if you want to remove an article from website contact us from top.

    by the end of this lab, you will see how some materials diffuse through a semipermeable membrane but others do not. the materials that you examine will differ in molecule size. some will be larger and some smaller. formulate an investigative question for this situation.

    James

    Guys, does anyone know the answer?

    get by the end of this lab, you will see how some materials diffuse through a semipermeable membrane but others do not. the materials that you examine will differ in molecule size. some will be larger and some smaller. formulate an investigative question for this situation. from EN Bilgi.

    Cell Membranes Flashcards

    Start studying Cell Membranes. Learn vocabulary, terms, and more with flashcards, games, and other study tools.

    Cell Membranes

    5.0 5 Reviews

    14 studiers in the last day

    • Explain the concepts of diffusion and osmosis and why they are important to cells physiology

    Click card to see definition 👆

    diffusion = tendency of all molecules to scatter evenly throughout the environment, move from higher to lower concentration, requires no energy - there must be a difference in concentration (concentration gradient)

    osmosis = movement of solvent (water) across a selectively permeable membrane

    Click again to see term 👆

    • Explain how temperature influences the movement of a substance

    Click card to see definition 👆

    things move faster as they are heated up

    Click again to see term 👆

    1/34 Created by ryan_padilla

    Terms in this set (34)

    • Explain the concepts of diffusion and osmosis and why they are important to cells physiology

    diffusion = tendency of all molecules to scatter evenly throughout the environment, move from higher to lower concentration, requires no energy - there must be a difference in concentration (concentration gradient)

    osmosis = movement of solvent (water) across a selectively permeable membrane

    • Explain how temperature influences the movement of a substance

    things move faster as they are heated up

    • Explain how molecular size influences the movement of a substance

    smaller size = faster movement

    • Explain how the concentration of a substance influences the movement of a substance

    diffusing molecules always move outward from an area of high concentration to low concentration - the difference in concentration levels between 2 locations is known as the concentration gradient

    • Provide examples of molecules that can diffusion through the cell membrane and molecules that cannot diffusion through the membrane

    In order for a cell to function effectively, it needs to be able to control which substances can enter and exit through its membrane. The cell membrane's main trait is its selective permeability, which means that it allows some substances to cross it easily, but not others. Small molecules that are nonpolar (have no charge) can cross the membrane easily through diffusion, but ions (charged molecules) and larger molecules typically cannot.

    Nonpolar and small polar molecules can pass through the cell membrane, so they diffuse across it in response to concentration gradients. Carbon dioxide and oxygen are two molecules that undergo this simple diffusion through the membrane. The simple diffusion of water is known as osmosis

    The cell membrane is made of a bilayer of phospholipids, with an inner and outer layer of charged,hydrophilic "heads" and a middle layer of fatty acid chains, which are hydrophobic, or uncharged. Charged ions cannot permeate the cell membrane for the same reason that oil and water don't mix: uncharged molecules repel charged molecules. Even the smallest of ions -- hydrogen ions -- are unable to permeate through the fatty acids that make up the membrane. If ions "want" to enter the cell due to a high concentration of that type of ion on one side of the cell, they can do so by entering through the protein channels that are embedded between the lipids

    • Describe the function of a controlled experiment

    an experiment or trial that uses controls, usually separating the subjects into one or more control groups and experimental groups

    in this case the positive controls were testing the iodine with starch, benedicts with simple sugars, and silver nitrate with salt- so we know what positive results will look like when we compare them to the substnces being tested

    • Explain what dialysis tubing bag represents in the diffusion experiment

    it mimics a cell's permeability - large molecules will not pass, small molecules will pass

    • Describe the outcomes of the diffusion experiment (i.e. which solutions can diffuse through the membrane and which solutions cannot diffuse through the membrane)

    salt and glucose were able to diffuse through the membrane, while starch was not able to

    • Describe the use of indicator chemicals to test for the movement of molecules and to determine the direction of diffusion

    benedict's test - simple sugars

    iodine - starch

    silver nitrate test - salt

    • State the tests used for the diffusion experiment and the positive and negative outcomes

    salt = + starch = - glucose = +

    • State which solutions moved through the membrane in the dialysis tubing experiment and which solutions did not

    salt and glucose moved through b/c small (hypotonic solution)

    starch did not move through b/c it was too large

    • Describe the appearance of elodea cells in culture water, 20% saline solution, and DI water solution

    culture water = chloroplasts distributed evenly throughout cell

    20 percent saline solution = chloroplasts packed tightly together near the middle of the cell

    DI water solution = chloroplasts spread out against the boundary of the cell membrane and wall

    • State the direction the water is moving for each of the environments the elodea is in (i.e. culture water, 20% saline solution, and DI water solution)

    culture water = isotonic , water not moving in or out

    20 percent saline solution = hypertonic, solute concentration is greater on the outside- shrinks elodea cell

