Sherry Chan EDS 533 Science Curriculum and Instruction Capillary Action Experiment 7 th grade Life Science November 11, 2011 Time: 50 minutes Georgia Standards: S7L2a Explain that cells take in nutrients in order to grow and divide and to make needed materials Objectives: Students will explain the concept of capillary action through conducting an experiment Students will apply capillary action to solving a real-life problem in gardening Essential Questions: How can the principle of capillary action be used to solve a real-life problem? How does capillary action help water move upward inside a plant? Materials: Lab worksheets 4 coffee filters One paper towel cut to the same length as the coffee filter (14 cm) One piece of string cut to the same length as the coffee filter (14 cm) Water source (a plastic container holding approx. 100mL of water with food coloring) 1 graduated cylinder (25 ml) 1 small plastic solo cup (large enough to hold 25 ml of water) 1 plastic pipette 1 pencil Timer Procedure (the Five E s Model): Logistics (3 min) Warn the students about handling the materials Students gather the materials needed for the experiment. They will work in partners and each table needs all the materials as listed above (Differentiation) pair low student with a medium student. Emphasize equal share of work during the experiment. Engage The Situation (7 min) Give students a scenario: You family is leaving for a two week vacation to visit Ms. Chan in Taiwan. You have several houseplants that need watering while you are away. What can you do to make sure that your houseplants will be sufficiently watered each day without asking a neighbor for help? Brainstorm some ideas on the whiteboard with the students Transition: Put the scenario in the back of your mind. Now we want to switch gears to talk about a related topic, which will hopefully help you come up with a great self-watering system for your houseplants. We are going to explore the concept of the capillary action. Who can guess what it means (Define capillary action)? Capillary action is one of the forces that help water defy gravity in a plant, and we will investigate how it works in the following experiment!! "!
Give background information: define a wick, introduce the materials, demonstrate how to fold the coffee filter and paper towel (differentiation for people who have trouble understanding this part of the experiment procedure) Students form hypothesis and write on the worksheet: When placing a wick (made of coffee filter, paper towel, or string) in water, which way would the water go? What materials of wick would absorb the water the fastest, coffee filter, paper towel, or string? Explore Capillary Action experiment (25 min) Students follow the lab procedure in the worksheet: 1. Using a pencil, poke a hole through the center of three of the coffee filters. 2. MAKING A COFFEE FILTER WICK: fold the fourth coffee filter in half lengthwise 3 times, then twist the filter to make a wick. Place one end of the wick through the hole on the first coffee filter and set aside. 3. MAKING A PAPER TOWEL WICK: fold the paper towel in half lengthwise 3 times, then twist the paper towel to make a wick. Place one end of the paper towel wick through the hole on the second coffee filter and set aside 4. MAKING A STRING WICK: put the string through the third coffee filter and set aside 5. Measure 25mL of dyed water from the water source into the graduated cylinder using the plastic pipette to get an accurate measure. Reminder: To get accurate measure, look at the bottom of the meniscus (see picture) 6. Pour the measured H 2 O into the plastic solo cup 7. Have the timer ready 8. Set the coffee filter with the coffee filter wick in the water, making sure the tip of the wick is submerged and just barely touching the bottom of the cup. The other filter is resting on the rim of the cup it SHOULD NOT be inside the cup! 9. Watch the clock OR set the timer for 5 minutes. 10. During this time, observe how the water is moving 11. After 5 minutes, remove the coffee filter and wick immediately and use the graduated cylinder to measure the amount of liquid left in the cup. 12. RECORD the amount of water ABSORBED by the wick 13. Dispose the wet coffee filter and wick. Pour out the water into the sink. 14. Repeat steps 5 13 using the paper towel wick in the coffee filter. 15. Repeat steps 5 13 using the string wick in the coffee filter. 16. Clean up the table and put away the equipment 17. Compile class data by putting the group s 3 sets of data on the board 18. Copy the class data and find the average amount of water absorbed for each type of wick 19. Write the conclusion Explain (5 min)! #!
