Question Video: Identifying the Organ That Does Not Produce Digestive Enzymes | Nagwa Question Video: Identifying the Organ That Does Not Produce Digestive Enzymes | Nagwa

Question Video: Identifying the Organ That Does Not Produce Digestive Enzymes Biology • Second Year of Secondary School

Which of the following organs does not produce any of the digestive enzymes? [A] Liver [B] Pancreas [C] Small intestine [D] Salivary glands [E] Stomach

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Video Transcript

Which of the following organs does not produce any of the digestive enzymes? (A) Liver, (B) pancreas, (C) small intestine, (D) salivary glands, or (E) stomach.

This question asks about digestive enzymes. So let’s begin with a quick review of what enzymes are.

An enzyme is a biological catalyst. You probably know that the prefix bio- means life and a catalyst is a substance that speeds up chemical reactions, which helps us understand that an enzyme is produced by living organisms to speed up reactions in the body. Enzymes speed up reactions by lowering the activation energy needed to start the reaction. These two graphs show the activation energy needed with and without an enzyme. We can see that the activation energy is higher in the left-hand graph than in the right-hand graph. So more energy is needed to start a reaction without an enzyme than when an enzyme is present.

You might be wondering how enzymes lower the activation energy of reactions. Enzymes are globular proteins with a special area called an active site. The active site is complementary in shape to a specific substrate. In biology, “complementary” means two molecules will fit together like pieces of a jigsaw puzzle.

In the first step of a reaction, a substrate molecule will bind to the enzyme’s active site to form an enzyme–substrate complex. The reaction can now proceed, and afterwards the enzyme will release the products. You may have noticed in the diagram that the enzyme is not changed or used up in the reaction. This is important because it means a given molecule of an enzyme can be reused again and again.

Digestive enzymes break large insoluble food molecules down into small soluble ones so they can be absorbed and used by the body. Some types of digestive enzymes are proteases, which break down proteins; carbohydrases, which break down carbohydrates; and lipases, which break down lipids. To answer our question about where digestive enzymes are made, let’s follow the path food takes through our digestive system.

Digestion begins in the mouth, where salivary glands release the digestive enzyme amylase to start breaking down the carbohydrate starch. This means we can rule out the salivary glands as a correct answer. Food is then swallowed and travels into the stomach. Here, the main enzyme released is pepsin, which breaks down proteins. So we can rule out the stomach as an answer as well.

As the food moves into the small intestine, it passes by the liver, which produces bile. Bile neutralizes the acidic mixture from the stomach and emulsifies lipids. That is, it breaks large fat droplets down into smaller ones, similar to how dish soap breaks up fat globules on your greasy cooking pans. Bile is not an enzyme because it does not decrease activation energy of a reaction to produce a new product. Instead, it reduces lipid droplet size, which increases their surface area to facilitate their digestion by lipases.

During the final stages of digestion, cells of the small intestine and pancreas release carbohydrases, proteases, and lipases. The small intestine and pancreas can therefore be ruled out.

This leaves us with the answer choice (A), the liver. We have learned that the liver makes bile, which is important for digestion but is not an enzyme. So the organ that does not produce any digestive enzymes is the liver.

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