Name: diffusion and osmosis
Uploaded: 2019-01-31T09:26:17.000Z
Duration: 3 min 31 s
Channel: JoVE

K12 Standards

Tennessee Academic Standards

High School

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

BIO1.LS1.7

Diffusion and Osmosis

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<p>Diffusion and osmosis are important concepts that explain how water and other materials that cells need are transported across cell membranes. </p>
<p>Let&#39;s talk about diffusion first. It is defined as the net movement of particles from an area of high concentration to an area of lower concentration. The graduated change in concentration between the two areas is referred to as the concentration gradient. Although diffusion is net directional, the particles are constantly moving in both directions due to random motion, so even at equilibrium when the particle density is the same throughout the concentration gradient, particles continue to move in both directions at a constant exchange rate. </p>
<p>Similarly, water moves across cell membranes by diffusion in a process called osmosis, but not everything can freely pass through cell membranes, which is why they are referred to as semi-permeable. This is important, because it means that cells can regulate and maintain different concentrations of solutes inside versus outside their membranes. Depending on the relative solute concentrations of solutions separated by semi-permeable membranes we refer to them as hypotonic, isotonic or hypertonic. Hypotonic is when the solute concentration is greater inside the cell in comparison to outside. Isotonic is when the inside solute concentration equals the outside concentration. Hypertonic is when the outside solute concentration exceeds the inside solute concentration. This can affect the movement of water into and out of the cell as water moves to the area of greater solute concentration. In turn, this can affect the shapes of the cells causing cell bloating in hypotonic solutions, no shape changes in isotonic solutions and the cell shrivels in the presence of hypertonic solutions. </p>
<p>The capacity for water to move into cells is different between plant and animal cells because of the presence of the additional plant cell wall. Cell walls are rigid and only permeable to small molecules. When water moves into plant cells the membrane gets pushed up against the cell wall creating hydrostatic or turgor pressure. This pressure limits the amount and rate at which water can enter the cell. </p>
<p>Diffusion is also a major limiting factor to cell size and helps explain why unicellular organisms are generally very small. Multi-cellular organisms are made up of many small cells giving a greater total surface area to volume ratio and increasing diffusion rates. Many aspects of our physiology, like breathing and digestion rely on diffusion. For example, human lungs have many small alveoli which are like small pockets. This extra surface area makes the lung more efficient at diffusion of gases in and out of the bloodstream. </p>
<p>In this lab, you will use two cell models, agar cube and dialysis tubing to test the principles of diffusion and osmosis.</p>

