StuDyiNG the CeLL
What are you made of ?
You could say atoms or elements. That would be right, but rocks & student desks & pizza boxes are made of atoms and elements too. What makes you different from those things ?
You could say organic compounds. That would be a better response I guess. Organic compounds come from living things. That answer would distinguish us from rocks & desks & pizza boxes. But other things are composed of organic compounds too; things like sugar and cow poop.
So I guess a better question is : what are you made of that makes you alive ?
A pretty big question, kind of philosophical. Since I'm a science teacher and not a philosopher, we'll just focus on the scientific units that make up each & every living thing on this planet : CELLS.
cell \'sel\ n 1 : the basic unit of structure & function in living things
In just a second we'll
review some of the dudes who were among the first to study cells. In
order for any of these guys to make any observations or discoveries, there had
to have been certain technological tools available to them. The biggest of
these tools was certainly the compound light microscope. An understanding
of the microscope is "a must" in any biology course.
I have
dedicated a page to the microscope in my "LAB REVIEW" Pages. To
look at that now, click here.
For now, here is a quick
exercise to review some important tools & techniques related to cell study.
Match the tool or technique with its description.
|
Tools & Techniques |
|
compound microscope
|
1.
microscope composed of one lens
2. microscope
that creates an image using two lenses
3. adding a
chemical that makes certain cell structures easier to see, usually kills the
cells
4. a high
resolution microscope used to study living cells
5. microscope
that provides images of the greatest magnification & resolution
6. microscope
with two oculars, usually used during dissections to observe relatively large
structures in more detail
7. small tools
used to remove or transplant cell organelles
8. machine
that can be used to separate cell organelles according to their densities
After you've done your best, check your answers <herE>.
OK, let's continue our review/study of the cell by reviewing the guys who first studied the cell. Number from 1-7 on a piece of paper & match each dude with his claim to fame.
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Anton van Leeuwenhoek (1670)
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Robert Brown (1831) |
Theodor Schwann (1838)
|
1)
first to use the term "protoplasm"
2) while studying cork, he
was the first to use the term "cell"
3) stated that all new
cells come from other living cells
4) studied many
microscopic organisms using a strong simple microscope
5) stated that all plants
are composed of cells
6) stated that all animals
are composed of cells
7) "discovered"
the nucleus
Think you got 'em all right ? Click <here> for the answers.
THE CELL THEORY :
1.
all living things are made up of cells & the products of those cells
2. all cells carry out their own life
functions
3. new cells come from other living cells
Comments :
- the exact wording of the cell theory may vary depending on what textbook you use, but it's always composed of those 3 ideas
- the "life functions" referred to in statement #2 are the same ones covered on my life functions page
- if you peek back to the scientists review, you may notice that statements #1 & 2 are primarily a combo of Schleiden & Schwann's research, & statement #3 is Virchow's big idea
- keep in mind that The Cell Theory is based on over 300 years of scientific investigations, beginning with Hooke in 1665 and continuing through today
- some notable questions or "exceptions" to the Cell Theory do exist
Exceptions to the Cell Theory :
1. Viruses - are they alive ?
According to the
Cell Theory we have to say "no" because a virus is not a cell.
Viruses are made of two chemicals, protein & nucleic acid, but have no
membranes, nucleus, or protoplasm. They appear to be alive when they reproduce after
infecting a host cell.
2. Mitochondria &
chloroplasts.
These cell
organelles (small structures inside the cell) have their own genetic material
& reproduce independently from the rest of the cell.
3. Where did the first cell come
from ?
According to
statement #3 of the cell theory, all cells come from other living cells.
So how did the first cell ever appear ? It's the old "chicken &
egg" dilemma. We will investigate this question (& its possible
answer) in more detail during the Evolution Unit.
CELL STRUCTURE & ORGANELLES
ORGANELLE \or-ga-'nel\ n : 1. smaller structures within a cell, each organelle has a certain function.
