Week 7 (Half term) 

Independent: pH of buffer solution.

Dependent: time taken for starch to be broken down.

Control: same enzyme concentration, temperature, starch volume.

Water bath, iodine in spotting tiles, stopclock, buffer solutions.  

Keep temperature constant to ensure validity

Increase Accuracy of time taken by reducing the time between removing each sample. e.g. remove samples every 15 seconds.

Mix solutions well, 

Repeat for reliability. . 

Describe: Amylase works fastest at its optimum pH (around pH 7). 

Explain :Too high/low slows it down because the rate of reaction reduces and the enzymes start to denature. 

1. Place amylase, starch, and buffer solution in test tube.
   
   

2. Keep in water bath at set temperature.
   
   

3. Every 30 seconds take sample, add to iodine on spotting tile.
   
   

4. Time how long until iodine stays orange-brown (no starch).
   
   

5. Repeat with different pH values.

Glucose is a carbohydrate. 

Starch is built from many glucose molecules

Proteins are made of many amino acids. 

Lipids are made of fatty acids (a hydrocarbon chain) and glycerol (a type of sugar). 

Do not confuse lipids and fats. Lipids is the correct word to use. Fats are a type of lipid. Cholesterol is another type of lipid. 

Iodine solution for starch

Benedict’s solution for glucose and waterbath

Biuret reagent for protein

Ethanol & water (emulsion test) for lipids

A colour chart can be used to make more accurate comparisons

A colorimeter can be used to give very accurate values for colour. 

Starch = blue-black with iodine.

Glucose = brick red with Benedict’s (after heating).

Protein = purple with Biuret.

Lipid = cloudy white emulsion.

1. Solid food should be ground and mixed with a small amount of water.

2. Add iodine to food → starch test.
   
   

3. Add Benedict’s, heat in water bath → sugar test.
   
   

4. Add Biuret → protein test.
   
   

5. Mix with ethanol then water → lipid test.
   
   

6. Record colour changes.