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Page 4A&P 1
Lab ManualLab Index Page 3 Page 4 Lab 3
Lab 2Cell Structure and Cell Membrane
CONTENT
1) Cell MembraneDiffusion RatePassive TransportOsmosis and Dialysis
2) Cell StructureProkaryotic CellsEukaryotic Cells
3) Cell ReproductionCell CycleMitosisCytokinesis
4) Chromosome Structure
5) Online Onion Root Tip Mitosis
What Do I Need To Hand In For This Lab?
Sketches
Red Blood Cell in Isotonic Solution Red Blood Cell in Hypotonic Solution Red Blood Cell in Hypertonic SolutionProkaryote CellEukaryote CellStages of Cell CycleMitosis StagesCytokinesisChromosome
Tables / Charts
Data Table for Diffusion of Different Molecular WeightsTable of Osmotic Potential and TimeGraph of Osmotic Potential vs TimeGraph of Osmotic Change vs Time (Osmotic Rate)Table of Dialysis TestsChart of Summary of Events During Phases of MitosisChart of % time in different phases of the cell cycle
Questions
Diffusion Questions 14Passive Transport Questions 13Osmosis Questions 17Dialysis Questions 16Cell Structure Questions 13Mitosis Questions 13
Cover Page
Lab 2 Cover Page
1) Cell MembraneMovement of Materials Through Cell Membranes
The cell membrane is arguably the most important structure ofany living cell. Inherent in the phenomenon of life is the abilityof a cell to isolate itself from its environment. Completeisolation, however, is not the goal; rather, cells seek to acquireessential materials from their surroundings, exclude useless ortoxic materials from entering the cytoplasm, and export to theenvironment useless or toxic molecules produced in the courseof normal metabolism.
This momentous task is accomplished by a thin (ca. 10 nm)layer of phospholipids and proteins that surround the cell. Thephospholipids are arranged in a bilayer such that thephosphate "heads" are oriented towards either the aqueousexterior or interior of the cell, whereas the fatty acid "tails" formthe hydrophobic ("water hating") interior of the membrane.Embedded within the bilayer are specific protein moleculesthat, in conjunction with the phospholipids, serve to perform theregulatory tasks noted above.
Figure 2.1 Cell Membrane Properties
To see how the cell membrane interactswith the surrounding fluids click here
Use Your Back Button to Return
Click Here to View an Animation on Membrane Fluidity MEMBRANE FLUIDITY
Click Here to View an Animation on the Cell Membrane CELL MEMBRANE
Click Here to View another Animation on the Cell Membrane CELL MEMBRANE 2
To perform their functions, cells must maintain homeostasis in spite of an ever changing environment. In order to maintain homeostasis, the cellmembrane regulates the movement of substances into and out of the cell, preventing the flow of some substances while allowing others to passthrough easily. The membrane is said to be selectively permeable, because not all substances penetrate the cell membrane the same.
The external and internal environments of a cell are water solutions of dissolved molecules and ions. Movement of these molecules and ions in thesolutions and through the cell membranes is by diffusion. Molecules and ions move from regions in which their concentration is high to regions in which
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it is lower by kinetic energy until they become distributed throughout the cell. When salt dissolves in a glass of water, the sodium and chlorine ions ofwhich it is composed become equally distributed in the water. Passive diffusion is the random motions of the solute and solvent molecules andrequires no added energy.
Active transport is a type of diffusion in which dissolved particles move against a concentration gradient. This type of diffusion does require an energyinput. For example, human red blood cells have almost 30 times more potassium than does blood plasma.
A special case of diffusion that occurs in living systems is osmosis. Osmosis is the diffusion of water molecules through a selectively permeablemembrane from a region in which they are more highly concentrated to a region in which their concentration is lower.
Both diffusion and osmosis result from the kinetic activity of molecules or ions. They are affected by a number of factors, such as temperature, themolecular weight of the diffusing substance, and the lipoid solubility of the solute. In this experiment, you will examine some of the factors regulatingthese processes.
