Lab 7 Study Guide to Chemical Experiments

Substrate in salivary amylase experiment

Starch.

Enzyme that digests starch

Salivary amylase.

Lugol's Iodine test

Tests for starch; dark blue/black = positive.

Benedict's solution test

Tests for glucose; greenish-red = positive.

Negative control tube

Tube 2 - contains starch and water only, no enzyme.

Expected Lugol's result in Tube 5

Strong positive (starch still present).

Expected Benedict's result in Tube 4

Strong positive (glucose produced by amylase activity).

Substrate in pepsin digestion experiment

Egg albumin (protein).

Enzyme that digests albumin

Pepsin.

Biuret test

Detects amino acids; purple/violet = positive.

Reason for negative result in Tube 1

Pepsin is not active at pH 8 (alkaline).

Tube showing optimal digestion by pepsin

Tube 2 - albumin + pepsin + pH 2 (acidic).

Tube 4 demonstration

Low pH alone doesn't digest albumin (no enzyme present).

Dye used to visualize fats

Sudan Red.

Effect of detergent in Step 3

The solution turns completely red; fats are emulsified.

Emulsification effect on fat globules

Breaks them into smaller droplets for easier digestion.

pH indicator used in pancreatic lipase experiment

Phenol red.

Color of phenol red at high pH

Pink at high pH, yellow at low pH.

Cause of pH drop (turn yellow)

Fatty acids released by lipase digestion of fats.

Tube showing full digestion

Tube 1 - contains both lipase and bile salts.

Reason Tube 2 stays pink

No bile salts = poor emulsification = less enzyme action.

Tube 3 demonstration

Bile alone does not digest fats; lipase is needed.

Tube 4 demonstration (water)

Water alone does nothing; heat doesn't digest fats.