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Cells in Their Environment 1.7 – pg. 28-29
NAME:
1. Explain in your own words the process of diffusion.
An easy way to picture diffusion is to imagine St. Clare’s gym. Our Gym has a fold-out
wall that separates the gym into two equal halves. Imagine the gym with the wall
folded out. Now, magically wave your hand and 30 students materialize in the middle
of one side of the partitioned gym. Of course the students will stand next to and near
each other socializing, but magically wave your hands again and the students
instantaneously begin to act as a molecule would. At that moment the students will
begin to walk away from each other and continue moving until they are spread
around the entire gym and find the position in the gym that has them all spread out at
equal distances from each other. This process of molecules moving apart to fill an
entire available space and to end up stopping when they are all equidistant from each
other is the process of diffusion. Explain what would happen if we folded the gym’s
wall partition back into the wall and opened up the other half of the gym to the
students acting like molecules.
2. Explain what is meant by impermeable, permeable, and selectively
permeable materials.
An impermeable material is a material through which liquids, objects, and gases
cannot pass. For example, a raincoat is impermeable to rain and sand. When it rains
and you are wearing a raincoat, the rain will not pass through the raincoat and wet
your skin. Additionally, if sand were sprinkled on the elbow of your raincoat, the sand
would not pass through the raincoat and touch your skin. On the other hand a
permeable material is a material that allows liquids, objects, and gases to pass through
it. For example, if I am wearing a knit top with large holes between the stitches, both
the rain and sand would pass through it and make contact with my skin. Finally a
selectively permeable material allows certain liquids, objects, and gases to pass
through it, while keeping other liquids, objects, and gases from not being able to pass
through it. For example, a long-sleeved t-shirt would not prevent the rain from
passing through, but it would keep the sand from making contact with your skin..
3. What type of membrane do cells have? Explain why.
Cell membranes are selectively permeable. Cells need to have selectively permeable
membranes because they need to be able to control what can enter the cell (good
things) and what cannot enter the cell (bad things) in order to make sure the cell
remains healthy and strong so that ultimately we remain healthy and strong.
4. Hypothesize why the pores in the cell membrane are of different sizes.
I guess that having different-sized pores in the cell membrane is an effective way of
making cell membranes selectively permeable. For example, imagine there existed
two molecules that are always present around the outside of a cell. Let’s call them
Molecule A and Molecule B. Molecule A is half the size of Molecule B. Both A and B are
good molecules for the survival of the cell, but too much of molecule B would actually
be bad whereas molecule A is needed in large quantities so that the cell can survive. In
this case the cell membrane would open one of its large pores so that both molecule A
and Molecule B could pass through the membrane into the cell. When the cell has
gotten enough of molecule B, it would close the large pore and molecule A and B
would no longer be able to pass through the cell membrane. Large quantities of
molecule A are still needed, so the cell opens smaller pores that allow molecule A to
continue passing through the cell membrane, but keep molecule B from passing
through it. In this case the different-sized pores make the membrane selectively
permeable to molecule A (allow it passage into the cell) and molecule B (don’t allow it
passage into the cell).
5. The pores of cells aren’t always open. Sometimes they are locked. In
humans and in many other animals, insulin acts like a key to a lock. Insulin
is a protein released by the pancreas into the blood. Once in the blood,
insulin molecules can reach all the cells of the body. An insulin molecule is
able to attach itself to the cell membrane of cells. When it does, one kind
pore opens. Sugar from the blood can then enter the cell through the open
pore.
a) Imagine a mechanism that would allow insulin to open a pore. Draw a
diagram showing how insulin would open the pore.
cell membrane
b) People who are unable to produce insulin have diabetes. What problem
would be caused by not producing insulin?
Because insulin, a protein naturally produced by the body, is needed to open specific
pores in the cell membrane that allow sugar to enter into the cell, people that cannot
produce insulin will not be able to get sugar into their cells through the process of
diffusion. Without sugar, the cells will be unable to create the energy they need to
power the functions of other organelles in the cell.
c) What organelles within the cell would be most affected by a lack of
insulin? Explain your choice.
The mitochondria would be most affected by the lack of insulin because the
Mitochondria would not be able to get the sugar it requires to generate the energy
needs of the cell.