    DI water solution = hypotonic, solute concentration is less on the outside, swells elodea cell

    Source : quizlet.com

    Osmosis and Diffusion

    Osmosis and Diffusion

    LAB OBJECTIVES

    At the conclusion of the lab, the student should be able to:

    define the following terms: diffusion, osmosis, equilibrium, tonicity, turgor pressure, plasmolysis

    describe what drives simple diffusion (why do the molecules move?)

    list the factors that may affect the speed of simple diffusion

    list which molecules, in general, can freely diffuse across the plasma membrane of a cell

    describe what drives osmosis (why do water molecules move?)

    explain why water moves out of a cell when the cell is placed in a hypertonic solution

    explain why water moves into a cell when the cell is placed in a hypotonic solution

    describe what physically happens to a cell if water leaves the cell

    describe what physically happens to a cell if water enters the cell

    Slideshow

    Membrane lab from Lumen Learning

    Introduction

    Understanding the concepts of diffusion and osmosis is critical for conceptualizing how substances move across cell membranes. Diffusion can occur across a semipermeable membrane; however diffusion also occurs where no barrier (or membrane) is present. A number of factors can affect the rate of diffusion, including temperature, molecular weight, concentration gradient, electrical charge, and distance. Water can also move by the same mechanism. This diffusion of water is called osmosis.

    In this lab you will explore the processes of diffusion and osmosis. We will examine the effects of movement across membranes in dialysis tubing, by definition, a semi-permeable membrane made of cellulose. We will also examine these principles in living plant cells.

    Part 1. Diffusion Across a Semi-Permeable Membrane: Dialysis

    Procedure

    Cut a piece of dialysis tubing, approximately 10 cm.

    Soak the dialysis tubing for about 5 minutes prior to using.

    Tie off one end of the tubing with dental floss.

    Use a pipette and fill the bag with a 1% starch solution leaving enough room to tie the other end of the tubing.

    Tie the other end of the tubing closed with dental floss.

    Fill a 250 mL beaker with distilled water.

    Add Lugol’s iodine to the distilled water in the beaker until the water is a uniform pale yellow color.

    Place the dialysis tubing bag in the beaker.

    The molecular formula for Lugol’s solution is I2KI (atomic mass = 127). Starch consists of long chains of glucose (atomic mass of each glucose = 180). Iodine turns a deep blue in the presence of starch. Formulate a hypothesis for each of the following. Remember to provide a reasonable explanation for your predictions.  

    The movement of starch

    The movement of iodine

    The color of the solution in the bag after 30 minutes

    The color of the solution in the beaker after 30 minutes

    Add the dialysis bag to the beaker and allow the experiment to run for 30 minutes. Record the colors of both the dialysis bag and the beaker.

    Table 1: Dialysis Tubing Data

    Dialysis tubing contents Beaker contents

    Pre-experimental color

    Pre-experimental contents 1 % Starch solution Dilute iodine water

    Post-experimental color

    Lab Questions

    Is there evidence of the diffusion of starch molecules? If so, in which direction did starch molecules diffuse?

    Is there evidence of the diffusion of iodine molecules? If so, in which direction did iodine molecules diffuse.

    What can you say about the permeability of the dialysis membrane? (What particles could move through and what particles could not?)

    What is the difference between a semi-permeable and a selectively permeable membrane

    Part 2. Plasmolysis—Observing Osmosis in a Living System, Elodea

    If a plant cell is immersed in a solution that has a higher solute concentration than that of the cell, water will leave/enter (circle one) the cell. The loss of water from the cell will cause the cell to lose the pressure exerted by the fluid in the plant cell’s vacuole, which is called turgor pressure. Macroscopically, you can see the effects of loss of turgor in wilted houseplants or limp lettuce. Microscopically, increased loss of water and loss of turgor become visible as a withdrawal of the protoplast from the cell wall (plasmolysis) and as a decrease in the size of the vacuole (Figure 1).

    Procedure

    Obtain a leaf from the tip of an Elodea Place it in a drop of water on a slide, cover it with a coverslip, and examine the material first at scanning, then low power objective and then at high power objective.

    Locate a region of health. Note the location of the chloroplasts. Sketch a few cells. For the next step, DO NOT move the slide.

    While touching one corner of the coverslip with a piece of Kimwipe to draw off the water, add a drop of 40% salt solution to the opposite corner of the coverslip. Do this simultaneously. Be sure that the salt solution moves under the coverslip. Wait about 5 minutes, then examine as before. Sketch these cells next to your sketch of cells in step two, note the location of the chloroplasts. Label it 40% salt solution.

    Lab Questions

    What happened to the cells in the salt solution?

    Assuming that the cells have not been killed, what should happen if the salt solution were to be replaced by water?

