Content Benchmark L.8.B.2
Students know cells grow, divide, and take in nutrients which they use to provide energy for cell
functions. E/S
All life and therefore, all cells are characterized by a number of basic functions. Cells need to
replicate or reproduce, materials need to move into and out of a cell, and the cell must obtain
energy and use energy.
Cellular Reproduction
While individual cells may die, cellular reproduction is necessary for the survival of a species.
Whether an organism is unicellular or multicellular, there are several types of cellular
reproduction. These include binary fission, budding, mitosis and meiosis.
The process of binary fission (“splitting into two”) occurs in prokaryotic cells, most notably
bacterial cells, but also in some protozoans. This is the simplest and quickest form of cellular
reproduction. In the case of bacteria, it involves the doubling of the bacteria’s single and circular
chromosome and the splitting of the cell into two new cells.
The division is a 3 step process:
1. The circular chromosome or DNA molecule replicates and attaches to the cell membrane.
2. The two DNA loops are pulled apart as the cell grows.
3. A new cell wall grows between the loops and separates the cell into two.
Under favorable conditions, bacteria can undergo binary fission every twenty minutes. Thus in a
24 hour period and 72 binary fission cycles, 1 bacterium would become (assuming all survived)
23.36 x 1021 bacteria. (At this point, the teacher might explain the difference between
exponential and arithmetic growth.) Of course these ideal conditions which include energy
supply, nutrients, pH and temperature are seldom achieved for this period of time.
To view variations in the rate of bacterial growth go to
http://www.textbookofbacteriology.net/growth.html
For a graphing activity on exponential growth go to
http://www.bam.gov/teachers/activities/epi_4_microbe_magic.pdf
To view an animation of binary fission and budding go to
http://www.bact.wisc.edu/Microtextbook/images/textbook/growth/bactdivision.swf
Figure 1. E. coli under going binary fission.
(From http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html)
In eukaryotic cells, mitosis is a part of the cell’s life cycle (See Figure 2). The life cycle of a cell
varies from cell type to cell type, but essentially is composed for four phases including G1, S or
synthesis, G2, and mitosis. The first three phases (G1, S and G2) are often called interphase.
Injury and growth of an organism are two of the major reasons why cells will undergo mitosis
and divide into two new cells.
Cells will also divide for greater efficiency. Generally speaking larger cells are less efficient than
smaller cells due to surface to volume ratios. As cells increase in size, there is less surface area
for each unit of volume, thus the exchange of materials into and out of a cell becomes more
difficult. As seen in the Table 1, as a cell gets larger the surface area increases by a square and
volume increase by a cube. Larger cells have less surface are per unit volume for the movement
of substances into or out of the cells. Therefore, larger cells are less efficient than smaller cells.
Table 1: Surface to Volume Ratios
Cube Size (cm)
Surface Area
Volume
1x1x1
2x2x2
3x3x3
6 cm2
24 cm2
54 cm2
1 cm3
8 cm3
27 cm3
Surface to
Volume Ratio
6 to 1
3 to 1
2 to 1
To illustrate this relationship the teacher can do a surface to volume activity for the class found
at http://www.accessexcellence.org/AE/AEC/AEF/1996/deaver_cell.html
Interphase is an active part of the cell’s life cycle. During G1 the cell is growing and carrying out
its normal functions, whether it is a skin cell, liver cell or muscle cell. When the proper trigger
mechanisms occur (see the reference below for greater details) the chromosomes will begin to
divide in the S phase, which may last for an hour or so. This is followed by G2 when the cell
now prepares for mitosis.
Figure 2. A typical eukaryotic cell life cycle.
(From http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html)
The process of mitosis involves the division of the nucleus followed by cytokinesis or the
division of the cell’s cytoplasm as seen in the illustration below.
Figure 3. An overview of the mitotic process.
(From http://ghr.nlm.nih.gov/handbook/howgeneswork/cellsdivide)
Depending upon the type of cell, it may take mitosis several hours to complete its cycle. In
mitosis, four basic phases can be identified which are briefly described below. Teachers may also
find that an extra phase, called prometaphase, is often placed between prophase and metaphase.