There are three experiments to perform for this portion of the lab.
1) Diffusion Rate2) Passive Transport3) Osmosis and Dialysis
In order to access the Cell Membrane Virtual Lab you will need to use the link supplied below. Instructions for performing each of the three experimentsare given in the Lab. When viewing the POWERPOINT be sure you are in SLIDE SHOW (Click on F5 at the top of your keyboard) mode to perform theinteractions.
EXPERIMENT # 1 Diffusion RateDiffusion is a process of equalization which involves movement of molecules from an area of high concentration to an area of lowconcentration. This exercise investigates diffusion as it applies to movement of particles in a semisolid material called agar. Molecules arein a constant state of motion. The motion of these molecules are influenced by many factors.
Factors Influencing Diffusion
1) Kinetic Energy Kinetic energy is the driving force which causes the molecules to move2) Nature of the environment The agar environment we will be using is a semisolid material through which we will measure the rate ofdiffusion of substances with different molecular size3) Size of the molecules Smaller molecules move faster than larger molecules
Click Here to View an Animation on Diffusion DIFFUSION
You can try this link to view an animated discussion on Diffusion
In order to access the Cell Membrane Virtual Lab you will need to usethe link supplied to the left. When viewing the POWERPOINT be sureyou are in SLIDE SHOW (Click on F5 at the top of your keyboard)mode to perform the interactions.
You will need to supply the following in your lab report for this experiment #1
1) Data Table for Diffusion of Different Molecular Weights2) Answers to Diffusion Questions 14
Click Here to AccessDATA TABLE FOR DIFFUSION OF DIFFERENT MOLECULAR WEIGHTS (MS WORD FILE)
DATA TABLE FOR DIFFUSION OF DIFFERENT MOLECULAR WEIGHTS (PDF FILE)
DIFFUSION QUESTIONS1) What are the three things which influence the movement of molecules and particles? 2) In agar, what size of molecules move the fastest?3) Which dye, the methylene blue or the potassium permanganate, diffused at the fastest rate? 4) Why did one dye diffuse faster than the other?
EXPERIMENT #2 Passive TransportObservations of Passive Transport in RBC
The plasma membrane is a Selectively Permeable membrane that surrounds the cell. The passive movement of water and dissolvedsubstances across the membrane requires permeability through the membrane. In order for substances to diffuse across the plasmamembrane, they must be permeable to the membrane. Substances such as oxygen and carbon dioxide easily diffuse across the plasmamembrane. Osmosis is the diffusion of water through a selectively permeable membrane. Water will generally move quite freely through thecell membrane by diffusion. Osmotic movement of water occurs when the solute (nonpenetrating) concentrations differ between theopposing sides of the cell membrane.
A difference in solute (nonpenetrating) concentrations means there is a difference in water concentrations and water will move from theregion of higher concentration to a region of lower concentration. For example, water osmotically moves into a cell when the fluid outside thecell has more water (less solutes) than the fluid inside the cell. In this case, as water moves into the cell, it swells as the water pressureinside the cell increases.
Tonicity is the ability of a solution to affect the movement of water by osmosis, thus the shape of the cell, is called tonicity. There are threepossible tonicities of solutions that produce three cell shapes. The three possible tonicities are as follows:
Isotonic solutions which produce a normal shaped cellHypotonic solutions which causes cells to swell Hypertonic solutions which causes the cell to shrink
ISOTONIC SOLUTIONSAn isotonic solution has the same concentration of solutes as within the cell. Equal concentrations of solutes means that thereare equal concentrations of water. There is no net diffusion of water, and the cells maintain a normal shape.
Click Here to View an Animation on Isotonic Solutions ISOTONIC SOLUTION
HYPOTONIC SOLUTIONSA hypotonic solution has a lower concentration of solutes than within the cell. Since the solution has a lower concentration ofsolutes, it has a higher concentration of water, and net water diffusion is into the cell. Water movement into the cell increases its
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internal pressure and the cell swells until it bursts or lysis.
