
VII. Eukaryotic Cells (have a nucleus)
A. Nucleus
1. Structure
a. large, membrane-bound (enclosed) structure containing unwound
chromosomes (chromatin) during most stages of the cell’s life cycle
2. Function
a. separates the chromosomes from the rest of the cell
i. the chromosomes control all of the chemical reactions (metabolism)
of the cell
B. Nuclear Membrane
1. Structure
a. phospholipid bilayer similar to the cell membrane
2. Function
a. controls the movement of material between the nucleus and thy
cytoplasm
C. Nucleolus
1. Structure
a. darkly stained area of the nucleus
b. there may be more than one
2. Function
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a. site of ribosome synthesis
D. Endoplasmic Reticulum (Smooth) (SER)
1. Structure
a. a system of tubules with a double membrane similar in structure to the
cell membrane
2. Function
a. site of lipid/fat synthesis
b. Involved in the detoxification of drugs or harmful chemicals
c. transports materials throughout the cell
E. Endoplasmic Reticulum (Rough) (RER)
1. Structure
a. smooth endoplasmic reticulum with ribosomes attached to it
2. Function
a. modifies and packages the proteins made by the attached ribosomes
b. transports the proteins to the Golgi apparatus
F. Golgi Apparatus
1. Structure
a. resembles a stack of pancakes
b. connected to the ER
2. Function
a. modifies and packages the proteins from the RER
i. packaged into small sacs called vesicles
b. synthesizes complex polysaccharides
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G. Vesicle
1. Structure
a. small bag or sac with a double-membrane
2. Function
a. transport proteins from the Golgi apparatus to the cell membrane
H. Vacuole
1. Structure
a. large bag or sac
2. Function
a. storage of food, water, waste or proteins
b. in plants, water in the large central vacuole helps to put pressure on
the cell wall to maintain the cell’s shape and rigidity
c. in some protists, a contractile vacuole functions to store excess water
and pump it out of the cell so the cell doesn’t burst
I. Lysosome
1. Structure
a. sac or bag containing digestive enzymes
2. Function
a. fuse with food vacuoles so that the enzymes can break down large food
molecules into their building blocks so that they can be used by the cell
i. fused structure is known as a digestive vacuole
b. involved in the recycling of dead cells
i. burst and the enzymes digest the contents of the whole cell
ii. called a “suicide bag”
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J. Mitochondrion (plural=mitochondria)
1. Structure (more detail later)
a. composed of an inner folded membrane and an outer membrane
b. has its own DNA and is capable of synthesizing some or its own
proteins
2. Function
a. site of the aerobic reactions of cellular respiration
K. Microtubules
1. Structure
a. proteins called tubulin
2. Function
a. shape and support the cell
b. serve as tracks that organelles can move along
L. Microfilaments
1. Structure
a. rods made of proteins called actin
2. Function
a. involved in dividing of cytoplasm (cytokinesis) during cell division
b. involved in the projection of pseudopodia
c. involved in cytoplasmic streaming (the movement of cytoplasm seen in
plants)
M. Cytoskeleton
1. Structure
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a. microtubules, microfilaments and intermediate filaments
2. Function
a. See microtubules and microfilaments
N. Structures found in Animal Cells (but not Plant Cells)
Figure 10 . A representative diagram of an animal cell.
http://micro.magnet.fsu.edu/cells/animalcell.html
1.
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1. Centrioles
a. Structure
i. microtubules, a pair of centrioles is found in each cell
b. Function
i. microtubules radiate from the centrioles during cell division to form
the spindle
O. Structures found in Plant Cells (but not Animal Cells)
Figure 11. A representative diagram of a plant cell.
http://micro.magnet.fsu.edu/cells/plantcell.html
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1. Central vacuole
2. Chloroplasts
a. Structure
i. outer membrane and inner membrane organized into interconnected
stacks
b. Function
i. Site of photosynthesis
3. Plastids
a. Structure
i. membrane-bound organelles
b. Function
i. storage of starch (amyloplasts/leucoplasts)
ii. storage of pigments (chromoplasts)
iii. food production (chloroplasts)
4. Cell Wall
a. Structure
i. mainly made of cellulose, a polysaccharide
ii. some have lignin
b. Function
i. give cell shape
ii. prevent cell from bursting in hypotonic environments
Here are some fascinating animations:
1. From Harvard: The Inner Life of the Cell
http://multimedia.mcb.harvard.edu/anim_innerlife.html
2. From John Kyrk: http://www.johnkyrk.com/CellIndex.html
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And http://www.johnkyrk.com/er.html
Here is a basic summary and an interactive labelling exercise:
http://www.mhhe.com//biosci/genbio/bio_prep/bioA3.html
P. The liver cell as an example of a typical animal cell
* IB specifically lists the following cell structures: free ribosomes, rough endoplasmic
reticulum (rER/RER), lysosome, Golgi apparatus, mitochondrion and nucleus and
expects that you can draw and label them on a diagram of a liver cell and be able to
label them on an electron micrograph of a liver cell.
