They're made of organelles. (If you want to see the rap we watched to introduce our new topic, you can check it out here.) Today, we started our unit on cells, the smallest unit of life. We talked a little about why the atoms and molecules we've been studying, while IN all living things, are not actually alive themselves, but cells, which can grow and reproduce and use energy are alive. We will go into depth about the different organelles found in the cell, but for today, we were mostly talking about the cell membrane, cell wall, and nucleus. The first activity we did was to make a slide of an onion skin and look at the onion cells under a microscope. They were all able to identify the cell wall and the nucleus in their onion cells. Then, the set up the Naked Egg experiment. I pre-soaked the eggs in vinegar which causes an acid-base reaction with the shell and leaves them with just the semi-permeable membrane holding the insides of the egg together. (You can try this at home--it just takes 2 days, changing the vinegar once in the middle--most of the kids seemed pretty fascinated by this phenomenon.) With the egg in this state, it makes a good representation of a cell. It has a membrane that will allow water and air to move through it, the clear part of the egg is like the cytoplasm in a cell, and the yolk is like the nucleus. We only very briefly talked about this in class, so you may want to go over the parts that are represented in the egg again. Next, the eggs were each placed in a cup and covered with either water, vinegar, or corn syrup. Each student made a hypothesis about how they thought the eggs might change depending on which liquid they are soaking in and they took them home to observe 24 hours later. We'll have a discussion in class next week about osmosis and how the egg/cell maintains homeostasis. Books: Life of a Cell, Andres Llamas Ruiz (available at the Livermore library) Videos: Cell Rap (we watched this in class) The Sci Guys: The Naked Egg and Osmosis--watch this after they have made their observations on the eggs they brought home. There are more activities to do with naked eggs if you'd like to try this again. We'll be talking about this next week when we discuss the cell membrane in more detail. Amoeba Sisters: Osmosis Amoeba Sisters: Inside the Cell Membrane Activities: Naked Egg experimenting--you can try out removing the shell of an egg, and then watch the Sci Guys video above for ideas on how to take the experiment we did another step farther.
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May 2020
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