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The food chain


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Created by MIT+K12.

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  • blobby green style avatar for user Philip Sagstetter
    Objection: At , the video says that destroying sharks would cause a large increase in seals. The many seals would destroy the fish populations beneath them, and the whole food chain would break down.
    Possible solution: I suspect that the seals would then mostly die off, and the whole food chain would grow back, with a few seals at the top. Like the current food chain has a few sharks at the top. Killing off most of the sharks, or any similar impact to the food chain, would produce initial chaos that would result in a new equilibrium of the food chain.
    But I don't mean to be critical. The video explains the food chain well for children, so I am probably nitpicking.
    (13 votes)
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    • leaf green style avatar for user Connor Mullins
      It is true that the food chain can repair itself when it comes to minor (and occasionally even major) disruptions, but if sharks were killed off to the extent where they weren't a huge predatory problem, the seal population exploded, the fish population was decimated, and the food chain was thrown out of whack, then even if stasis did return in the food chain, the whole set up of the ocean where seals live (and where they don't - chain reactions) would be changed dramatically. SO yes, equilibrium may return, but it would dramatically alter the way our world (yes, even the land) functions. There is only so much a system can handle before it breaks and has to reform in a new way.
      (15 votes)
  • aqualine ultimate style avatar for user ckontomaris
    Why are humans consumers (), if we have farms to make our own food?
    (3 votes)
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    • piceratops ultimate style avatar for user Quinn McLeish
      Good question. The reason is because we ourselves are not actually making the food. The plants we grow turn the energy from sunlight into glucose, which they use in order to grow. Although we do what we can to make sure the plant grows in favourable conditions, and to help it produce good quality food, it is still the plants that do the actual conversion of sunlight to food. We have to eat plants (and animals that also eat plants) in order to survive, whereas the plants are self-sufficient in terms of food.
      (11 votes)
  • leafers seed style avatar for user Krasen
    I still don't get why they aren't too many sharks, now they eat the others and get little energy transferred but how is that related to their population ?
    (4 votes)
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    • leaf green style avatar for user Eóin Brady
      Sharks are scraping the bottom of the energy barrel. The level of energy available to tertiary consumers at the top trophic level is not high enough to support a large population. If you can imagine that sunlight energy is trapped within photosynthetic plants and organisms, the stored energy is used for respiration, growth and repair, coupled with the energy of a consumer obtaining the producer and converting the food into energy and further respiring themselves 90% of the energy is lost, every time it passes aong the food chain. Fish, phyto plankton and seals all use the energy so the shark gets very little battery life from its prey. They must consume larger quantities of nutrients to sustain life, this creates competition. There is not enough food/energy to sustain a large population of sharks.
      (12 votes)
  • blobby green style avatar for user perliczka7
    I don't understand why the producers have the highest amount of energy? I mean, how does the energy level relate to the amount of calories? Shark meat certainly has more calories that seaweed, right?
    (2 votes)
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    • piceratops ultimate style avatar for user ninjazain
      The plant uses some of the energy it makes, then another animal eats what is left of that energy, using some of it, then yet another animal comes along and eats what is left of that energy. The only reason sharks might contain as much energy as a plant is because there are not that many sharks, all that energy is compressed into like 5 or 6 animals, so sharks have as much energy. Also keep in mind how much seaweed there is ( a lot) since there is that much seaweed and each of them has as much energy as a shark, the seaweed combined will have more energy. Also keep in mind how much a shark eats, a white shark can eat 200 lbs in a single meal!
      (4 votes)
  • male robot hal style avatar for user Isaac Zhao , " The 3.1415 Eater"
    At around to I don't agree, humans do make their own food, thus we are producers aren't we?
    (2 votes)
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    • aqualine ultimate style avatar for user ZephTzou
      Good question Issac. The reason that humans are not producers is because if we didn't have anything to eat, we couldn't "make" food out of thin air. Plants and algae, however, don't need to eat (except in the special cases of carnivorous plants). Plants and some algae make their own food by a process called photosynthesis. Basically, the plant makes glucose (a type of sugar) from light, water, and air. The glucose is it's food and it doesn't need to consume any other living thing for it. The basic definition is that any living thing that consumes, or eats, any other living thing is considered a consumer. Humans HAVE to eat to survive, so that makes us consumers!

      Hope this helps!
      (5 votes)
  • starky sapling style avatar for user Vivienne
    Endangerment could be stopped for many animals if humans didn't hunt endangered animals for nothing but money
    (2 votes)
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    • orange juice squid orange style avatar for user Mikayla
      I don't disagree with you, however think about they humans you are talking about. Most of them are from 3rd world countries and they only do what they do so they can provide for their family. I still think that killing animals that are endangered is awful, however I believe that using the suffering people as a scapegoat is also wrong. If people helped the people first, then I am positive that the endangered list would go down as well.
      (2 votes)
  • primosaur sapling style avatar for user IsaacGalaxyAurora798
    What about primary consumer, secondary consumer and beyond? What does it mean?
    (2 votes)
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    • starky sapling style avatar for user Carley R.
      the first consumer is the FIRST animal that's eats the producer, the secondary consumer is the animal that ate the first consumer who ate the producer so therefore the second consumer ate the first consumer AND the producer. The third consumer ate the second consumer, the first consumer, AND the producer. So the animal that ate the other animal ate the animals that that animal ate and he animals that that animal ate an so on if there is anything else that you don't understand tell me and I can explain whatever you don't understand.
      (3 votes)
  • purple pi teal style avatar for user Sophia
    Just a bit curious. What does photosynthesis mean?
    (1 vote)
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  • piceratops ultimate style avatar for user Joe
    If there is very little energy left for the top consumers how do they not run out of energy?
    (1 vote)
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    • piceratops ultimate style avatar for user Quinn McLeish
      There is very little energy for top consumers, but there is plenty availible to support life for a small population. If the energy supply for sharks suddenly increased, shark numbers would also increase. If it continues to decrease then sharks will gradually die out.
      (4 votes)
  • mr pants orange style avatar for user olivia arizabal
    we (humans) need to be careful about how we hunt .we are biting of more than we can chew by over hunting.that is why most speices are exstint!!
    (2 votes)
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Video transcript

