Digestion and Absorption

Question 1

ingestion

Answer 1

consumption of a substance

Question 2

digestion

Answer 2

process where large molecules are hydrolysed by enzymes into small molecules that can be absorbed across cell membranes and assimilated

Question 3

absorption

Answer 3

taking molecules into the bloodstream

Question 4

assimilation

Answer 4

process which uses the products of digestion to build new molecules

Question 5

egestion

Answer 5

the discharge of undigested material from the digestive system

Question 6

digestion of carbohydrates (5)

Answer 6

• Mechanical digestion: chewing increases surface area
• Salivary amylase: starch -> maltose (mouth has neutral pH which is optimum)
• No carbohydrate digestion in stomach due to acidic pH
• Pancreatic amylase in small intestine: starch -> maltose
• Membrane-bound disaccharidases e.g. maltase in small intestine: maltose -> glucose
  o Also includes sucrase and lactase

Question 7

digestion of lipids (3)

Answer 7

• Bile: emulsifies fats into micelles to increase surface area and is alkaline so neutralises stomach acid
• Micelles can be absorbed from the lumen of the small intestine to the epithelial cells
• Pancreatic lipase: triglycerides -> fatty acid + glycerol

Question 8

digestion of proteins (2 + 3 names of enzymes only)

Answer 8

• Pepsin in stomach: protein -> polypeptide (HCl provides optimum pH)
• Mechanical digestion: stomach churns food
• Pancreatic protease: polypeptide -> amino acids
• Endopeptidases
• Exopeptidase
• Dipeptidase

Question 9

endopeptidases

Answer 9

hydrolyse bonds in the middle of a protein molecules to produce peptide molecules to increase surface area for exopeptidase

Question 10

exopeptidases

Answer 10

hydrolyse the terminal amino acids to form dipeptides and single amino acids

Question 11

dipeptidases

Answer 11

hydrolyse dipeptides into amino acids

membrane-bound to epithelial cells of ileum

Question 12

features of ileum (5)

Answer 12

• Long allows time for digestion and absorption
• Longitudinal and circular muscles for peristalsis
• Lining is folded into villi covered in microvilli for high surface area
• Epithelial cells: thin for short diffusion pathway and contain many mitochondria for active transport
• Rich blood supply maintains steep concentration gradient

Question 13

absorption of glucose and amino acids

Answer 13

occurs by co-transport with sodium

Question 14

absorption of triglycerides (6)

Answer 14

1. Micelles break down into glycerol and fatty acids which are non-polar so can diffuse across the cell membrane into epithelial cells
2. Endoplasmic reticulum in epithelial cell recombines them to form triglycerides
3. Golgi apparatus packages triglycerides with lipoproteins and cholesterol to form chylomicrons
4. Chylomicrons move out of the epithelial cell by exocytosis and enter lacteals found in the centre of each villi
5. Pass into the blood system via lymphatic vessels
6. Triglycerides in chylomicrons are hydrolysed by enzymes in endothelial cells of blood capillaries and diffuse into cells