Click Here to View an Animation on Hypotonic Solutions HYPOTONIC SOLUTION
HYPERTONIC SOLUTIONSA hypertonic solution has a higher concentration of solutes than within the cell. Since the solution has a higher concentration ofsolutes, it has a lower concentration of water, and net water diffusion is out of the cell. Water movement out of the cell decreasesit internal pressure and the cell shrinks and crenates.
Click Here to View an Animation on Hypertonic Solutions HYPERTONIC SOLUTION
Because red blood cells have very flexible cell membranes, they can be used to show the effects that solutions of different tonicities have ona cell shape. Most cells in the body have the ability to counteract the effects of changes in tonicity. These cells may have special proteinsembedded into the cell membrane which act to equalize the internal pressures within the cell to inhibit major changes in their shape. Redblood cells lack these proteins in their cell membranes.
The blood which we will be using in this experiment is human blood. If you become exposed in any way to the blood you must immediatelynotify your instructor. He will probably tell you to restart your computer so that you do not become infected with a disease.
Click Here to View an Animation on Passive Transport Diffusion PASSIVE TRANSPORT DIFFUSION
Click Here to View an Animation on Passive Transport Diffusion PASSIVE TRANSPORT FACILITATED DIFFUSION
Click Here to View an Animation on Passive Transport Diffusion PASSIVE TRANSPORT OSMOSIS
In order to access the Cell Membrane Virtual Lab you will need to usethe link supplied to the left. When viewing the POWERPOINT be sureyou are in SLIDE SHOW (Click on F5 at the top of your keyboard)mode to perform the interactions.
You will need to supply the following in your lab report for this experiment #2
1) Sketch of red blood cell in isotonic solution2) Sketch of red blood cell in hypotonic solution3) Sketch of red blood cell in hypertonic solution4) Answers to Passive Transport Questions 13
PASSIVE TRANSPORT QUESTIONS1) Describe the appearance of red blood cells in an isotonic solution2) Describe the appearance of red blood cells in a hypotonic solution3) Describe the appearance of red blood cells in a hypertonic solution
EXPERIMENT #3 Osmosis and Dialysis
There are two parts to this experiment #3. PART 1 will consider OSMOSIS and PART 2 will consider DIALYSIS.
In order to access the Cell Membrane Virtual Lab you will need to usethe link supplied to the left. When viewing the POWERPOINT be sureyou are in SLIDE SHOW (Click on F5 at the top of your keyboard)mode to perform the interactions.
PART 1 OSMOSIS
Osmosis is the diffusion of water through a selectively permeable membrane. Water will generally move quite freely through the cellmembrane by diffusion. Osmotic movement of water occurs when the solute (nonpenetrating) concentrations differ between the opposingsides of the cell membrane. A difference in solute (nonpenetrating) concentrations means there is a difference in water concentrations andwater will move from the region of higher concentration to a region of lower concentration. For example, water osmotically moves into a cellwhen the fluid outside the cell has more water (less solutes) than the fluid inside the cell. In this case, as water moves into the cell, it swellsas the water pressure inside the cell increases.
The device you will be using to collect data for the experiments is an osmometer. This is a device used to measure osmotic force.
When you are finished with PART 1 of experiment # 3, be sure that you include the following with your lab report.