At the middle school level it is probably not necessary to include this phase for student
understanding of the mitotic process. In older textbooks, this is often called late prophase.
Nevertheless mitosis is a continuous process, and these terms are convenient terms used to
denote various landmark changes occurring during this process.
1. Prophase – chromosomes coil and shorten and the nuclear membrane fragments.
2. Metaphase – movement of the chromosomes to the equatorial plate.
3. Anaphase – separation of the sister chromatids.
4. Telophase – reorganization of the nuclear membrane.
For a general description and diagrams of binary fission, the cell cycle and mitosis go to
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html
If the teacher wants an advanced description of mitosis and mechanisms that regulate it, visit
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellCycle.html
The process of cytokinesis may begin during or after telophase, however the process is different
in plants and animals. In plant cells, a cell plate (using molecules which have been formed in the
Golgi bodies) forms near the equatorial plate. This cell plate eventually forms a cell wall that
divides the plant cell into two cells. In animal cells, a cleavage furrow divides the cytoplasm in
half.
Figure 4. Comparison of cytokinesis in animal and plant cells.
(From http://fig.cox.miami.edu/~cmallery/150/mitosis/c7.12.9cytokinesis.jpg)
The process of cell division does not always proceed correctly. In cancer, the division of
cancerous cells out paces that of normal cells. When this happens, errors often occur which
results in the abnormal functioning of the cells.
For further description go to How Cancer Growth at Nova Online
http://www.pbs.org/wgbh/nova/cancer/grow_flash.html
Information regarding cancer is also available through Cancer Warrior at
http://www.pbs.org/wgbh/nova/cancer/program.html
The process of cell reproduction in gametes or sex cells is similar to that of non-sex cells, but
involves the reduction of chromosomes by half. This process, called meiosis, is also known as
reduction division because the chromosome number is reduced by this process. While mitosis
involves the replication of the DNA and division once, meiosis also replicates the DNA once, but
divides twice. It is this second division that reduces the chromosome number by half.
Figure 5. An overview of the meiotic process.
(From http://ghr.nlm.nih.gov/handbook/howgeneswork/cellsdivide)
Prior to start of meiosis, cells have a full count of chromosomes or a diploid number. In humans
this would be 46. The first division of meiosis proceeds much like mitosis, except the
homologous chromosomes (paired chromosomes containing genes for the same traits) are
separated and not the chromatids as in mitosis. After the first division two cells are produced,
each with half the number of chromosomes or in the case of humans 23. These cells are often
termed haploid or having one set of chromosomes. Each of these 23 chromosomes consists of
paired chromatids.
As the gametes proceed to second division the DNA is not replicated. This second division is
very much like mitosis as the sister chromatids are separated. However, the result is much
different. See the Table 2 below for a comparison of the mitosis and meiosis. Also, genetic
variation is increased during the first division of chromosomes. When the homologous
chromosomes pair up in Prophase I their chromatids can become twisted. When this occurs they
may exchange chromosomal segments in a process called crossing over.
Figure 6. Crossing over. This illustration also shows how crossing over can lead to increased genetic variation by
producing four different types of gametes.
(From http://regentsprep.org/Regents/biology/units/reproduction/crossingover.gif)
To view the steps and descriptions of meiosis go to
http://www.cellsalive.com/meiosis.htm
Table 2: Comparison of Major Characteristics of Mitosis and Meiosis
Characteristic
DNA Replication
Divisions
Cells Produced
Chromosome Number
Crossing Over
Daughter are cells
Mitosis
Once
One
2
Diploid
No
Genetically the
same
Meiosis
Once
Two
4
Haploid
Yes
Genetically
different
Figure 7. Comparing the overall process of mitosis and meiosis.
(From http://ghr.nlm.nih.gov/handbook/illustrations/mitosismeiosis.jpg)
Budding occurs in organisms such as yeast or hydra. After mitosis occurs, the cytoplasm does
not divide equally. Instead one of the new nuclei migrates to the cell membrane and is
surrounded by a small amount of cytoplasm, which then “buds” off. Note the illustration of
budding in yeast below.
