This lesson introduces how the process of cellular respiration fits in the water cycle by using explanations of the water cycle, respiration, and photosynthesis.
The quiz following the lesson will test how well you understand the place of respiration within the water cycle.
Watch out! That raindrop that’s falling? That comes straight from your dog’s stinky breath. Okay, maybe not, but it could happen! This lesson is all about what happens when we breathe.We tackle the questions: what happens when humans and other animals let off water and carbon dioxide, and how does that fit into the big picture? The truth is that there are many different ways that water and carbon dioxide are recycled by the water cycle. Our breath being absorbed by the atmosphere and dumped back down in the form of rain or snow is one of them.
Respiration is the most important metabolic process for animals that can’t make their own energy. It allows organisms to gather oxygen from the air in exchange for carbon dioxide and water vapor . Particularly, we’re talking about respiration in the presence of oxygen.The chemical equation for respiration is:glucose + oxygen = water, carbon dioxide, energyIn other words, every time we take in glucose in the form of food and breathe in oxygen, we exhale carbon dioxide and water vapor. Plus, we get energy! For this lesson, we’re most interested in what happens to the water that we give off as a result or respiration.
The Water Cycle
The water cycle is a cycle that describes the use, storage, and recycling process of water on Earth.
It is arguably the most important of all the cycles because the way water is spread across the globe and redistributed is critical to life on our planet.A very basic explanation of the water cycle is that the majority of water is stored in our oceans. With added energy from the sun, much of that liquid water turns into gas, or water vapor, and is absorbed by the atmosphere in a process called evaporation.
Then, the water vapor gathers and cools down in a process called condensation. When enough water condenses in the atmosphere, it falls back to the earth during a process called precipitation, also known as rain, snow, and hail. A lot of that precipitation then makes its way, above or underground, back to major bodies of water like lakes and oceans.
There is more to this cycle as we’ll see shortly, but it’s important to know the basics.
Now that know a little bit more about the respiration and water cycle, let’s discuss what happens to all that water. There’s no simple answer. Unfortunately, we can’t simply put tracking devices on water molecules and see where they end up, so we, as scientists, have to assume where the molecules go.Even more difficult is trying to follow the exchange of atmospheric water vapor, which is literally invisible.
There are several possible paths the water might take after being exhaled during respiration. Let’s go over two scenarios, both beginning with the knowledge that when we exhale, we release water in gas form into the atmosphere.Most likely, the water vapor that we expel is combined with the vapor from other sources, like evaporated water from lakes and oceans, unused water vapor from plants, or even melted and evaporated snow and ice.
Once all of those molecules get packed together, or condensed, the water falls to the earth again, where it either works its way down into the earth’s crust to form aquifers, or rock that can hold groundwater, or creates runoff, which flows to water storage reserves like lakes and oceans. Eventually, the same molecules may again evaporate and follow the same cycle. Going back to our dog’s breath example from the beginning of the lesson, you can now see how the water your dog breathes out can come down as rain at a later point in time.Another option is that the water we exhale is absorbed by plant life surrounding us. Photosynthesis is the complementary chemical reaction to respiration, meaning that plants need water and carbon dioxide to produce their energy.
If we were to breathe in close quarters with plants, some portion of the water we exhale would be absorbed by pores in a plant’s leaves.From there, the water makes its way throughout the plant to complete the process of photosynthesis, allowing the plant to create its own energy and grow. It’s important to note that much of the water used by plants is actually broken down into hydrogen and oxygen due to photosynthesis, and it’s this hydrogen fuel that give plants part of their energy. When the plant has used all the water it needs, what’s left exits the leaves and is released as water vapor into the atmosphere.
From the atmosphere, the process is very similar to the one stated before in which water condenses and again falls to the ground.
As you can see, trying to determine where to place respiration in the water cycle can be a bit complicated, because water vapor is all around us. The majority of water molecules are in the air after they are evaporated and will follow the water cycle.
After they have condensed in the air, they will eventually fall to the ground in the form of precipitation, although it can be absorbed by various other forms of life. Eventually, the vapor is once again absorbed by the atmosphere, or it breaks down into oxygen and hydrogen parts.