THE INTERESTING HISTORY OF CELLS – TEACHER HANDOUT
Grade Level:
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High-school biology
Objectives:
The students will:
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Identify the major structures of prokaryotic and eukaryotic (plant and animal) cells.
Compare and contrast prokaryotes and eukaryotes.
Propose a phylogenetic tree of the three domains (archae, bacteria, and eukarya)
based on a short reading.
Form a hypothesis about evolutionary history of mitochondria and chloroplasts based
on characteristics of major groups of bacteria, chloroplasts, and mitochondria.
Will compare their proposed hypothesis with the “Endosybiont Hypothesis” of Lynn
Margulis.
Speculate on the advantages of endosymbiosis, multicellularity, and exoskeletons
(major events in the history of animal life).
Make a timescale of some of the major events in cell history.
Background Information:
The students should already be familiar with the following topics:
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Phylogenetic trees
Basic cell structure
Metabolic processes: fermentation, respiration, and photosynthesis.
Symbiotic relationships (parasitism, commensalisms, and mutualism).
Time Requirement:
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Two 70-minute blocks or three 45-minute class periods
Teacher Preparation:
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Make copies of the handouts.
Materials (one per student):
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Student handout - “The Interesting History of Cells”
Evaluation:
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Answers on student handout, even if technically incorrect, should be defensible.
Check for understanding during classroom discussion.
The Interesting History of Cells
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THE INTERESTING HISTORY OF CELLS – TEACHER HANDOUT
There are two basic types of cells,
prokaryotic cells and eukaryotic cells.
Figure 1. A PROKARYOTIC CELL
The prokaryotes are very small singlecelled organisms (1 – 10 micrometers),
which include the bacteria and archaea.
They have a single chromosome, which
is a closed loop of double-stranded DNA.
Prokaryotes do not have membranebound organelles (e.g. nucleus,
chloroplasts, mitochondria, ER, etc.).
wall _____
1. ____Cell
_________
Cell membrane
2. __________________
DNA / nucleosome
3.
4. _Ribosomes
_________________
From Pearson Prentice Hall, 2005.
The eukaryotes include all of the remaining organisms (protista, fungi, animalia, and
plantae). Some eukaryotes are single-celled organisms and others are multicellular
organisms. They all have cells with a nucleus and membrane-bound organelles.
They can be quite large (10 – 100 micrometers).
Use your textbook (or the internet) to identify the structures in each of the cells on
this page.
Figure 2.
Nucleolus
5. _________________
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6. __________
Nucleus ______
7. _Mitochondrian_________
8. _Golgi Apparatus____
9. _Rough E.R._______
10. _Smooth E.R.
______
13._Chloroplast__________
12. _Cell Wall_________
11. _Cell Membrane
The Interesting History of Cells
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Figure 3.
16. Nucleolus______
15. _Nucleus________
14. _Ribosomes_____
17. Mitochondria_
18. _Cytoskeleton___
19. Gogi Apparatus
23. Centrioles_________
20. Rough E.R.__
22. Cell Membrane_________
21. Smooth E.R.
24. Compare and contrast prokaryotes and eukaryotes
Eukaryotes
Prokaryotes
• Small (1-10 microns)
• Cell membrane
• All are single-celled
• Ribosomes
• Closed loop of DNA
• No membranebound organelles
The Interesting History of Cells
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• Large 10 – 100
microns
• Some are
multicellular
• Have a nucleus and
membrane-bound
organelles
DNA
page 3
Archaea vs. Bacteria
All organisms are placed into one of three domains. The three domains of life are: bacteria,
archaea, and eukarya. The archaea and bacteria are both prokaryotes and (as the name suggests)
the eukarya are eukaryotes.
Even though the archaea and the bacteria are both prokaryotes, they differ from each other in some
important ways. For example, the archaea and bacteria differ in the types of molecules (e.g.
peptidoglycans) that are present in their cell walls. Furthermore, the DNA of the archaea is more
similar to that of the eukarya in a number of ways. For example, the DNA of the archaea and eukarya
include introns (segments of DNA that do not code for proteins). The bacteria do not contain introns in
their DNA. Also, the archaea have genes that resemble those of the eukarya, but do not resemble
those of the bacteria. The first amino acid placed in a protein is methionine (Met) in both the archaea
and eukarya, but not in the bacteria. The ribosomal RNA (rRNA) of the archaea and the eukarya
resemble each other, but are different from those of the bacteria. Finally, most species of archaea live
only in extreme environments (swamps, salt lakes, hot
Figure 4. Phylogenetic tree of 3 domains
springs, deep-sea vents, etc.), whereas the bacteria live
in a wide variety of habitats (Strickberger, 2005).
25. Use the information above to fill in the probable
phylogenetic tree (Figure 4).
