Intro Quiz: Impacts on Food Webs

Video: Impacts on Food Webs

﻿Hello, welcome to lesson four of the topic ecological relationships and classification. This lesson is called impacts on food webs. And in this lesson, all you will need is a pen and paper and a quiet space to be working. So make sure you've got no distractions around you and you've got everything you need in front of you. Pause the video now to make sure you've got those things. If you think you're ready, then let's get started and begin today's lesson. So in today's lesson, we're going to look at what interdependence is and then move on to biotic and abiotic factors and how these and other things impact food chains. And then we're going to look at the process of bioaccumulation before we do our end of lesson exit quiz. So the big question we're asking today is what will happen to us if bees become extinct? Have a think, pause the video, and have a write down of what ideas you might have and then we'll come back to this question at the end of the lesson and see how your answers have improved. So interdependence, as you should know, students rely on teachers for their education. But teachers also rely on students to be able to do their job. We say that these two populations are interdependent because they depend on each other for resources. For example, during lockdown when there were no teachers, the students found it harder to learn. And in the same situation without students, the teachers found it harder to teach. They depend on each other and so they are interdependent. In this example, the deer and the birds are also interdependent. The deer relies on the bird to keep its skin clean and free of bugs and the bird relies on the deer for a source of food because what it does is it picks and eats the bugs out of its coat. So what would happen if the deer population decreased? What would happen if the bird population decreased? Because they depend on each other, one change in one will have a big change in the other. In this example too, the flowers and the bees are dependent on each other. They are interdependent. Pause the video and think why, why are they interdependent? The reason is because the flower relies on the bee to help pollination and to help reproduce and the bee relies on the flower to get its pollen from it. One change in one will have a big change in the other. If the population of bees were to decrease, then the flowers wouldn't be able to pollinate. And if the population of flowers decrease, then the bees wouldn't be able to get their pollen. This, however, is not an example of interdependence. This is an example of competition between animals of the same species. And in this example, the mosquito only benefits from the human, the human does not depend on the mosquito for resources. So that is only a one-way relationship. So a question for you, which one of these definitions is the best for interdependence? Pause the video to select your answer, and resume to check. Well done if you picked option two! Interdependence is when organisms depend on each other for resources. Have a look at this example here. Is this interdependence? Why or why not? Pause the video, have a think of your answer. This is an example of interdependence. The squirrel relies on the nut for a source of food, but the nut also relies on the squirrel to help spread its seeds because when the squirrel eats the nuts and then it leaves via waste, then the seeds are spread into the surrounding environment. How about this one, is this an example of interdependence, and why and why not? This is not an example of interdependence. This is an example of competition because one, it's between the same species, and two, they're not relying on each other for anything. They're competing against each other in this example. And what about this one, is this interdependence? Why and why not? This is an example of interdependence. Now the clownfish relies on the sea anemone as a home and a shelter, somewhere that it lives. And the sea anemone relies on the clownfish because the clownfish scares off or eats other small fish that might eat the plants, the sea anemone. So this is an example of interdependence because they depend on each other. Now food chains and food webs can be impacted by a variety of different factors. Let's have a look at these. So some of these factors are biotic. That means living factors. And this includes food, predators, and disease. All these things are living things. But they can also depend on abiotic, non-living factors. Such as temperature, rainfall, light, and space. So biotic is living things, abiotic is non-living things. When you put an a in front of a word, it just means non. For example, symptomatic is when you've got symptoms. Asymptomatic is when you don't have symptoms. Typical means when it's normal and atypical means when it's not normal. So how about this one, is this a biotic or abiotic factor? Temperature, shout it out. That's an abiotic factor because it is non-living. Levels of oxygen, five seconds. It's abiotic, oxygen is non-living. A new virus. That one's biotic, because a virus is a disease and diseases are actually living things. The availability of food. That's biotic, because all food is coming from either animals or plants, living things. Space. Space is an abiotic factor. It's a non-living factor. What about if new predators arrived? Would that be a biotic or abiotic factor? That's biotic because a new predator is a living thing. So it's a biotic factor. So how do these biotic and abiotic factors impact our food chains and food webs? Well let's look at this example. Here is our food chain, just a simple food chain. The plants or the producer, the dandelion, relies on light for the process of photosynthesis to make its own food. Light is an example of an abiotic factor. So when this abiotic factor, light, was to decrease, then that would mean less photosynthesis would be able to happen and that would cause the dandelion population to decrease. That then has an impact up our food chain. Because if there are less dandelions, then there are less food for the rabbits so the population of rabbits would decrease. And then there's going to be less food for the foxes so the population of foxes would decrease. So one small change in one of these factors has big impacts up the food chain. And that's because those organisms are interdependent on each other. How about another example? Let's say a virus or a new disease arrives that targeted rabbits and it killed lots of rabbits. The population of rabbits is going to decrease. How is this going to impact the rest of our population? Pause the video and have a think. This is going to impact our population both up and down the food chain. Going up the food chain, the foxes would now have less food because the foxes eat rabbits. And so the population of foxes would also decrease. But the rabbits used to eat the dandelions and now there's less rabbits. So there's going to be an increase in the population of dandelions 'cause less rabbits are eating them. I want you to have a go at this one on your own. Let's say a new predator arrived that killed lots of foxes and it ate lots of foxes. How would this affect the