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Course: Middle school biology > Unit 5
Lesson 2: Matter and energy in foodwebsWorked example: analyzing a generic food web
We can analyze the arrows in a food web to identify producers, primary consumers, secondary consumers, and decomposers. Created by Khan Academy.
Want to join the conversation?
- Does this mean humans are decomposers? Because (usually) we would be the ones eating primary or secondary consumers but aren’t necessarily a regular meal for any other creatures.
I need answers…(8 votes)- Fortunately, we are not decomposers. We are: Omnivorous, Primary, Secondary, and Tertiary Consumers.(11 votes)
- you know this very much looks like the food web from analzing ocean food webs but without the fish and replaced with blocks.(11 votes)
- i understud BUT now im confused(5 votes)
- why cant the producers eat stuff(3 votes)
- They can use the sun as ingredients and use it to make their own form of food.(4 votes)
- Aren't there tertiary consumers, and apex predators, like lions, tigers, hawks, and bears, are you going to ignore those organisms?(2 votes)
- tertiary and apex predators are basically the same as secondary consumers- they eat other organisms(2 votes)
- I understand why the decomposer doesn't have an arrow coming out of it, but why couldn't organism 4 in this food web be an apex predator and that be the reason it doesn't have an arrow coming out of it? Is it because an apex predator will eventually die and be decomposed and therefore even an apex predator will have an arrow coming out of it?(3 votes)
- yes, i would think so(1 vote)
- Is there any animal that is a producer(4 votes)
- not many ppl know this but sea slug and leaf sheeps can make photosynthesis but need to eat a producer 1st (also i found out that a oriental hornets can make electricity neat)(1 vote)
- why does he give us little time to pause and think about it(2 votes)
- What does it mean if two arrows are pointing to two different oragnisms? For example, Organism A has an arrow pointing to Organism B, but Organism B also has an arrow point to Organism A. Is that even possible?(1 vote)
- I know they did not mention this, but i've seen food webs with "tertiary consumers". I cannot figure out what that is, Can someone help?(1 vote)
- Tertiary consumers are the consumers at the top of the food chain, or the apex predator, like a lion or tiger.(1 vote)
Video transcript
- [Narrator] What we have here
is a diagram of a food web that shows us how matter and energy are transferred between
organisms in an ecosystem. But it's a little bit abstract, they don't tell us what
these organisms are. They just say organism one, organism two, organism three, and so forth. But even this gives us some information about which organism are the producers, the primary consumers,
the secondary consumers, and the decomposers. So the first thing I want
you to think about is which arrows show us going from producers, I'll write it like, to primary consumers? Pause the video and think about that. Which arrows show producers
to primary consumers? All right, now in a food web, the giveaway that something is a producer is that it doesn't have
arrows coming into it, it only has arrows coming out of it. And so organism one is a producer. Organism five is also a producer. Where are they getting their
matter and energy from? Well, they're getting their
matter from the environment and the energy, in most
cases, is coming from the sun. And the things that eat the producers, those are primary consumers. So this is an arrow that
goes from a producer to a primary consumer. This is an arrow that goes from a producer to a primary consumer. And this is an arrow
that goes from a producer to a primary consumer. Now, with that out of the way, which arrows show us going
from a primary consumer to a secondary consumer? Pause the video and think about that. Well, I just said that these things that are consuming the producers, these are primary, I'll
just say P for primary, primary consumer. This is a primary consumer. This is a primary consumer, as well. Now secondary consumers are by definition things that aren't decomposers, but they're eating primary consumers. So they're going to have arrows coming in from primary consumers and out to either other secondary
consumers or to decomposers. So organism three right over
here is a secondary consumer. So we're going from a primary consumer to a secondary consumer. So this arrow is from a primary consumer to a secondary consumer. This arrow over here is interesting. It's a secondary consumer being consumed, but you can see that organism four only has arrows going into it, which is a pretty good clue
that this is a decomposer. So I'm not going to call
organism four a secondary, a secondary consumer. So let's keep going. What about the arrow that
goes from organism six to organism seven? That looks like primary
consumer to primary consumer. Well, it turns out that something can be both a primary consumer
and a secondary consumer. So this is also a secondary consumer. Why, because it's eating
a primary consumer and it's not a decomposer, so this is also another example of an arrow from a primary consumer to a secondary consumer. Last but not least, what are the arrows
that go from a consumer, that go from a consumer, to a decomposer? And we already broke
this down a little bit, no pun intended. Pause the video and try
to think about that. Well, this is the only decomposer that's depicted in this diagram, and so this is going from
a consumer to a decomposer, right over here. This is from a consumer to a decomposer, and that's all we have here. And to be clear, you don't have to go only from a consumer to decomposer. You could have gone from a producer straight to a decomposer. You could have arrows that
look like that, as well, because if a plant dies
and it gets decomposed, well, it's going to be,
that matter and energy is going to be used by that decomposer.