Microexplorations
Objectives:
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Students will compare structural differentiation in terrestrial plants to marine algae.
Students will recognize various young stages of aquatic animals and match them with corresponding adult
stages.
Students will identify living plankton and draw distinguishing features.
Students will describe adaptations plankton have to keep them near the surface of the water.
PRE-ACTIVITY:
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PLANT CELLS
Students will familiarize themselves with how to use a microscope.
Students will practice describing what they see under a microscope.
Students will apply what they see under the microscope to their understanding of cells.
Students will use collected plant material for later comparison with marine algae.
Materials:
Compound microscopes; lens paper; cover slips; microscope slides; forceps; Lugol’s
iodine; piece of onion; Elodea (Anacharis) leaf*; toothpicks
* Available at aquatic pet stores
Procedure:
ONION CELL
1. Obtain and clean the microscope, slide, cover slips, lens paper and a dropper bottle of
iodine.
2. Get a slide ready by placing a small drop of iodine in the center. Put the slide on the
side of you desk. Take care when handling the iodine. It is a stain, and will stain
your fingers as well as the cell.
3. Remove a thin, small piece of onion epidermis. This is most easily done by snapping
off a small piece of the interior of an onion section, then peeling off a single layer with
your forceps.
4. Place your section of onion epidermis in the drop of stain on the slide you just prepared.
If the onion becomes wrinkled, smooth it out using toothpicks. Lower the cover slip
over your specimen, and blot any excess stain with a paper towel.
5. Observe your slide under low power.
6. Switch to the next highest magnification. Adjust light if needed.
7. Draw a picture of one onion cell on your data sheet. ON your drawing label the
following organelles: cell wall, cytoplasm, and nucleus.
8. Using the fine adjustment knob, look carefully for “empty” spaces within the
cytoplasm. If you see any of these vacuoles, add them to your sketch. Also look
carefully at the inside edge of the cell wall. Can you see the plasma membrane that
encloses the cytoplasm? If so, add this to your drawing as well.
ELODEA LEAF
1. Remove your slide and wash it. Now prepare a slide of an Elodea leaf. Again, put a
small drop of iodine in the center of your clean slide. With forceps, remove one leaf
from the Elodea sprig and place it in the iodine on your slide. Add a cover slip and blot
away excess stain.
2. Observe your slide under low power.
3. Switch to high power magnification. Adjust your light for best visibility. On your data
sheet draw one Elodea cell. (Don’t forget to indicate the magnification used.) Label the
following parts of the Elodea cell: cell wall, cytoplasm, nucleus, and chloroplast.
4. Look carefully and try to see the plasma membrane and vacuole. If visible, add these
to your drawing.
5. Remove and clean slide.
PRE-ACTIVITY WORKSHEET
ONION CELL
(high-power)
1. Draw a picture of an onion cell.
2. On your drawing, label the following organelles:
cell wall, cytoplasm, and nucleus
3. Look carefully and try to find the
cell membrane and vacuole.
Add these to your drawing.
4. Draw a picture of an Elodea cell.
5. On your drawing, label the following organelles:
cell wall, cytoplasm, chloroplast and nucleus
6. Look carefully and try to see the
cell membrane and vacuole.
Add these to your drawing.
ELODEA CELL
(high-power)
ACTIVITY:
INVESTIGATING ALGAE AND ZOOPLANKTON
Materials*:
Compound and dissecting microscopes; MagiScopes; Petri dishes; Eye droppers; Plankton ID
booklets; Plankton sample; Kelp; Sea lettuce; Plankton handout; Colored pencils; Clipboards
Prepared slides; Masking tape; Magnets; Glue; Extension Cords; Power strips; Towels.
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All materials (except the terrestrial plants) can be provided by the S.E.A. Laboratory, however, if you have
your own microscopes, glue, etc., please let us know. We want to save our equipment as much as possible!