Eukarya
Archaea
26. Explain what may be surprising to some
about this phylogenetic tree.
Bacteria
The archaea and bacteria are both prokaryotes, but they are not
closely related to each other.
The domain bacteria is a very diverse group. The table below provides some general
information about representative groups of bacteria.
Table 1. General characteristics of representative bacteria.
Group
Photosynthesis
Respiration
Green nonsulfur bacteria
Yes. Do not
produce O2.
No
Gram-positive
bacteria
No
Aerobic
Respiration
Purple Bacteria
Yes. Do not
produce O2.
Aerobic
Respiration.
Cyanobacteria
Yes. Produce O2.
Aerobic
Respiration
Flavobacter
No.
Thermotogales
No.
No
Anaerobic
Respiration
(Taylor, 2005; “Microbial Physiology, 2005).
The Interesting History of Cells
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Notes
Very large group. Some cause disease
(e.g. strep throat and anthrax), some make
antibiotics (e.g. actinomycetes), and some
produce toxins (e.g. botulism).
Some of these bacteria are parasites that
are able to invade the cells of their host.
They live their entire lives inside of and
divide in eukaryotic cells. Some do not
contain the genes for glycolysis and
fermentation but do have the genes for the
Krebs cycle.
This group is good at forming symbiotic
relationships with other species (e.g. a
lichen is a cyanobacteria that lives in a
fungus cell). Some have thylakoid
membrane systems. Contain
photosystems I and II.
Generally live in very hot environments
(e.g. hot-springs).
The Eukaryotes
The first eukaryotes show up in the fossil record about 1.5 billion years ago. They have two
organelles that are very unique: the mitochondria and the chloroplasts.
Table 2. Unique features of the mitochondria and chloroplasts (Kimball, 2005; Taylor, 2005)
Mitochondria
Has its own DNA which is a double-stranded loop
Has its own machinery for transcription and
translation
Is between 1 and 10 micrometers long
Has a double membrane
Independently replicates inside of the cell
Do not contain the genes to perform glycolysis
Contain the genes for the Krebs cycle
Perform aerobic respiration
Chloroplasts
Has its own DNA which is a double-stranded loop
Has its own machinery for transcription and
translation
Is between 1 and 10 micrometers long
Has a double membrane
Independently replicates inside of the cell
Contain photosystems I and II
Contain thylakoids
Perform photosynthesis
27. Write a hypothesis about what mitochondria may have originally been before they were
organelles. State at least two pieces of evidence to support your hypothesis. Use the
information from Tables 1 and 2.
Mitochondria originally a prokaryote – one closely related to the purple bacteria.
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Purple bacteria can invade eukaryotic cells.
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Both mitochondria and purple bacteria can divide independently inside of eukaryotic cells.
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Both contain genes for the Krebs cycle
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Mitochondria similar to prokaryotes (has own DNA, own machinery for transcription and translation,
similar size)
28. Write a hypothesis about what chloroplasts may have originally been before they were
organelles. State at least two pieces of evidence to support your hypothesis. Use the
information from Tables 1 and 2.
Chloroplast originally a prokaryote – one closely
related to the cyanobacteria.
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Cyanobacteria form symbiotic relationships
with other species.
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Both have thylakoid membranes and
photosystems I and II
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Both photosynthesize
and produce O2.
Mitochonria
Chloroplasts similar to
prokaryotes (has own
Chloroplasts
DNA, own machinery
for transcription and translation, similar
size)
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Figure 5. Phylogenetic tree showing the placement of
the mitochondria and chloroplasts (NJSAS, 2005).
29. Fill in the placement of mitochondria and
chloroplasts in Figure 5.
The Interesting History of Cells
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30. Look up the “Endosymbiont Hypothesis” in your textbook.
a. What does it state?
Mitochondria and chloroplasts were originally bacteria that formed a symbiotic
relationship with other bacteria.
b. Does it agree with your hypothesis? Yes____
31. Define symbiosis: The condition whereby different species live in close
association with each other.
32. There are three types of symbiotic relationships, mutualism, parasitism, and
commensalisms. The eukaryotic cell is in a mutualistic relationship with each of the
organelles discussed.
a. Explain how you think the host cell benefits by having mitochondria living in it.
Mitochondria generates ATP that the host may be able to use.
b. Explain how you think the mitochondria benefit by living inside of another cell.
The host provides a stable environment within which the mitochondria can live.
c. Explain how you think the host cell benefits by having chloroplasts living in it.
Chloroplasts fix carbon / produce glucose that the host can use.
d. Explain how you think the chloroplasts benefit by living inside of another cell.
The host provides a stable environment within which the chloroplast can live.