- [Voiceover] Sharks are one of the scariest animals in the ocean and almost nothing else dares to eat them. But if nothing's eating sharks, then why isn't the ocean just overrun with sharks? We can answer the question with "food chains." Now to understand food chains, we first have to talk about food and energy. We eat food during breakfast, lunch, and dinner to give us energy. What do we do with that energy? Well first, we use that energy to do work, like moving boxes. Second, we use some of the energy to grow. Third, feel your skin. Is it a little warm? We also produce heat when we break down food, so some of the energy in the food is lost as heat. And finally, some of that energy is lost as waste. So remember, we use the energy in food to grow, do work, and produce heat and waste. Animals and plants also get energy from the food they eat, and we can classify them based on the source of their food. Producers are living things that make their own food like little factories. For example, plants like seaweed and microscopic plantlike creatures called phytoplankton in the oceans make their food by using energy from the sunlight and nutrients in the environment in a process called "photosynthesis." Consumers are living things that can't make their own food, and so instead they eat other living creatures. Humans are consumers, and so are sea urchins, sharks, fish, seals, and sea otters. Some living things only eat the waste or dead bodies of other creatures, and these are called "decomposers." Shrimp and bacteria are examples of decomposers. These different groups are connected by food chains. A food chain shows who eats whom in an ecosystem. It always starts with a producer because they can make their own food. Then this producer gets eaten by the first consumer, who gets eaten by the second consumer, who sometimes gets eaten by a third and a fourth consumer. For example, seaweed's eaten by the sea urchin, who's eaten by the sea otter, who's then eaten by the shark. Or the phytoplankton's eaten by the fish, who's eaten by the seal, who's also eaten by the shark. Notice that even though the animals might be different, the idea stays the same. The chain always starts with a producer and ends with a consumer. Why is that? Well the food chain doesn't just show who eats whom. Because we get our energy from our food, a food chain also shows the flow of energy from one creature in the chain to another. So a food chain always has to start with a producer because they can harness the energy in sunlight to make food. The energy in this food is then the source of all the rest of the energy that enters the food chain. But remember that living things don't just use the energy in food to grow and get bigger. We also use the energy to do work and produce heat and waste. But only the energy that's used for growth can be transferred through the food chain, since that's what's being eaten by the consumers. So in fact, only about 10% of the energy is transferred from one member of the food chain to the next. That continuous loss of energy means that if you look at the food chain in terms of how much energy gets to each member of the chain, you actually get a pyramid. The producers form the base of the pyramid because they make the food that's the source of the energy. Then with each member of the food chain, energy is lost as work, heat, or waste until very little remains for the top consumer. So remember that our model food chain was composed of the producer, first, second, and third consumer? Now you know why there isn't always a fourth consumer, and only very rarely a fifth consumer. There wouldn't be a lot of energy left for that animal. Now you also know why the oceans aren't overrun by sharks, even if there isn't a fourth consumer eating sharks and controlling their population. There just isn't enough energy getting to the third consumer level to support such a large population of sharks. Cool! Now you noticed that the shark was a top consumer in both the example food chains, and this is because in the real world, just like how you eat carrots, beef, and all kinds of food, other animals also eat many different things. For example, seals also eat squid and penguins, and seaweed's also eaten by fish and snails. So we have many different food chains all in the same ecosystem. We can then combine all these food chains to make a food web. Since a food web is the combination of the many food chains that exist in the ecosystem, it's a much more realistic picture of what goes on in the environment. Unfortunately, human beings have had huge and terrible impacts on the food webs in the ocean. One way we've done this is by destroying shark populations. Sharks are hunted either for their fins, which are eaten in shark fin soup, or killed accidentally as bycatch when trying to catch fish like tuna. Up to 100 million sharks are killed every year. That's a number bigger than all the people who live in Switzerland, Canada, Cambodia, Denmark, Australia, and Zimbabwe combined. This is bad because as we saw in our food chains, sharks are the top consumers. This means they keep the populations of other animals in check. So for example, killing all the sharks would mean more seals, who would need so much fish to support themselves that they would destroy the fish populations. The whole ecosystem would break down. So what can you do to save sharks? First of all, don't eat shark fin soup. And second, try to buy and eat fish that's been caught without bycatch. Remember, we've said that sharks are the top consumers, but in many ways, it's actually human beings, and we need to eat responsibly if we don't want to destroy the food chain.