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This lesson defines complete digestive tracts and which organisms have them. We’ll also go over some of the advantages of having a complete versus incomplete digestive tract.

What Is a Digestive Tract?

As we snack on chips, veggies, or fruit while we work, we’re getting some good energy to fuel our brains. However, where does this energy come from, and how do our bodies extract it from food? The answer is the digestive tract, which is a group of tissues or organs designed to break down food. Some animals, including humans, have a complete digestive tract, meaning it has a clear beginning (the mouth) and a separate end (the anus).

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Other, less complex animals, like sea sponges, or jellyfish, have only one opening.These animals take in food from the same opening they release waste. Sound gross? Good thing humans have a complete digestive system! Let’s look more closely at the human digestive tract.

The Human Digestive Tract

Humans, like other more complex animals, have a complete digestive tract. It starts at the mouth, where food is ground up and the digestion of carbohydrates, like those found in bread or sweets, begins.

Next, the food is transported by the esophagus down to the stomach, which is a specialist in breaking down carbohydrates and some protein. It does this using tiny proteins called enzymes that speed up the chemical reaction of breaking down food. It also has an abundance of acid, which dissolves food into liquid.Next, the food goes into the small intestine, a very different environment.

The small intestine is basic, or lacks acid, unlike the stomach. This environment is suited for absorbing nutrients and breaking down mainly protein and fat. Here, we can see the advantage of efficient digestion. The stomach has a very harsh environment, perfect for liquefying food. But, the small intestine has a totally different environment for absorbing nutrients.Since each organ is separate, they can do their jobs to the best of their abilities.

After the small intestine is the large intestine, which absorbs water. Again, the structure and environment of the large intestine is different, so it can do a different job. After the large intestine is the rectum for storing waste and the anus for expelling waste. While the food moves through the digestive tract, a person is free to continue eating to gain more energy and nutrients.

Complete Digestive Tract Advantages

More recently evolved and more complex organisms usually have a complete digestive tract.

Scientists think it evolved to provide two main advantages: to allow for continuous intake of food and to more efficiently absorb nutrients.The first advantage of a complete digestive tract is continuous food intake. Organisms with an incomplete digestive tract have a limited amount of space. Everything has to come out the same way it came in. Think of it like a line at the cafeteria.

If there was only one entrance and exit, the cafeteria would be a mess. People would get their trays and then have to wade back through a sea of people that are already in line to get a seat. The line would probably back up, and the cafeteria wouldn’t be able to serve as many people.Now, think of what normally happens when there is a separate entrance and exit. People get their food and keep moving in the same direction. They can easily leave the line to find a seat, so the line moves quickly. This is analogous to a complete digestive system.

The food comes in one end and moves in that direction until it exits. Our digestive system can hold way more food this way, allowing us to extract more nutrients.The second advantage of a complete digestive tract is its efficient absorption of nutrients. Since the digestive tract is a long tube, organisms can house lots of organs. Different organs in our digestive system perform different functions, so each organ can specialize in a particular task.

Think about group work for a large project. The project will run a lot smoother if each group member is an expert in their part. For example, one student might have excellent notes, and another might be a PowerPoint whiz. The project would, ideally, be done faster and better than if there was only one person doing each job.

Lesson Summary

A complete digestive system is a digestive system that has different start and end points. Organs in the digestive system break down food into usable parts for the body and help us get energy.

The other type of digestive system is an incomplete digestive system, which has the same opening for food and exit for waste.Complete digestive systems are better able to absorb nutrients, since each organ is separate and can specialize. It also allows for continuous intake of food, which lets animals grow bigger and develop more complex structures.

Humans have a complete digestive system with specialized organs, like the stomach and small intestine, that do different jobs, allowing for more efficient absorption of nutrients.

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