A Little Bit More
Although most of us know how important the smaller, less obvious organisms are to a healthy environment, we need to be reminded of this from time to time. The sun is our ultimate source of energy, but its energy must be captured by green plants before it can be utilized by animals. Surprisingly, it’s not the world’s forests or even grasslands, but tiny planktonic plants, that are responsible for the bulk of the world’s photosynthesis! What these tiny plants lack in size, they make up for in sheer numbers. Tiny animals, like copepods, use these tiny plants as food and provide an all-important link in the food chain for the larger animals living in the waters of the world.
Although planktonic animals and plants are generally thought of as an “ingredient” of saltwater, they’re an integral part of bodies of freshwater too. Plankton (singular or plural) consists of organisms, whether phytoplankton (phyto-plant, plankton-wanderer) or zooplankton (zoo-animal) in a kind of thin “soup” that is suspended in open water, floating at the will of the currents. Most of the world’s oceans and much of the fresh water is too deep for sunlight to reach the bottom, so photosynthesis by bottom-dwelling plants cannot occur. The phytoplankton, however, float near the surface where they obtain adequate sunlight for growth even above the deepest ocean or lake. So, even in the mid ocean, photosynthesis can occur in the upper reaches of the water column.
Activities
Science – What’s in my water?
Objectives: Clearer understanding of plankton in our water
Materials: Several identical, clear containers and various water sources
This activity is going to have a variety of outcomes depending on your water but I think it’s well worth doing, especially since it’s so simple. We’ve just discussed how our freshwater bodies of water contain plankton and this activity will provide an opportunity for you to see, or not see, the presence of phytoplankton in your own local waters.
Set up a series of water-filled glasses in a well-lit part of your classroom or home and see what develops. Select all the same kind/size glasses for this activity and make sure that they’re clear – not colored – so you can visually monitor any changes that may occur over time.
The water sources I’d recommend are:
• water from your tap or drinking fountain (likely to be chlorinated)
• water from a nearby pond or stream (scoop from the surface so you don’t get sediment)
• water from an active aquarium (if you have one at hand)
• distilled water (this may a bit difficult to acquire – chemistry dept or de-humidifier)
• water from a bottle of bottled water
• water from a well (this may be the same as tap water for you) not chlorinated
• rainwater might be interesting too. See if you can capture some rainwater directly as it falls, not water on the ground
1. Collect the various waters you’ve decided to sample and be sure to keep them uncontaminated
2. Fill identical containers (glasses, cups, or whatever that is clear) with each one of the water samples and then cover. You can use a plastic wrap to seal the top
3. Label each of the containers with the water it contains (we need to be sure we know the source for each container of water)
4. Place the containers in a well-lit area (probably best on a windowsill) in a row (all containers need to be available to the same amount of light)
5. On lined paper, make a chart that lists the different sources of water in the experiment down the left side of your paper and across the top, note a series of spaces for the dates as you monitor each sample
6. For each date that you monitor the samples, note the clarity of each of the containers ( these should be basically all the same on day one, although the pond/stream water may be a bit discolored) and place that information under your beginning date
7. This activity will require at least 2 weeks and best if it goes for 4 weeks (my own well water took only 4 days to show a hint of green growth on the bottom) to complete but it should be easy enough to monitor all of the samples daily.
8. Each time you monitor the samples, be sure to note any changes, as well as, no changes – negative results can be as important as positive results in science
9. Once you begin to see any kind of change (you’re most likely to see changes on the bottom or sides of the container first) in a sample’s clarity, be sure to note the color and clarity for each sample on your chart. As the time proceeds there should be some greening of the sides and possibly even the water as the phytoplankton become more numerous in some of the samples. You may find, however, that some samples never show any signs of change at all but that tells you something too.
Some questions you might want to ask:
Before you even started with the actual experiment, what might you predict? Water samples taken from places that were more “natural” are more likely to show phytoplankton growth sooner and denser than samples affected by chlorine or distillation
At the end of your activity, are all of the samples showing “some” sign of phytoplankton growth? If not, why not? It’s most likely that not all of the samples will show phytoplankton growth. This is most likely because there was little, if any, phytoplankton in the sample to begin with
As you look at the samples, are some markedly less clear than others? If so, why? Some of the samples should be less clear than others. As the phytoplankton grows and multiplies, it becomes more numerous and reduces the water’s clarity.
Probably, none of the samples will become very cloudy with phytoplankton. Why not?
Even in containers with a reasonable amount of phytoplankton, there will only be so many nutrients that will promote growth. It’s most likely that the growth in a given jar will reach a certain point and then greatly diminish.
If you wanted to encourage lots and lots of phytoplankton to grow in your sample, what might you do? You could put some fertilizer in the water to encourage rapid plant growth
Key Concepts
Food Webs /Food Pyramids, Identification, Life Cycles, Populations and Ecosystems, Predator/Prey Relationships
Questions
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