1) Table of Osomotic Potential and Time2) Graph of Osmotic Potential vs Time3) Graph of Osmotic Change vs Time (Osmotic Rate)4) Answers to Osmosis Questions 17
Click Here to Access TABLE OF OSMOTIC POTENTIAL AND TIME (MS WORD FILE)
TABLE OF OSMOTIC POTENTIAL AND TIME (PDF FILE)
Click Here to Access GRAPH OF OSMOTIC POTENTIAL AND TIME (MS WORD FILE)
GRAPH OF OSMOTIC POTENTIAL AND TIME (PDF FILE)
Click Here to Access GRAPH OF OSMOTIC CHANGE AND TIME (MS WORD FILE)
GRAPH OF OSMOTIC CHANGE AND TIME (PDF FILE)
Click Here to View an Animation on Osmosis OSMOSIS
Click Here to View Another Animation on Osmosis OSMOSIS 2
Click Here to View a Different Animation on Osmosis OSMOSIS 3
Click Here to View an Animated Discussion on Osmosis OSMOSIS DISCUSSION
OSMOSIS QUESTIONS1) Over the 90 minute period, what distance did the column of sugar move?2) Which term is used to describe the tonicity of the distilled water? (Hypotonic or Hypertonic)
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3) Explain why the sugar solution rises in the thistle tube over time.4) Explain why the diffusion rate of water changed over the 90 minute period of time. 5) We began the experiment by pouring a 20% sucrose solution into the thistle tube. Describe what the makeup of the sucrosesolution probably is after the 90 minute period. (more or less than 20%). 6) Describe why this change in sucrose % has changed. 7) From the knowledge you have gained, explain why it is not a good idea to drink salt water when you are thirsty.
PART 2 DIALYSIS
Dialysis is the separation of solutes according to their size by diffusion through a permeable membrane. Depending upon the molecularpore size of the membrane, solutes will either diffuse across the membrane or be restricted by their size. In our experiment the solutemolecules always move from the stronger concentration (hypertonic) to the weaker (hypotonic). Dialysis involves the movement of some,but not all, of the dissolved substances in a solution. The substance that moves has small molecules, so these can pass through the poresin the membrane, but other substances, with larger molecules, cannot escape. This process occurs normally in the kidney. Substances withsmall molecules, such as salts, glucose and urea, continuously pass out of the blood through a membrane under pressure, but usefulsubstances are later reabsorbed. Waste substances are then excreted as urine.
In this exercise you will measure diffusion of small molecules through dialysis tubing, an example of a semi permeable membrane. Themovement of a solute through a semi permeable membrane is called dialysis. The size of the minute pores in the dialysis tubing determineswhich substance can pass through the membrane. A solution of glucose and starch will be placed inside a bag of dialysis tubing. Distilledwater will be placed in a beaker, outside the dialysis bag. The dialysis bag with the starch glucose solution will be inserted into the beaker ofdistilled water. After 30 minutes have passed, the solution inside the dialysis tubing and the solution in the beaker will be tested for glucoseand starch. The presence of glucose will be tested with glucose test strips. The presence of starch will be tested with Lugol's solution (iodinepotassium iodide).
When you are finished with Part 2 of experiment # 3, be sure that you include the following with your lab report.
1) Table of Dialysis Tests2) Answers to Dialysis Questions (16)
Click Here to Access TABLE OF DIALYSIS TESTS (MS WORD FILE)
TABLE OF DIALYSIS TESTS (PDF FILE)
DIALYSIS QUESTIONS1) Considering tonicity, how would you describe the relative tonicities of the: a) dialysis bag solution b) beaker solution? 2) By analyzing the differences between the tonicities of the solutions in the bag and the beaker, where should water diffuse to? a) into the bag b) into the beaker3) Did starch diffuse from the bag? Why or why not?4) Did glucose diffuse from the bag? Why or why not?5) Did osmosis occur during this experiment? Why or why not?6) Did dialysis occur during this experiment? Why or why not?
2) Cell Structure
There is diversity in the form and function of cells that make up living organisms. Singlecells, such as Amoeba, can be freeliving organisms able to exist independently. Somecells live in a loosely organized colony of similar cells that move from place toplace. Others are fixed as part of the tissues of higher plants and animals and depend onintegrated activities with other cells.