Figure 8. Budding in yeast.
(From http://www.clt.astate.edu/mhuss/YEAST.jpg)
Figure 9. Budding in a hydra.
(From http://fig.cox.miami.edu/~cmallery/150/mitosis/c7.13.2.hydra.jpg)
Cellular Transport
In order to survive a cell must exchange gases, chemicals and other materials between itself and
its environment. This exchange occurs when these substances pass through the cell membrane or
are taken in or out by the formation of vacuoles or vesicles from the cell membrane. The cell
membrane is semipermeable (or selectively permeable) meaning that some, but not all
substances will pass through the membrane.
An explanation of diffusion is needed in order to understand this process. In diffusion, molecules
will move from areas of higher to areas of lower concentrations or towards equilibrium between
two areas. Note the illustration below.
Figure 10. Diffusion involving one or two solutes. In each case molecules
continue to move until an equilibrium is reached.
(From http://kentsimmons.uwinnipeg.ca/cm1504/membranefunction.htm)
This movement is influenced by what is known as diffusion pressure. Diffusion pressure includes
the difference in concentration between two areas, temperature and any external pressure that
may be applied. For example, the greater the difference in concentration between two areas will
accelerate the movement of molecules from the higher to lower concentration. This difference is
also know as the concentration or diffusion gradient. The concentration gradient will often
determine whether molecules move into or out of a cell.
The movement of molecules across the membrane is often divided into two categories called
passive transport requiring no extra energy to move molecules and active transport which
requires additional energy to move molecules across the membrane. In passive transport,
molecules move with or down the concentration gradient, while in active transport molecules
move up or against the concentration gradient. In moving down the concentration gradient,
molecules use their kinetic energy for movement. This can be likened to a rock rolling down a
hill. But to move against the gradient or moving a rock up hill requires energy. A rock will not
“roll” itself up hill.
Gases such as oxygen and carbon dioxide will move into or out of a cell by simple diffusion, a
type of passive transport. On the other hand, movement of small molecules or ions is dependent
upon the concentration of water in either side of the membrane. The difference in water
concentration on either side of the membrane provides the “energy” to move these other
substances.
Osmosis is the term used to describe the diffusion of water. Osmosis is defined as the movement
of water molecules across a semipermeable membrane from areas of high water concentration to
areas of lower water concentration. This movement of water may aid the movement of other
molecules.
Figure 11. Osmosis
(From http://www.okc.cc.ok.us/biologylabs/Images/Cells_Membranes/osmosis.gif)
In osmosis, the concentration of water is dependent upon the concentration of dissolved
substances (solutes) that are in the water (the solvent) on either side of the membrane. If solutes
are high then the relative water concentration is low, and if solutes are low then the relative water
concentration is high. Note in the illustration how this effects the movement of water. In Figure
10, the solutes are too large to move through the membrane.
Figure 12. Hypotonic, Hypertonic and Isotonic : In the upper part of the diagram both sides have equal
concentrations of solutes and therefore are isotonic to each other. In the bottom half, the right side is hypertonic to
the left as it has more solutes, while the left is hypotonic to the right because it has less solute.
(From http://www.visit-islay.com/biology/int2/cells.htm)
Each term (hypertonic, hypotonic and isotonic) is defined by the concentration of solutes in the
water. A hypertonic solution has a higher concentration of solutes relative to another solution.
(Note: You cannot hold a solution in your hand and state it is hypertonic. The question that will
be asked is “Hypertonic to what other solution?”). Likewise “hypo” means less solutes and “iso”
means equal solutes.
Therefore, water will move from a hypotonic solution into a hypertonic solution. In Figure 13,
the first cell (a) is hypotonic to the surroundings and water leaves the cell. On the other hand, the
second cell (b) is hypertonic to the surroundings and water enters the cell.
Figure 13. An illustration of water movement in hypertonic and hypotonic solution.