Procedure:
1. Prior to my arrival, the instructor will set up twelve stations. Study the Student Stations
handout I have provided. Stations that have the microscope symbol on them need to be
positioned near an outlet or in an area where an extension cord can safely connect the outlet
to the microscope. Plants you collected for your pre-activity should be placed in the
PLANT VS KELP station and prepared slides of plant cells should be in the PLANT VS
ALGAE station. Expect most of the stations to get slightly wet.
2. We will need to arrive early to setup microscopes and prepare slides with benthic algae and
phytoplankton from a plankton tow, mount prepared slides and lock microscopes in a
focused position to prevent damage.
3. The instructor will divide the students into groups of 2-3, one for each station. Each student
group will spend about 5 minutes at each of 6 stations. Students will complete a portion of
their worksheet at each station. Depending on teacher preference, the students can each
have their own worksheet, or they may complete one as a group effort.
A BRIEF DESCRIPTION OF EACH STATION IS LISTED BELOW:
PLANT VS KELP
Students will compare the EXTERNAL features of kelp to that of a plant. We will
provide the kelp and the instructor will provide one of the plants used in the preactivity.
PLANT VS ALGAE
Students will compare the INTERNAL features of green algae to that of a plant
collected in the pre-activity.
ZOOPLANKTON DON’T SINK!
Students will observe and describe the adaptations zooplankton possess that keep them
from sinking in the water.
PHYTOPLANKTON DON’T SINK!
Students will observe and describe the adaptations phytoplankton possess that keep
them from sinking in the water.
WHO AM I?
Students will be presented with larval specimens and adult specimens. Their task will
be to determine which larvae becomes which adult.
YOUR OWN PLANKTON SAMPLE!
Students will take their own samples from a previously collected plankton tow and
investigate for themselves the different plants and animals that are commonly found in
the plankton.
POST-ACTIVITY:
THE GREAT PLANKTON RACE
Materials:
One large aquarium (or 2- liter soda bottle with the lid cut off); Toothpicks; Washers;
“Plankton” Video*; Paper clips; Rubber bands; Several stopwatches; Yarn; Styrofoam peanuts;
Paper; Examples of possible planktonic forms*
 The S.E.A. Laboratory can provide these materials. Please return the video if you check it out.
Procedure:
1. In the classroom, students will design a plankton model from various materials. Point out to
students that each model should be constructed to sink as slowly as possible, but must not
float at the surface. They may also add eyes or other features to their model.
2. Students will take turns explaining the adaptations of their plankton to the class.
3. Students will place their models in the large aquarium just below the surface. Stopwatches
will be used to record the time each takes to sink to the bottom.
4. After all the students have “raced” their models, the top 4 with the slowest times will
advance to the semi-final sink off. Then, the top two go to the championships. Have
winners describe adaptations that led to their victory.
Follow up questions:
1. Why is important for plankton to be near the surface of the water?
Phytoplankton need to be near the sunlight in order to photosynthesize. This allows them to
grow and reproduce. Zooplankton need to be near the surface in order to eat the
phytoplankton! There are many zooplankton who live off the decaying matter that sinks
below the sunlight zone, but they still need a mechanism to keep from sinking. Those
that don’t end up at the bottom of the ocean and provide food for the organisms that
live there.
2. Why don’t they float on the surface?
Most plankton do not float on the surface because the UV rays would damage their
bodies and they would be more likely to be tossed around by waves. There is some
plankton that does drift on the surface. They are a class of plankton called neuston.
Examples of neuston include: The Portuguese Man-Of-War, the By-The-Wind Sailor
(another jelly-like animal), and bacteria that live on the surface film of the water. There
is also one insect called a water strider. It is the only insect that lives in the ocean. It is
closely related to the water striders that are common in lakes and ponds. The water
strider isn’t a marine animal in the strict sense because it cannot swim and will drown
if it falls through the surface, but it manages to live throughout the world’s oceans.