Cells vary in size. Many bacteria are roughly 1 micrometer long, which is equal to 106 meter. The yolk of an ostrich egg, also a single cell, is the size of a small orange. Cellshave special functions, such as the transport of oxygen and carbon dioxide by red bloodcells. Other cells have different specialties. Whatever the cells form and function, the cell isrecognized as the basic unit of living matter, containing all those properties and processesthat are collectively called life.
Click Here to View a movie of an Amoeba Moving AMOEBA MOVING
Figure 2.2 Amoeba
Biologists recognize two basic types of cells. Eukaryotic cells (Greek karyon meanskernel or nucleus, eu means good or true) have a welldefined nucleus, which is separatedby a membrane from the rest of the cell in which the organelles are found. Examplesinclude protozoa and the cells of fungi, plants, and animals. Prokaryotic cells, asexemplified by bacteria and cyanobacteria, lack a nuclear membrane and cytoplasmicorganelles. The cyanobacteria (bluegreen algae) have a welldeveloped photosyntheticapparatus that is similar to the components of the chloroplasts of higher plant cells.
The differences between prokaryotic and eukaryotic cells are evident, but they do haveseveral characteristics in common. They both are surrounded by a cell (plasma)membrane that is similar in structure, though functionally different. The cell membrane ofprokaryotic cells is the site of energyyielding reactions that take place inside theeukaryotic cell mitochondria.
Figure 2.3 Sperm and Egg
Prokaryotic Cells
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Flesispiria rappiniFirst described as "Flexispira rappini", this bacterium was subsequentlydetermined to be closely related to Helicobacter spp. Note the spiralconfiguration of organism’s cell wall, and the presence of bipolar multipleflagella.
**Utilizing the electron micrographs, images provided inyour lab book and text book, sketch a representativeprokaryote cell and identify the following: Cell wall, DNAregion, Cytoplasm
Figure 2.5 Gramnegative "Flexispira rappini" bacteria,magnified 6976 X
Figure 2.6 Light microscopic image 400 X. Brucella spp., gramnegativecoccobacilli
Figure 2.7 Light microscopic image 1000 X. Brucella spp., gramnegativecoccobacilli
Figure 2.8 Diagram of Eschirichia coli
Figure 2.9 Light microscope (430X) reveals bacteria adhering to vaginalepithelial cells
Eukaryotic Cells Generalized CellEukaryotic cells differ from prokaryotic cells primarily inthe association of their DNA with proteins and theorganization of this complex into large structures calledchromosomes. A cell’s group of chromosomes issurrounded by the nuclear envelope, a membrane thatseparates these contents of the nucleus from thecytoplasm.
**Using the images of the microscopicslides in your lab book and text book,sketch a typical eukaryotic cell and identifythe following: Cell membrane, Cytoplasm,Endoplasmic reticulum, Nucleus,Nucleolus, Golgi body, Nuclearenvelope, Mitochondria, Lysosome,Ribosomes
Figure 2.10 Generalized Eukaryotic Cell
You can use the links below to study cell structure in more detail
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INTERACTIVE CELL 1INTERACTIVE CELL 2CELL ORGANELLE IDENTIFICATIONANIMAL CELL ORGANELLES
Figure 2.11 Animal Cell Model
Figure 2.12 TEM of Animal Cell
Figure 2.13 TEM of white blood cells.Note the nucleus of the cell.
Figure 2.14 Blood Cells. The image above is of a scanning electronmicroscope. One can see red blood cells, several white blood cells
including lymphocytes, a monocyte, a neutrophil, and many small discshaped platelets.
CELL STRUCTURE QUESTIONS1) Is the cell in this electron micrograph to the right prokaryotic or eukaryotic?2) What structural differences did you observe between prokaryotic and eukaryotic cells?