Ask the students: What happened in your experiment? Why did the water move up the wick? How can you explain that using what we have learned about capillary action? Go over the definition of capillary action o Capillary action the movement of liquid through a narrow space as the result of cohesion and adhesion. The cohesion is the attractive force between similar molecules (liquid in this case) while adhesion is the attractive force between dissimilar molecules (liquid and solid). Relate capillary action with the results in the experiment Relate capillary action with water transport in plants o A misconception about capillary action is that it is what causes water to move upwards in a plant (Sookbirsingh) (Cohesion-Tension Theory is the more commonly accepted explanation) o Capillary action plays a role, but other forces are also involved: transpiration, water potential energy, and root pressure o Transpirational pull is the primary mechanism in water movement up the xylem Why does this experiment not demonstrate diffusion? (Address misconception) o Diffusion is the movement of particles down a concentration gradient by random motion. The particles have kinetic energy and may collide with the wall, each other, or go through a pore (Liang). The water does go down the concentration gradient on the wick in the experiment. However, the movement involves the water molecules latching onto the fiber molecules of the wick due to adhesion instead of simply going through the pores in the wick material by random collision. Diffusion is the net movement of particles as a result of a concentration gradient (Odom), and therefore, the molecules of the porous barrier in diffusion should not contribute to the direction of the particle movement. The concentration gradient should be the main contributor. (However, from my research, I feel that many cases that we consider to be proper examples of diffusion are not pure diffusion examples. For instance, we say that water moves upward in a plant by osmosis, which is the diffusion of water through a semi-permeable membrane. According to Koning, however, movement of water by diffusion alone would be too slow. It is mainly bulk flow, which is facilitated by aquaporins. So osmosis is actually both diffusion and bulk flow. Koning also argues that the cell membrane is not semipermeable but differentially permeable, but that is another story) Why does this experiment not demonstrate osmosis? (Address misconception) o Osmosis is the net movement of solvent molecules from across a semipermeable membrane from a hypotonic solution (less solutes) to a hypertonic solution (more solutes) (Odom). The result is the equalizing of solutes in both compartments. In the experiment, there is a net movement of water down its concentration gradient. If water is considered to be the solvent in this case, we cannot say the wick is like the solutes because the wick is not dissolved in the water the wick is not broken down into its individual molecules. The wick also cannot be the semipermeable membrane because it does not separate two solutions of different concentration. Expand (10 min) Revisit the initial scenario: How can you use the principle of capillary action to make a self-watering device for your houseplants? (Differentiation) if students are having trouble making connections between the experiment and the watering-device, the teacher can draw pictures on the board to help cue them Which wick material would help make a more efficient self-watering device? (Closure) Watch youtube video clips on water-wicking devices (just portions of each): o http://www.youtube.com/watch?v=y_1m1njwlxa&feature=related o http://www.youtube.com/watch?v=ndeqcxcibbc! $!
Assessment Strategies: Access students prior knowledge with the brainstorming activity Facilitate the class during the experiment Solicit answers for the explain and expand questions to gauge students understanding of capillary action Grade the worksheets Questions Planned How can you explain your results from the experiment using capillary action? What do you think determines the rate of capillary action? Can you think of any technology that uses capillary action? Can you think of any hazards that could be caused by capillary action? Safety Considerations Warn the students about colored water in the water source. No horsing around and spilling the water, which would be hard to wash off if it gets onto their clothes Warn the students about handling the graduated cylinder since it is made of glass and may break Tell the students that if they break the cylinder, they should not handle the glass pieces themselves but get my assistance. There is a special disposal can for shattered glass. Behavior Management Plan Everyone should stay in his/her original seat next to his/her partner. No switching partners unless instructed to do so. No one should leave his/her work desk unless instructed as by the experiment procedure. There should be no socializing during the lab. There should be no playing around with the equipment Transitions and Methods for Classroom Management Only teach this lesson once students have been introduced to diffusion and osmosis Set expectations at the beginning of the lesson Transition from Engage to Explore with the introduction of capillary action and experiment hypothesis (see procedure) Transition from Explore to Explain by relating the results of the experiment with capillary action Transition from Explain to Expand by revisiting the initial scenario about the self-watering device Resources Coffee Filter Diffusion Lab Lesson Plan (7 th grade life science on-level and TAG versions) from Taylor Road Middle School o Main inspiration for this lesson o The on-level version uses absorption of water by the coffee filter wick as a demonstration of diffusion, which I consider to be a manifestation of a misconception about diffusion o The TAG version asks the students to compare absorption rate between the coffee filter wick and the paper towel wick. It claims that this is a demonstration of diffusion and osmosis, which I consider to be a misconception about diffusion and osmosis o The TAG version inspired the scenario portion in this lesson Odom, Arthur L. Secondary & College Biology Students Misconceptions about Diffusion & Osmosis. (Oct.,1995). The American Biology Teacher, Vol. 57, No. 7, pp. 409-415. http://www.jstor.org/stable/4450030.! %!