(From http://www.chem.ufl.edu/~itl/4411/colligative/lec_i.html)
The importance in maintaining a proper osmotic balance with a cell’s environment can be seen in
the illustration of red blood cell (RBC) shown below. In order to keep its proper shape and
function, a RBC must be isotonic to the surrounding blood plasma. If the plasma has a higher
concentration of solute or is hypertonic to the RBC, the RBC will shrink or undergo crenation.
The reverse happens in a hypotonic solution. In this case the RBC may burst or undergo
cytolysis. For this reason it important that hospitals prepare IV solutions with utmost care.
Figure 14. Effects on red blood cells placed in isotonic, hypertonic and hypotonic solutions.
(From http://www.ndpteachers.org/perit/osmosis2.gif)
While it is critical for a red blood cell to be isotonic with the surrounding blood plasma, some
cells will not always seek to be in an isotonic situation with their environment. For support,
herbaceous or non-woody plant cells need to be hypertonic to their surroundings. In this
condition water will move into the plant cell creating an internal pressure or turgor on the cell
wall. Thus, the cell becomes rigid or turgid which in turn provides support for the plant. Without
this turgor pressure, the non-woody plant would wilt.
Figure 15. Effects of water movement in plant cells.
(From http://www.bbc.co.uk/schools/gcsebitesize/img/biturgidity.gif)
Figure 16. Plant wilting. When plant cells lose their turgor pressure wilting will occur.
(From http://www.scienceisnthard.com/Droop.jpg)
Table 3: Summary of Osmosis
Relative
solute
concentration
of solution
compared to
cell: high,
low, equal
Relative
water
concentration
of solution
compared to
cell: high,
low, equal
Cell
immersed in
solution will:
gain, lose
water
Isotonic
Equal
Equal
Hypertonic
Higher
Hypotonic
Lower
Solution
compared to
a cell
Plant cell
will:
plasmolyze,
become
turgid
Animal will:
crenate,
undergo
cytolysis
No change
No change
No change
Lower
Lose
Plasmolyze
Crenate
Higher
Gain
Become
Turgid
Undergo
Cytolysis
Ions and larger molecules (amino acids or simple sugars) need assistance in order to move across
the membrane. Their size, polarity or charged nature prevents movement through or across the
cell membrane. In these cases, special carrier proteins will assist in their movement into or out of
the cell. This movement is called facilitated diffusion. Since the molecules are moving with the
concentration gradient and require no added energy it is also an example of passive transport.
Figure 17. Example of facilitated diffusion.
(From http://fig.cox.miami.edu/~cmallery/150/memb/c8x14facilitated.diff.jpg)
In some cases substances need to move against the concentration gradient. The most notable
example in the human body is found in the nerve cells. When a nerve cell “fires” or sends an
impulse, ions are exchanged between the inside and outside of the nerve cell. In order to reset
itself these ions must move back to their original location. This involves moving ions against
their concentration gradient. To accomplish this ion gates are activated by energy molecules
called ATP (adenosine triphosphate) and allow this movement to take place.
Figure 18. The NaK Pump found in nerves pumps these ions against their
concentration gradient with the aid of energy – ATP molecules.
(From http://www.mhhe.com/biosci/genbio/enger/student/olc/art_quizzes/genbiomedia/0645.jpg)
Figure 19. Comparing Passive and Active Transport.
(From http://www.accessexcellence.org/RC/VL/GG/ecb/ecb_images/12_04_passive_active_transport.jpg)
Finally, some molecules or substance are simply too large to move into or out of the cell. In these
cases, the cell will form vacuoles to move these substances. This is called endocytosis (moving
into the cell) and exocytosis (moving out of the cell). White blood cells called macrophages
(“large eaters”) will engulf bacteria in a process called phagocytosis (an example of
endocytosis). Once engulfed the bacteria is digested by the cell’s lysosomes.
Figure 20. Illustration of phagocytosis.
(From http://faculty.southwest.tn.edu/rburkett/GB1-os22.jpg)
Cells may also get rid of waste products in a reverse process called exocytosis. This process
involves moving substances out (exo) of the cell (cytosis).
