The following puzzles are based on what biologists call the cell wall transport system.

Cells use a phospholipid bilayer as a membrane to bind together the contents of the cell. In order to transport substances into and out of the cell, proteins serve as doors in the cell membrane. These proteins facilitate transport of certain substances according to certain rules:

Uniport

Some proteins allow only one-way transport of substances.
In the following puzzles, these will serve as one-way doors.

 

Antiport

Other proteins allow one substance to enter the cell while it ejects another substance.
In the following puzzles, if you cross one of these barriers,
there must be something on the other side to switch places with you.

 

Symport

Still other proteins allow substances to pass only when they are accompanied by a partner.
In the following puzzles, you must have something accompany you through the barrier.

 

These facilitated transport systems are used to limit the movements of the black ball, which you control, and the blue balls (objects). To solve the puzzle, you must maneuver all of the objects into the receptors, which are designated by the circled blue r's. The puzzle is complete only once all of the receptors are filled by one object each. To solve the example below, keep in mind that you are not necessarily supposed to carry around objects, but transport them according to the cell wall transport rules.

 

 

Solution

Moving your black ball to the upper-middle square will move the object down to the lower-middle square (through the antiport barrier). Notice that if you tried to move to the upper-left square, you would not be able to continue moving through the puzzle.

 

Next, moving your ball around to the lower-middle square will move the object to the receptor in the lower-right square (through the antiport barrier). Since every receptor is now filled, the puzzle has been solved.

 

Below is the way the solution will normally be printed. The puzzle will be shown again with letters corresponding to each compartment. A table of letters will also be printed, with the first line summarizing how the black ball should be moved, from compartment to compartment, in order to solve the puzzle. The following lines detail how each object is moved by the movements of the black ball. Each object has its own separate line.

Finally, for the fans of Cell Wall Transport System puzzles, you may be wondering why the list of puzzles got shorter all of a sudden. Well, I took the first three puzzles and have included them in a set of easy warm-up puzzles for students. But the more challenging ones are still here, just renumbered. Old puzzle 4 is now 2, 5 is now 1, 6 is now 3, and 8 is now 6.