I was in the middle of this nice little picnic lunch, staring down at the best-looking blackberry and thought, where did this berry come from? The store, duh. But like, how did the berry get the energy to grow and become a berry?
And how does consuming this berry give me, or any other animal, energy? Let's find out together in this episode on the cycling of matter and flow of energy in an ecosystem. Sometimes we just look at a thing and say, well yeah, Blackberry bushes grow blackberries and I get to eat them.
But how does the plant grow the blackberry? And how is it now a little snack pack of energy for my lunch today? And when it is consumed, does it just go away? These are a lot of questions and this episode is full of a lot of information, so feel free to pause and deep dive into any of the topics that pop up here from time to time. Today we are going to look at how stuff changes into other stuff.
but never really leaves, and how energy from the sun ends up powering this human, or this shark, wolf, or hawk. Let's first look at how matter cycles through an ecosystem. In physics, we learned that the law of conservation of mass states that matter can neither be created nor destroyed.
We can see this happening in an ecosystem. The best place to start is with something like composting for a simplified example. First, plant material here is growing on a farm.
The plants are getting matter from the soil, and they're also getting matter from the air or atmosphere. Carbon dioxide is being pulled from the air, and nitrogen and water are being pulled from the soil. This water, nitrogen, and carbon dioxide doesn't just go away. This matter is combined to make living matter or biomass and is conserved.
The amount of matter that we have before and after is going to be exactly the same. Once this plant material dies, if it's not eaten, it can be placed in a pile, something like this, where it is being composted. The plant matter is being returned to the environment.
Decomposers like worms and bacteria are really good at breaking down all of this waste. Some of this matter goes back into the atmosphere and a lot of it becomes part of the future soil to use to grow the next crops and the cycle starts over again. This cycle doesn't just apply to plants.
When animals, including humans, eat plants like this blueberry, the matter becomes part of us. Through our waste products or when we die, that matter is going to be returned to the environment. Let's take a closer look at this process and add in a few more steps.
Organisms in an ecosystem fall into a trophic or nutritional structure, each organism falling into a certain place on the food chain. For most ecosystems, the main source of energy is the sun. This is because all of our lovely plant friends are autotrophs, basically superheroes who can gather up the sun's energy and through a process called photosynthesis, make little snack packs of chemical energy.
Pretty much everyone relies on these guys and for that reason they are called primary producers. The primary producers make energy from the sun usable for everyone else. They take carbon dioxide and water, and convert them into oxygen and sugar, or glucose, using the sun's energy. Among other processes, the plant uses these components to grow and become more… plant. So these guys are here at the beginning of the food chain.
This plant biomass, its matter, and the energy it has stored in its chemical bonds, then gets transferred to the next organism, the one who consumes the plant. A heterotroph, like a grasshopper. Or a mouse. Or caterpillar.
Or a rabbit. These herbivores are called primary consumers, the first consumers. So now, the plants are eaten, but the plant matter and energy still remain. And the way to acquire that energy is to, you guessed it, consume the primary consumer.
Carnivores have entered the chat. Secondary consumers like spiders, snakes, and birds are the next link in our food chain. And if an ecosystem is big and healthy enough, it might be able to support a higher level of carnivore who eats carnivores for some of that passed down solar energy.
Animals like owls, wolves, or alligators are called tertiary consumers and usually no one is consuming them. Except truly we and all of our waste end up back on the decomposer's dinner table. This is usually how matter cycles through an ecosystem from the producers to the consumers then back to the decomposers.
But would it even be an ecosystem if things were that simple? I think not. Food chains aren't a great example, because birds don't just eat caterpillars. They eat grasshoppers, and worms, and all kinds of other stuff.
Food chains would be like thinking humans only eat nachos. Although delicious, I would really miss salads, and pizza, and mac and cheese. Because of this, ecosystems are really made up of food webs, which are multiple food chains that interact together.
See? Complicated. It's important to note that not all food webs are the same. The size and scope of a food web in an ecosystem is directly impacted by things like water and temperature and the amount of sunlight those plant friends are getting.
A food web in a forest ecosystem might look something like this. A variety of primary producers are supporting a variety of primary and secondary consumers. So in this food web there is enough food or energy to support a tertiary consumer like this great horned owl.
But in contrast, a desert ecosystem might have a food web that looks more like this. The primary producers are limited by the lack of water. This means that there are less primary consumers because there are not enough primary producers to support a larger population. And that leaves even less secondary consumers. So at this point, we understand that matter isn't created or destroyed.
It just moves around this ecosystem from one organism to the next in and out of the soil and the atmosphere. But what about the energy that comes from consuming this matter or biomass? If you're still here liking this video, let us know. And hit that subscribe button so you never miss an episode.
The energy flow in an ecosystem follows the laws of thermodynamics. Energy cannot be created or destroyed in an isolated system. However, it can be converted from one form to another.
This energy conservation is never really totally efficient, and most energy is lost as heat. Energy flow is moving in the same direction as matter in our food chain or food web. But because organisms are using some of this energy to live, it gets released back into the environment more quickly. Let's take a look back at our simple food chain to better understand.
We've already looked at photosynthesis and understand that plants are able to take material or matter from their environment and make biomass or more plant. Photosynthesis takes in water and carbon dioxide and with the energy from the sun makes sugars or glucose. But why does the caterpillar eat the plant?
How does it get energy? Well, we can simply turn the arrow around and now we have the equation for another process called cellular respiration. Those sugars are going to be combined with oxygen in animals like the caterpillar.
The caterpillar is basically going to rearrange the sugar and oxygen into water and carbon dioxide through cellular respiration. During that rearranging, chemical bonds are broken, releasing energy. Deep diving into this process is for another episode.
The caterpillar is then able to use that energy to grow, to go through metamorphosis, reproduce, and it also stores some of that energy in its own biomass. This is the energy that the secondary consumer, the bird, will get when it consumes the caterpillar. This process also repeats with the tertiary consumer, when the owl consumes the bird. When the owl dies, there is still energy stored in the biological molecules.
That energy doesn't just disappear. The decomposers take all of that leftover energy and make use of it to live and reproduce. As energy gets passed along from one place to another within an ecosystem, it's not in a particularly efficient way.
When energy transfers from plant to caterpillar to bird to owl, most of that energy is lost along the way. To understand, let's take a look at the trophic or nutritional pyramid with our same food chain friends. So let's look at our caterpillar.
Let's say the caterpillar only has one calorie of energy in its biomass, to gain that one calorie it has to consume 10 calories of leaves. So where did all of those missing calories go? Some of the energy was lost as heat through cellular respiration. Then the caterpillar uses some energy to grow. Some of this energy gets pooped out.
It needs to move around. You know, do caterpillar stuff. So then only one calorie out of the 10 consumed is actually left over as the caterpillar squishy stuff.
This continues going from one layer to another. Only 10% of the energy gets transferred or stored in the next layer. This is called the 10% rule.
So if we start at the bottom with the producers at 100%, What percent goes to the next level? Only 10% goes to the next level, to the caterpillar, like we just saw. What percent of the caterpillar energy goes to the next level?
10% of that. So now we are down to 1%. And what about the next level?
10% of that. We are losing energy at every level, because organisms have to live their lives. So it makes sense that we would have way less tertiary consumers than producers in an area.
So the next time, you're enjoying a nice picnic. Thank photosynthesis and cellular respiration for making your mouth possible and giving you energy. And if you want to learn more science, you can check out this video next. Biomass. Hey chill out.