Digestion and Absorption

Question 1

Explain complete breakdown of starch (4)

Answer 1

• Salivary amylase hydrolyses starch into maltose
• By hydrolysisng glycosidic bonds
• Maltose hydrolysed into glucose
• By maltase

Question 2

Describe how glucose is absorbed from the ilium into the blood (5)

Answer 2

• Na+ ions ACTIVELY TRANSPORTED out of epithelial cell into blood (by sodium-potassium pump)
• Creates concentration gradient of Na+
• Na+ and glucose enter by facilitated diffusion using (complementary) cotransporter proteins
• Na+ diffuse into cell down its concentration gradient
• Glucose moves into cell against its concentration gradient
• Glucose moves into blood by facilitated diffusion

Question 3

Why do epithelial cells contain many mitochondria?

Answer 3

To produce the large amount of ATP they need for active transport (Na+)

Question 4

Describe how amino acids are absorbed from the ilium into the blood (5)

Answer 4

• Na+ ions actively transported out of epithelial cell into the blood via sodium potassium pump
• Creates concentration gradient of Na+
• Amino acids and sodium diffuse into cell via facilitated diffusion through cotransport protein
• Na+ diffuses into cell down its concentration gradient
• Amino acids move into cell against their concentration gradient
• Amino acids diffuse into blood via facilitated diffusion

Question 5

Describe protein digestion to the ileum (5)

Answer 5

• Proteins hydrolysed by proteases in the stomach
• Endopeptidases hydrolyse peptide bonds within polypeptide chain
• Producing many smaller polypeptide chains (larger SA)
• Exopeptidases hydrolyse peptide bonds at terminal ends of protein removing ONE amino acid at a time
• Exopeptidases produce amino acids and dipeptides
• Dipeptidase enzymes embedded in epithelial cell membrane hydrolyse peptide bond in dipeptides into amino acids allowing them to be absorbed into cell

Question 6

Where are lipids only digested?

Answer 6

In the lumen of the ileum (small intestine)

Question 7

Where is bile produced?

Answer 7

Liver

Question 8

Describe the role of bile salts

Answer 8

• Emulsify fat droplets
• Form micelles
  to make digestion of lipids faster and more efficient

Question 9

Explain the process of lipid digestion (5)

Answer 9

• Lipid droplets mixed with bile salts (emulsified) to form smaller droplets
• Increase SA for more rapid hydrolysis by lipase
• Triglycerides hydrolysed into glycerol, fatty acids and monoglycerides
• Glycerol and fatty acids form MICELLES
• Micelles make fatty acids soluble in water and bring fatty acids to surface of epithelial cell membrane
• Fatty acids enter cell by simple diffusion (micelles do NOT cross cell membrane)
• S.E.R fatty acids and glycerol recombined to form triglycerides
• Triglycerides modified (at golgi) and proteins added to form lipoproteins (chylomicrons) and packaged into vesicles.
• Chylomicrons transported into lymph vessel by exocytosis