    Source : courses.lumenlearning.com

    Selective Permeability of Dialysis Tubing Lab: Explained

    ABSTRACT: This experiment was conducted to investigate the selective permeability of dialysis tubing. The permeability of the tubing to glucose, starch and iodine (potassium iodide) was tested. The dialysis tubing was clipped to form a bag so that glucose and starch was fed into the bag through the other end, and was also clipped to

    Skip to content SchoolWorkHelper

    Your online site for school work help and homework help. Science, English, History, Civics, Art, Business, Law, Geography, all free!

    Essay Writing Help Science

    Sociology & Philosophy

    Law & Politics History Business English Art

    Selective Permeability of Dialysis Tubing Lab: Explained

    You are here:

    HomeScienceSelective Permeability of Dialysis Tubing…

    ABSTRACT:

    This experiment was conducted to investigate the selective permeability of dialysis tubing. The permeability of the tubing to glucose, starch and iodine (potassium iodide) was tested. The dialysis tubing was clipped to form a bag so that glucose and starch was fed into the bag through the other end, and was also clipped to avoid the seeping of the solution.

    Water with several drops of iodine added to it until it was visibly yellow-amber was added to a 400ml beaker. The bag was then placed in the beaker, which was stirred with a magnetic stirrer. It was left there for 30 minutes. It was seen that the color of the solution in the bag changed to blue-black color, this showed that iodine was able to pass through the membrane into the bag.

    The solution in the beaker became pale yellow-amber, this showed that starch didn’t pass through the membrane into the beaker. To confirm the presence of glucose in the beaker and also the bag, a Benedict test was performed on the solutions including tap water (control) too.

    The beaker solution turned into light brown color after Benedict solution was added to it and suspended in water bath for 10 minutes. The bag solution also changed to brown color, while tap water remained blue. This experiment showed that dialysis tubing is selective in its permeability to molecules. It was permeable to glucose and iodine but not starch.

    INTRODUCTION:

    PURPOSE: The purpose of the experiment was to test the permeability of dialysis tubing to glucose, starch and iodine.

    Living cells need to obtain nutrients from their environment and get rid of waste materials to their surroundings. This exchange of materials between the cell and its surroundings is crucial to its existence. Cells have membranes composed of a phospholipid bilayer embedded with proteins.

    This cell membrane can distinguish between different substances, slowing or hindering the movement of other substances and allowing others to pass through readily. This property of the cell is known as selective permeability (Ramlingam, 2008).

    Selective permeability is a property of a cell membrane that allows it to control which molecules can pass (moving into and out of the cell) through the pores of the membrane. Selective permeable membranes only allows small molecules such as glucose, amino acids to readily pass through, and inhibits larger molecules like protein, starch, from passing through it.

    The dialysis tubing is a semi-permeable membrane tubing used in separation techniques and demonstration of diffusion, osmosis, and movement of molecules across a restrictive membrane (Todd, 2012). It separates dissolved substances of different molecular sizes in a solution, and some of the substances may readily pass through the pores of the membrane while others are excluded. The dialysis tubing is made up of cellulose fibers. This is shaped in a flat tube.

    In this experiment, the selective permeability of dialysis tubing to glucose, starch and iodine (potassium iodide) will be tested. This experiment consists of two tests; the test for starch and the test for reducing sugar. When iodine (potassium iodide) is added to a solution in which starch is present, the solution turns blue-black or purple otherwise it remains yellow-amber.

    And when Benedict’s reagent is added to a solution in which reducing sugar is present and it is heated in a water bath, the solution turns green, yellow, orange, red, and then brick red or brown (with high concentration of sugar present). Otherwise, the solution remains blue.

    QUESTION:

    Will glucose, starch and iodine (potassium iodide) readily pass through the pores of the dialysis tubing?

    HYPOTHESIS:

    Glucose, starch and iodine (potassium iodide) will readily pass through the membrane of the dialysis tubing.

    PREDICTION:

    The solution in the bag and the beaker will both turn blue-black due to the presence of iodine and starch; the presence of glucose in the bag and beaker will be investigated using Benedict test.

    MATERIALS:

    Beakers Dialysis Tubing Test Tubes Test Tubes rack Clips Water Bath Water

    SOLUTIONS:

    Benedict’s reagent Glucose Starch

    Iodine (Potassium Iodide)

    EXPERIMENT PROCEDURE:

    1) 250 ml of tap water was added to a beaker. Several droppers of Iodine (Potassium Iodide) solution was added to the water until it was visibly yellow-amber in color. The color was then recorded.

    2) The dialysis tubing was soaked in water for a few minutes until it began to open. One end of the bag was folded and clipped in order to secure it so that no solution seeped through.

    Source : schoolworkhelper.net

    Do you want to see answer or more ?
    James 8 day ago
    4

    Guys, does anyone know the answer?

    Click For Answer