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Evolution and Photosynthesis
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by Leslie Haines
Walter M. Williams High School
Burlington, North Carolina
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| | Evolution/Comparative Anatomy
Use this to help students understand the change in the architecture of the vertebrate brain over the course of evolution.
- Take a rectangular piece of bubble wrap (about 18 x 24; size not crucial) and roll it up jelly-roll fashion.
- Use two rubber bands to separate the roll into three sections, which will represent the forebrain, midbrain, and hindbrain (it's helpful if one of the end sections is a little larger than the other two; this will become the forebrain).
- Explain to students that this configuration represents the layout of the forebrain, midbrain, and hindbrain in early vertebrates (like in fish).
- As students observe, take the larger of the end sections, open it out, and fold it back over the other two. As you do this, double the two remaining sections up on each other, and smush them up so they fit within the first section (you should wind up with a ball-shaped structure, with the hindbrain and midbrain on the inside of the sphere, covered by the forebrain). As you are folding, explain that the forebrain has been enlarged and that the cerebrum in more recent vertebrates (like birds and mammals) has come down and enveloped the other two sections.
Photosynthesis: Photosystems and Light Reactions
Use this as a quick and simple way to help students understand how the arrangements of the pigments in the photosystems work to relay photons of light to the reaction center chlorophyll.
- Ask the class to imagine that each student represents one of the pigments found in the photosystem. Choose a student more or less in the middle (maybe one wearing green!) and tell them they are the reaction center chlorophyll.
- Pick up three or four tennis balls. Tell students that each ball represents a photon of light energy at a different wavelength.
- After warning them, toss a tennis ball to some student other than the reaction center student. Ask, "What happens next?" With any luck, they will say, "The energy is passed to the center," and will then pass the ball to the center.
- Do this three or four times, until the reaction center person is struggling to hold on to the balls. Ask, "What happens when the reaction center has more photons than it can handle?" Again, students should answer, "It loses an energized electron." At that point, the reaction center person will toss a ball toward the ceiling.
You can modify this by having the "pigments" stand at the foot of some stairs and placing other students at various levels on the stairs above; the students on the stairs would then represent the electron transport chain. When the reaction center person tosses the ball up, the first electron acceptor would catch it, pass it down the line, and so on. A second group of students could stand on an upper landing to represent the second photosystem, and so forth.
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