3) Observe the electron micrograph to the right.
a) Is the cell prokaryotic or eukaryotic?b) Identify the labeled structures. (A, B, C)
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3) Cell ReproductionA typical multicellular organism begins life as a zygote, which is formed from the union of a sperm and an egg. The egg and sperm, though unequal insize, give an equal number of chromosomes to the zygote. Each gamete contributes the haploid number (half) of the total number of chromosomes.The zygote, therefore, contains a diploid number (full) of chromosomes (a haploid set from each parent). For example, the diploid complement of thehuman zygote is 46 chromosomes. The haploid complement of the egg and sperm is 23 chromosomes. The reduction from the diploid number to thehaploid number is brought about by a type of cell division called meiosis, which occurs in the formation of the gametes. After fertilization, the zygotegives rise to all the cells that make up the organism by repeated cell divisions, called mitosis.
The Cell Cycle
The series of events that comprises the life span of an actively dividing cell is termed the cell cycle. The cell cycle involves an interphaseduring which the cell outwardly appears dormant, and an M phase (for mitosis), during which the cell is actively dividing.
For convenience, the process of mitosis is divided into four distinct stages: prophase, metaphase, anaphase, and telophase. The replicationof deoxyribonucleic acid (DNA) and the synthesis of ribonucleic acid (RNA) and proteins that are essential for mitosis occur duringinterphase. Note in the images below that the replication of DNA occurs during a period of interphase called the S (for synthesis) phase. Thedoubling of DNA during the S phase provides a full complement of DNA for the daughter cells that will result from the next mitotic division.During interphase, there are also two phases called G (for gap) phases.
The G1 phase preceding DNA replication is the period betweenthe end of one mitotic division and the beginning of the S phaseof the next division. It is during G1 that a cell may begin apathway that leads to differentiation, rather than continue the cellcycle. During the G2 phase, the structures directly involved withmitosis, such as the spindle fibers, are assembled. Thecombination of G1, S, G2, and M phases makes up the cell, ormitotic, cycle.
The mitotic process usually occupies only 10% of the total timetaken by the cell cycle. It is important to learn to distinguishamong the several parts of mitosis. The organization of DNAstrands into chromosomes and the separation of thechromosomes are termed karyokinesis. Division of the cell bodyis termed cytokinesis.
**Using images in your text book and lab bookas a resource, construct a cell cycle image thatwould include identifying the following stages ofthe cell cycle: G1 phase, S phase, G2 phase,M phase
Figure 2.14 Cell Cycle
Click Here to View an Animation on the Cell CycleCELL CYCLE
Mitosis Mitosis in animal cells can be observed in the images presented below. The images are from a prepared slide of salamander skin.
**Construct a table which summarizes the events at each stage of mitosis. Use the link below to access the SummaryTable
TABLE OF SUMMARY OF EVENTS IN MITOSIS (MS WORD FILE) TABLE OF SUMMARY OF EVENTS IN MITOSIS (PDF FILE)
**From the images below, sketch each of the stages of mitosis and label as: Interphase, Prophase, Metaphase,Anaphase, Telophase Use this link to view an animation of Mitosis MITOSIS 1
Use this link to view another animation of Mitosis MITOSIS 2 Use this link to view a different animation of Mitosis MITOSIS 3 Use this link to view a different animation of Mitosis MITOSIS 4
InterphaseInterphase cells are characterized by a distinct nucleus bounded by a nuclear membrane. The nucleolusmay or may not be identifiable. Immediately adjacent to the nuclear envelope is a cytoplasmic organellereferred to as the centrosome, which contains the centrioles. INTERPHASE ANIMATION
ProphaseKaryokinesis begins with prophase. During prophase two pairs of structures called centrioles areorganized with in the centrosome. They begin to move apart, migrating around the nucleus toward opposite
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poles of the cell. Spindle fibers radiate from each pair of centrioles like spokes on a wheel. The centrioleswill continue to migrate until they lie at opposite poles of the cell. The spindle fibers are arranged so as toattach to the condensing DNA which are now referred to as chromosomes. PROPHASE ANIMATION
