A Little Bit More
When we think of the natural world, we automatically think of the larger animals and plants that we can easily see. Although we know intellectually how important the smaller, less obvious organisms are to a healthy environment, we need to be reminded from time to time just how valuable they are.
The sun is our ultimate source of energy, of course, 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. The tiny animals, like the copepods, which use these plants as a food source, thus provide the all-important second link in the food chain for the larger animals living in the waters of the world. Together, these tiny plants and animals are truly a life support system.
Although plankton are generally thought of as a product of saltwater, they’re an integral part of freshwater too. Plankton (singular or plural) consists of organisms, whether phytoplankton (phyto-plant and 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 and are able to obtain adequate sunlight for growth well above the deepest oceans of the world.
Activities
Science – Grow Your Own
Objectives: Opportunity to see a mini ecosystem
Materials: Aquarium or pond water, quart jar, dried grasses or aquatic plant material, and magnifying glass, hand lens, or dissecting scope
This is an easy-to-do activity that will help open students’ eyes to a rarely seen dimension of our natural world. If a child ever wondered how tiny fish and tadpoles, for example, ever find small enough food to eat, this exercise will help answer that question.
It’s possible to create your own mini ecosystem in a jar with just a little preparation. The organisms you end up with are smaller than copepods but will give students an idea of some of the tiny organisms that support the food chain for small animals. These organisms are often used by aquarists as a first food to feed baby fish until they’re large enough to eat other kinds of larger foods like copepods, daphnia, and brine shrimp.
1. To get this started, the whole process will be speeded up if you use some water from a fish tank or local stream or pond that already has plenty of organisms living there (but there will be too few to see easily). Don’t use tapwater as this has chlorine and will kill your organisms. Getting a bit of yucky stuff along with the water will probably ensure that you’ve gotten plenty of “starter material”.
2. Place your water along with some dried grass, chopped cabbage, lettuce leaves, or chopped up aquarium plants in a glass jar (quart jar is plenty big) and place in a warm part of your room. Avoid placing the jar in direct sun as this may heat up too much.
3. Keep an eye on your jar and figure on about a week to determine whether your culture is growing. You’ll know it’s full of infusoria when the water looks cloudy. If you shine a flashlight through the water, it’s easy to see the clouds of minute organisms swirling in the water.
4. Once your jar is full of organisms, you can place a drop of water on a slide and view with an hand lens, magnifying glass, or place beneath a dissecting scope for a really good look. However you choose to view these organisms, it should be readily apparent just how small they are and how they can serve as food for the many larger-but-still- tiny creatures that live in an aquatic environment.
One Step Further: A few questions you may want to ask
Where did all of these organisms come from in the first place? The water you collected already had some of these organisms present but they were in small enough numbers so you couldn’t easily see them in the water
Why do you think we put some kind of plant material in the water? The plant material, whether from the water or even dried grasses, had live or encysted organisms on their surfaces that helps to “seed” the mini environment. The plant material also serves as a food source for all kinds of organisms. As always, there needs to be a prime source of energy in any “environment” and the plants acted as that source.
Why were there so many organisms in the jar after only a week? Most of these tiny organisms grow and reproduce extremely quickly. Within a week’s time, if the environment is suitable, their numbers have grown to many times the original population.
What would happen if we left our quart jar sit on the table for many weeks? The infusoria would reproduce to a point where they’d overpopulate the space and die either from lack of food or from their own waste products.
Why don’t we see large concentrations of these organisms in the wild? In the wild, these populations are constantly being depleted by other organisms. It would be very unusual for their numbers to reach the same level you have in your jar of water.
Key Concepts
Food Webs /Food Pyramids, Growth and Development, Populations and Ecosystems, Predator/Prey Relationships
Questions
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