enzymes and digestion

🔹 What Are Enzymes?

• Enzymes are biological catalysts – they speed up chemical reactions without being used up.

• Made of proteins.

• Each enzyme has a specific shape that fits the substance it works on – like a lock and key.

🔹 How Enzymes Work

• The substrate fits into the enzyme’s active site.

• The reaction happens, then the products are released.

• This is called the lock and key model.

🔹 Factors Affecting Enzyme Activity

🔹 Digestive Enzymes

🔹 Bile and Enzymes

• Bile is made by the liver, stored in the gall bladder.

• It’s not an enzyme but helps enzymes:

  • Emulsifies fats (breaks them into tiny droplets) → increases surface area for lipase.

  • Neutralises stomach acid → enzymes in the small intestine work best in alkaline conditions.

🔹 Required Practical: Investigating Enzyme Action

You need to know how to investigate how pH affects amylase:

• Add starch solution and amylase to a test tube.

• Use a water bath to control temperature.

• Add iodine to spotting tiles to test for starch.

• Take samples every 30 seconds.

• Time how long it takes for iodine to stop turning blue-black (starch broken down).

• Repeat with different pH buffers.

🔍 Purpose of Digestion

• Breaks large, insoluble molecules into small, soluble ones that can be absorbed into the blood.

• Enzymes speed up this process (biological catalysts).

🧠 Key Organs in the Digestive System

🧪 Enzymes in Digestion

🟡 Bile – What It Does

• Made in liver, stored in gall bladder.

• Not an enzyme, but helps digestion:

  • Emulsifies fats: breaks them into small droplets to increase surface area for lipase.

  • Neutralises stomach acid: makes conditions alkaline for enzymes in the small intestine.

🧪 Required Practical: Enzyme Activity

Investigate the effect of pH on amylase activity:

1. Add starch, amylase, and buffer solution to a test tube.

2. Keep in water bath at a constant temperature.

3. Every 30 seconds, take a sample and mix with iodine in a spotting tile.

4. If starch is present = blue-black.

5. Record time taken for iodine to stop changing colour.

🧠 Summary of Digestion