diffusion and osmosis

<h4>Cell Membranes and Diffusion</h4>
<p>In order to function, cells are required to move materials in and out of their cytoplasm via their cell membranes. These membranes are semipermeable, meaning that certain molecules are allowed to pass through, but not others. This movement of molecules is mediated by the phospholipid bilayer and its embedded proteins, some of which act as transport channels for molecules that otherwise would not be able to pass through the membrane, such as ions and carbohydrates.</p>
<h4>Cell Size and the Surface-Area to Volume Ratio</h4>
<p>One reason cells are so small is the need to transport molecules into, throughout, and out of the cell. There is a geometrical constraint on cells due to the relationship between surface area and volume that limits the ability to bring in enough nutrients to support a larger cell size. The ratio between surface area and volume (SA:V) decreases as the cell increases in size due to the different scaling factors of surface area and volume. This means that as the cell grows larger, there is less membrane area able to supply nutrients to a greater cell volume.</p>
<p>Some ions are brought into the cell by diffusion, which is the net movement of particles from an area of high concentration to an area of lower concentration. This is known as moving &#8220;down&#8221; a concentration gradient. Diffusion is net directional; while the net movement of particles is down the concentration gradient, they are constantly moving in both directions due to the random motion of particles. This means that particles in solutions at equilibrium are still moving, but at a constant exchange rate so the solution remains evenly mixed. In an aqueous environment such as the cell, this process involves dissolved ions, known as solutes, moving through water, the solvent. It can take place in an open environment, such as dye spreading through a beaker, or across a cell membrane, such as ions moving through a protein channel.</p>
<h4>Osmosis and the Movement of Water</h4>
<p>Water moves across cell membranes by diffusion, in a process known as osmosis. Osmosis refers specifically to the movement of water across a semipermeable membrane, with the solvent (water, for example) moving from an area of low solute (dissolved material) concentration to an area of high solute concentration. In this case, the semipermeable membrane does not allow the solute to pass through. This can be thought of as water moving down its own concentration gradient and involves the same random process as diffusion.</p>
<p>Solutions that are separated by semipermeable membranes can be described as hypertonic, hypotonic, or isotonic depending on the relative solute concentrations in each. A solution that is hypertonic (<em>hyper-</em> meaning &#8220;above&#8221; in Greek) has a greater concentration of solutes than an adjacent solution, while a hypotonic (<em>hypo-</em> meaning &#8220;below&#8221; in Greek) solution has a lower concentration of solutes. In this situation, water will move from the hypotonic solution to the hypertonic solution until the solute concentrations are equal. Solutions that are isotonic (<em>iso-</em> meaning &#8220;equal&#8221; in Greek) have equal concentrations of solute, and therefore do not have a concentration gradient<sup> 1</sup>.</p>
<h4>Osmosis and the Plant Cell</h4>
<p>The capacity for water to move into cells is different between plant and animal cells due to the presence of a cell wall in plants. Cell walls are rigid and only permeable to very small molecules. As water moves into the cell, the membrane is pushed up against the cell wall, creating hydrostatic, or turgor, pressure. This pressure limits the rate and amount of water that can enter the cell. The likelihood of water moving into a cell is referred to as water potential, defined quantitatively as the pressure potential plus the solute potential. The pressure potential is dependent on the pressure inside the cell and the solute potential depends on the solute concentration in the cell.</p>
<p>Water potential can be observed in action in a living plant cell, such as <em>Elodea</em>, an aquatic plant. Under the microscope, a phenomenon called cytoplasmic streaming, or cyclosis, in which cytoplasm and organelles such as chloroplasts move throughout the cell, can be monitored. This process changes visibly when the cells are immersed in different solutions. Interestingly, this motion allows chloroplasts to function more efficiently in photosynthesis; they move in and out of the shadows, collecting photons when they re-enter the lighted regions of the cells<sup>3</sup>.</p>
<p>The process of osmosis is essential for the mechanism whereby plants get water from their roots to their leaves, even dozens of feet above ground level. In brief, plants transport sugars and other solutes to their roots in order to generate a gradient between the inside and outside of the root; water from the soil then moves in to the root by osmosis. From that point, a process called transpiration results in the water being pulled up tubes inside the plant called the xylem and evaporating out the leaves. Ideally, once this water column is established, it remains intact throughout the life of the plant.<sup>4</sup></p>
<p>This naturally occurring phenomenon has been used to develop valuable technologies. One example is in water purification. Recently, NASA has begun to study using the process of forward osmosis to clean and reuse wastewater aboard the International Space Station, as well as for Earth-bound applications.<sup> 2</sup> This process uses semi-permeable membranes to remove impurities from water, making it safe to drink. This technology was deployed recently to aid in relief efforts after a severe flood in Western Kenya<sup>5</sup>.</p>
<h4>References</h4>
<ol class="references">
	<li><strong>Soult, Allison.</strong> LibreTexts, Chemistry. <em>8.4 Osmosis and Diffusion. </em>[Online] October 19, 2017. <a href="https://chem.libretexts.org/LibreTexts/University_of_Kentucky/UK%3A_CHE_103_-_Chemistry_for_Allied_Health_(Soult)/Chapters/Chapter_8%3A_Properties_of_Solutions/8.4%3A_Osmosis_and_Diffusion" style="word-break:break-all;" target="__blank">https://chem.libretexts.org/LibreTexts/University_of_Kentucky/UK%3A_CHE_103_-_Chemistry_for_Allied_Health_(Soult)/Chapters/Chapter_8%3A_Properties_of_Solutions/8.4%3A_Osmosis_and_Diffusion</a>.</li>
	<li><strong>Levine, Howard.</strong> NASA Forward Osmosis Bag. <em>NASA Kennedy Space Center, Cape Canaveral, FL, United States. </em>[Online] July 11, 2018. <a target="__blank" href="https://www.nasa.gov/mission_pages/station/research/experiments/846.html">https://www.nasa.gov/mission_pages/station/research/experiments/846.html</a>.</li>
	<li>Dodonova SO, Bulychev AA (2011). 'Effect of Cytoplasmic Streaming on Photosynthetic Activity of Chloroplasts in Internodes of <em>Chara Corallina</em>'. <em>Russian Journal of Plant Physiology</em>. <strong>59</strong>: 35&#8211;41. doi:10.1134/S1021443711050050.</li>
	<li><em>Osmosis and Plant Nutrition. </em><strong>Hammer, Michael.</strong> 2000, The Rhododendron, Vol. 40.</li>
	<li><strong>Hydration Technology Innovations.</strong> Humanitarian Forward Osmosis Water Filtration. [Online] [Cited: August 21, 2018.] <a href="http://www.htiwater.com/divisions/humanitarian/lead_story.html" target="__blank">http://www.htiwater.com/divisions/humanitarian/lead_story.html</a>.</li>
</ol>

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Prepare agar cube diffusion and dialysis lab materials with phenolphthalein, NaOH, HCl, starch, NaCl, dextrose, and dialysis tubing for high school science.

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Explore how agar cell size, cell shape, and dialysis tubing affect diffusion, surface area to volume ratio, and movement of molecules across a membrane.

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<ul><li><a href="#" data-time="0.0">Preparation of Solutions for the Agar Cube Experiment
</a></li><li><a href="#" data-time="61">Preparation of Agar with Phenolphthalein
</a></li><li><a href="#" data-time="109">Preparation of Dialysis Tubing and Solutions
</a></li></ul>

