00:01
So for this question, why don't we start out with asking ourselves? because the question is saying that some factor limits the length of food chains, why don't we ask how long food chains are typically? and i'm sure you can come up with a couple of examples on your own.
00:17
But for this one, i have a pretty basic, like usually at the first level, you'll have your primary producers or your plants in a terrestrial biome, like grasses or flowers or cereals, something like that.
00:35
And then those are consumed by herbivores.
00:38
And then herbivores are consumed by carnivores.
00:41
And sometimes there might be another step in here with the omnivore potentially.
00:50
They could also be here as well.
00:56
And there could be a higher predator or like an apex predator who could consumes this predator here, this carnivore.
01:05
But typically a food chain isn't going to be that much longer than between like three to five organisms.
01:11
At some point it becomes unsustainable.
01:14
And now our question is, why might that be? that's the question at hand in our textbook.
01:22
And when we get there, before we get there, let's really think about what exactly is being transferred in a food chain.
01:32
And what i mean by that is why do we eat? what do we get from food? and what do plants get from the sun? well, energy.
01:43
We eat because we need the energy that's in food and suns or, excuse me, plants under go photosynthesis in order to get energy.
01:53
So at each level here of consumption, we're seeing some sort of energy transfer between trophic levels.
02:02
That's what each of these stages are.
02:05
And so now that we have that, let's start out with, okay, this is a transfer of energy.
02:10
We know from the laws of thermodynamics that no energy transfer is totally efficient, meaning some energy is always lost as heat or usually heat, not always, but that's the main way.
02:26
So we do know that energy is going to be lost between these levels.
02:31
And then we also need to think where does this energy come from? well ultimately all the energy in the system comes from the sun because in this we're using a terrestrial bio for simplicity's sake in this case the primary producers take in light energy from the sun and because they are the primary producers they are the only organisms that can in this ecosystem take in energy from the sun and not from the consumption of other organisms in order to make their own energy, this is the source of all of the energy in the system.
03:10
So in this stage, technically there should be a little bit of sunlight coming in too.
03:18
And so plants get this energy from the sun.
03:22
They take in light energy and as they undergo photosynthesis, they convert then to chemical energy.
03:28
And they store this kind of chemical energy and they use it for themselves.
03:34
To grow, to reproduce, to do all of the basic functions that they need to do as organisms.
03:40
So that actually extends some energy...
