Dracula's Dinner

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Dracula’s Dinner

You have about 100,000 kilometres of blood vessels in your body—laid end-to-end, that’s enough to circle Earth 2.5 times! There are three different kinds of vessels: arteries, veins, and capillaries. Arteries carry blood away from the heart; veins carry blood back to the heart. Tiny hair-like capillaries connect the smallest arteries with the smallest veins. Capillaries are so tiny, red blood cells have to squeeze through them single file. You can use bath beads and a few other supplies to see how red blood cells fit through capillaries.

For a printable version of this project, click here.

Materials

• 3 big glass jars
• ice cream bucket, big mixing bowl, or sink
• salt
• food colouring
• box of wallpaper paste
• water
• Vaseline (petroleum jelly)
• funnel (The funnel we used had a spout with a 19 mm inside diameter. If you can't find one with this measurement, get one of your parents to cut an old funnel until it's the right size.)
• bath beads (see-through or clear ones work best)

Before You Start
In this experiment, the funnel acts like a capillary.
The round bath beads are red blood cells. Try to push a bath bead (blood cell) through the funnel (capillary). Right now the round beads will not fit through the funnel--if they do, your funnel spout is too big.

Instructions

1. Fill a jar with 2 cups of cold water.
2. Add 3 tablespoons of salt and a few drops of blue food colouring.
3. Fill a second jar with 2 cups of hot water.
4. Add 3 tablespoons of salt and a few drops of red food colouring.
5. Mix 1 cup of wallpaper paste with 2.25 cups of water in the third jar. The mixture should look like mashed potatoes.

Now you can experiment with the different mixtures to find out which ones help the bath bead (red blood cell) move through the funnel (capillary). Of course, put the funnel over a bucket, bowl, or sink so you don’t spill liquid everywhere. Before you start, try to figure out which mixtures will be the most helpful. (Don’t peek, but if you need any hints, see the Ideas below.)

Ideas

1. Try covering a bath bead with Vaseline. The bead gets pretty slippery, but it’s still larger than the funnel. Does the lubrication allow the bead to slide through the funnel without breaking?
2. Soak a bath bead in the cold (blue) salt water for a few seconds. The bead may contract a bit. Does it fit through the funnel? Or does it just dissolve and break?
3. Soak a bath bead in the hot (red) salt water for a few seconds. The bead gets squishy--like when you use it in a bathtub full of hot water. Is the bead squishy enough to fit through the funnel? What happens to the shape? Does it break?
4. Soak a bath bead in wallpaper paste for about 20 minutes. What does it look like now? The bead should look like a red blood cell—like a jelly donut. This shape is called a biconcave disc meaning it curves inward in the middle. As with a red blood cell, the bath bead’s great jelly-donut shape allows it to fit through the funnel (the capillary). Why? The cellulose from the wallpaper paste passed through the thin skin of the bath bead making the bead very squishy. But it's not any weaker so it doesn't dissolve like the others you tried.

A Step Further

Notice how the surface of the bath bead stretched after soaking in the paste. Even though the bead still has the same amount of liquid inside, the surface area of the bead increased. The large surface area and biconcave shape allow many more oxygen molecules to come in contact with the surface of the red blood cell making it an effective oxygen carrier.
Some people have a condition called sickle cell anemia. Their red blood cells look like crescent moons or sickles instead of like jelly donuts. Sickle cells can get stuck in tiny capillaries blocking blood flow to different parts of the body. There is not yet any cure for this often painful and sometimes deadly disease.