12.9 Digestion and Absorption

Question 1

what is the digestive system

Answer 1

a tube that extends from the mouth through the body to the anus

Question 2

each organ of this system has a…

Answer 2

specialised role to perform in the breakdown and absorption of food molecules and absorption of water

Question 3

what are digestive juices and where are they produced

Answer 3

produced by the gland cells of the digestive system and they release hydrolytic enzymes and other molecules that facilitate digestion

Question 4

what do these enzymes do (from digestive juices)

Answer 4

hydrolyse large insoluble food molecules (polymers) into smaller soluble molecules (monomers) which can then be absorbed through the lining of the intestine

Question 5

polypeptides and proteins are hydrolysed by what and into what

Answer 5

hydrolysed into amino acids by proteases

Question 6

carbohydrates are hydrolysed by what and into what

Answer 6

hydrolysed into simple sugars by carbohydrases

Question 7

fats are hydrolysed by what and into what

Answer 7

hydrolysed into glycerol, fatty acids and monoglycerides by lipases

Question 8

what are the 4 glands

Answer 8

• salivary glands
• stomach
• pancreas
• Ileum

Question 9

what enzymes do salivary glands excrete

Answer 9

salivary amylase

Question 10

what enzymes does stomach excrete

Answer 10

endopeptidases (pepsin) and exopeptidases

Question 11

what enzymes does pancreas excrete

Answer 11

pancreatic amylase, lipases and exopeptidases

Question 12

what enzymes does ileum excrete

Answer 12

membrane bound dipeptidases and dissacharides

Question 13

ingest meaning

Answer 13

food going in

Question 14

egest meaning

Answer 14

food going out

Question 15

excretion meaning

Answer 15

getting rid of metabolic waste (from reactions) + happens in liver and kindeys

Question 16

role of the salivary glands

Answer 16

secretes salivary amylase (the enzyme which hydrolyses starch to maltose)

Question 17

role of the stomach

Answer 17

food is mixed with gastric juice which is acidic
- kills microorganisms
- contains endopeptidases and exopeptidases which hydrolyses polypeptides to dipeptides

Question 18

role of the pancreas

Answer 18

secretes pancreatic juice containing amylase (and other carbohydrates), endopeptidases (pepsin), exopeptidases, lipases

Question 19

role of the small intestine (ileum)

Answer 19

• adapted to provide a large SA for the absorption of the products of digestion
• maltase enzymes are embedded in the epithelium cell membrane of the small intestine. this enzyme hydrolyses maltose to glucose, so it is available for rapid absorption
• also sucrase, lactase enzymes and dipeptidase enzymes

Question 20

digestion of starch

Answer 20

• food enters the mouth and is broken up by teeth (mechanical digestion) then mixed with saliva
• salivary amylase starts to hydrolyse glycosidic bonds in the starch producing maltose (chemical digestion)
• in the stomach this salivary amylase is denatured due to acidic pH
• in the small intestine pancreatic amylase continues to hydrolyse the starch to maltose
• maltose is then hydrolysed to glucose by maltase enzymes in the membrane of the epithelial cells. the glucose can then be absorbed
• in mammals, cellulose is not hydrolysed as the enzyme cellulase is not produced

Question 21

where is amylase located

Answer 21

synthesised and secreted from salivary glands and pancreas

Question 22

product of reaction catalysed by the enzyme amylase

Answer 22

starch to maltose

Question 23

where is maltase located

Answer 23

within the membrane of epithelium cell membrane of ileum (membrane-bound dissacharidase ‘maltase’)

Question 24

product of reaction catalysed by the enzyme maltase

Answer 24

maltose to glucose

Question 25

describe the role of the enzymes of the digestive system in the complete breakdown of starch (4)

Answer 25

1 salivary / pancreatic amylase hydrolyses starch into maltose 2 by hydrolysing glycosidic bonds 3 maltose is hydrolysed into glucose 4 by maltase

