Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.
How do you obtain energy? Well, you probably know that you obtain your energy from the food you eat, but what about plants? How do they obtain energy? Unlike us, plants can use the sunlight to make their own food! And this is one of the main things that separates plants from animals.
The way an organism obtains energy places it into one of two categories, autotrophs or heterotrophs, or those that can make their own food vs. those that must eat food.
Both of these groups are important in our ecosystems. Without autotrophs, heterotrophs wouldn't have any food sources. Let's take a look at a food chain:
A food chain shows how energy flows from producers (autotrophs) to consumers (heterotrophs) to decomposers, who break down the energy so that it can be reused.
At the base of the food chain are autotrophs. Autotrophs are considered producers. Most autotrophs are green plants or algae, but we can throw a few cyanobacteria into this category as well. Many autotrophs use the process of photosynthesis to convert energy from the sunlight into carbohydrates, so they are called phototrophs. Pretty cool, huh? They don't have to eat food; all they need is water and sunlight! No worrying about their food running away or having enough money to buy it from the grocery store - the only thing they need to worry about is a cloudy day!
Because autotrophs are the producers, they are the ones that provide a food source for the consumers. As stated, they begin the food chain. And remember those carbohydrates? Well, that's what the consumers 'consume' to obtain their energy. You see, the producers produce the food, and the consumers consume the food. See how easy that is?
Now, all you have to remember is that producers who use photosynthesis are called phototrophs, which are a type of autotroph. Maybe you can think about it this way. Autotrophs produce their food automatically. And phototroph and photosynthesis both have the word 'photo' in them - because if I could make my own food using sunlight, it would probably be a pretty photo-worthy opportunity.
Okay, well, now that we have established what an autotroph is and what their role in the food chain is, let's take a look at the heterotrophs. Heterotrophs get their energy by consuming food from external sources. In most cases, this food is produced by an autotroph. Now, you may be thinking, 'But I get some of my food out of a box of cereal, or from a granola bar,' but the source of the grains in the cereal and the nuts in the granola bar come from green plants that once grew in some farmer's field. Even the cocoa beans that make up chocolate and the coffee beans that we roast for our coffee come from autotrophic plants.
But we humans aren't the only heterotrophs - in fact, all animals are heterotrophs in some sense. There are different categories of heterotrophs to keep in mind. Herbivores get their energy directly by consuming the primary producers, the plants, while carnivores get their energy by consuming the herbivores or other consumers. Some heterotrophs, like fungi, don't actually ingest their food - they absorb it. But, no matter how heterotrophs get their food, they are all dependent upon autotrophs for that food. And so as the herbivore consumes the producer, and the carnivore consumes the herbivore, and another carnivore consumes that carnivore, energy moves up the food chain.
But what happens when not all the autotrophs are consumed? Or when the consumers die without passing on their energy to another consumer? Where does the energy go? Well, their energy is passed onto another group of heterotrophs called decomposers. Decomposers get their energy by breaking down the dead remains of animals or their waste products or decomposing plants - all together called detritus. These are the recyclers of the food chain, preventing the buildup of detritus and recycling it back into the soil, where it can be reused or passed along to consumers who consume the decomposers. Some examples of decomposers include mushrooms and other fungi, insects, worms and bacteria.
And there you have it - a short look at how energy travels through the food chain! Remember, a food chain shows how energy flows from producers (autotrophs) to consumers (heterotrophs) to decomposers, who break down the energy so it can be reused. Each member of the food chain is essential.
The primary producers that start the food chain are the autotrophs. They convert sunlight into usable energy in the form of carbohydrates. These mostly include green plants and algae. Next up are the heterotrophs. They must consume autotrophs to obtain their energy and are therefore also called consumers. These include all animals from reptiles to humans. If the consumer is a plant eater, it is an herbivore, but if they consume other consumers - basically if they are meat eaters - they are called carnivores. But wait! We have another class of heterotrophs that consume dead or decaying material called detritus. These are the decomposers, and they help recycle unused energy back into the food chain.
After this lesson, you should have the ability to:
- Summarize how energy flows through the food chain
- Describe how autotrophs get their energy and provide examples of autotrophs
- Explain how the heterotrophs get their energy and describe the different types of consumers
- Define detritus and identify the decomposers' role in the food chain
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