(i)

A → Starch
B → Oil/Fat/Lipid
C → Reducing/simple sugar/glucose

(ii)

A (Starch) → Glucose/fructose
B (Oil/Fat/Lipid) → Fatty acids/glycerol
C (Reducing/simple sugar/glucose) → Glucose/No digestion occurs/remains the same

(iii)

A → Mouth
B → Duodenum/small intestine
C → Not digested/passes through the system

(iv)

C (Reducing/simple sugar/glucose) is absorbed in the small intestine (ileum)

(i)

Blue black

(ii)

Pale blue black/purple/brown/brownish yellow

(iii)

Reducing sugar/maltose

(iv)

Functions of saliva in eating

1. It moistens/softens food to make it easy to swallow
2. It digests cooked starch/carbohydrates to maltose/reducing sugar

(v)

Reasons for warming the contents of the test tubes to about 37^oC

1. To bring the contents to body temperature (i.e 37^oC) because the enzymes in the saliva functions properly at 37^oC
2. A temperature of 37^oC activates the enzyme in saliva to speed up its reaction with food substance

(vi)

Aims of the experiment

1. To show that yam contains starch
2. To show that saliva digests starch/carbohydrates to reducing sugar/maltose

(i)

A → Fats and Oils/Lipids
B → Protein
C → Reducing Sugar/Glucose
D → Starch

$\frac{1}{2}$ mark each x 4 = 2 marks

(ii)

Colour Formed For A (Fats and Oils/Lipids)

Red-stained oil layer

Colour Formed For B (Protein)

Colour change from pale blue to lilac/violet/purple

Colour Formed For C (Reducing Sugar/Glucose)

Colour change from blue to green/yellow/orange/brick red

Colour Formed For D (Starch)

Color change from yellow-brown to blue-black/purple

$\frac{1}{2}$ mark each x 4 = 2 marks

(iii)

Part(s) of the digestive system where the food substances A, B and D are digested

A (Fats and Oils/Lipids) → Small Intestine (1 mark)
B (Protein) → Stomach ($\frac{1}{2}$ mark) and Small Intestine ($\frac{1}{2}$ mark)
D (Starch) → Mouth ($\frac{1}{2}$ mark) and Small Intestine ($\frac{1}{2}$ mark)

Total marks = 3 marks

(iv)

End product of digestion for food substances A, B and D

A (Fats and Oils/Lipids) → Fatty acids and glycerol ($\frac{1}{2}$ mark)
B (Protein) → Amino acids ($\frac{1}{2}$ mark)
D (Starch) → Glucose ($\frac{1}{2}$ mark)

Total marks = 1.5 marks

(v)

Functions of food substances A (Fats and Oils/Lipids)

1. Energy Source & Storage: A concentrated source of energy, storing more calories per gram than carbs or protein.

2. Essential Fatty Acids: Provide linoleic and alpha-linolenic acids, necessary for body functions but not produced internally.

3. Vitamin Absorption: Necessary for absorbing vitamins A, D, E, and K.

4. Structural Components: Form cell membranes and are vital for brain health and nerve function.

5. Protection & Insulation: Subcutaneous fat insulates against cold, while visceral fat cushions vital organs like the heart and kidneys.

6. Hormone Production: Involved in producing and regulating hormones, like leptin for appetite signaling.

Any 1 x $\frac{1}{2}$ mark = 0.5 mark

Functions of food substances B (Protein)

1. Enzymes: Speed up (catalyze) chemical reactions, like breaking down food for energy.

2. Structure: Provide frameworks for cells, tissues (collagen in skin/bones), muscles, hair, and nails.

3. Transport & Storage: Carry molecules like oxygen (hemoglobin) and store essential nutrients (iron, calcium).

4. Immunity: Form antibodies to fight off invaders like bacteria and viruses.

5. Signaling: Act as hormones and receptors, sending messages between cells (e.g., insulin).

6. Movement: Enable muscle contraction (actin, myosin).

7. Fluid & pH Balance: Help maintain the right balance of fluids and acidity in the body.

8. Energy: Can be used as an energy source if Carbohydrates and fats and oils are insufficient.

Any 1 x $\frac{1}{2}$ mark = 0.5 mark

Functions of food substances D (Starch)

1. Energy Production: Digested into glucose, which cells convert to ATP (adenosine triphosphate) for immediate energy to power bodily functions.

2. Energy Storage: Excess glucose is stored as glycogen in the liver and muscles for later use, maintaining blood sugar levels.

3. Building Macromolecules: Used as building blocks for vital molecules like DNA, RNA, and ATP.

4. Protein Sparing: Ensures protein is used for building tissues rather than being broken down for energy, preventing muscle loss.

5. Lipid Metabolism: Helps in the breakdown of fats, preventing the buildup of ketones (ketosis).

6. Digestive Health (Fiber): Fiber, a complex Carbohydrates, adds bulk to stool, promotes regularity, and supports a healthy gut.

Any 1 x $\frac{1}{2}$ mark = 0.5 mark

Total marks = 1.5 marks