Year 12 - Digestion and absorbtion

Question 1

Describe the complete digestion of starch

Answer 1

Salivary/Pancreatic amylase hydrolyses starch into maltose by hydrolysing glycosidic bonds

Maltose is hydrolysed into glucose by maltase

Question 2

Describe how glucose is absorbed from the ilium into the blood

Answer 2

Na+ (sodium ions) are actively transported out of epithelial cell into the blood (by sodium potassium pump);​

This creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell)​

(Cotransporter proteins have 2 binding sites complementary to Na+ and glucose. ​

Na+ and glucose enter by facilitated diffusion using a complementary cotransporter protein​

Na+ diffuse into the cell down its concentration gradient.​

Glucose moves into the cell against its concentration gradient / down an electrochemical gradient​

Glucose moves into the blood by facilitated diffusion

Question 3

Describe and explain the role of enzymes in the complete digestion of polypeptide chains

Answer 3

Endopeptidases hydrolyse peptide bonds within the polypeptide producing shorter polypeptides. ​

This increases surface area for exopeptidases to act on. ​

Exopeptidases hydrolyse peptide bonds at the end of polypeptides producing amino acids (or dipeptides) ​

Dipeptidases hydrolyse the peptide bond in a dipeptide producing two amino acids. ​

Amino acids can be absorbed

Question 4

Describe the purpose of bile salts in lipid digestion.

Answer 4

Smaller droplets have a larger surface area to volume ratio​

More surface for lipase to act ​

faster hydrolysis of triglycerides into glycerol, fatty acids and monoglycerides.

Question 5

Describe the role of micelles in absorption of fats into cells of the ileum

Answer 5

Micelles are bile salts and fatty acids​

Make the fatty acids more soluble in water​

Carry fatty acids to cell lining of the ileum​

Maintain higher concentration of fatty acids at cell lining than inside the cell. ​

Fatty acids (only) absorbed by simple diffusion;

Question 6

Describe how and where triglycerides are reformed and absorbed.

Answer 6

Fatty acids and glycerol recombine to form triglycerides at Smooth endoplasmic reticulum. ​

Triglycerides are modified by addition of proteins to make chylomicrons and then packaged into vesicles at the golgi apparatus. ​
Chylomicrons are transported into lymph/lacteal vessel by exocytosis.