Cellular Energy - Photosynthesis
Energy needs to be obtained and utilized in living organisms. Energy can be obtained from the
food we eat during the process of cellular respiration or some autotrophic organisms, like plants,
can obtain energy from the sun via photosynthesis.
Photosynthetic organisms such as plants, some forms of bacteria, algae and protozoans have the
ability to utilize sunlight to generate organic compounds (ex. simple sugars) which can be stored
and used later as an energy source for cellular functions. The general formula for photosynthesis
is shown below.
H2O + CO2 + Energy → C6H12O6 + O2
(Water and Carbon dioxide and Energy yields Glucose and Oxygen)
This formula is a very brief summary of the overall process of photosynthesis. It must be
remembered that water and carbon dioxide do not directly combine to form glucose. In a
complex process of reactions (Figure 21) these two molecules are utilized in different sets of
reactions called the light reactions (light dependent reactions) and Calvin cycle (light
independent reactions).
Figure 21. Overview of photosynthesis.
(From http://www.progressivegardens.com/knowledge_tree/photosynthesistotal.jpg)
For teachers wanting to know a more detailed description of photosynthesis, the following
information is provided. However, it should be noted that it is beyond what is needed by
students in middle school. Addition links are also provided.
In the light reactions, light energy is captured by chlorophyll which is found in the chloroplasts.
Water is needed to replace electrons that chlorophyll loses as it captures and passes the sun’s
energy along to other reactions. This energy is used to form two energy molecules called ATP
and NADPH. The energy from these molecules will be utilized in the Calvin Cycle. Once their
energy has been passed to the Calvin Cycle these two return to the Light Reactions as ADP and
NADP+ to pick up more energy.
In the Calvin Cycle carbon dioxide joins a molecule called RuBP that is present in the
chloroplast to make a six carbon compound. With energy from the light reaction this six carbon
compound is converted into 2 molecules called G3P. G3P can be used to form various organic
compounds as shown in Figure 21. Initially glucose will be formed which the cell usually stores
as starch or is used to form sucrose and is transported to other parts of the plant. The starch or
sucrose can later be converted back to glucose which will be utilized in cellular respiration.
In addition to this description, a more detailed explanation of photosynthesis is available at
Kimball’s Biology Pages – college level description at
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/LightReactions.html
Online Biology Book – honors level high school description at
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html
Cellular Energy – Cellular Respiration
In cellular respiration cells utilize food, most often glucose to provide energy to the cell. A
summary of the process can be seen below. Chemically, the equation for cellular respiration is
the reverse of photosynthesis.
C6H12O6 + O2 → CO2 + H2O + Energy
(Glucose and Oxygen yields Carbon dioxide and Water and Energy)
Figure 22. A summary of cellular respiration.
(From http://fig.cox.miami.edu/~cmallery/150/makeatp/c9x6cell-respiration.jpg)
Similar to the formula for photosynthesis, the above equation is only a summary of the overall
set of reactions that are needed to obtain the energy from a molecule of glucose. The first part of
this reaction called glycolysis (“sugar breakdown”) takes place in the cytoplasm. The cell
provides energy in the form of ATP to split a molecule of glucose. As a result, a small amount of
energy is released and two molecules of pyruvic acid or pyruvate (the nonaqueous form) are
produced. The pyruvic acids molecules still hold a large amount of energy. In the presence of
oxygen this energy can be obtained when pyruvic acid passes into the mitochondria.
In the mitochondria, the energy that was locked up in the chemical bonds of pyruvic acid is
converted into more energy molecules called NADH + H+ and FADH2 in the Krebs cycle. Later
in the Electron Transport Chain all the electrons in the molecules of NADH + H+ and FADH2 are
used to make ATP which can be used for cellular work.
As a result of cellular respiration, about 40% of the energy that is in a glucose molecule is
converted into energy (in the form of ATP) that can be used by the cell for cellular work. A
question that might be asked by students is “What happens to the other 60%?” This 60% is given
off as heat during these reactions. In living organisms this heat goes to warm the body. You
might ask your students what happens when they go outside on a very cold day and forget their
coat. Most often they will answer that they shiver. Your next question, “And why do you
shiver?” The answer is to produce heat. To shiver the muscles need energy, therefore breakdown
glucose. And as we have seen this produces heat energy.