<ol class="note-items"><li data-note-item="1" data-parent-collapse="">Preparation of Solutions for the Agar Cube Experiment
<button class="expand">Expand</button><ul class="lab-items"><li data-sub-note-item="1-1"><div class="lab-step">IMPORTANT: Wear gloves, goggles, and appropriate personal protective equipment &#8211; chemicals can be hazardous at high concentrations.
</div></li><li data-sub-note-item="1-2"><div class="lab-step">For the diffusion indicator solution, weigh out 1 g of phenolphthalein and add it to a beaker containing 100 mL of 95% ethanol.
</div></li><li data-sub-note-item="1-3"><div class="lab-step">To make the basic solution for the agar, measure 80 mL of water into a beaker, and then add 0.4 g of NaOH.
</div></li><li data-sub-note-item="1-4"><div class="lab-step">Stir until the solute is dissolved then bring the total volume of the solution to 100 milliliters to make a 0.1 molar solution.
</div></li><li data-sub-note-item="1-5"><div class="lab-step">To make the diffusing acid, measure out 25 mL of HCl and add it to 475 mL of water. NOTE: Plan to make around 500 mL of this HCl solution per work group.
</div></li></ul></li><li data-note-item="2" data-parent-collapse="">Preparation of Agar with Phenolphthalein
<button class="expand">Expand</button><ul class="lab-items"><li data-sub-note-item="2-1"><div class="lab-step">IMPORTANT: Agar needs time to cool, so prepare several hours in advance of the class.
</div></li><li data-sub-note-item="2-2"><div class="lab-step">To prepare the agar, first weigh out 20 g of dehydrated agar powder and then add this to 1 L of water.
</div></li><li data-sub-note-item="2-3"><div class="lab-step">Heat the solution to near boiling or until it becomes fully clear.
</div></li><li data-sub-note-item="2-4"><div class="lab-step">Then, cool the agar to 55 &#176;C and add 10 mL of the phenolphthalein ethanol solution.
</div></li><li data-sub-note-item="2-5"><div class="lab-step">Slowly add the 0.1 molar sodium hydroxide solution to the agar until it becomes vibrant pink.
</div></li><li data-sub-note-item="2-6"><div class="lab-step">Take a clean tray with deep sides and pour the agar to a depth of 3 cm.
</div></li><li data-sub-note-item="2-7"><div class="lab-step">Place the tray into the refrigerator for a few hours.
</div></li></ul></li><li data-note-item="3" data-parent-collapse="">Preparation of Dialysis Tubing and Solutions
<button class="expand">Expand</button><ul class="lab-items"><li data-sub-note-item="3-1"><div class="lab-step">To prepare the 1% starch solution, weigh out 10 g of soluble starch and add it to 500 mL of distilled water set on a magnetic stir plate.
</div></li><li data-sub-note-item="3-2"><div class="lab-step">When the solute has dissolved, bring the final volume of the solution up to 1 L with more water.
</div></li><li data-sub-note-item="3-3"><div class="lab-step">To prepare 1M NaCl, dissolve 58.4 g of NaCl in 500 mL of distilled water, in a 1 L container. Then, bring the volume up to 1 L with distilled water.
</div></li><li data-sub-note-item="3-4"><div class="lab-step">To prepare 1M dextrose, add 180.2 g of dextrose powder to 500 mL of distilled water in a 1 L beaker. Once dissolved, bring the volume up to 1 L with distilled water.
</div></li><li data-sub-note-item="3-5"><div class="lab-step">Cut the dialysis tubing into 20 cm pieces.
</div></li><li data-sub-note-item="3-6"><div class="lab-step">Place the pieces to soak in distilled water; make sure they are kept moist at all times. NOTE: Excess tubing can be stored at 4 &#176;C in 20% ethanol to prevent bacterial growth.
</div></li></ul></li></ol>

<div class="section-question"><h4 class="question-sect">What is diffusion?</h4><p>Diffusion is the net movement of particles from an area of high concentration to one of lower concentration.
</p></div><div class="section-question"><h4 class="question-sect">How is movement of molecules into and out of cells regulated?</h4><p>Movement of molecules into and out of cells is mediated by the semi-permeable cell membrane.
</p></div><div class="section-question"><h4 class="question-sect">What is osmosis?</h4><p>Water moving across cell membranes by diffusion is referred to as osmosis.
</p></div><div class="section-question"><h4 class="question-sect">How do plant cell walls affect osmosis?</h4><p>In plant cells, the additional cell wall means the amount of water that can enter a cell is limited by turgor pressure.
</p></div><div class="section-question"><h4 class="question-sect">How does diffusion affect cell size and physiology?</h4><p>Increased diffusion rates at larger cell sizes means unicellular organisms are typically very small. In multicellular organisms, physiology may be adapted for greater surface area in organs where diffusion is necessary.
</p></div>

Preparation of Solutions for the Agar Cube Experiment
ExpandIMPORTANT: Wear gloves, goggles, and appropriate personal protective equipment &#8211; ...

<p>To begin we will prepare the necessary solutions for the lab. For the diffusion indicator solution weigh out one gram of phenolphthalein and add it to a beaker containing 100 milliliters of 95%ethanol. To make the basic solution for the agar measure 80 milliliters of water into a beaker, then weigh out 0.4 grams of sodium hydroxide and add the sodium hydroxide to the water.</p><p>Stir until the solute is dissolved then bring the total volume of the solution to 100 milliliters to make a 0.1 molar solution. Now to make the diffusing acid measure out 25 milliliters of hydrochloric acid and add it to 475 milliliters of water. You solutions are now ready for use.</p><p>To prepare the agar, first weigh out 20 grams of dehydrated agar powder and then add this to one liter of water. Heat the solution to near boiling or until is becomes fully clear. Next cool the agar to 55 degrees Celsius and add 10 milliliters of the phenolphthalein ethnol solution to the cooled agar solution.</p><p>Slowly add the 0.1 molar sodium hydroxide solution to the agar until it becomes vibrant pink. Then take a clean tray with deep sides and pour the agar to a depth of three centimeters. Place the tray into the refrigerator for a few hours.</p><p>Once the agar is set it is ready for the class. To prepare the 1%starch solution weigh out 10 grams of soluble starch and add it to 500 milliliters of distilled water set on a magnetic stir plate. When the solute has dissolved bring the final volume of the solution up to one liter with more water.</p><p>To prepare one molar sodium chloride and one molar dextrose, dissolve 58.4 grams of sodium chloride and 180.2 grams of dextrose powder in separate one liter containers of distilled water as just demonstrated for the starch. After obtaining the dialysis tubing remove the tubing from the shipping container and cut the tubing into 20 centimeter pieces. Then soak the pieces in distilled water and store the excess tubing at four degrees Celsius in 20%ethanol to prevent bacterial growth.</p><p>Please take time to review the material list and the student protocol video to be fully prepped for the lab.</p>

