6: Membranes (part 2: Membrane Transport) – Ellen McHenry's Basement Workshop

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If you want to split this long lesson into two lessons, there is a break in the video at 45 minutes. The first 45 minutes is about passive transport, and the last 20 minutes are on active transport.

The membrane is the barrier a cell uses to separate itself from the rest of the environment. It is important to bring useful things across this membrane to the inside such as food particles or water, and to remove waste from the inside of the cell to the outside. Membrane transport allows cells to maintain homeostasis, “eat”, send messages, etc.

1) DRAWING LESSON

64 minutes

Template page for drawing 6

Info pages for drawing 6

Finished drawing sample for lesson 6

2) ACTIVITIES

Activity 6.1 – Diffusion through a membrane

NOTE: This demonstration will take at least four days.
You will need:
• an egg (or several eggs, if you want to have “back-ups”)
• a glass (or small jar) of vinegar
• a glass (or small jar) of corn syrup (or you can substitute honey or pancake syrup)
• a glass of water
• a piece of string (for measuring the circumference of the egg)

What to do:
Put the egg into a glass (or jar) of vinegar. (You may want to cover the glass or screw a lid on the jar in order to avoid the constant smell of vinegar.) Let it sit for a day or two until the shell of the egg has been completely dissolved and the egg has nothing but a soft membrane around it. At this point, be very careful when handling the egg. Remove the egg from the vinegar and rinse it off. Gently wrap the string around the center of the egg and make a mark on the string to indicate the size of the egg. You might even want to lay this piece of string on a ruler and get the measurement in centimeters or inches. Then put the egg into the glass of syrup. Again, let it sit for several days. Take the egg out and measure it again. Did it get bigger or smaller? Can you figure out why? Now put the egg into a glass of water and let it sit overnight. Take it out and measure it again. What happened?

What is supposed to happen:
The egg should get smaller after sitting in the syrup because the water will diffuse out of the egg and into the syrup. The concentration of water is higher inside the egg than outside, so water will flow out. The syrup molecules would like to diffuse into the egg where the concentration is lower, but they cannot because they are too large to go through the membrane. After the egg is taken out of the syrup and put into water, the concentration of water is greater outside the egg, so water will diffuse back into the egg again.

Here are some video links that can help you: