Performance Benchmark L.12.B.1
Students know cell structures and their functions E/S
Content Background
The smallest thing that exhibits all of the characteristics of life is a single cell. Some organisms
are made up of only one cell while complex organisms are made up of trillions. The
understanding of the Cell Theory, types of cells, and cellular organelle structure and function is
essential to any biology student.
Cell Theory
The Cell Theory is the summation of 150 years of research by many scientists, like Theodor
Schwann and Matthias Schleiden. The research groups worked independently on topics of
animal cells, plants cells, and cellular reproduction. These pieces contributed to what is now
known as the Cell Theory. The Cell Theory has three main components:
1. All living things are composed of at least one cell.
2. Cells are the most basic unit of structure and function.
3. All cells come from preexisting cells.
Prokaryotic vs. Eukaryotic
Cells can be separated into two groups based on the presence or absence of membrane bound
organelles. The first group lack organelles and are called Prokaryotic. Bacteria are prokaryotic.
Figure 1. A diagram of a
prokaryotic cell.
http://library.thinkquest.org/C00
4535/prokaryotic_cells.html
Eukaryotic cells contain many membrane bound organelles. Each organelle has very specific job
to complete, like protein synthesis, trash clean up, or energy production. All organisms except
bacteria are eukaryotic.
Figure 2. A diagram of a
Eukaryotic cell.
http://library.thinkquest.org/C00
4535/eukaryotic_cells.html
Eukaryotic Cell Organelles
1. Cell membrane –
The cell membrane separates the cell from the surrounding environment. It is composed of two
layers of lipids with a variety of proteins and carbohydrates embedded in it. The membrane is
often described with the Fluid Mosaic Model. It states that the embedded proteins and lipid
layers actually move about, thus giving the membrane a fluidity to it. Some proteins form
channels to help move material through the cell membrane. Other proteins are chemical
receptors that signal the cell to begin or stop some metabolic activities. The carbohydrates
bound to the membrane allow the organism’s immune response system to differentiate between
its own cells from foreign invaders.
Figure 3. A diagram of
the two lipid layers of a
cell membrane showing
the variety of embedded
proteins and
carbohydrates.
http://academic.brooklyn.
cuny.edu/biology/bio4fv/
page/pm_mos.htm
The membrane is semi permeable. Some things pass freely through the membrane while other
substances must be transported across. Transport can be either a passive or active process.
Passive transportation across the membrane does not
require the expenditure of energy. Substances, like
water and gases, can move freely across the
membrane into and out of the cell. This process is
called diffusion or the random movement of
molecules from areas of high concentration to areas of
low concentration until equilibrium is reached. A
special type of diffusion is osmosis, the diffusion of
water through a selectively permeable membrane.
Water will also move into and out of a cell from areas
of high concentration of water to low areas of
concentration of water until an osmotic balance is
reached.
Figure 4. Passive transport of lipid soluble
molecules through a selectively permeable
membrane
http://www.emc.maricopa.edu/faculty/farabee/biob
k/BioBooktransp.html#Cells%20and%20Diffusion
Active transport allows a cell to move substances
against the concentration gradient but it requires the
expenditure of energy. One process uses the embedded membrane proteins to pump ions into or
out of the cell. Another process, called endocytosis, actually has the cell membrane making
pockets of materials by encircling a substance creating a vesicle. The vesicle then breaks off to
the inside of the cell and releases the material to the cell. Endocytosis of a liquid is called
pinocytosis and of a solid is called phagocytosis. The movement of materials out of the cell is
called exocytosis.
Figure 5. An example of active transport. Protein channels
are being used to move materials opposite the concentration
gradient.
http://images.google.com/imgres?imgurl=http://www.rpi.edu/dept/ch
em-eng/BiotechEnviron/Membranes/bauerp/mem2.gif&imgrefurl=http://www.rpi.ed
u/dept/chem-eng/BiotechEnviron/Membranes/bauerp/mech.html&h=291&w=444&sz=5&hl=e
n&start=1&tbnid=TfwmPfvnL4G8pM:&tbnh=83&tbnw=127&prev=
/images%3Fq%3Dactive%2Btransport%2Bproteins%2Brpi%26svnu
m%3D10%26hl%3Den%26lr%3D%26rls%3DGGLD,GGLD:200433,GGLD:en
Figure 6. An example of active
transport by endocytosis.
http://www.sp.uconn.edu/~bi10
7vc/fa02/terry/membranes.html
2. Cell wall
The cells of plants, bacteria, and algae are enclosed by a
rigid cell wall. The main purpose of the cell wall is to
support and protect the cell. The cell wall lies outside of
cell membrane and is usually composed of cellulose.
The cell wall has large pores which allows all materials
to pass (it is completely permeable). Sometimes, strands
of membranes pass through the pores connecting
neighboring cells. Animal cells do not contain cell
walls.
Figure 7. The structure of a cell wall.