<ul><li><a href="#" data-time="0.0">Diffusion in Agar
</a></li><li><a href="#" data-time="263">Movement of Molecules Across a Semi-Permeable Membrane
</a></li><li><a href="#" data-time="441">Results
</a></li></ul>

<ol class="note-items"><li data-note-item="1" data-parent-collapse="">Diffusion in Agar
<button class="expand">Expand</button><ul class="lab-items"><li data-sub-note-item="1-1"><div class="lab-step">NOTE: In this exercise, you will be given agar containing an indicator chemical called phenolphthalein. When phenolphthalein is exposed to the normal alkaline conditions in the agar, it will look pink. But when it is exposed to neutral or acidic conditions, it changes from pink to clear. You will make different size and shaped agar cubes as a model for cells to study the impact of cell size and shape on diffusion rate.
</div></li><li data-sub-note-item="1-2"><div class="lab-step">To make the first set of cells, measure out and cut a small cube of agar where each side measures one centimeter. 
</div></li><li data-sub-note-item="1-3"><div class="lab-step">Next, measure and cut out a medium cell cube with sides of 2 cm and a large cell of 3 cm on each side.
</div></li><li data-sub-note-item="1-4"><div class="lab-step">Knowing the length of the sides of your cube cells, calculate their surface area using this equation, where lower case a represents the length of the sides: Surface Area = 6a^2
</div></li><li data-sub-note-item="1-5"><div class="lab-step">Record these values in the appropriate column in Table 1. <a href="https://www.jove.com/CDNSource/lm/labs/6/Table_1_Diffusion_and_Osmosis.xlsx" style="display:block;margin:20px;" target="__blank">Click Here to download Table 1</a>
</div></li><li data-sub-note-item="1-6"><div class="lab-step">Then, use the same length value and the equation below to calculate the volume of each cube and add these to the table: Volume = a^3 HYPOTHESES: The experimental hypothesis might be that the acid will diffuse completely to the center of the small cell faster than the medium and large cells. The null hypothesis could be that the acid will diffuse to the center of the small and two larger cubes at around the same time.
</div></li><li data-sub-note-item="1-7"><div class="lab-step">Add 100 mL of 0.1 M HCl to each of the three 400 mL beakers to make the diffusion baths.
</div></li><li data-sub-note-item="1-8"><div class="lab-step">Working in a team, have one experimenter ready with the timer and the second and third experimenters ready to drop each cube into one of the beakers.
</div></li><li data-sub-note-item="1-9"><div class="lab-step">When the first experimenter says go, simultaneously drop all three cubes into their respective beakers and start the timer.
</div></li><li data-sub-note-item="1-10"><div class="lab-step">Observe carefully until one of the cubes becomes completely clear or 10 min have passed.
</div></li><li data-sub-note-item="1-11"><div class="lab-step">Stop the timer, remove the agar cubes from the beakers and place the cubes into a Petri dish.
</div></li><li data-sub-note-item="1-12"><div class="lab-step">Make a note of which of the three cells became clear or had the smallest remaining pink area. Then, also note which cell had the most remaining pink agar.
</div></li><li data-sub-note-item="1-13"><div class="lab-step">Next, in Table 1, calculate the surface area to volume ratio for each cell. Surface Area: Volume Ratio = (surface area)/volume
</div></li><li data-sub-note-item="1-14"><div class="lab-step">As the cell size increases, note whether the surface area to volume ratio increases or decreases. Also consider whether this correlates with your observation of the depth of diffusion into the agar cells. If cells rely on diffusion to deliver essential nutrients and molecules to the whole cell, discuss with your group if it would be better to have a smaller or larger surface area to volume.
</div></li><li data-sub-note-item="1-15"><div class="lab-step">Now, with the remaining agar, cut three rectangular shaped blocks of different sizes and record their length, width, and height. This will test what happens when the shapes of cells are different. 
</div></li><li data-sub-note-item="1-16"><div class="lab-step">Calculate the surface area of your rectangular cells using the formula below, where length is l, width is w, and height is h. Surface Area = 2lw + 2lh + 2wh
</div></li><li data-sub-note-item="1-17"><div class="lab-step">Then, calculate the volume of your rectangles using this formula: Volume = l * w * h
</div></li><li data-sub-note-item="1-18"><div class="lab-step">Repeat the experiment by dropping the new shapes into the hydrochloric acid solution for 10 min or until one cube becomes completely clear.
</div></li><li data-sub-note-item="1-19"><div class="lab-step">Remove the cell shapes from the solutions and observe the depth that the hydrochloric acid diffused into each of these cells, and which shapes have the smallest and largest remaining pink areas not reached by the solute.
</div></li><li data-sub-note-item="1-20"><div class="lab-step">Using the surface area and volume data you recorded for your rectangular shapes, calculate the surface area to volume ratio of these cells. Surface Area: Volume Ratio = (surface area)/volume
</div></li><li data-sub-note-item="1-21"><div class="lab-step">Consider whether these values correlate to which cells had the most and least complete diffusion. Additionally, discuss with the group whether these rectangular cells displayed a similar or different pattern of diffusion to that observed with the cube shaped cells, and what this might mean.
