Intracellular & Extracellular Digestion

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  • 0:01 Types of Digestion
  • 0:39 Extracellular Digestion
  • 2:26 Intracellular Digestion
  • 3:26 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll explore intracellular and extracellular digestion. We'll go over what each term means, and see examples of each type of digestion.

Types of Digestion

Did you ever think about what happens when you have your snack? Sure, you chew and swallow, but how does the food actually get to your brain cells? The answer is through your digestive system. During digestion, we break food down into smaller parts called nutrients that our cells can use. This type of digestion is called extracellular digestion. But there is also another type of digestion, known as intracellular digestion. Today we're going to explore both types of digestion and check out some examples you might not be as familiar with.

Extracellular Digestion

The prefix 'extra' means outside, which tells us that extracellular digestion occurs outside the cell. During extracellular digestion, food is broken down outside the cell either mechanically or with acid by special molecules. These special molecules are called enzymes. Nearby cells then absorb the newly broken down nutrients. Humans use extracellular digestion when we eat. Our teeth grind the food, enzymes and acid in the stomach liquify it, and additional enzymes in the small intestine break the food down into parts our cells can use.

Although fungi don't have a digestive tract like humans, they still use extracellular digestion! Fungi and other decomposers essentially suck the life out of the substrate they grow on. Picture some delicious, red strawberries overcome by mold on your kitchen counter. The mold is actually a fungus, secreting chemicals that break down the strawberries. The fungi cells then absorb the nutrients released. If you let those strawberries sit a while longer, they would be completely liquefied! Gross, right?

Another example of extracellular digestion is the hydra, or sea anemone. Although a hydra could pass for an underwater plant, it is actually an animal. A large cavity, called the gastrovascular cavity, fills the center of the animal, with one opening for both food and waste. When unsuspecting prey swim into the opening, stinging cells paralyze the prey. The hydra uses its tentacles to push the prey further into the cavity, where enzymes are secreted to break down the food. Once the food is broken down into nutrients, the cells of the hydra can absorb it for energy.

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