Aquatic Solutions and Our Cells INDEX
Activity One (HTML l PDF)- An Introduction to Solutions
Key concepts:
Water is essential to life. Our cells are largely water, being surrounded in water and using water to transport essential dissolved materials. Every cell can be modeled as an aquatic solution of inorganic and organic compounds separated from the outside world by a thin membrane. This membrane regulates the flow of water and dissolved materials in and out of the cell.
Students:
1. Take a pretest.
2. Zoom into the virtual laboratory and explore the response of the erythrocyte to the changing salinity of the outside solution. Consider the week's challenge: how does a cell "know" to respond to changing concentrations in the surrounding liquid?
3. Draw a preliminary model with a membrane separating the inner and outer solutions.
4. Read and reflect upon human illnesses that occur when a membrane's structure and functions are altered (e.g. Cholera).
Activity Two (HTML l PDF) - Getting to Know the Water Molecule
Key concepts:
Water molecules are small and highly polar. Their polar nature gives water its unusual properties. On a microscopic level, water is a network of these polar molecules linked together by hydrogen bonds.
Students:
1. Derive a model of water based on their experiments with alternative computer models of charged, noncharged and polar particles.
2. Look at the shape and behavior of a single water molecule.
3. Employing kinesthetic movement, investigate further the power of hydrogen bonds to "clump" water together.
4. Revise their model of erythrocytes in solution.
Activity Three (HTML l PDF) - Into Solution: the Role of Charge
Key concepts:
Water is a great solvent, but all substances that water can dissolve must be either polar or ionic (either positively or negatively charged). The polar water molecules attract charged particles and push out non-charged particles. Water is attracted to itself, to other polar molecules, ionic substances, and to non-polar substances.Students will:
1. Explore both on the computer and in kinesthetic modeling, the interaction between ions, polar or a neutral molecules with the polar water molecules. Students should be able to reason why some substances can be dissolved in water, but others cannot.
2. Explore on a computer model the effect of temperature on solubility, and be able to explain why cooling or heating may affect solubility.
3. Revise their model of erythrocytes in saline solution from Activity One to include their experiences with dissolving.
Activity Four (HTML l PDF) - Gradients and Barriers
Key concepts:
Water moves, carrying particles of different sizes in solution. Dissolved particles are always moving about randomly in the water; the flow always goes from a region of high concentration to a region of low concentration.Students will:
1. Consider the way solutions move, consulting a computer model of dissolved materials diffusing within a container.They will understand that that movement across a semi-permeable membrane is a special case of diffusion, which is called osmosis.
2. Vary concentrations on either side of the membrane barrier, being able to describe the role of particle concentration, particle size, pore size and other relevant variables. They will understand that, in cells, osmosis is the process that maintains a cell's normal shape and concentration of water and many ions.
3. Insert barriers with various pore sizes and be able to predict changes in concentrations, membrane shape.
Activity Five (HTML l PDF) - Modeling Molecular Movements Across a Membrane and Disease
Key concepts:
Many diseases are the result of structural changes in the cell membrane; some of these changes may result from genetic disorders (mutations), some are caused by toxins, produced by certain bacteria and others by the actions of viruses.
Students will:
1. Summarize as a class their enhanced model of the Erythrocyte Case that has incorporated their understanding of the molecular structure of water and aquatic solutions, diffusion and the origin of osmotic pressure. They apply this knowledge to the behavior of the erythrocyte in solutions of various salinity.
2. Read and discuss case studies of illnesses, Cystic Fibrosis and Cholera. Students will explore the idea that certain diseases are the result of various damages of the structure and function of cell membrane, some (Cholera) caused by a bacterial toxin, or resulted from genetically determined deficiencies in the membrane structure (CF). Their focus is on water and ions' movement in response to the structural changes in the membrane.
3. Adjust their models to explain macroscopic phenomena of CF and Cholera.
4. Take a posttest.