Hi. It’s Mr. Andersen and this is environmental science video 8. It is on energy flow in ecosystems.
In the last video we talked about the importance of producers producing food that is consumed
by consumers. But we did not talk about where that energy comes from. What is the major
energy source on our planet? It is going to be the sun. And this model also does not show
that we are losing energy to heat at each step along the way. And so a better model
is an ecological pyramid that looks like this. And so the producers on our planet produce
food, make energy usable. Where did that energy originally come from? It came from either
the sun or chemicals. And so all plants do photosynthesis and so they are taking energy
from the sun and putting it into the energy of the bonds of the food. Now some chemosynthetic
bacteria can do the same thing with chemicals, like hydrogen sulfide. They are making that
energy usable. Now once they have made that energy usable they can respire it. And so
can all of the consumers that sit above or below them on this trophic level. Now we measure
this amount of energy that is converted through productivity in one of two ways. Either gross
primary productivity or net primary productivity. Gross is the overall amount of energy converted
and net is just how much the plant gets after it uses some of the energy for respiration.
Now each of the levels within this food chain are going to be a trophic level. And we are
losing energy along the way and so a good way to measure this is using an ecological
pyramid. We can measure the efficiency, in other words how much energy makes it to the
next level. We can measure the energy at each level or we could measure the biomass, how
much living material do we have. And so energetics is the study of how energy gets from something
like the sun into organisms. What is the most important first step is going to be photosynthesis.
In photosynthesis we take carbon dioxide in the air, water, and energy and sunlight and
we convert that into oxygen and glucose. If you have not memorized the equation for photosynthesis
now is the time to do it. You should know what is going into the reaction and what is
coming out of the reaction. And why that is important is we can simply turn the arrow
around and now we have the equation for cellular respiration. So that is what you are doing.
You are taking in the oxygen that is produced by plants, taking in the sugar and you are
converting that into carbon dioxide and water. The nice thing is that this can be recycled
again back into plants. And so this is really how we take energy, put it in plants, store
it in the food so we can utilize it as well. Now one major misconception is that plants
are doing respiration as well. They are making the sugar for themselves to release that energy.
Now something very similar to photosynthesis is called chemosynthesis. And so if we look
down deep in the oceans at these hydrothermal vents we are producing not only heat but we
are producing a chemical called hydrogen sulfide. Also methane can be used this was. And so
certain chemosynthetic bacteria, look how similar this is to photosynthesis, can use
the energy in the bonds of the hydrogen sulfide to make glucose. They release water and then
sulfur. And so the equation looks very similar to photosynthesis. Now what happens is things
living around the chemosynthetic bacteria can take in that glucose and they can use
oxygen to do cellular respiration. And so we have a totally different system. It is
built on the energy inside the chemicals. So no matter where the energy comes from we
can measure the amount that gets into the producers using productivity. Now the bad
news is that hardly any of that energy actually gets into the plant. Ninety-nine percent is
going to move through it, bounce off of it. The plant does not get it. Only one percent
actually goes into the producer and we call that the gross primary productivity. It is
the amount of energy that the plant actually gets. Now what is the plant going to do? It
has to survive. And so it is doing respiration. That is where most of the energy goes. And
a small percent of it goes to what is called the net primary productivity. That is the
amount the plant gets if we subtract the amount that it used for respiration. So the bad news,
not much energy goes into the producers. What is the good news? There is so much energy
contained within the sun. If we look at the productivity on our planet we could compare
different terrestrial and aquatic biomes all the way from the tropical rainforest which
has high productivity. We are measuring that as the amount of material per meter squared
per year all the way down to something like a desert. It is not very productive at all.
What is interesting is cultivated land actually does not produce that much. We could compare
that to aquatic systems like coral reefs which are incredibly productive. We could even look
at how it changes over time. So this is net primary productivity. So this is terrestrial,
on land. And watch what happens as it changes over an eleven year period of time. You could
see that is just moving back and forth. It is moving from the southern hemisphere to
the northern hemisphere. You can see there is no production in areas where we have massive
deserts. But what is causing that change? It is simply going to be the seasons. During
the summer we are going to have way more production where there is way more sunlight. And so an
accurate model of measuring how energy is used is an ecological pyramid like this. And
so what we are really looking at here is the net primary productivity, the amount at this
level. And so if we start here with the producers, let’s say that that small percent is actually
one hundred percent, what percent goes to the next level? Well we are losing energy
at each level. And that is because the organism has to survive. It does respiration so we
are losing heat at each level. And so in general, of the one hundred percent that the producers
get only ten percent goes to the next level. What percent of this goes to the next level?
Ten percent of that. So now we are down to one percent. And what about the next level?
Ten percent of that. And so we are losing a huge amount of energy at each step along
the way. And that is going to be why we have way less tertiary consumers then we are going
to have producers in an area. A good way to study this is using an energy pyramid. And
let’s look at an actual energy pyramid from Silver Springs Florida. What we are looking
here is the amount of energy. They are measuring it in kilocals per meter squared per year.
And so it is 20,000 kilocals. Now where is the energy found? Just looking at this picture
it is going to be for the most part in these trees. What amount makes it to the next level
to the consumers? Well when they studied it, it was this amount. So what is the ecological
efficiency? What amount made it to the next level? Well you could just take this and divide
it by that. And we could find that sixteen percent moved to the next level. We could
look at the secondary consumers. You can see it is around ten percent there. And we could
look at the tertiary consumers and you can see that it is around five percent. And so
ecological efficiency is going to be somewhere between five and twenty percent depending
on how efficient that ecosystem is. Now what are we really missing on this energy diagram
are the decomposers. They are going to make use of a lot of the energy as well. Another
way to measure it is biomass. Just how much material is made. What is different here that
we do not measure it over a given period of time. We measure what is called standing crop.
It is the amount that is there at one point in time. But you can see the same thing occurs
if we are looking at a Wisconsin lake or a field or a coral reef the amount of biomass
that we have at the producer level is going to be way more than what we have at the levels
above it. And so did you learn the following. Can you fill in all the blanks? Pause the
video. If not I would say the energy comes from chemicals through chemosynthesis to producers.
We could measure productivity as gross or net primary productivity. How do we utilize
that energy? This would be respiration all the way down to heat. We then have the trophic
levels. Those are going to be the feeding levels. Ecological pyramids measure efficiency.
And we can also measure the biomass. And I hope that was helpful.