</div></li></ul></li><li data-note-item="2" data-parent-collapse="">Movement of Molecules Across a Semi-Permeable Membrane
<button class="expand">Expand</button><ul class="lab-items"><li data-sub-note-item="2-1"><div class="lab-step">Before beginning the experiment, add 250 mL of distilled water to each of four 1 L beakers.
</div></li><li data-sub-note-item="2-2"><div class="lab-step">Then, label the beakers from 1-4, and add 0.5 mL of iodine to the first beaker. HYPOTHESES: In this experiment, the experimental hypothesis is that some of the solutes will be able to pass through the dialysis tubing membrane and others will not. The null hypothesis is that there will be no difference in the ability to diffuse through the dialysis tubing membrane between the solutes.
</div></li><li data-sub-note-item="2-3"><div class="lab-step">To prepare the dialysis tubing, remove the pieces one at a time from the distilled water bath and tie a tight knot at one end of each tube. These tubes, when filled, will act as model cells with the dialysis tubing acting like the semipermeable membrane.
</div></li><li data-sub-note-item="2-4"><div class="lab-step">Add 10 mL of starch solution to the first tube and tie off the open end, making sure to leave space in case the tubing expands during the experiment.
</div></li><li data-sub-note-item="2-5"><div class="lab-step">Then add 10 mL of the NaCl and dextrose solutions to the second and third pieces of tubing, respectively, and tie off both tubes, again, leaving space in case of expansion.
</div></li><li data-sub-note-item="2-6"><div class="lab-step">After adding 10 mL of distilled water and tying off the fourth tube, weigh each of your model cells.
</div></li><li data-sub-note-item="2-7"><div class="lab-step">Record the initial weight values in grams and the colors of the starting solution in each tube in the appropriate columns of Table 2. <a href="https://www.jove.com/CDNSource/lm/labs/6/Table_2_Diffusion_and_Osmosis.xlsx" target="__blank" style="display:block;margin:20px;">Click Here to download Table 2</a>
</div></li><li data-sub-note-item="2-8"><div class="lab-step">After quickly rinsing the outside with tap water, place each piece of tubing in its corresponding beaker for 1 h at room temperature. NOTE: For example, the starch solution tube should be placed into the beaker containing the iodine.
</div></li><li data-sub-note-item="2-9"><div class="lab-step">At the end of the diffusion period, weigh the tubes again.
</div></li><li data-sub-note-item="2-10"><div class="lab-step">Then, observe the tubes carefully, noting any color changes. 
</div></li><li data-sub-note-item="2-11"><div class="lab-step">Record all of these data in Table 2. 
</div></li><li data-sub-note-item="2-12"><div class="lab-step">Next, to perform a Benedict&#39;s Reagent test for simple sugars, make a water bath by adding 250 mL of water to a 600 mL beaker and placing it onto a hot plate.
</div></li><li data-sub-note-item="2-13"><div class="lab-step">Set the plate to high, to boil the water. 
</div></li><li data-sub-note-item="2-14"><div class="lab-step">Label two new glass test tubes as H<sub>2</sub>O and dextrose, respectively.
</div></li><li data-sub-note-item="2-15"><div class="lab-step">Use a graduated cylinder to transfer 1 mL of solution from the water and dextrose beakers into the corresponding test tubes.
</div></li><li data-sub-note-item="2-16"><div class="lab-step">Then, add 2 mL of Benedict&#39;s Reagent to each tube. 
</div></li><li data-sub-note-item="2-17"><div class="lab-step">Once the water is boiling, place each test tube into the water bath for 3-5 minutes.
</div></li><li data-sub-note-item="2-18"><div class="lab-step">After this time, note the color of the solution in each tube. 
</div></li><li data-sub-note-item="2-19"><div class="lab-step">Then use this key to assess whether the test is positive or negative and record these data in the appropriate column in Table 2. <a href="https://www.jove.com/CDNSource/lm/labs/6/Lab_6_Diffusion_Figure_1.png" style="display:block;margin:20px;" target="__blank">Click Here to download Figure 1</a>
</div></li></ul></li><li data-note-item="3" data-parent-collapse="">Results
<button class="expand">Expand</button><ul class="lab-items"><li data-sub-note-item="3-1"><div class="lab-step">First, look at the mass of your four dialysis tube cells at the beginning versus the end of the experiment. Calculate the change in mass for each of the four cells and plot it onto a bar chart.
</div></li><li data-sub-note-item="3-2"><div class="lab-step">Note which cells demonstrated the most change, and whether any of the cells appeared visibly different in size.
</div></li><li data-sub-note-item="3-3"><div class="lab-step">For the experiment with the starch and iodine indicator, note whether there was a color change in the fluid in the artificial cell. Also consider whether there was a color change in the water in the beaker, and what both of these observations say about the properties of the dialysis tubing membrane.
</div></li><li data-sub-note-item="3-4"><div class="lab-step">Finally, in the Benedict&#39;s Reagent test for dextrose, note whether this simple sugar was able to pass through the semipermeable membrane of the &#8220;cell&#8221; into the water in the beaker. Discuss with the class which of the molecules you think could and could not pass through the semipermeable membrane.
</div></li></ul></li></ol>