From single-celled organisms to multicellular organisms
Ediacaran Fauna
The first multicellular organisms show up in
the fossil record about 600 million years
ago. These organisms were soft-bodied
(no shell or hard skeleton) and lived in the
shallow seas. Members of this group may
include the first ancestors of the jellyfish,
sea-pens, sea stars, and worms
(Strickberger, 2005).
Figure 6. Ediacaran fossils (540 – 600 mya)
(UCMP, 2005).
33. What selective pressures would give
multicellular organisms an advantage
over single-celled organisms?
Answers will vary.
• Can consume a larger variety of food
• Can enter previously unoccupied niches
• Etc.
The Interesting History of Cells
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Cambrian Fauna
Between 520 and 542 million years ago, many more
animal fossils show up. Unlike the Ediacaran fossils, many
of the Cambrian fossils have shells and exoskeletons.
Most of them have gone extinct, leaving no descendents.
However, a small group of them ended up being the
ancestors of modern groups of animals alive today
(chordates, arthropods, etc.) (Strickberger, 2005).
Figure 7. Examples of Cambrian
fossils (520 – 542 mya).
(UCMP, 2005)
34. What selective pressures would make it more likely for
an organism to survive and reproduce if they had a
shell or exoskeleton?
Answers will vary. – Offers protection.
35. Geologic Timescale of Major Events in Cell History
a. Tape two pieces of paper together, end-to-end.
b. Make a timescale that begins 5 billion years ago
and continues until the present (10 cm = 1 billion
years). Use a ruler!
c. Label the timescale every 500 million years (5 cm).
d. Find out when the major events listed in Table 3 occurred (use this handout and your
textbook).
e. Write down how long ago they occurred in the second column.
f. Calculate how many cm from the present (time = 0) these events will be placed on
your timescale.
Table 3. Timescale of Major Events in Cell History
How long ago it
occurred (in billions of
years)
4.5
Distance from the
present on the
timescale (cm)
45
3.8
38
1 eukaryote
1.5
15
First multicellular organisms (Ediacaran)
0.6
6
Development of modern phyla (Cambrian)
0.54
5.4
First land plants
0.46
4.6
Dinosaurs ruled the earth
0.15
1.5
2 x 10-7
2 x 10-5
Major Event in Cell History
Formation of the earth
1st prokaryote
st
Scientist first observes a cell under the
microscope
36. Genetic variation is very important for the survival of a species. Name three processes
that you have learned about in this class that can cause an individual to have different
genes than other members of the population.
a) Crossing over /
b) Mutation / gene
c) Endosymbiosis
recombination
duplication
The Interesting History of Cells
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References:
Pearson Prentice Hall. (2005). PHSchool.com. Retrieved November 10, 2005 from:
http://www.phschool.com/science/biology_place/biocoach/cells/common.html
UCMP. (2005). Learning About the Vendian Animals. University of California, Berkeley.
Museum of Paleontology. Retrieved November 10, 2005 from:
http://www.ucmp.berkeley.edu/vendian/critters.html
UCMP. (2005). The Cambrian Explosion. Understanding evolution. University of California,
Berkeley. Museum of Paleontology. Retrieved November 10, 2005
from:http://evolution.berkeley.edu/evosite/evo101/VIIB1cCambrian.shtml
NJSAS. (2005). Evolutionary tree of life. NJ chapter of the Society for Amateur Scientists
Retrieved November 10, 2005 from: http://njsas.org/life/tree_of_life.php
Cain, Damman, Lue, and Yoon. (2002). Discover Biology (2nd Ed.) [online tutorial]. Sunderland,
Mass.: Sinauer Associates; New York: Norton. Retrieved November 10, 2005 from:
http://www.nicertutor.com/doc/class/bio100/<img%20src=http://www.nicerweb.com/doc/class/
bio100/Locked/media/ch06/DB06100.jpg
Cain, Damman, Lue, and Yoon. (2002). Discover Biology (2nd Ed.) [online tutorial].
Sunderland, Mass.: Sinauer Associates; New York : Norton. Retrieved November 10,
2005 from:
http://www.nicerweb.com/doc/class/bio100/Locked/media/ch06/DB06090.jpg
Taylor, C. (2005). Bacteria. Paleos: The trace of life on earth. Retrieved November 10, 2005
from: http://www.palaeos.com/Kingdoms/Prokaryotes/Thermotogales.htm
Microbial Physiology. (2005). Lecture 7: Energy generation and storage. London
Metropolitan University. Retrieved November 10, 2005 from:
http://learning.unl.ac.uk/bi203/lecture07.html
Strickberger, M.W. (2000). Evolution. Sudbury: Jones and Bartlett.
Kimball, J.W. (2005).Endosymbiosis and The Origin of Eukaryotes. Kimball’s Biology Pages.
Retrieved November 10, 2005 from:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Endosymbiosis.html
The Interesting History of Cells
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