MetaphaseDuring metaphase, the chromosomes migrate toward the central region of the cell. The chromosomes aremaneuvered into position by the spindle fibers that are attached to the kinetochore (middle) of eachchromosome. METAPHASE ANIMATION 1 METAPHASE ANIMATION 2
AnaphaseAnaphase begins when the pairs of chromatids are pulled apart by the spindle fibers and become daughterchromosomes. The process continues as the chromatids are pulled toward the poles of the cell. When thechromosomes reach the poles, telophase begins. ANAPHASE ANIMATION
TelophaseDuring telophase, the spindle fibers disappear, two daughter nuclei are organized and the new nuclearmembranes are formed. In late telophase, the cytoplasm becomes deeply furrowed, or pinched in betweenthe two nuclei, and cytokinesis takes place. This results in two daughter cells having equivalent nuclearcontents and equal amounts of cytoplasm. TELOPHASE ANIMATION
Figure 2.15 Stages of Mitosis
Cytokinesis
A major event in cell division is the separation of the two new individual cells.Cytokinesis takes place by furrowing. To visualize how furrowing takes place,imagine wrapping a string around a balloon and slowly tightening the string untilthe balloon has been pinched in two. In life, the animal cell is pinched in two,forming two individual cells, each with a single nucleus.
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Figure 2.16 Cytokinesis
**Based on the images in your text book and lab book and theimages you have viewed on cell mitosis, construct a sketch ofCytokinesis and identify the following: Cell furrow, Daughter cells Click Here to View an Animation on Cytokinesis CYTOKINESIS
Figure 2.17 Cytokinesis
MITOSIS QUESTIONS
1) If the chromosome number of a typical cell is 16before Mitosis, what is the chromosome number ofeach newly formed nucleus after nuclear divisionhas taken place?
2) Why must the DNA be duplicated during the Sphase of the cell cycle, prior to mitosis?
3) Observe the sketches to the right and belowlabeled AE and identify the stage of mitosis in each.
A B
C D E
4) Chromosome StructureChromosomes are condensed versions of the DNA molecule. Chromosomes consist of a pair of chromatids with very similar DNA patterns and acentral point of attachment of the chromatids, called the centromere.
**Using the images in your lab book and text book, sketchan image of the chromosome and identify the following:Chromatid, Centromere, Chromosome
Use this link to view an animation giving more information onChromosomesCHROMOSOMES
Use this link to view an animation detailing chromosome structureCHROMOSOME STRUCTURE
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Figure 2.18 Chromosome
5) Online Onion Root Tip Mitosis Growth in an organism is carefully controlled by regulating thecell cycle. In plants, the roots continue to grow as they search forwater and nutrients. These regions of growth are good forstudying the cell cycle because at any given time, you can findcells that are undergoing mitosis.
In order to examine cells in the tip of an onion root, a thin slice ofthe root is placed onto a microscope slide and stained so thechromosomes will be visible. Use the link given above to accessa virtual study on root tip mitosis. The cells you'll be looking at inthis activity were photographed with a light microscope and thendigitized so you can see them on the computer.
Although slicing the onion root captures many cells in differentphases of the cell cycle, keep in mind that the cell cycle is acontinuous process. Scientists have divided the process into 5phases, each characterized by important events, but thesedivisions are still arbitrary.
In this activity, you will be presented with cells from the tip of anonion root. You will classify each cell based on what phase it isin. At the end you will count up the cells found in each phaseand use those numbers to predict how much time a dividing cellspends in each phase.
Use this link to start this portion of the lab.
ONLINE MITOSIS LAB
Figure 2.19 Events of Mitosis
**You will need to record your results in the table referred to below.
DATA TABLE FOR MITOSIS LAB (MS WORD FILE)
DATA TABLE FOR MITOSIS LAB (PDF FILE)
Figure 2.20 Cells in thetip of an Onion Root
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