Sugar Respiration in Yeast

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1 Experiment

Membrane Transport
Objectives ► Referring to energy, what two ways can substances enter a cell? What is active transport? What is passive transport? How is osmosis related to diffusion? How can we demonstrate active transport? How can we demonstrate Brownian movement? How can we demonstrate diffusion (2 ways)? How can we demonstrate osmosis (3 ways)? In terms of relationships between substances, how can we define “hypertonic”, “isotonic”, and “hypotonic”? What is the relationship between the size of a molecule and its rate of diffusion?


Supplies ► Materials Needed
Active Transport: Baker’s Yeast 0.75% Na2CO3 0.02% Neutral Red Erlenmeyer Flasks Flame or Hot Plate Brownian Movement: India Ink (Carmine Dye or Whole Milk may be substituted) Slides and Cover Slips

2 Diffusion: Beaker of Distilled Water 1.5% Agar-agar (or Gelatin) in petri plate Potassium Permanganate (KMnO4) Crystals Potassium Dichromate (K2Cr2O7) Crystals Methylene Blue Crystals Metric Ruler (to measure in mm) Osmosis—Thistle Tube: Thistle Tube Osmometer Salt, Sugar Distilled Water Scale Artificial Cell: Dialysis Tubing or Sacs Sugar String Beakers Distilled Water Scale Osmosis and Red Blood Cells: Distilled Water; Salt Solutions: 12-15% Salt Salt Solutions: 0.85% Salt (This is human, isotonic saline.) Blood (Human or Animal): Lancets and Alcohol if Human Blood is used Slides and Cover Slips Microscope


Key Terms ► Active Transport
Brownian Movement Cell Physiology Dialysis

3 Diffusion Gradient Hypertonic Hypotonic Isotonic Membrane Transport Osmosis Passive Transport


Introduction ► The individual cell is a dynamic microcosm, demonstrating in miniature all the processes and events that occur in the macrocosm, making the apparent function of the whole organism the actual function of many individual cells working in unison. It is important that we understand how the individual cell, the microcosm, functions so that we can more fully understand how the organism as a whole, the macrocosm, function. For instance, we can say that if an action potential (or nerve impulse) is to be generated in a part of the nervous system, a certain electrical stimulation must be present and certain ions must be moving through appropriate channels. What we sometimes forget is that these events—in this case the electrical stimulation and the ionic movement—occur at the cellular level. What seems to be happening in the organism is happening only because the events are occurring at the level of the individual cell. We could use similar analogies for every system in the body. In lecture you examined the molecular intricate of the phospholipid bilayer known as the cell membrane, and you became aware that the cell membrane is selectively permeable, meaning that only certain substances can enter and leave the cell by freely crossing the membrane. You know, for instance, that the membrane is replete with channels, gates, and carrier molecules that either facilitate, inhibit, or repel assorted ions and molecules as they randomly approach the demarcation barrier. This demarcation barrier, the cell membrane, is functional in maintaining cellular integrity. You also know that since the cell is microcosm, ions and molecules must cross the barrier, both as nutrients entering the cell and as wastes leaving the cell. In cell physiology, we examine how events occur within the cell. Cellular functions follow the basic principles of physiology. Many of these functions do not lend themselves to easy demonstration, particularly this early in an introductory course. However, at this point we can demonstrate a number of functions directly related to membrane transport. And membrane transport is one of the main keys to cell physiology...
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