17Mar2016 – 6th meeting of Pond Biology

This was a Snail Day (handing them out to take home) but we did manage some other topics too.

– Notes from class:

– We discussed everyone’s ponds and how the Daphnia are doing.
– Scientists who study biology, and more specifically ecology or environmental science, are very interested in how organisms get their energy and their carbon. Now why in the world is carbon so important? I asked the kids if they have ever seen a science fiction movie or read a story where humans were described as carbon-based lifeforms. And we are indeed carbon based, with carbon being the foundational element of life on Earth. Some of the students mentioned other important elements and molecules like oxygen, water, and hydrogen, and while it is true that they are very important, carbon is the basis for ALL life on earth. For example, there are lifeforms to whom oxygen is toxic (anaerobic bacteria, the bacteria that live in the heat vents in the bottom of the ocean), but there is no life form not made up of carbon building blocks on Earth anywhere.

No, this isn’t a trapdoor snail, but here are some links about your Japanese trapdoor snail:

USGS Fact Sheet about trapdoor snails
Wikipedia entry on the snails


In short,


make it from CO2 = autotrophs

obtain it from other organisms = hetereotrophs


make it from sun = phototrophs

obtain it from other organisms = chemotrophs

Back to energy and carbon: Scientists classify organisms based on how they get their energy (food) and their carbon. Let’s take humans again. How do we get our energy?
– The kids shouted out meat, bread, fish and other things. In short, we eat other organisms for our energy, things like plants and animals (and even fungi if you eat mushrooms or bread).. That makes us chemotrophs. Where do animals get their energy from? Well, other animals and plants. Again, animals are chemotrophs. Where do plants get their energy from? The kids shouted “The sun”! Exactly correct.
– Plants are pretty important for life on Earth because they are phototrophs, and make their energy from the sun, or more specifically, turns light energy into chemical energy (by splitting water into oxygen gas) that is then used to fix the carbon in a CO2 molecule to make glucose. Since they also grabbing their carbon from CO2 (carbon dioxide), they are also autotrophs.
– Guess what, we humans need to eat other organisms to get our carbon too! That makes us hetereotrophs (the stem “troph” comes from the Greek work “to eat”).


– We also spent a small amount of time talking about snails and the waste they produce (all those small black dots in the bottom of the bin were snail poop. What breaks down the snail waste? Bacteria and fungi. We spent some time looking at the snails before handing them out for everyone to take home. We had Japanese trapdoor snails and baby pond snails, and of course we ran out of the baby pond snails (much more popular than I thought they would be!). I will have to bring more trapdoor snails for the next meeting, since they are larger and easier to observe in a pond.

Extra Learning:
I only introduced these concepts in class, but there are plenty of resources with more information.
The Difference between a Autotroph and a Heterotroph – from Diffen.com

More Information about how plants make energy from sunlight:

A more detailed explanation of photosynthesis:

The chlorophyll converts light energy (photons) into chemical energy, in the form of high-energy electrons. This chemical energy is used to split 2 water molecules, producing 4 electrons, 4 protons, and 2 oxygen atoms, which combine to form oxygen gas (O2).

2H20 ā€“> 4 eā€“ + 4 H+ + O2

Where Does the CO2 Come In?

The chemical energy captured in step one above is used in step two of photosynthesis, that is, to convert CO2 into carbohydrates (sugars). This is called carbon fixation, a.k.a., the Calvin cycle, which takes place in the chloroplast stroma.


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