PROTOPLASM \pro-to-paz-'um\ n : 1. general term for the living material in a cell
YOU HAVE TWO MISSIONS RELATED TO THIS SECTION :
Mission #1 : be able to identify all cell organelles in a diagram or picture
Mission #2 : be able to describe the function of each cell organelle
All cells have a cell membrane, cytoplasm and genetic material (DNA). From there things can vary in terms of the other organelles present in the cell, the shape of the cell, or the function of the cell.
In this course we concern ourselves mostly with the differences between prokaryotic cells & eukaryotic cells, and between animal cells & plant cells.
The
prokaryotic-eukaryotic difference is easy; prokaryotic cells do not have a
nucleus & eukaryotic cells do. Remember that all prokaryotic organisms are
classified in the Moneran Kingdom. The organisms in the other four Kingdoms
have eukaryotic cells.
(If you want to review the
5 Kingdoms, check out my "5 Kingdoms Page".)
The animal-plant cell differences aren't too bad either. Basically, some organelles are found in plant cells and not animal cells & vice versa. More on that in a minute.
First ......
LET'S LABEL SOME ORGANELLES !!!
A little note : cell diagrams tend to be either overly complicated (fancy 3-D graphics) or too simplified (bare minimum "know this" stuff). Diagrams like the ones here have been seen in Regents Review Books & tests so I figure they are the most practical for us to use.
Identify each of the numbered
organelles in the animal cell below.
(Try to do it first
without using the word bank.)
|
WORD BANK |
|
cytoplasm |
Check here to click your work
---
I mean, click
here to check your work.
Before
we label a plant cell, let's take a
sTudY BReaK
!!!
OK, time to label a typical
plant cell (notice the green?). Usually, plant cell diagrams focus on
structures that distinguish plant cells from animal cells. So some of the
organelles that animal & plant cells have in common (like ribosomes, golgi
bodies, endoplasmic reticulum) get left out all together. Label the
diagram below & see what I mean ...
PLANT CELL
|
WORD BANK |
|
cell wall |
Take a look at the answers.
PLANT CELLS vs ANIMAL CELLS
If you can label diagrams of a plant or animal cell, then you pretty much know what the differences are between them.
This table summarizes the differences :
|
ORGANELLE |
ANIMAL CELL |
PLANT CELL |
|
centrioles |
visible |
none (not visible) |
|
cell wall |
none |
present |
|
chloroplasts |
none |
present |
|
vacuole |
small |
large |
ORGANELLES & THEIR FUNCTIONS
Now that you know what each
organelle looks like, it's time to get the functions of each organelle to stick
to your brain somewhere. Choose an organelle from the word bank for each
description in #1-15.
|
WORD BANK |
|
cell membrane |
1.
liquid inside the cell, mostly water
2. made of lipids &
proteins, it is the boundary of the cell; it controls what substances enter or
leave the cell
3. "control center of
the cell" where genetic material (DNA) is found
4. nonliving border that
surrounds plant cells, made of cellulose
5. very small organelles
that are the sites of protein synthesis
6. system of tubes through
the cytoplasm involved in transporting materials
7. a flat stack of tubes
involved in "packaging" materials that will exit the cell
8. site of cellular
respiration (where energy is released from nutrients)
9. storage sac for water
or other materials
10. controls what enters
or exits the nucleus
11. dark round structure
within the nucleus that produces ribosomes
12. specialized vacuole
that stores digestive enzymes
13. structure in animal
cells involved in cell division
14. spherical structure
that contains the centrioles
15. site of photosynthesis
in plant cells
OK, let's have even more fun & check your answers !
Um, some last minute thoughts on organelles :
- Some organelles have two names : golgi apparatus = golgi bodies; cell membrane = plasma membrane.
- The organelles that you, an average biology student, would see in lab using a compound light microscope would be : the cell membrane, cell wall, nucleus, nucleolus, chloroplasts, large vacuoles. Other organelles require higher magnification and better resolution microscopes that typical high schools don't have on hand.
