SB1e-f

Question 1

What do protein, starch and lipid molecules turn into after digestion?

Answer 1

Protein molecule → Amino acids
Starch molecule → Glucose molecules
Lipid molecule → Fatty acids & glycerol

Check Biology book page 12.

Question 2

What is synthesis?

Answer 2

Building larger molecules from smaller subunits.

Question 3

What is a catalyst?

Answer 3

A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. In living organisms, catalysts that speed up breakdown (e.g. digestion) and synthesis reactions are called enzymes.

Question 4

What are enzymes?

Answer 4

Biological catalysts that increase the rate of reactions.

Question 5

What are substrates and products?

Answer 5

The substances that enzymes work on are called substrates, and the substances that are produced are called products.

Question 6

State the name of 4 enzymes, where they are found and which reaction they catalyse.

Answer 6

Amylase - found in saliva and small intestines: break down starch to small sugars (such as maltose).

Catalase - found in most cells (especially liver cells): break down hydrogen peroxide made in many cell reactions to water and oxygen.

Starch synthase - found in plants: perform synthesis of starch from glucose.

DNA polymerase - found in the nucleus: perform synthesis of DNA from its monomers.

Question 7

How do you test for starch?

Answer 7

Using iodine solution. The solution turns yellow-orange → blue-black.

Question 8

How do you test for reducing sugars (glucose, fructose)?

Answer 8

Using Benedict’s solution. The solution is added to a food solution and is placed in a warm water bath. Turns blue (no sugar) → green (very little sugar) → orange (more sugar) → red (lots of sugar). May form precipitate (solid at the bottom of the beaker).

Question 9

How do you test for protein?

Answer 9

Using biuret test. Potassium hydroxide is mixed with food solution. Then 2 drops of copper sulfate solution are added. Turns blue → purple if protein is present.

Question 10

How do you test for fats and oils (lipids)?

Answer 10

Using ethanol emulsion test. Food solution is mixed with ethanol and shaken. Some of the mixture is poured into water and shaken again. Fats and oils dissolved in the ethanol float to the surface, forming a cloudy emulsion.

Question 11

How do we measure the amount of energy in a food?

Answer 11

By burning it in a calorimeter.

Question 12

What does a food energy test consist of? (6)

Answer 12

1. Thermometer
2. Stirrer
3. Clamp
4. Calorimeter
5. Water
6. Burning food

Check Biology page 15.