I'm Ann from the Ontario Science Centre. I'm here with my daughter Sophia and my
son Nathan. Today we're going to be exploring bubble membranes a twist on
making bubbles. You're going to need some sugar, dish soap, water, cotton string,
measuring spoon, a teaspoon, scissors straws, a pencil, thread and a shallow
bowl. Sophia and Nathan are going to start by making the bubble solution
we're gonna make it in this measuring cup let's start with 140
ml of water, 10 ml of soap and 2 teaspoons of sugar. if you have a recipe
that has glycerin in it that would be okay too. I didn't have glycerin at home
so I'm using sugar. Give it a good stir and now they're gonna make the bubble
contraption. To make the bubble contraption, you cut a straw in half and you cut a
piece of string about the length of your arm. There you go,
about the length of your arm.
Thread the string through the two pieces of straw,
and then tie the string,
and then cut the hanging edges or the hanging threads all go and tuck the knot
into the straw. Perfect. Hold it up. So you get a rectangle like that. So depending
on the size of your bowl you'll make it a different size. Okay, so today we're
going to do a couple things. You have five tasks to do today. First, to create a
bubble membrane. Second, to put an object through the bubble membrane. Third, to
create a pore in the bubble membrane or a hole in the bubble membrane and to
create the pore or hole you'll need a piece of thread that's already looped.
It is easier to do it beforehand if your hands are going to be very soapy so
it is hard to create this loop. Okay put the loop create a pore on the bubble
membrane and then remove that pore so the membrane reforms. And the last thing
you're going to do is use a straw that hasn't been in the soapy solution to
make a bubble within the bubble. Sophie and Nathan are going to get you started
by creating a bubble membrane and then trying to put something through it.
Nathan's gonna try and put the pencil
through it. Oh hot dang it. All right, any other thoughts on how you might get the
pencil through it
Oh the tip poked it.
Nice. Oh alright, so see if you can get the entire pencil all the way through.
Nathan, can you show us your finger maybe leave the pencil for a second and show us how
you do that with your finger. Okay so Nathan can also do it with his
finger.
So what is going on here. Soap is an amphipathic molecule, which means it has
hydrophilic head or water-loving head that's attracted to water and a
hydrophobic tail which is attracted to fats. If we take the cross section of
the membrane and we look at how the molecules are arranged in the
bubble membrane, we can see that they line themselves up in two rows, trapping
water in the middle. The hydrophilic heads are pointing towards the water in
the middle and the hydrophobic tails are pointing towards the air on the outside.
If we want to pass an object through the membrane, only objects that are
chemically similar to the bubble membrane can pass through. So when the
pencil is dry and doesn't have soap on it, it pops the membrane and cannot go
through. However you saw that Sophia and Nathan added soap to the pencil, coated
the pencil in soap. Now the outside of the pencil looks like a bubble, has the
same chemical properties of a bubble and so when they put the pencil through the
membrane it went straight through the membrane without popping it.
Understanding this concept then allows you to do things like create a pore like
you did with the thread, removing that pore and also creating a bubble within a
bubble.
So how's a bubble membrane like the cell membrane? You and I and all living things
are made up of cells and cells are surrounded by a membrane that controls
what enters and leaves the cell. Membranes are made of molecules called
phospholipids. Phospholipid has a hydrophilic head and two hydrophobic
tails. Sound familiar? They are very similar to our soap
molecule, which is amphipathic. Phospholipids are also amphipathic. If we
look at the cell close up, inside the cell the phospholipids line themselves
up so that they're hydrophilic heads point towards the inside of the cell and
the outside of the cell, which are composed mostly of water and their
hydrophobic tails point towards the middle. They form this double layer. We
call this a phospholipid bilayer. This creates a barrier between the inside and
the outside of the cell and controls what enters and leaves the cell. Because
this molecule is very similar to the soap molecule, soap bubbles actually are
very similar to our membrane. They have the same consistency and they behave in
a similar way to our cell membranes. Just like in the bubble membrane, only
substances that are chemically similar to our cell membrane will pass through
the cell membrane. So here we've got oxygen. It is small and it's nonpolar,
which means it's not hydrophilic. Oxygen passes easily through the cell membrane
into the cell or alternatively it can pass from the inside the outside. However,
big molecules like glucose, which is also hydrophilic, can't pass through the
membrane, they actually get stuck in the middle layer of the membrane
where the hydrophobic tails are. Instead, they have to pass through a pore or a
channel so our cell membranes have pores or channels made out of proteins. So just
like you created a pore with the thread, here we've got a pore or a channel
through which the glucose molecule can pass. In terms of a bubble within a
bubble, the cell is exactly that. So the cell membrane is one bubble and inside
the cell membrane you've got a whole bunch of little bubbles the organelles. Each organelle is surrounded by its own membrane. So the mitochondria has a
membrane, the chloroplasts in plants have membranes, the nucleus has a
membrane. So your cell is a bubble within a bigger bubble. Bubbles: fun and
educational. For more information on this concept, please consult our companion
documents.