o o Provides a list of propositional knowledge statements required for understanding diffusion and osmosis Provides a list of common misconceptions regarding diffusion and osmosis Koning, Ross E. 1994. Water and Water Movement. Plant Physiology Information Website. http://plantphys.info/plant_physiology/watermove.shtml. (11-13-2011). Koning, Ross E. 1994. Osmosis. Plant Physiology Information Website. http://plantphys.info/plant_physiology/osmosis.shtml. (11-13-2011). o Koning provides detailed knowledge about osmosis and water movement and talks about misconceptions regarding osmosis Liang, Barbara. The Cell: Passive Transport Diffusion. http://www.wisconline.com/objects/viewobject.aspx?id=ap1903 o Provides animation pictures of diffusion Using Wicks to Water Plants. http://www.youtube.com/watch?v=y_1m1njwlxa&feature=related Water Wicks for Potted Plants. http://www.youtube.com/watch?v=ndeqcxcibbc o Do-It-Yourself videos that teach you how to make self-watering devices Damonte, Kathleen. Up Goes the Water. NSTA WebNews Digest: Science and Children: Home Connections. http://www.nsta.org/publications/news/story.aspx?id=49197 o Claims that water moves up the plant by capillary action Sookbirsingh, Rudey. The Cohesion Tension Theory. http://independent.academia.edu/rudysookbirsingh/papers/135072/the_cohesion_the ory o Dr. Sookbirsingh argues that a misconception about capillary action is that it is the driving force for water upward movement in a plant Xylem: Cohesion-Tension Theory. Wikipedia. http://en.wikipedia.org/wiki/xylem#cohesion-tension_theory o Although Cohesion Tension Theory faces many objections, it is the most widely accepted theory regarding water movement in plants Facebook Correspondence with Dennis Woo (Caltech MD/PhD candidate) o Provides some explanations for why diffusion and osmosis do not play a role in the case of wicking water with coffee filter o See Appendix for the correspondence! &!
Appendix Me: Hi Dennis! I am so bothered by this lesson plan that I received from my mentor the other day, so I decided that I should ask one of my smart friends about it. What is the force that makes water go up a wick made of coffee filter? In other words, what force makes the coffee filter wick absorb the water? The Lesson is supposedly on Diffusion, but I am thinking that the phenomenon has more to do with capillary action than diffusion. My mentor even argued that the absorption is due to osmosis, because the water is moving down its concentration gradient and the piece of coffee filter could be argued to be a "semi-permeable" membrane. Can semi-permeable membrane be defined that way? Please enlighten me! Thanks, my smart friend! :) Dennis:!As for your question, the force that makes water travel up a wick made of paper would be CAPILLARY ACTION so I agree with you. Usually, we talk about capillary action as being opposed to gravity so you're right in that's it a bit hard to call this an example of diffusion because diffusion describes the RANDOM motion of particles. If you took an upright wick of coffee paper and applied water to the middle, the motion would not be random because the water moving downwards would be moving faster than the water moving upwards since the downward motion has gravity+adhesion whereas the upward motion only has adhesion (which we call capillary action). However, if you laid the paper unfolded and flat on the table and applied water to it, then I would call that diffusion and not capillary action. I would also argue that the movement of water through paper is not an example of osmosis. Osmosis requires the concentration of a solute to become equilibrated within separate compartments of a solvent. In the example of the coffee paper, we would have to say that the coffee paper (solute) becomes "dissolved" in the water (solvent) and that the wet coffee paper is a solution. I would say the wet coffee paper is not a solution because you can pick up wet coffee paper which you are unable to do with a liquid, it does not change its shape to fit a container as would a liquid, and if you throw the wet coffee paper in an actual solution it won't mix or dissolve like an actual liquid would. I also don't think the coffee paper can be called a semi-permeable membrane but for a completely different reason. If I remember, cellulose has pores that allow things to pass through as long as they're under ~3,000 kda (proteins are usually around ~50 kda for comparison). So let's say you get a fish tank and you fill it with water. You separate it into Compartment A and Compartment B by building a bridge out of coffee paper. Any solute you place into Compartment A will diffuse into Compartment B because the pores are so large that I cannot imagine any solute being unable to pass through. For this reason, I would say that coffee paper is permeable, not semi-permeable. When the coffee paper is in the coffee machine, it allows everything to pass through except for the coffee rinds but the rinds are so large they're clearly not considered solutes. Technically, you can place cells (or very, very large proteins) into Compartment A that will be unable to pass through as long as they're greater than 3,000 kda but at that size I would! '!
say you have a colloid instead of a solution. If we're talking about capillary action and diffusion in the context of biology, I would say that capillary action can describe water and that diffusion can describe ions, small molecules and proteins. Capillary action is the adherent attraction between the water and the sides of the capillary but we cannot talk about capillary action in the case of non-water molecules. We talk about diffusion as occurring when a solute (not water since water is the solvent in living organisms) moves down its concentration gradient so diffusion doesn't really apply. In the case of real cells, you have solutes inside of your cell and outside of your cell. When you eat popcorn, the salt stays outside of your cells because the plasma membrane is semi-permeable and it's actually water that moves instead of the solutes. Technically, water is undergoing diffusion but we always call this osmosis in the context of biology. This is a very long answer but that's only because you asked a very good question. I hope that clears things up and that I'm not misinforming you. And tell me how you're doing.! (!