In This Lesson:
Cells, Cell History,
General
Characteristics
(Lesson 2 of 5)
Today is Friday (!),
October 9th, 2015
Pre-Class:
Compare the two animals below. Write in your notebook any and
all observations you make about the two animals with only your
eyes, especially their differences. Write as many as you can!
http://www.alaska-in-pictures.com/data/media/1/snowshoe-hare-portrait_6139.jpg
http://www.theage.com.au/ffximage/2007/09/14/svLYNX_narrowweb__300x434,0.jpg
Today’s Agenda
• Be able to make an educated guess as to the function of an
unfamiliar structure.
• Know at least a little about the history of the cell’s discovery.
• Be able to recite the three parts of the Cell Theory.
• Software art?
– Brain break.
• Where is this in my book?
– Academic: P. 172 and following…
– Honors: P. 55 and following…
By the end of this lesson…
• You should be able to describe the Cell
Theory and how cells were first discovered.
• You should be able to define the general
properties of cells.
Lynx and Hare
http://media-2.web.britannica.com/eb-media/43/6543-004-D65BF551.gif
Why?
• Why do these animals have those traits?
– What’s the “form?”
– What’s the “function?”
Form and Function
• As the Zoo’s rhyme goes:
– Eyes on the side, I like to hide; eyes in the
front, I like to hunt.
• The structure (or form) of something is
always secondary to its function.
http://www.shawcreekbirdsupply.com/barn_owl.jpg
http://upload.wikimedia.org/wikipedia/commons/9/9e/House_Sparrow_(M)_I_IMG_7881.jpg
Form and Function
• Why does this giraffe have a long neck?
• Form: Long neck.
• Function: Reaches food up high.
http://www.beenthereyet.com/images/PhotoGallery/giraffe.jpg
Form and Function
• Why does this butterfly have “eyes?”
• Form: Eye spots.
• Function: Confuses predators.
Form and Function
• Why does this cheetah have the black “tear
drops” on its face?
• Form: Black “tear lines.”
• Function: Keeps out sun glare.
http://www.rachelinafrica.com/wp-content/photos/Cheetah_face_Mauritius_IMG_3002.jpg
Form and Function
• What color is this polar bear’s fur? And what
color is its skin?
• Form: Clear fur, black skin.
• Function: Lets light in, skin warms in sun, can
still blend in.
http://stevenbell.blogspot.com/images/11-02-05-sleepy-bear.jpg
Form Follows Function
• A characteristic’s form is always shaped by
its function.
• You could also say, “Form follows function.”
Function Following Form?
• An opposite example
might be headlights in
NASCAR.
• For those of you that
don’t know, the
headlights aren’t real.
They’re stickers!
• In this case, the “look”
isn’t for any purpose at
all.
– This doesn’t happen in
biology.
http://news.sportslogos.net/wp-content/uploads/2012/12/headlight.jpg
Form & Function Activity
• Turn to your neighbor and think of at least
five examples of an instance of form (or
structure) following function in nature.
You have 1 minute (less if we’re off topic).
– Imaginary bonus points if you can think of
something whose function and structure are
not consistent with one another.
Discovering The Cell
• It all started way back in 1665 when Robert
Hooke looked at a piece of cork under a
microscope.
Robert Hooke?
http://en.wikipedia.org/wiki/File:13_Portrait_of_Robert_Hooke.JPG
http://askabiologist.asu.edu/research/buildingblocks/images/hookecork.jpg
Anton van Leeuwenhoek
• Hooke saw dead cells,
but Leeuwenhoek first
observed living
unicellular (one-celled)
organisms in pond water,
along with blood and
sperm cells.
• Done around the time
Hooke saw cork.
http://www.teachersparadise.com/ency/en/media/5/5e/anton_van_leeuwenhoek.png
So they got credit and fame
immediately, right?
• Of course not!
• Many times across science’s history, research that
breaks ground takes a while to really set in.
• In this case, it took nearly 200 years, when
Schwann and Schleiden (and Virchow, to some
extent) confirmed that cells are the smallest
units of life, and gave Cell Theory its start.
Cell Theory
(write this down - it’s important)
• Cell theory is a way to fit the concept of
cells into the rest of biology. It has 3 parts:
– “All living things are made of one or more
cells.”
– “Cells are the basic units of structure and
function [organization] in organisms.”
– “All cells arise from existing cells.”
Johnson, G. & Raven, P. (2004). Biology. Holt, Rhinehart, and Winston: Austin
Cell Theory Video
• It turns out the Cell Theory had a bit of a
weird origin.
– Let’s take a look…
Why is the Cell Theory
important?
• It disproved the theory of Spontaneous
Generation!
• Hypotheses based on Spontaneous
Generation on the coming slides…
Spontaneous Generation
• Maggots come from rotting meat.
http://www.pestcontrolrx.com/.a/6a00e55272212588330105368eaecd970c-500wi
Spontaneous Generation
• Rats come from damp roofs.
The coming rat
plague!
http://www.smrestore.com/Galleryimages/WaterDamage1-Water%20in%20ceiling.jpg
Disproving
Spontaneous Generation
• So how do you disprove something like
this?
• It seems obvious, but can you prove it?
– Design an experiment!
