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1.5.1 Phytoplankton "See the Light"

Materials

  • 2 glass aquaria or two 1-liter glass jars
  • 1 liter of tap water (or pond water if available)
  • dried grass or hay
  • medicine dropper
  • grow lights

Engage

Ask students what they remember about the oxygen cycle-most early elementary students are familiar with photosynthesis as the oxygen/carbon dioxide exchange between plants and animals. There are no trees in Antarctica. So, where's the oxygen coming from? Encourage speculation.

Explain/Explore

At the lowest end of the food web are phytoplankton, the "food" of tiny marine animals, particularly krill. Phytoplankton make their food through photosynthesis. Fueled by the energy of sunlight, they convert carbon dioxide and water into simple, sugary food. During photosynthesis, they release oxygen as a waste product. They also incorporate carbon dioxide.

Length of day and extent of sea-ice cover are both important environmental factors given the extreme seasonal cycles. Depending on the latitude, there may be enough light for the microscopic plants to grow in the winter; they only need about four hours of daylight. The amount of light that the plants receive depends on:

  1. the amount of light reaching the liquid water (thickness of ice/snow cover)
  2. the "mixed layer depth," or how well the top layer of the ocean is "mixed" based on the effects of weather (wind, air temperature) and sea-ice cover (melting and freezing cycle). See Activity 1.4.3.

Procedure

Create a phytoplankton culture in a hay infusion:

  1. If using tap water, allow it first to age in an open container for several days.
  2. Prepare a hay infusion in two identical glass aquarium tanks or a 1-liter glass jar containing equal amounts of water and an amount of fresh cut hay or grass (not cut by a gas mower).
  3. Using grow lights hung over the tanks, expose one (the light treatment) to 24 hours of continuous light, and the other (dark treatment) for only four hours during the school day, with all light blocked off by opaque material during the remaining hours.
  4. Record differences observable in the color of the water-greener will indicate more growth. Photos or video may be taken to keep track of color changes: be sure to indicate a descriptive "slate" with the date in the shot for later reference.
  5. Record findings in a brief lab report: conditions; variables; results; conclusions.

(NOTE: Sometimes the plants run out of nutrients in culture so students may have to add new hay to the infusion)

Expand/Adapt/Connect

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Go on-line to see Robin Ross' suggestions for how to add "grazers" to the environments, when North American spring permits. And also to find data to compare and contrast hours of daylight as winter becomes spring, and plot this with analogous records from Palmer Station.

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Have students plot daylight hours on maps, comparing and contrasting results from various classes participating in LFA 2.




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Last Update: 1/18/97
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