Velocity of molecular movement
Summarize the results of Activity 3, diffusion through nonliving membranes, below. List and explain your observations rel- ative to tests used to identify diffusing substances, and changes in sac weight observed. Sac 1: 40% glucose suspended in distilled water
Sac 2: 40% glucose suspended in 40% glucose
Sac 3: 10% NaCl in distilled water
Sac 4: 40% sucrose and Congo red dye in distilled water
The Congo red dye did not diffuse from the sac into the water; the water in the beaker did not turn red. The sucrose did not diffuse from the sac; upon boiling, some of the sucrose bonds are hydrolyzed, releasing glucose and fructose. Using Benedict’s test then indicates the presence of glucose if sucrose passed through the membrane; the Benedict’s test was negative. Water moved into the sac by osmosis; the sac gained weight.
What single characteristic of the differentially permeable membranes used in the laboratory determines the substances that can pass through them? In addition to this characteristic, what other factors influence the passage of substances through living membranes?
A semipermeable sac containing 4% NaCl, 9% glucose, and 10% albumin is suspended in a solution with the following com- position: 10% NaCl, 10% glucose, and 40% albumin. Assume that the sac is permeable to all substances except albumin. State whether each of the following will (a) move into the sac, (b) move out of the sac, or (c) not move.
Summarize the results of Activity 5, Experiment 1 (diffusion through living membranes—the egg), below. List and explain your observations.
The diagrams below represent three microscope fields containing red blood cells. Arrows show the direction of net osmosis.
Which field contains a hypertonic solution? _________ The cells in this field are said to be ___________________. Which
field contains an isotonic bathing solution? ____ Which field contains a hypotonic solution? ________ What is happening
to the cells in this field? ____________________________________________________
What determines whether a transport process is active or passive?
For the osmometer demonstration (Activity 4), explain why the level of the water column rose during the laboratory session.
The thistle tube was immersed in a dialysis sac which, in turn, was immersed in water. Since water will move down its concentration gradient if it is able, water diffused from the beaker into the sac, where its concentration was much lower.
As a result, the fluid column (molasses and entering water) rose in the thistle tube.