– Talk to your partner and take a minute and 57
seconds.
Francisco Redi
• Redi filled six jars with decaying meat:
– 3 were open containers
– 3 had fine nets over them
• Sure enough, the three open containers
had maggots and the three with nets
didn’t.
• Where did the maggots come from?
• What was the purpose of the sealed jars?
Some More About Cells
• Cells are the smallest unit of life.
– BioScale!
– http://learn.genetics.utah.edu/content/begin/cells/sc
ale/
– Scale of the Universe
• As we all know, cells are tiny. How many cells are
in the human body?
• Your body contains…
100,000,000,000,000 cells
(that’s 100 trillion, which is also not enough money to pay our national debt)
Cell Size
• Average cell size:
– 10-100 micrometers
• Biggest cells?
Large Cells
• Ostrich Egg
http://aidanmoher.com/blog/wp-content/uploads/2010/01/ostrich_egg_size.jpg
Large Cells
• Sciatic Nerve
WARNING:
Graphic picture
next slide…
http://www.acticare.com/conditions/images/sciatic_nerve2.jpg
Large Cells
• Sciatic Nerve
http://www.ilizarov.org/new1/upload/8142007102508AM3.JPG
Back to Form and Function
• So now the big question. Why is it cells are
so small? Why aren’t big organisms just
made of bigger cells?
Let’s try an alternate question…
• If you buy a gallon of water in
one bottle…
• …and then you buy a gallon of
water in many bottles…
• …which option gets you more
water?
– Either choice. They’re the same.
• But which option uses more
packaging material?
– The smaller bottles.
• Key: Think of packaging material
like surface area.
https://pfiesterpfit.files.wordpress.com/2011/05/gallon_of_water.jpg
http://www.exchange3d.com/images/uploads/aff4269/Arrowhead.jpg
Cell Size
• To answer the question of why cells are so
small, we’re going to look at a similar
relationship in biology.
– Which of these spheres has a greater surface
area? Volume?
http://upload.wikimedia.org/wikipedia/commons/3/33/Sphere.jpg
Cell Size
• Head to your lab tables. I would like each group
to quickly calculate the surface area and volume
of both books at the tables.
– Volume = length x width x height
– Surface area = area of each side (front cover, back
cover, all four other sides) added to one another
• You can use inches.
• Have one side of your table do one book, the
other side do another.
What’d you get?
• I got this:
• TEXTBOOK
– Textbook: 146.625 in3 volume
– Textbook: 255.5 in2 surface area
• Surface area is less than twice the volume.
• THE HOT ZONE
– The Hot Zone: 28 in3 volume
– The Hot Zone: 78 in2 surface area
• Surface area is almost THREE TIMES the volume
Surface Area to Volume Ratio
A Review
Cube 1
2 cm
2 cm
Cube 2
2 cm
4 cm
4 cm
4 cm
Cube 1
Cube 2
Proportion
Volume
8 cm3
64 cm3
8x more volume
Surface Area
24 cm2
96 cm2
4x more surface
Proportion
3x more surface 1.5x more surface
SA to Volume Ratio
Surface Area to Volume Ratio
• Generally speaking, smaller objects have more
surface area relative to their volumes than larger
objects.
• So why are larger organisms composed of many,
many small cells, instead of being composed of
larger cells?
Surface Area to Volume Ratio
• Imagine that you are a cell. You need to get some
tiny but important molecule to the center
of…yourself…as fast as possible.
• Having a larger surface area to volume ratio
means you have more area for the
molecule to enter but a smaller distance for
it to go once it gets inside.
– Cells like to do things fast, so this is very handy.
Membrane Action et cetera
• Cells take in and release substances
through their membranes.
• Like Goldilocks, the size of the cell has to be
just right for things to work efficiently.
– Not too big, not too small
• What exactly the cell is doing will be part of
our next few lessons.
A Little Preview
• Find a blank section of your notebook and
label it “Unit 2 Predictions.”
• I will provide you with four scenarios.
Three of them will be “live,” and the other
will be a diagram.
• Your job is to [SILENTLY] write a detailed
prediction and possible explanation for
what will happen in each situation.
Unit 2 Predictions
• Take your time doing this. Be thorough.
• Do not talk during this. The point is to get your
brain moving on this topic, not to mooch off
someone else’s brainpower.
• Like I said, be detailed. Write what will
happen. Write what will happen at the
molecular level. What will we see? Why?
Prediction 1
• If I add three drops of this food coloring to
this beaker of water, what will happen?
• What will it look like at first? Will it
change? How will it be different? Why?
• What are the molecules doing?
Prediction 2
• If I put a baby carrot in a beaker of water
and another baby carrot in a beaker of
water plus lots of salt, what will happen?
• Will the carrots change? Will the water
change? Will both? Why?
Prediction 3
• I am going to spray this “room spray” in the
classroom. What will happen? Describe in
detail!
Prediction 4
• In this tube, water can
cross the border in
the middle. The
solute cannot. There
is more solute on the
right than on the left.
http://www.biologycorner.com/resources/osmosis.jpg
Closure
• Which has a greater surface-area-tovolume ratio – an elephant or a mouse?
http://www.upali.ch/bilder1/elemaufus.jpg