This is a comprehensive and detailed practice material that contains lab questions and answers on diffusion and osmosis for Bio 1112.
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PRE-LAB QUESTIONS
1. A concentration gradient affects the direction that solutes diffusion. Describe how
molecules move with respect to the concentration.
a. Molecules are always in motion due to kinetic energy present in every atom.
Molecules move from high areas of concentration to low areas of concentration.
Once equilibrium is achieved molecules will move in each direction at an equal
rate. (Stanford Virtual Lab). The definition of concentration gradient is the change
in molecular density over a given area. The image from the diffusion and osmosis
lab is a good visual example of how concentration gradients affect the direction
of a solute diffusion.
(Stanford Virtual Lab)
2. How does size affect the rate of diffusion?
a. The Lipid bilayer selects the molecules that can dissolve through the cell
membrane. The smaller the size and the electrical charge of the molecule has
the easier time crossing the membrane. The simple rate of diffusion allows small
uncharged molecules to pass through the cell membrane. (Stanford Virtual Lab).
Facilitated diffusion allows larger molecules to use specific channels to pass
through the cell membrane. (Stanford Virtual Lab).
3. Does polarity affect the rate of diffusion? Explain your answer.
a. Small non-polar molecules exhibit a higher rate of diffusion than larger ones.
(Stanford Virtual Lab) according to our textbook, “The plasma membranes are
amphiphilic: they have hydrophilic and hydrophobic regions. This difference in
size helps to move some material through the membrane and hinders the
movement of others. Non-polar and lipid soluble material with a low molecular
weight can easily slip through the membrane’s hydrophobic lipid core” (Mary Ann
Clark Texas Wesleyan University et al., 2018, pp. 135)
4. If a piece of celery is placed in a glass of pure water, are the celery cells hypertonic,
hypotonic or isotonic compared to the water? In which direction will water move?
a. Placing the celery into the pure water, the water the celery is in a hypotonic state
Because, the water is greater outside the cell than inside the cell. According to
Kahn, “An ideal solution for a plant cell is a hypotonic state since the plasma
membrane can only expand to the limit of the rigid cell, so the cell won’t burst.”
(Tonicity: Hypertonic, Isotonic & Hypotonic Solutions (Article), n.d.)
a. Water potential is always zero. Water will always move from high water potential
to low water potential. (Water Potential, 2013, 03:15–05:21) The more negative
the water potential, the higher the concentration of the solute. (Stanford Virtual
Lab). Most cells are hypertonic and extracellular water flows into the cell, but if a
cell is placed in pure water a cell will burst (lysis) as a result of increased pressure
of the water moving into the cell. (Stanford Virtual Lab)
6. Why don’t red blood cells swell or shrink in blood plasma?
a. Red blood cells in plasma don’t swell or shrink because they are in an isotonic
state. And isotonic state means they have the same amount of water flowing into
the cell that they do outside of the cell. This happens to red blood cells in plasma.
(Libretexts, 2020a) the picture below shows how red blood cells will act in each
state, hypertonic ( they will shrink), hypotonic ( they will swell), and isotonic
means that they will be constant due to water flowing in and out evenly.
(Libretexts, 2020a)
7. Research how osmotic power plants work. Summarize what you learned in 1-2
paragraphs. Include references to information sources used.
An osmotic power plant works by mixing freshwater and seawater together to create power. This
technically that captures this energy is called pressure retarted osmosis (PRO). “Fresh water
mixes with the seawater in the membrane module and this osmotic process increases the
volumetric flow of high pressure water and is the key energy transfer in the power production
process. The diluted, brackish water from the module is split and the brackish water is used to
generate power. (Brandon Wulff, 2015)
In the past osmotic power had a huge environment impact due to the size of the footprint
it takes. However today companies like Statkraft are trying to develop more cost and space
saving technologies to help in our environmental impacts.
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