rest of the food chain? You want to use the words increase and decrease in your answer. So pause the video as you write down an answer and resume once we're done. Let's check your answer, then. There would be a decrease in the number of foxes as they would be eaten. There would be an increase in the number of rabbits as they would have less predators. And there would be a decrease in the number of dandelions as more rabbits would eat them. Now if you wrote something different, just check why you wrote what you wrote. Because the numbers of organisms in food chains is constantly changing and although there might be these decreases and increases at first, other things would happen that would change it alter on. Just pause the video while you mark your answer and add anything in that you need to do. Well done if you got that right, though. That's really impressive. Good work! There are also human factors that can impact food web and food chains. On the screen are four images of human factors. Pause the video and see if you can work out what these factors are that have detrimental effects on other populations. Let's see how you did. So global warming, hunting or poachers, deforestation, and pollution are all massive things that humans do and contribute to that affect other populations of organisms and affect food webs and food chains. Here is a food web. Pollution means that not enough sunlight is able to get to the algae. Explain the effect on bacteria population. Well the arrow goes from the algae to the bacteria, which means algae is a food source of bacteria so if I've got less algae, I'm going to think, "Well, what's that going to mean for my bacteria?" Well, they're going to have less food. And I want to say use either the words decrease or increase in my answer so the population of bacteria is going to decrease. Let's check what the answer is. There would be a decrease in the population of bacteria because less sunlight would mean there is less photosynthesis of algae which is where bacteria get their energy from. Okay, so now it's your turn. Look at the food web. More and more barracuda are being hunted by humans to eat. First, I want you to explain the effect on the clownfish population, and then explain the effect on the zooplankton population. Again, you need to use the words increase and decrease, just like I did in the previous example. Pause the video as you complete this task and resume when you're done. Okay, ready to look at the answers? So for question one, there would be an increase in the population of clownfish because there would be less barracuda, which is their predator. Mark your answer now. Pause the video to do that, and then you can resume to look at the next answer. For question two, there would be a decrease in the population of zooplankton because there would be more clownfish, which is their predator. Again, please mark your answer. Well done if you got it all right. That's really good work! Make sure you're ready to move on. Have a look at this image. What is this farmer doing? This farmer is spraying a chemical over his plants. And we're going to have a look at what this chemical is. So pesticides or insecticides are sprayed over crops in order to kill unwanted pests. So it sprays a toxin, and what that toxin does is it kills anything that you don't want. However, there is a problem. Because some of these toxins are also absorbed by the crops and the plants. And what happens if the toxins enter the food chain? The primary consumer, in this example the slugs, then eats the producer and also gets the toxin in their system. This is because the toxin is not easily broken down. And it hangs around, it remains in the organism. You can see here that each of these four slugs has eaten three lettuces so they've got three doses of the toxin in them and because it doesn't disappear, it stays in their system and then is passed up the food chain again to our secondary consumer. So in our example here, the secondary consumer is the thrush and one thrush eats two slugs. So each thrush gets a dosage of six toxins from this pesticide. Six doses of this chemical is now in it because it hasn't been broken down. And the same thing will happen again. Our final top predator is the hawk, and one hawk eats two thrushes. So what amount of dosage is the hawk going to get? That's right, the hawk is going to get 12 doses, six times two, of this chemical, of these toxins. And this is really dangerous for our top predator. This is the process of bioaccumulation. The buildup of toxins going up the food chain. And as you can see, this has the biggest impact on the top predator. Have a look at the following statements. Are these statements true or false? If they're false, rewrite the statement so it's correct. Pause the video as you complete this task. Ready to mark your answers? Have a look at the answers. First of all check, did you get the ones false and true correct, and then when the ones are false, have you corrected your answer so it now makes sense? Pause the video and check your work. Well done, let's move on. Here is a task for you. Scientists measured the concentration of an insecticide in three animals and a microscopic plant called chlamydomonas. The food chain for these four organisms is shown below. In the food chain above, the heron contained the highest concentration of insecticides. Explain why. And there are some key words that you should include. Absorb, eat, insecticide, concentrated, broken down, builds up, bioaccumulation. Have a go at writing down an answer on your piece of paper. And pause the video while you do this and resume when you're ready to check your answer. Let's correct your work. This was my answer. So as you go up the food chain, the concentration of insecticide increases. This is because it is first absorbed by the chlamydomonas and the daphnia eat lots of these and pass it up the food chain. The insecticide is not easily broken down, so it builds up in the food chain. The fish eats lots of daphnia and the heron eats lots of fish. This is bioaccumulation. There is an increasing concentration of toxins with increasing trophic level. Mark your work. Make sure you've included all those key words and add anything you've missed. That's quite a difficult question, so well done for getting in some points from there. Remember this question at the beginning of the lesson? What will happen to us if bees become extinct? What I want you to do now is use everything that you've learned in today's lesson and see if you can answer that question. Has your answer improved from what you wrote at the beginning of the lesson? Pause the video and write down what you've learned. And well done, that's it! You have learned a lot today again, so well done for that lesson. And now all you need to do is complete the exit quiz and show off everything that you know, well done!

Worksheet: Impacts on Food Webs

Exit Quiz: Impacts on Food Webs

Completed: Impacts on Food Webs

This lesson looks at how changes in the environment can affect different organisms within a food web, including the process of bioaccumulation.

Science

Impacts on Food Webs

Introductory Quiz

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