1. From the click4biology website: http://click4biology.info/c4b/2/cell2.3.htm
2. http://homepage.smc.edu/wissmann_paul/cell/Default.htm
Ultrastructure of a liver cell.
1:Nucleolus; 2:Chromatin; 3:Dense Chromatin; 4:Nuclear Pores;
5:Mitochondria;
6:Rough Endoplasmic Reticulum; 7:Ribosomes; 8:Golgi Apparatus;
9:Smooth Endoplasmic Reticulum;
10:Peroxisomes; 11:Lysosomes; 12:Bile Capillary; 13:Desmosomes;
14:Microvilli.
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3. http://faculty.une.edu/com/abell/histo/Histolab4a.htm
4. http://intranet.canacad.ac.jp:3445/bioibsl1/4424
5. Kupffer cell of liver: http://www.unimainz.de/FB/Medizin/Anatomie/workshop/EM/externes/Schiller/Leber1E.html
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Ec = euchromatin; Grg = glycogen granules; Hc = heterochromatin; Hec =
Hepatocytus (hepatocyte = liver cell);
L = lumen of the sinusoid (which is a special capillary); Mi = mitochondrion (of the
crista-type); Mn = Membrana nuclearis (nuclear membrane);
Mpl = Macrophagocytus stellatus (Kupffer cell; belongs to the macrophages); Mt =
microtubules;
Mv = microvilli (immobile processes of liver cells); N = Nucleus (nucleus); P =
Plasmalemma (cell membrane);
Ph = phagolysosome; Pin = pinocytosis; Ps = Pseudopodia (pseudopods = mobile
cell processes); RER = rough endoplasmic reticulum;
Sp = Spatium perisinusoideum (Disse's space); V = Clathrin-coated vesicle
(endocytotic vesicle); Va = vacuole (belongs to L).
Here is a table to compare prokaryotic and eukaryotic cells: http://glencoe.mcgrawhill.com/sites/0035456775/student_view0/chapter4/image_powerpoints.html
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References:
1. Sadava, Heller, Orians, Purves and Hilllis: Life: The Study of Biology (8th
Edition)
2. A pretty complete history of cell theory:
http://fig.cox.miami.edu/~cmallery/150/unity/cell.text.htm
3. More on the cell theory:
http://science.howstuffworks.com/innovation/scientific-experiments/scientificmethod4.htm
4. The Microbial World (only three chapters are available online):
http://www.microbiologytext.com/index.php?module=Book&func=displayarticl
e&art_id=27
5. About Robert Hooke: http://www.ucmp.berkeley.edu/history/hooke.html
6. http://people.eku.edu/ritchisong/301notes1.htm
7. About Anton Van Leeuwenhoek: http://www.vanleeuwenhoek.com/
8. Bacterial cell: http://micro.magnet.fsu.edu/cells/bacteriacell.html
9. Prokaryotic cell structure: http://textbookofbacteriology.net/structure.html
10.
Plant cell: http://micro.magnet.fsu.edu/cells/plantcell.html
11.
Animal Cell: http://micro.magnet.fsu.edu/cells/animalcell.html
12.
Labelled rat liver cell (but more detail than is really needed):
http://www.unimainz.de/FB/Medizin/Anatomie/workshop/EM/externes/Schiller/Leber1E.html
13.
Plant Cell “Tour”:
http://bcs.whfreeman.com/thelifewire9e/default.asp#542578__591194__
14. Ribosomes: http://micro.magnet.fsu.edu/cells/ribosomes/ribosomes.html
15. http://www.utm.utoronto.ca/~w3bio315/lecture2.htm
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16. Gram staining information:
http://health.upenn.edu/bugdrug/antibiotic_manual/Gram1.htm
17. Prokaryotes: http://sites.google.com/site/cellbiologypowerpoints/home
18. Prokaryotic cytoskeleton:
http://www.nature.com/milestones/milecyto/full/milecyto21.html
19. http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit1/proeu/proeu.html
20. Endospore: http://pscantie.myweb.uga.edu/definition.html
21. http://www.mansfield.ohio-state.edu/~sabedon/biology.htm
Videos about the cell:
The Cell from BBC (3 part series): All 3 parts can be found here:
http://www.youtube.com/playlist?feature=iv&annotation_id=annotation_503353&sr
c_vid=hScXxGeL0sA&list=PL914F66193FA5E8B6
Part One: The Hidden Kingdom
Part Two: The Chemistry of Life
Part Three: The Spark of LIfe
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