Last week, on Monday, students presented their cell models
(photos posted below). They were all very good! I noticed a few misconceptions
during the presentations, so we spent a few minutes reviewing some organelles.
Since we had the field trip to McLaughlin the Friday before,
I asked students to write two paragraphs about the field trip. The Knoxville
area, where we planted the seedlings, has an interested history so I asked the
kids to use this restoration project to illustrate John Muir’s quote: “When
we try to pick out anything by itself, we find it hitched to everything else in
the Universe.”
On Wednesday, I had three “stations”
for them. One was focused on microscopy, and the other two were worksheets –
origin of life on Earth and development. I was at the microscope station
talking to them about the parts of a microscope, showing them how to prepare a
wet mount, and helping them prepare a slide with a piece of elodea, and a slide
with their cheek cells (picture below). While one student was with me, the
others were working on their two worksheets in their classroom, with Chris.
This was the last “official” class covering cells. My goal was to have them
think about how the first cell evolved, and to get an initial appreciation of
development. This was the last “official” class because on Wednesday we will
discuss the worksheets (recall that they are due on Wednesday!).
We have covered all concepts of the 7th
grade standards concerning cells:
Cell Biology
1. All living
organisms are composed of cells, from just one to many trillions, whose details
usually are visible only through a microscope. As a basis for understanding
this concept:
a. Students know cells
function similarly in all living organisms. b. Students know the
characteristics that distinguish plant cells from animal cells, including
chloroplasts and cell walls.
c. Students know the
nucleus is the repository for genetic information in plant and animal cells.
d. Students know that
mitochondria liberate energy for the work that cells do and that chloroplasts
capture sunlight energy for photosynthesis.
e. Students know cells
divide to increase their numbers through a process of mitosis, which results in
two daughter cells with identical sets of chromosomes.
f. Students know that as
multicellular organisms develop, their cells differentiate.
Today we started the evolution/genetics
unit. I started by having them tell me what they knew about evolution. They
mentioned adaptation, human evolution, and inheritance. We had a good
discussion about how these terms are related to evolution, and then I provided
a definition, and an example of evolution by natural selection. The example was
about the peppered moth during the industrial revolution. We had talked about
this example before, and I was surprised to hear how many details they
remembered! I then talked to them about Darwin - his voyage, and observations
about the finches. I briefly mentioned that Darwin wasn’t the only person
working on the idea of evolution by natural selection (talked about Wallace), and we played a
natural selection game at the end of class. The purpose of the game was to
illustrate evolution by natural selection at two different levels – predator
and prey. Each student had a tool (2 had spoons, 2 had forks, and 2 had plastic
tweezers); we walked to a patch of grass by the parking lot where I had
previously thrown 100 colored toothpicks (25 of each color - green, yellow, blue and orange), and they had 5
minutes to find, and get toothpicks using their tools. Before leaving the
classroom, I asked them to predict the results. As predicted, colors that
could camouflage with the background (yellow toothpicks were blending in with
fallen leaves, and green toothpicks are hard to see in the grass) were the most
successful at surviving since only 8/50 were found. Orange and blue toothpicks
were more easy to spot – 28/50 were found.We spent the last few minutes of class discussing how this game is relevant to evolution by natural selection.
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| This is an aggregation of cheek cells. You can see the nucleus in most of the cells. |
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