At this point students might ask why is oxygen needed? As in photosynthesis, energized
electrons are used to pass energy along. At the end of the Electron Transport Chain these
electrons need to be removed to make room for others. Oxygen, an electron grabber picks up the
spent electrons and along with H+ (hydrogen ions) forms water.
If oxygen is not available the pyruvic acid will not be broken down and carried into the
mitochondria. To avoid a possible toxic buildup, the pyruvic acid is converted into ethanol (in
bacteria and yeast) or lactic acid (in animals, including humans).
A detailed explanation of the Krebs cycle and Electron Transport Chain is not needed at this
level, but for teachers who want a detailed description of what happens in these reactions can
access the following sites.
Kimball’s Biology Pages – college level description at
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellularRespiration.html
Online Biology Book – honors level high school description at
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookGlyc.html
Table 4: Comparison of Photosynthesis and Cellular Respiration
Photosynthesis and Cellular Respiration
Photosynthesis






produces food
stores energy
uses water
uses carbon dioxide
releases oxygen
occurs in sunlight
Cellular Respiration






uses food
releases energy
produces water
produces carbon dioxide
uses oxygen
occurs in the dark as well as light
Content Benchmark L.8.B.2
Students know cells grow, divide, and take in nutrients which they use to provide energy for cell
functions. E/S
Common misconceptions associated with this benchmark
1. Students assume that a majority of the mass in plants comes from water or other
substances from the soil. Students do not think that carbon dioxide plays a major role.
Students have a difficult time imagining that carbon dioxide has mass. To help students
understand that it does have mass, teachers can bring dry ice to class to demonstrate that
carbon dioxide does have mass.
The Annenberg Video series called A Private Universe has an excellent section on student
misconceptions about photosynthesis. The Section entitled Biology: Why Are Some Ideas So
Difficult explores student misconceptions on this subject and ways in which teachers can
over come them. Teachers need to register to view the video, but it is free. The home page
can be found at: http://www.learner.org/index.html
2. Students inaccurately think that respiration only occurs in the lungs and do not realize
the difference between respiration and cellular respiration.
Respiration is the physical and mechanical process of exchanging oxygen and carbon dioxide
between the atmosphere, the lungs and blood. Cellular respiration is the chemical process in
the cells whereby oxygen is used to help breakdown food (normally glucose) to create energy
that can be utilized by the cells.
Teachers can refer to the following two sites to aid in clarifying this misconception. The first
describe role of the lungs and the second describe cellular respiration.
The process of breath at
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookRESPSYS.html
Cellular respiration at
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookGlyc.html
3. Students incorrectly believe that plants obtain energy by photosynthesis and animals
obtain energy by cell respiration.
While plants utilize the sun’s energy to produce food, it is the process of cellular respiration
that chemically breaks down this food to obtain energy for cellular use. Animals and plants
both use cellular respiration to obtain energy from the food whether they ingest it or produce
it themselves. While plants do produce and give off oxygen in the process of photosynthesis,
some of this oxygen is utilized by the plant during the process of cellular respiration.
A comparison of these processes can be found at
http://www.cmg.colostate.edu/gardennotes/141.pdf
An additional summary chart of these processes can be found at
http://www.winterwren.com/apbio/handouts/cells/cellenergy.pdf
4. Students incorrectly think that interphase is a period of rest during the cell cycle.
During interphase the cell is quite active. After mitosis the new cells begin growing in size
and performing their designated functions, whether acting as muscle cells or digestive cells
producing enzymes for digestion in the stomach. Prior to mitosis, chromosomes in the
nucleus need to be replicated along with other molecules necessary for cell division. Thus the
cell is never at “rest”.