Diffusion in Agar
ExpandNOTE: In this exercise, you will be given agar containing an indicator chemical called phenolphthalein. When phenolphthalein is ...

<p>In this exercise, you will be given agar containing an indicator chemical called phenolphthalein. When phenolphthalein is exposed to the normal alkaline conditions in the agar, it will look pink. But when it is exposed to neutral or acidic conditions, it changes from pink to clear.</p><p>You will make different size and shaped agar cubes as a model for cells to study the impact of cell size and shape on diffusion rate. To make the first set of cells, measure out and cut a small cube of agar where each side measures one centimeter. Next, measure and cut out a medium cell cube with sides of two centimeters and a large cell of three centimeters on each side.</p><p>Knowing the length of the sides of your cube cells, you should now calculate their surface area using this equation. Where lower case a represents the length of the sides. Record these values in the appropriate column in your table.</p><p>Then use the same length value and this equation to calculate the volume of each cube and add these to the table. The experimental hypothesis might be that the acid will diffuse completely to the center of the small cell faster than the medium and large cells. The null hypothesis could be that the acid will diffuse to the center of the small and two larger cubes at around the same time.</p><p>Add 100 milliliters of 0.1 molar hydrochloric acid to each of the three 400 milliliter beakers to make the diffusion baths. Working in a team, have one experimenter ready with the timer and the second and third experimenters ready to drop each cube into one of the beakers. When the first experimenter says go, simultaneously drop all three cubes into their respective beakers and start the timer.</p><p>Observe carefully until one of the cubes becomes completely clear or 10 minutes have passed. Then stop the timer, remove the agar cubes from the beakers and place the cubes into a Petri dish. Make a note of which of the three cell became clear or had the smallest remaining pink area.</p><p>Then also note which cell had the most remaining pink agar. Next, in your table, calculate the surface area to volume ratio for each cell. As the cell size increases, does the surface area to volume ratio increase or decrease?</p><p>How did this correlate with your observation of the depth of diffusion into your agar cells? If cells rely on diffusion to deliver essential nutrients and molecules to the whole cell, would it be better to have a smaller or larger surface area to volume? Now, with the remaining agar, cut three rectangular shaped blocks of different sizes and record their length, width, and height.</p><p>This will test what happens when the shapes of cells are different. Calculate the surface area of your rectangular cells using this formula where length is l, width is w, and height is h. Then, calculate the volume of your rectangles using this formula.</p><p>Repeat the experiment by dropping the new shapes into the hydrochloric acid solution for 10 minutes or until one cube becomes completely clear. Then remove the cells shapes from the solutions and observe the depth that the hydrochloric acid diffused into each of these cells. And which shapes have the smallest and largest remaining pink areas not reached by the solute.</p><p>Using the surface area and volume data you recorded for your rectangular shapes, calculate the surface area to volume ratio of these cells. How do these values correlate to which cells have the most and least complete diffusion? Did you see a similar or different pattern to the one observed with the cube shaped cells?</p><p>Before beginning the experiment, add 250 milliliters of distilled water to each of four one liter beakers. Then label the beakers from one to four and then add 0.5 milliliters of iodine to the first beaker. In this experiment, the experimental hypothesis is that some of the solutes will be able to pass through the dialysis tubing membrane and others will not.</p><p>The null hypothesis is that there will be no difference in the ability to diffuse through the dialysis tubing membrane between the solutes. To prepare the dialysis tubing, remove the pieces one at a time from the distilled water bath and tie a tight knot at one end of each tube. These tubes, when filled, will act as model cells with the dialysis tubing acting like the semipermeable membrane.</p><p>Add 10 milliliters of starch solution to the first tube and tie off the open end, making sure to leave space in case the tubing expands during the experiment. Then add 10 milliliters of the sodium chloride and dextrose solutions to the second and third pieces of tubing, respectively, and tie off both tubes. Again, leaving space in case of expansion.</p><p>After adding 10 milliliters of distilled water and tying off the fourth tube, weigh each of your model cells. Record the initial weight values in grams and the colors of the starting solution in each tube in the appropriate columns of the table. After quickly rinsing the outside with tap water, place each piece of tubing in its corresponding beaker for one hour at room temperature.</p><p>At the end of the diffusion period, weigh the tubes again. Then, observe the tubes carefully, noting any color changes. Record all of these data in the table.</p><p>Next, to perform a Benedict's Reagent test for simple sugars, make a water bath by adding 250 milliliters of water to a 600 milliliter beaker and placing it onto a hot plate. Then set the plate to high. Label two new glass test tubes as H2O and dextrose, respectively.</p><p>And then use a graduated cylinder to transfer one milliliter of solution from the water and dextrose beakers into the corresponding test tubes. Then, add two milliliters of Benedict's Reagent to each tube. When the water boils, place each test tube into the water bath for three to five minutes.</p><p>After this time, note the color of the solution in each tube. Then use this key to assess whether the test is positive or negative, and record these data in the appropriate column in the table. First, look at the mass of your four dialysis tube cells at the beginning versus the end of the experiment.</p><p>Calculate the change in mass for each of the four cells and plot it onto a bar chart. Which cells did you observe demonstrated the most change? Did the cells also appear visibly different in size?</p><p>For the experiment with the starch and iodine indicator, did you notice a color change in the fluid in the artificial cell? How about the water in the beaker? Finally, in the Benedict's Reagent test for dextrose, does it appear that this simple sugar was able to pass through the semipermeable membrane of the cell into the water in the beaker?</p><p>Discuss with the class which of the molecules you think could and could not pass through the semipermeable membrane.</p>

Characteristics of Life

Biology is a natural science that studies life and living organisms, including their structure, function, development, interactions, evolution, ...

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Levels of Organization

Biological organization is the classification of biological structures, ranging from atoms at the bottom of the hierarchy to the Earth&#x27;s biosphere. ...

the-tree-of-life-bacteria-archaea-and-eukaryotes

The Tree of Life - Bacteria, Archaea, and Eukaryotes

Prokaryotic Cells

Prokaryotes are small unicellular organisms that include the domains &#8212; Archaea and Bacteria. Bacteria include many common microorganisms, such as ...

Introduction to Virus

Viruses are unique biological entities that blur the boundary between living and non-living systems. Although they lack cellular structure and metabolic ...

