1. What is the tonicity of the left side of the container relative to the right? Right to left?
Theresa's NHCC Biol 1000 & 1001 Pages
Last
updated 3/27/2004.
Sample Osmosis and Diffusion Questions
In the following diagram, the two solutions
are separated by a semipermeable membrane. This membrane is permeable
only to water molecules. Use this information to answer 1 & 2 below.
1. What is the tonicity of the left side
of the container relative to the right? Right to left?
1. The left side of the container is
hypertonic to the right, and the right side of the container is hypotonic to the
left.
2. What is the net direction of water
movement in the container? (Why?)
2. The net direction of water movement in
the container is from right to left. This is because the water concentration is
higher on the right side than on the left. The NaCl cannot cross the membrane.
(If the semipermeable membrane were not present, the NaCl molecules would
diffuse to the right.)
3. Compare & contrast diffusion & osmosis.
3. Diffusion is the movement
of particles (any particles, including water) down their concentration gradient
(in other words from an area of high particle concentration to an area of low
particle concentration). Osmosis is diffusion of a solvent (usually water)
across a semi-permeable membrane. Diffusion and osmosis are both spontaneous
processes, so the second law of thermodynamics is the "driving force" behind
both diffusion and osmosis. Therefore, as diffusion and osmosis occur, free
energy decreases and entropy increases.
4. What is tonicity?
4. Tonicity is the relative solute concentration
of one solution compared to the solute concentration of another solution. The
three tonicity terms are: hypertonic (the solution has a higher solute
concentration than the other solution), hypotonic (the solution has a
lower solute concentration than the other solution), and isotonic (the
two solutions have equal solute concentrations).
5. What mechanisms have organisms developed to deal with diffusion/osmosis
problems created by
their environment?
5. Freshwater algae (like Spirogyra) and freshwater plants (like Elodea) live in a hypotonic environment, and they have cell walls that lend physical support that helps to prevent their cells from exploding in freshwater environments (osmotic pressure offsets the pressure of the water trying to flood into the cells). Land animals (like us) carry their own aqueous environment around with them, so they try to keep their blood and/or extracellular fluids isotonic to the insides of their cells. Freshwater protozoans (like Paramecium, Amoeba, ...) have contractile vacuoles to collect and pump out excess water that floods into them constantly from their hypotonic freshwater environment.
(6). This one is just to make you think:
how do living systems maintain their ordered states?
(6). To keep from "losing order", living systems
must take in energy (in other words, eat or absorb sunlight, ...). (This is
according to the second law of thermodynamics.)
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