3. Nucleus
http://genomics.energy.gov
This membrane bound organelle houses the control center of
the cell. The nucleus protects and maintains the integrity of the DNA, the molecule that contains
the coded instructions of the cell. An analogy would be the nucleus is a safe for the original blue
prints (DNA) for a large project. Copies of the blue prints can be sent out of the nucleus but the
original must stay safe.
Figure 8. The nucleus. The drawing
above is from
http://www.cdli.ca/~dpower/cell/nucleus.
htm
The microscopic photograph to the right
is from
http://web.mit.edu/esgbio/www/cb/org/
organelles.html
4. Ribosomes
The site of protein synthesis is the ribosomes. The
instructions from the DNA are delivered to the ribosomes
by mRNA. Once the instructions are read, amino acids
are delivered to the ribosome by tRNA and put into
proper order to construct the specific protein. Ribosomes
located on the rough endoplasmic reticulum usually
produce proteins to be exported from the cell and
ribosomes floating in the cytoplasm usually produce
proteins to be used by the cell.
Figure 9. Ribosomes located on rough
5. Endoplasmic reticulum
endoplasmic reticulum.
The endoplasmic reticulum (ER) is a system of
http://web.mit.edu/esgbio/www/cb/org/r
ough_er-em.gif
membrane channels throughout the cell. There are two
types of ER, rough and smooth. The rough ER is studded
with ribosomes giving it a rough appearance while the smooth ER lacks ribosomes. The ER’s
primary purpose is to transport materials around the cell. The ER also provides a large
membrane surface area on which many biochemical processes take place. It also divides the cell
into compartments so more than one biochemical reaction can be completed concurrently.
6. Vacuoles
Vacuoles are fluid filled membrane organelles
and primarily functions as long term storage. In
plant cells, a single vacuole can occupy most of
the cell space filled mostly with stored water.
In animal cells, vacuoles are usually small
(relative to the cell) and may contain proteins,
fats, or carbohydrates.
Figure 9. This is a plant cell with a
large central vacuole identified.
http://bio.winona.edu/berg/Image.htm
7. Lysosomes
Lysosomes are membrane bound sacs that contain
digestive enzymes that can collect, breakdown, and
recycle worn out organelles. Lysosomes in immune
defense cells, like white blood cells, engulf and destroy
bacteria and viruses. In some organisms, lysosomes
may also be used to digest macromolecules.
Figure 10. The process of Lysosomes
engulfing damaged organelles is shown.
http://sun.menloschool.org/~cweaver/ce
lls/e/lysosomes/
8. Chloroplasts
Chloroplasts are only found in plant and certain types of algae. Chloroplasts contain the pigment
chlorophyll, giving plants their green color. The chloroplast is where photosynthesis takes place.
The process of photosynthesis converts light energy from the sun into chemical energy in the
form of glucose.
Figure 11. Chloroplasts. The
photograph to the left is from
http://en.wikipedia.org/wiki/Chloroplast
The chloroplast rendition below is from
http://evogen.jgi.doe.gov/second_levels
/chloroplasts/cpDNA_info.html
9. Mitochondria
Mitochondria are double membraned organelles. The outer membrane forms the boundary of the
organelle, while the inner membrane is folded increasing the surface area necessary to produce
energy (ATP and NADH) from the breakdown of sugars. The breakdown of macromolecules to
release stored chemical energy is called cellular respiration. An average cell may contain 500
mitochondria. Cells that require large amounts of energy, like muscle cells, may contain
thousands of mitochondria.
Figure 12. Mitochondria. The photograph to the
left is from
http://en.wikipedia.org/wiki/Mitochondria
The mitochondria rendition above is from
http://www.nsf.gov/news/overviews/biology/inter
act08.jsp
10. Golgi apparatus
Golgi apparatus (or Golgi bodies) looks like stacks of flattened membrane sacs. The Golgi
apparatus is responsible for processing, packaging, and storing products of the cell to be
delivered to the cell membrane for release from the cell.
Figure 13. Golgi apparatus. The products of the
cell are transferred from the ER to the Golgi and
then, through a series of steps for packaging. The
package is delivered to the cell membrane for
release from the cell.
http://publications.nigms.nih.gov/insidethecell/ch
apter1.html#4
11. Cytoplasm
Cytoplasm is the watery environment inside the cell and includes everything from the cell
membrane to the nuclear membrane. It consists mostly of water with small quantities of salts
and dissolved gases. The space outside the various organelles is more specifically called the
cytosol. The cytosol also contains structural elements called the cytoskeleton which give the cell
structure and may aid in the cellular movement of cilia and flagella.
12. Centrioles
Centrioles are a pair of organelles found in animal cells but not in plant cells.
During cell division, the centrioles move to opposite ends of the cells and form the spindle that
pull the chromatids apart and move them to the opposite poles so two daughter cells can form.
Figure 14. This is late prophase showing the
centrioles at each pole of the cell and the
formation of a spindle between the centrioles.
http://www.brooklyn.cuny.edu/bc/ahp/MBG/MB
G3/M.Pro.late.html
Plant vs. Animal Cells
Plant and animal cells have many key differences.