To help understand the mitosis students can “act out” this process following the procedures
found at
http://www.smv.org/JIL/mll/middle/MLL7-8VS-CA-mit.pdf
Teachers can find lesson plans and activities about mitosis at
http://www.biologylessons.sdsu.edu/classes/lab8/lab8.html
5. Students have the misconception that diffusion is the process whereby all substances
move into or out of a cell.
Diffusion involves movement of molecules from areas of high to areas of low concentration.
While some of the smallest molecules like oxygen, carbon dioxide or water move across the
cell’s membrane by simple diffusion, most other molecules need assistance in moving across
the cellular membrane. It now appears that water transport across the membrane is aided by
“aquapores” at times. Ions, sugars, amino acids and other larger molecules require special
protein pores or channels to move into or out of the cell. Also there are times during active
transport that molecules will move against the concentration gradient, that is, they move from
low to high concentrations.
Teacher can find a unit on teaching diffusion at
http://biology.arizona.edu/sciconn/lessons/mccandless/tchrinfo.html
6. Osmosis always will reach equilibrium.
Equilibrium is not always the “goal” of osmosis. Red blood cells may need to be at
equilibrium with the surrounding plasma, so that they do not burst. On the other hand plants
might wilt or plant roots would not take in water if they are at equilibrium with their
surroundings.
Teachers can help to correct this misconception by doing the “classic” egg osmosis lab.
Directions for this lab can be found at the following sites
http://www.lessonplanspage.com/ScienceOsmosisExperiment412.htm
and
http://www.speedway.k12.in.us/hs/projects/SStevens/Biology%20I/Labs/Cells/Osmosis%20
Egg%20Lab.pdf
Content Benchmark L.8.B.2
Students know cells grow, divide, and take in nutrients which they use to provide energy for cell
functions. E/S
Sample Test Questions
Questions and Answers to follow on a separate document
Content Benchmark L.8.B.2
Students know cells grow, divide, and take in nutrients which they use to provide energy for cell
functions. E/S
Answers to Sample Test Questions
Questions and Answers to follow on a separate document
Content Benchmark L.8.B.2
Students know cells grow, divide, and take in nutrients which they use to provide energy for cell
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. CELLS Alive!
The website Cells Alive has detailed information, animations, and videos that cover the cell
cycle, mitosis and meiosis that can be utilized by the teacher to illustrate these processes to
students.
Teachers can access this website at
http://www.cellsalive.com/
2. Osmosis and Diffusion Labs
Teachers can find laboratory activities or demonstrations on diffusion and osmosis at the
following websites.
Students can do the diffusion lab found at
http://www.biologycorner.com/worksheets/diffusion.htm
Another lab is I Shrunk the Carrots found at
http://www.usoe.k12.ut.us/curr/science/sciber00/7th/cells/sciber/osmosis2.htm
Teachers can construct an egg osmometer with instructions found at
http://www.accessexcellence.org/AE/ATG/data/released/0519-NancyIversen/activity.html
3. Private Universe Project in Science – Focus Photosynthesis
In the Annenberg series entitled the Private Universe Project in Science, teachers should view
the segment called Biology: Whys Are Some Ideas So Difficult (Workshop 2). In this video
teachers will find an excellent discussion on the difficulties in teaching photosynthesis to
students. To view this and any Annenberg video you will first need to register, but it is free!
You will find other useful videos at this site too.
Teachers can access this video segment at
http://www.learner.org/resources/series29.html
4. Photosynthesis from the Teachers Domain
To introduce photosynthesis to your students have them view the video clip on
photosynthesis found at Teachers Domain (PBS). After several trial viewings you will need
to register at this site – it is simple, safe, and free!
The video can be found at
http://www.teachersdomain.org/resources/tdc02/sci/life/stru/photosynth/index.html
5. Harvard-Smithsonian Center for Astrophysics Digital Video Library - Photosynthesis
Also teacher might want to have students view how we came to out present understanding
of photosynthesis by looking at its history of discovery. This clip explains the process of
photosynthesis. Leaves from plants grown in the light contain starch, but leaves from plants
grown in the dark do not contain starch.
To view this 5 minute video go to
http://www.hsdvl.org/video.php?record_serial=229