KS3 Biology - Dependence on other organisms

In this video we're learning about dependence on other organisms. We'll look at what an ecosystem is and how organisms are interdependent. We'll see how energy moves through ecosystems and then look at why insects are so important in ecosystems. Let's begin with what is an ecosystem. An ecosystem is all the living organisms in an area and the environment itself. And when we say environment we just mean all the non-living parts like air, soil and water. The organisms we can see here, like this tree, bear, fish and algae, are the living parts of the ecosystem. Importantly, the organisms in an ecosystem are interdependent, which basically means that they all need each other to survive. In other words, if one organism is removed from an ecosystem, it's likely to affect all the other organisms in that ecosystem as well. For instance, if the algae died off, the fish would run out of food and die as well, which in turn means the bears wouldn't have enough food either and they could die themselves. Next, let's see how energy moves through ecosystems. Almost all energy in ecosystems originally comes from the sun. During photosynthesis, organisms like plants use light energy, usually from the sun, carbon dioxide and water to make glucose and oxygen. They then use that glucose to build bigger organic molecules like large carbohydrates and proteins. And so these organic molecules are basically used to store chemical energy. When other organisms, like animals, eat these plants, this chemical energy passes on to them. This is why almost all life depends on plants, because they make energy from the sun available to lots of other living things. Respiration, which is carried out by plants and animals, releases the chemical energy stored in food so that those plants and animals can use it for things like movement and growth. It uses glucose and oxygen to form carbon dioxide and water, and it also releases energy. Now, you can think of respiration and photosynthesis as almost exact opposites. The oxygen and glucose produced by photosynthesis are used in respiration, and the carbon dioxide and water produced in respiration are used in photosynthesis. This is another reason why plants are so important to ecosystems, as they make sure that there is enough oxygen in the atmosphere for respiration in other organisms, while reducing carbon dioxide levels as well. To finish up, let's take a look at why insects are so important in ecosystems. We know that many flowering plants depend on insects for pollination. This allows the plants to reproduce, and some of these plants go on to produce seeds, fruits and nuts, which act as a food source for animals and humans. This means the ecosystem functions normally. Without pollination, however, these plants can't reproduce, and as a result seeds, fruits and nuts aren't produced either. This means the ecosystem is disrupted because there's less food available to animals. In many cases, this is also likely to reduce human food supplies as well. If you haven't heard yet, you can find all of our videos on our website, cognito.org. You'll also find questions, flashcards, exam-style questions, and passpapers, and we track all of your progress so that you always know what to study next. So sign up for free by clicking here, or browse our playlist here on YouTube.