1. Plant cells have a cell wall.
2. Plant cells have chloroplasts and are photosynthetic.
3. Plant cells have a large central vacuole that can take up 95% of the cells volume.
4. Animal cells have centrioles
5. Lysosomes are common in animal cells and very rare in plant cells.
Figure 15. A typical animal cell.
http://www.cod.edu/people/faculty/fancher/ProkE
uk.htm
Figure 15. A typical plant cell.
http://www.lclark.edu/~seavey/genetics04/lecture
s/lecturejan21.html
Performance Benchmark L.12.B.1
Students know cell structures and their functions E/S
Common misconceptions associated with this benchmark:
1. Cells are resting when they are not dividing
Cells are most metabolically active during interphase, the period between cell divisions. They are
typically engaged in biosynthesis and growth during this time.
2. Respiration occurs in the lungs and is solely the process of gas exchange.
Respiration has two stages - gas exchange which occurs in lungs, gills, or stomata, and
biochemical changes that occur in the cells (cellular respiration).
3. Cellular respiration is characteristic of animal cells but not plant cells. Plant cells
photosynthesize instead.
All eukaryotic cells capture energy from the breakdown of sugars via cellular respiration in the
mitochondria.
4. Plant and animal cells obtain their nutrients (food) from the environment.
Plant cells have the unique capacity to synthesize their own nutrient building blocks, 6-carbon
sugar molecules, from inorganic substances such as CO2 and H2O. All other organisms and their
cells must take in organic molecules derived directly or indirectly from plants.
5. Everything a cell needs gets into it by diffusion.
Only the smallest molecules such as H2O, CO2, and O2 can diffuse freely into and out of cells.
Larger more charged molecules such as sugar and salt ions require active transport across the
membrane.
The above list of misconcepts came from the site listed below.
http://www.biologylessons.sdsu.edu/classes/lab7/altern.html
Performance Benchmark L.12.B.1
Students know cell structures and their functions E/S
Sample Test Questions
1. Which organelles are most directly involved in protein synthesis?
a. Nucleus and Ribosomes
b. Chloroplast and Mitochondria
c. Cell Membrane and Cell wall
d. Ribosomes and Lysosomes
2. Which organelle is involved in cellular respiration in both animal AND plant cells?
a. Nucleus
b. Chloroplasts
c. Mitochondria
d. Vacuole
3. Which statement best describes the cell membrane in a typical plant cell?
a. The membrane selectively controls what enters and exits the cell.
b. It is composed of protein and carbohydrates only.
c. It has the same permeability to all substances inside and outside of the cell.
d. It is a composed of two protein layers with lipids floating inside.
For Questions 4 and 5 refer to the diagram below. Cell I and II are typical cells.
4. Cell II is most likely a plant cell because it contains
a. A
b. B
c. E
5. In both cells, organelle E is the site of
a. photosynthesis
c. resource storage
d. F
b. respiration
d. protein synthesis
6. A network of membranes throughout the cell that aid in the transportation of materials around
the cell is the
a. endoplasmic reticulum
b. chloroplast
c. nucleus
d. ribosome
7. If the ribosomes stop working in a cell which cellular process would be most affected?
a. photosynthesis
b. aerobic respiration
c. protein synthesis
d. excretion of cellular wastes
Performance Benchmark L.12.B.1
Students know cell structures and their functions E/S
Answers to Sample Test Questions
1.
2.
3.
4.
5.
6.
7.
(a)
(c)
(a)
(d)
(b)
(a)
(c)
Performance Benchmark L.12.B.1
Students know cell structures and their functions E/S
Intervention Strategies and Resources.
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. Interactive models
This website has interactive animated plant and animal models. Students can click on the
organelles and get a description of its structure and function. It is a good resource for
visual learners. It also has many links for students under “homework links”. It even has
links to puzzles and self quizzes.
You can access these models at:
http://www.cellsalive.com/mitosis.htm
2. On-line Biology Textbook
This website is a hyperlinked biology textbook. It is a good site to use to supplement the
classroom text. It contains hyperlinked definitions and diagrams that will help students
decode the reading.
You can access this
http://web.mit.edu/esgbio/www/chapters.html
3. On-line cell biology and quizzes
This site is very interactive. Its goals are for students to:
1. Recognize the differences between prokaryotic and eukaryotic cells
2. Recognize the differences between plant and animal cells
3. Understand the function of the major organelles in these cells
The site allows students to examine each cell, “zoom in” for more information, and even
has “Pop up questions” to self quiz. At the conclusion, it has a “Construct a Cell” self
quiz. Students are asked to construct a plant, animal, or prokaryotic cell and check their
accuracy.
You can access the quizzes here:
http://www.wiley.com//legacy/college/boyer/0470003790/animations/animat
ions.htm
4. On-line quizzes and concept maps
This is a good site for computer savvy students. “Organize-It is a new kind of self –
testing system. It’s designed to practice your knowledge of how ideas fit together.” It
has student arrange a list of terms into a “concept map” like list. It treats the organization
as a quiz and students can check their answers.
You can access this site at:
http://biologyinmotion.com/organize-it/