Grade Four, Life Sciences:
2. All organisms need energy and matter to live and grow.
b. Students know producers and consumers (herbivores, carnivores, omnivores, and decomposers) are related in food chains and food webs and may compete with each other for resources in an ecosystem.
The food chain is composed of decomposers at the bottom of the chain, followed by primary producers, primary consumers, secondary consumers, and at the top of the chain are tertiary consumers.
Starting from the bottom of the chain, the decomposers are usually found in soils. As you can see in the picture above, earthworms and fungi are just a few examples of decomposers. These organisms break down dead and decaying matter, carrying out this important process that allows the decaying matter to be turned into nutrients to be used by plants.
Plants are known as primary producers. They make their own food through a process called photosynthesis, using sunlight, water, and carbon dioxide to make sugar and oxygen. Species who only eat plants are herbivores.
Herbivores are also known as primary consumers. Insects, squirrels, and birds are some examples of herbivores because they only consume, or eat, plants.
Secondary consumers include carnivores, which consume only other animals, and omnivores, which consume both plants and meat. Secondary consumers got their name because they eat species that are dependent on plants. Some examples of carnivores are raccoons, snakes, and foxes. Humans are a good example of omnivores, since most of us receive our food from both other animals and plants.
Tertiary consumers, or top carnivores, are species that eat animals that are secondary consumers. These consumers are at the top of the food chain. Good examples of tertiary consumers are wolves and lions, since they eat animals that eat meat and/or plants. Think of wolf that eats a cat that ate a mouse.
Source: Image from: http://en.wikipedia.org/wiki/Food_web#mediaviewer/File:Trophiclevels.jpg. Creative Commons.
Simply stated, a food chain usually includes a plant, an animal that eats the plant, and a predator that eats the plant eating animal. In other words: producer→ primary consumer→ secondary consumer. An example of a basic food chain following this pattern is: grass→ rabbit→ hawk.
A food web is a more complex food chain. Food webs include every organism and how it is relate to other living organisms. Look at the picture labeled "b." Here, you can see how one organism eats several other organisms and is eaten by several other organisms.
Source: Image from: http://en.wikipedia.org/wiki/Food_web#mediaviewer/File:TrophicWeb.jpg. Creative Commons.
We need food for energy. We use energy to grow, move, and repair cells and tissue. Most living organisms use the sun's energy. This energy is transferred to the body by the food we eat. If you remember, plants produce their food using the sun's energy. When plants are eaten by primary consumers, they also consume the energy that the plant received from the sun. Let's use the example of the food chain below to understand how energy is transferred from organism to organism:
To visualize this, we can say that a plant has consumed 1000 units of energy from the sun. When the giraffe eats the plant, it takes in only 100 units of energy. The giraffe lost 90% of the energy. The lion then eats the giraffe. The lion also loses 90% of the energy, so it only consumes 10 units of energy.
This video gives us a visual of the food chain and food webs. Here, you will hear the definitions of the links that compose the food chain (primary producers, primary consumers, secondary consumers, and tertiary consumers). You will also see some examples of basic food chains, and an explanation of what a food web is. You will also be introduced to the energy pyramid.
Source: Video from youtube.com; makemegenious.com