Diffusion Worksheet PDF

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Diffusion worksheet...

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Class Exercise—Rare Epithelial Transport Note: This exercise will be done in class; answers will be posted to Canvas afterward. 1. What factors do you have to consider in determining how a molecule moves across a cellular layer?

2. A rare example of a sodium-secreting epithelium: The choroid plexus is a specialized region of epithelial cells and capillaries that lines portions of the ventricles of the brain. It secretes cerebrospinal fluid (CSF), which is very similar in composition to the ECF. Note that epithelial cells have typical K+ and Na+ content, but concentrate Cl-, unlike most cells. Using the diagram below, answer the questions that follow. = channel = ATPase a. Are the given transporters placed on the correct membranes for apical secretion of CSF? Circle one: yes no

Lumen (CSF)

b. If not, how should they be arranged? OR, if so, why is the orientation appropriate? Explain.

ECF

Na+

Na+ K+

Choroid Plexus Cell

c. The Na+-K+- 2Cl- symporter is also present in the membranes of these cells and aids in the secretion of ions and therefore water from the ECF to the CSF. It does not hydrolyze ATP. On which membrane would you find this symporter? _______________________ d. The movement of K+ and Cl- on the Na+-K+-2Cl- is what type of transport? ____________________________

Multiple multiple choice practice: 3. Select all true statements regarding movement across membranes. a. movement by carrier is always active b. movement of nonpolar molecules will reach a maximum as concentration is increased c. diffusion is directly proportionate to molecular size d. channels have an active site and show specificity, competition, and saturation 4. Which is correctly paired with method of movement? Molecule Method of movement a. K+ out of a cell channel-mediated diffusion b. urea into RBC active transport c. estrogen out of gonads facilitated diffusion d. glucose out of epithelial cell 2o active transport

Discussion Exercise: Membrane Movement & Epithelial Transport Note: Key will be posted after discussion 1. a. To understand the rationale behind the form of movement across membranes (simple diffusion, channel, facilitated diffusion or active transport) for a certain molecule, it is important to know relative intra- vs. extracellular concentrations as well as characteristics of the molecule (size, charge or polarity). Given the cell below, write the following molecules both inside and outside the cell: glucose, Na+, K+, Ca2+, O2, CO2, and H2O. Use large print to show where in greater concentration; use small print to show where lesser concentration.

b. Which molecules can move by simple diffusion?

c. Which require some type of transporter (channel or carrier)?

2. Match the items in column 1 with the means by which they are most likely to be transported (column 2). In column 3, write the ONE letter that best corresponds to your rationale for selecting the means of transport. If you do not see a rationale that fits, you may write in your own rationale. COLUMN 2: MEANS OF TRANSPORT: 1 - simple diffusion 2 - facilitated diffusion 3 - movement through a water-filled channel 4 - active transport 5 – endocytosis 6 - exocytosis COLUMN 3: RATIONALE FOR TRANSPORT: A - is polar molecule B - is nonpolar molecule C - is an ion D - is small E - is not an ion F - moving down concentration gradient G - moving against concentration gradient H - following electrochemical gradient Column 1: Movement of ... Na+ from ECF into cells Aldosterone into target cell Glucose into renal proximal tubule cell Glucose into muscle cell

Column 2 - Moves by

Column 3 - Why?

Discussion: Epithelial transport application problem: Epithelial transport of H+ and the bicarbonate ion (HCO3-) in the nephron of the kidney play a major role in acidbase balance in the body. H+ and HCO3- are synthesized within the epithelial cells from CO2 and H20 in an enzymatically catalyzed reaction. The movement of these ions is linked to Na+ transport. The relative concentrations and the net direction of movement of all are shown in the table. Where should the transporters be placed, and what is the specific method of movement for the molecule? Ion Na+ H+ HCO3-

Direction Absorbed Secreted Absorbed

Concentration Typical ICF vs ECF concentrations High in lumen High in cell

lumen

ECF

The following transporters are present in these epithelial cells: Na+ channel Na+/K+ ATPase + + Na /H co-transporter Na+/HCO3- co-transporter 1.a. In a Na+-absorbing epithelium such as tubule epithelium is the ATP-ase on the: (circle one) luminal membrane (L)

ECF membrane (E)

b. Which membrane is the apical membrane?

L

E

c. On which membrane should you find the Na+/H+ co-transporter? d. This transporter is a(n) (circle one): anti-porter e. Where would you expect to find the Na+ channel?

L

E

symporter L

E

2. a. Given, that the Na+/HCO3- co-transporter is on the ECF membrane, do you think it is an antiporter or a symporter?

b. Based on the info above and your answer to 2a, which molecule(s) move by 2o active transport? Circle one: Na+ HCO3Both Neither 3. Draw and label a graph of secondary active transport of a molecule....