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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.

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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.

Intracellular Digestion

Intracellular digestion, on the other hand, occurs inside a cell.

The prefix ‘intra’ means in, so intracellular means inside the cell. Single-celled creatures, like amoebas, have to get their food directly from the environment. They use a process called phagocytosis to engulf and grab food and bring it inside a cell. Once inside a cell, the food is sent to the lysosome, an organelle, where it will be broken down into parts a cell can use.

The lysosome is filled with acid, and kind of acts like the stomach of the cell.Although as humans we use extracellular digestion to get nutrients, our immune cells use intracellular digestion to protect us from invaders! Our white blood cells hunt down and capture intruders, called pathogens. They reach out and grab the pathogens, pulling them inside the cell. Then they send them to the lysosome, where strong acids and enzymes break them down.

Lesson Summary

Digestion is the process of breaking down food into nutrients.

Extracellular digestion takes place outside the cell. In humans, the digestive tract mechanically and chemically breaks down food so intestinal cells can absorb nutrients for the body. In the hydra, food is trapped in the gastrovascular cavity.Enzymes or special molecules secreted by the hydra, break down prey for absorption. Fungi also use extracellular digestion and secrete enzymes to break down the substrate they grow on. Intracellular digestion takes place inside the cell. Single celled organisms like amoebas engulf their prey and pull it into their cells using phagocytosis.

The prey is then moved to the lysosome, or organelle, for intracellular digestion. Intracellular digestion is also used by the white blood cells in our human immune system to capture and eliminate invaders.

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