Size and Structure of Viral Genomes

Viral genomes exhibit remarkable diversity in size, structure, and composition, influencing their replication strategies and interactions with host cells. ...

Compare and contrast existing models, identify patterns, and use structural and functional evidence to analyze the characteristics of life. Engage in argument about the designation of viruses as non-living based on these characteristics.
EXPLANATION: Students begin to develop patterns of living and non-living organisms in kindergarten and build on detailed characteristics of different classifications of living organisms throughout elementary and middle school. Biology 1 discussions introduce viral particles and viral cycles, building on student understanding of living organisms to engage in an argument regarding the classification of a viral particle as either living or non-living.

BIO1.LS1.1

What are Cells?

Cells are the smallest and basic units of life, whether it is a single cell that forms the entire organism, e.g., in a bacterium, or trillions of them, ...

Eukaryotic Compartmentalization

One of the distinguishing features of eukaryotic cells is that they contain membrane-bound organelles, such as the nucleus and mitochondria, that carry ...

Eukaryotic Evolution

The endosymbiont theory is the most widely accepted theory of eukaryotic evolution; however, its progression is still somewhat debated. According to the ...

Animal and Plant Cell Structure

Animal and plant cells not only differ in their structure, function, and mode of nutrition but also in how they reproduce, specialize, and organize into ...

Evaluate comparative models of various cell types with a focus on organic molecules that make up cellular structures.
EXPLANATION: Students explicitly discuss the structure and function of major cellular organelles in seventh grade. Building on this understanding, Biology I students should shift their focus to the different types of cells found in organisms and how the role of each cell type relates to its composition and the prevalence of different organelles within that cell. An example might include the absence (or enucleation) of the nucleus in red blood cells in mammals providing for increased levels of oxygen transport in organisms or the lack of centrioles in most neurons. Varying cell types can include both prokaryotic and eukaryotic cell types.

BIO1.LS1.2

Nucleic Acids

Nucleic acids are the most important macromolecules for the continuity of life. They carry the cell&#39;s genetic blueprint and carry instructions for its ...

The DNA Helix

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most viruses. DNA ...

DNA Base Pairing

Erwin Chargaff&#8217;s rules on DNA equivalence paved the way for the discovery of base pairing in DNA. Chargaff&#8217;s rules state that in a ...

The Central Dogma

The central dogma explains the flow of genetic information from DNA nucleotides to the amino acid sequence of proteins.
RNA is the Missing Link Between ...

DNA Packaging

Overview

Eukaryotes have large genomes compared to prokaryotes. In order to fit their genomes into a cell, eukaryotes must pack their DNA tightly inside ...

Organization of Genes

Overview

The genomes of eukaryotes can be structured in several functional categories. A strand of DNA is comprised of genes and intergenic regions. ...

Karyotyping

Describing the number and physical features of chromosomes can reveal abnormalities that underlie genetic diseases. This description is facilitated by ...

Replication in Prokaryotes

Overview

DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to ...

Replication in Eukaryotes

Overview

In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high ...

Mutations

Overview

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. ...

Transcription

Overview
Transcription is the process of synthesizing RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene ...

Translation

Lesson: Translation
Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following ...

RNA Structure

Overview
The basic structure of RNA consists of a five-carbon sugar and one of four nitrogenous bases. Although most RNA is single-stranded, it can form ...

RNA Stability

Intact DNA strands can be found in fossils, while scientists sometimes struggle to keep RNA intact under laboratory conditions. The structural variations ...

pre-mRNA Processing

In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or ...

Types of RNA

Overview
Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs ...

MicroRNAs

siRNA - Small Interfering RNAs

Small interfering RNAs, or siRNAs, are short regulatory RNA molecules that can silence genes post-transcriptionally, as well as the transcriptional ...

piRNA - Piwi-interacting RNAs

PIWI-interacting RNAs, or piRNAs, are the most abundant short non-coding RNAs. More than 20,000 genes have been found in humans that code for piRNAs while ...

CRISPR and crRNAs

Bacteria and archaea are susceptible to viral infections just like eukaryotes; therefore, they have developed a unique adaptive immune system to protect ...

lncRNA - Long Non-coding RNAs

In humans, more than 80% of the genome gets transcribed. However, only around 2% of the genome codes for proteins. The remaining part produces non-coding ...

What are Proteins?

Protein Organization

Protein Folding

Protein Families

Protein families are groups of homologous proteins; that is, they have similarities in amino acid sequences and three-dimensional structures. Protein ...

conservation-of-protein-domains-over-different-proteins

Conservation of Protein Domains Over Different Proteins

Protein domains are small structurally independent units that are part of a single amino acid chain.&#160; Although these domains are often structurally ...

Globular and Fibrous Proteins

Many proteins can be classified into two distinct subtypes - globular or fibrous. These two types differ in their shapes and solubilities.
Globular ...

Intrinsically Disordered Proteins

Intrinsically disordered proteins are a group of proteins that do not fold into specific three-dimensional structures. Their structural flexibility allows ...

Protein Complex Assembly

Proteins can form homomeric complexes with another unit of the same protein or heteromeric complexes with different types.&#160; Most protein complexes ...

Conjugated Proteins

Simple proteins and protein complexes contain only amino acids. In contrast, many other proteins, called conjugated proteins, covalently bond with ...

Allosteric Proteins-ATCase

Binding sites linkages can regulate a protein&#39;s function.&#160; For example, enzyme activity is often regulated through a feedback mechanism where the ...