Question 26

only what can be transported across the epithelial cell membrane

Answer 26

only monosaccharides (monomers)

Question 27

why can only monosaccharides (monomers) can be transported across the epithelial cell membrane

Answer 27

they are small enough and are complementary to the binding sites of specific carrier / channel proteins that move specifically complementary monomers across the epithelial cell membrane

Question 28

how are the monosaccharides (monomers) transported across the epithelial cell membrane

Answer 28

the monosaccharides (glucose, fructose, galactose) are absorbed by facilitated diffusion and co-transport using specific carrier proteins (due to their specifically shaped binding sites)

Question 29

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

Answer 29

1 Na+ (sodium ions) are actively transported out of epithelial cell into the blood (by sodium potassium pump) 2 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. only when both molecules bind will the molecules be moved across the membrane) 3 Na+ and glucose enter by facilitated diffusion using (complementary) cotransporter proteins 4 Na+ diffuse into the cell down its concentration gradient 5 glucose moves into the cell against its concentration gradient / down an electrochemical gradient 6 glucose moves into the blood by facilitated diffusion

Question 30

endo meaning

Answer 30

within

Question 31

exo meaning

Answer 31

out

Question 32

process of protein digestion

Answer 32

1 proteins / polypeptides are hydrolysed by enzymes called proteases. this process begins in the stomach 2 endopeptidases hydrolyse the peptide bonds within the polypeptide chain 3 this produces many smaller / shorter polypeptide chains and increases the SA (conc of substrate) for the next enzyme. this makes digestion faster and more efficient. this enzyme has acidic optimum pH and so it doesn't denature in the stomach acid 4 exopeptidases hydrolyse the peptide bonds at the terminal ends of the protein, removing 1 amino acid at a time 5 exopeptidases are specific: 1 group are complementary to the N terminal end and another group are complementary to the C terminal end. amino acids and dipeptides are produced. 6 the dipeptidases - enzymes embedded in the cell surface membrane of the epithelial cells. these hydrolyse dipeptides into amino acids which can now be absorbed by facilitated diffusion, active transport and cotransport.

Question 33

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

Answer 33

1 Na+ (sodium ions) are actively transported out of epithelial cell into the blood (by sodium potassium pump) 2 this creates a concentration gradient of Na+ (between lumen of the ilium and the epithelial cell) 3 Na+ and amino acid enter by facilitated diffusion using (complementary) cotransporter proteins 4 Na+ diffuse into the cell down its concentration gradient 5 amino acids moves into the cell against their concentration gradient / down an electrochemical gradient 6 amino acids moves into the blood by facilitated diffusion

Question 34

Process of lipid digestion

Answer 34

- lipids are only digested within the lumen of the ileum - in the stomach the lipids are churned into fat droplets - bile is produced in the liver, stored in the gall bladder and is released into the small intestine with the food - bile contains bile salts, which emulsify fat droplets (and form micelles) - this increases SA of the lipids for that action of lipase enzymes - this makes digestion of lipids faster and more efficient - lipases hydroxide lipids into glycerol, fatty acids and monoglycerides

Question 35

Process of lipid digestion and absorption

Answer 35

- lipids droplets are mixed with bile salts to form smaller droplets (emulsified) - (smaller droplets) increase SA for faster hydrolysis by lipase - triglycerides hydrolysed into glycerol, fatty acids and monoglycerides - bile salts, glycerol and fatty acids form micelles - micelles make fatty acids soluble in water and bring fatty acids to the surface of the epithelial cell membrane - fatty acids enter the epithelial cell by simple diffusion (micelles do not cross the cell membrane) - At SER fatty acids, glycerol are recombined to form triglycerides - at Golgi apparatus triglycerides are modified, proteins are added to form lipoproteins (chyloproteins) and packaged into vesicles (chyloproteins are water soluble and so can be carried into the blood) - chylomicrons are transported into a lymph vessel by exocytosis they then can enter the blood