- You should know a few more details about the plasma (cell) membrane. It is composed of lipids (fat molecules) & protein in what is described as the "Fluid Mosaic Model".
The Fluid Mosaic Model of the cell
membrane looks like so :
All of the molecules (lipids & proteins) "float" around, exchanging positions. This gives the membrane flexibility. The microscopic spaces between the molecules allow certain materials to enter or leave the cell. This is the primary function of the plasma membrane. The membrane is described as "selectively permeable", meaning it selects what substances enter or leave. In other words, not all substances are allowed to pass through the membrane.
Now that you know everything there is to know about cells,
may I suggest you brush up on
your understanding of the microscope ?
Check out my Microscope Page.
|
Back
to Biology Topics Outline |
Please e-mail questions,
|
Lubey's |
StuDyiNG
the CeLL - ANSWER PAGES
Answers to "Tool &
Techniques for Cell Study" :
1. simple microscope
2. compound microscope
3. staining
4. phase-contrast
microscope
5. electron microscope
6. stereomicroscope
7. microdissection
apparatus
8. ultracentrifuge
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back
Answers to
"Cell Scientists Matching" :
1) J. Purkinje
2) R. Hooke
3) R. Virchow
4) A. von Leeuwenhoek
5) M. Schleiden
6) M. Schwann (has an
"a" in last name - animal cells)
7) R. Brown
<--back
Answers to "Animal Cell
Diagram" :
1. lysosome
2. endoplasmic reticulum
3. chromosome (DNA)
4. golgi body (apparatus)
5. vacuole
6. mitochondria
7. ribosome
8. nucleolus
9. nucleus (nuclear membrane would also be
OK)
10. centrioles
11. plasma membrane
12. cytoplasm
NOTES & TIPS :
#1 - generally, lysosomes are illustrated as
"shaded-in" circles or ovals.
#2 - channels running through the cytoplasm
#3 - the genetic material of the cell.
humans have 46 chromosomes in each body cell (except eggs & sperm).
this cell is eukaryotic because its genetic material is inside a nucleus.
#4 - stacks of membranes (like pancakes)
#5 - an "empty" oval or circle
#6 - you can recognize the mitochondria by
the zig-zag line that is usually drawn in them. these represent internal
membranes where respiration reactions occur.
#7 - very small dots, sometimes on the
endoplasmic reticulum, sometimes out floating in cytoplasm
#8 - drawn as a dark circle inside the
nucleus
#9 - generally depicted as the largest
"shaded-in" circle inside the cell
#10 - drawn in pairs, two cylinder-like
structures at right angles to each other
#11 - the outer boundary
#12 - the watery fluid that everything else
floats in
Answers to "Plant Cell Diagram":
1. nucleus
2. nucleolus
3. plasma membrane
4. cytoplasm
5. cell wall
6. vacuole
7. chloroplast
NOTES & TIPS
:
#1 - looks like an animal cell nucleus ---
usually the largest "shaded-in" circle
#2 - same as an animal cell --- dark circle inside
the nucleus
#3 - the plasma membrane in a plant cell is
just inside the cell wall
#4 - cytoplasm is cytoplasm, everything else
floats around in it
#5 - outermost boundary in a plant cell,
looks like a picture frame. it is nonliving, not very flexible, and made
of a polysaccharide called cellulose
#6 - drawn as "empty" areas in the
cell, usually very large in plant cells
#7 - small dark ovals. sometimes get
confused with mitochondria --- remember that mitochondria have the zig-zag,
chloroplats are usually shaded "solid"
back to the plant cell diagram
ANSWERS to
"Organelle Functions" Matching :
1. cytoplasm
2. cell membrane
3. nucleus
4. cell wall
5. ribosomes
6. endoplasmic reticulum
7. golgi apparatus
8. mitochondria
9. vacuole
10. nuclear membrane
11. nucleolus
12. lysosome
13. centrioles
14. centrosome
15. chloroplast
<--
back
sTudYBReaK !!!
OK, breaks over --- back to work