Amyloid Fibrils

Amyloid fibrils are aggregates of misfolded proteins.&#160; Under most circumstances, misfolded proteins are either refolded by chaperone proteins or ...

Cooperative Allosteric Transitions

Cooperative allosteric transitions can occur in multimeric proteins, where each subunit of the protein has its own ligand-binding site. When a ligand ...

Antibody Structure

Phosphorylation

Ligand Binding Sites

Proteins are dynamic macromolecules that carry out a wide variety of essential processes; however, the activities of most proteins depend on their ...

Protein Kinases and Phosphatases

Proteins undergo chemical modifications that trigger changes in the charge, structure, and conformation of the proteins. Phosphorylation, acetylation, ...

Protein-protein Interfaces

Many proteins form complexes to carry out their functions, making protein-protein interactions (PPIs) essential for an organism&#39;s survival. Most PPIs ...

GTPases and their Regulation

Guanine nucleotide-binding proteins (G-proteins), also known as GTPases, are a superfamily of proteins that regulate many cellular processes, such as cell ...

Conserved Binding Sites

Many proteins&#8217; biological role depends on their interactions with their ligands, small molecules that bind to specific locations on the protein ...

Covalently Linked Protein Regulators

Proteins can undergo many types of post-translational modifications, often in response to changes in their environment. These modifications play an ...

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The Equilibrium Binding Constant and Binding Strength

The equilibrium binding constant (Kb) quantifies the strength of a protein-ligand interaction. Kb can be calculated as follows when the reaction is at ...

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Protein Complexes with Interchangeable Parts

Groups of proteins may form a complex where each protein in this complex has a different role in the overall execution of the complex&#8217;s function. ...

Cofactors and Coenzymes

Mechanical Protein Functions

Proteins perform many mechanical functions in a cell. These proteins can be classified into two general categories- proteins that generate mechanical ...

Allosteric Regulation

Structural Protein Function

Structural proteins are a category of proteins responsible for functions ranging from cell shape and movement to providing support to major structures ...

Ligand Binding and Linkage

Allosteric proteins have more than one ligand binding site; the binding of a ligand to any of these sites influences the binding of ligands to the other ...

Protein Networks

An organism can have thousands of different proteins, and these proteins must cooperate to ensure the health of an organism. Proteins bind to other ...

Integrate evidence to develop a structural model of a DNA molecule. Using the model, develop and communicate an explanation for how DNA serves as a template for self-replication and encodes biological information.
EXPLANATION: Discussions of DNA in earlier grades have been limited to discussions of genes and the role of genes in the appearance and activities of an organism. Biology 1 represents a student's introduction to a molecular model of a DNA as well as the organization of DNA into genes and genes subsequently into chromosomes. Students should address interactions between genes in proteins which regulate both the shape and reproduction of DNA molecules. It is important to note that not all segments of DNA are transcribed for proteins. Portions of DNA are involved in regulating the expression of genes or affect the structure of the chromosomes (replication origin, centromeres, and telomeres).

BIO1.LS1.3

What is the Cell Cycle?

The cell cycle refers to the sequence of events occurring throughout a typical cell&#8217;s life. In eukaryotic cells, the somatic cell cycle has two ...

Interphase

The cell cycle occurs over approximately 24 hours (in a typical human cell) and in two distinct stages: interphase, which includes three phases of the ...

The Cell Cycle Control System

Positive Regulator Molecules

Inhibition of CDK Activity

S-Cdk Initiates DNA Replication

M-Cdk Drives Transition Into Mitosis

Mitogens and the Cell Cycle

Replicative Cell Senescence

Abnormal Proliferation

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Cells Coordinate Growth and Proliferation

Mitosis and Cytokinesis

In eukaryotes, the cell division cycle is divided into distinct, coordinated cellular processes that include cell growth, DNA replication/chromosome ...

Chromosome Duplication

Cohesins

Condensins

The Mitotic Spindle

Centrosome Duplication

Spindle Assembly

Attachment of Sister Chromatids

Forces Acting on Chromosomes

Separation of Sister Chromatids

The Spindle Assembly Checkpoint

Anaphase A and B

Anaphase Promoting Complex

The Contractile Ring

Determining the Plane of Cell Division

The Phragmoplast

Distribution of Cytoplasmic Content

Create a model for the major events of the eukaryotic cell cycle, including mitosis. Compare and contrast the rates of cell division in various eukaryotic cell types in multicellular organisms.
EXPLANATION: Students first discuss mitosis in seventh grade, specifically focusing on the role of mitosis in creating genetically identical daughter cells. Biology 1 discussions should connect a student's understanding of gene expression and protein function with the process of mitosis to explore the differentiation of cell types from otherwise identical daughter cells. Discussions should also include varying rates of mitotic division and the relationship between these rates of division and the function of specific cell types within eukaryotic organisms. Examples may include the extremely limited use of mitosis by neurons due to their interconnectedness within neural networks or the rapid rates of mitosis with growing root tips.

BIO1.LS1.6

What are Membranes?

A key characteristic of life is the ability to separate the external environment from the internal space. To do this, cells have evolved semi-permeable ...

Utilize a model of a cell plasma membrane to compare the various types of cellular transport and test predictions about the movement of molecules into or out of a cell based on the homeostasis of energy and matter in cells.
EXPLANATION: Students are first introduced to the structure of the plasma membrane and an initial discussion of passive transport to maintain homeostasis in the seventh grade. Biology I discussion of passive transport is still relevant, but discussions of transport should extend to include additional types of cellular transport and how they are accomplished by proteins embedded in the plasma membranes.

Diffusion and Osmosis

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Cell Membranes and Diffusion

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