paper 1: Digestion and Absorption

Question 1

define digestion

Answer 1

the hydrolysis of large insoluble biological molecules into small, soluble biological molecules

Question 2

what is the function of salivary glands

Answer 2

secrets amylase that hydrolyses starch into maltose

Question 3

what is the function of the oesophagus

Answer 3

carries food from mouth to stomach by peristalsis

Question 4

what is the function of the stomach

Answer 4

food is mixed with acidic gastric juice killing microorganisms’ proteases

Question 5

what is the fucntion of the pancreas

Answer 5

secretes pancreatic juice containing amylase, protease and lipases

Question 6

what is the function of the small intestine

Answer 6

food is further digested by enzymes here

Question 7

what is the function of the large intestine

Answer 7

absorbs water from food turning the remains into faeces

Question 8

what is the function of the rectum

Answer 8

stores faeces before periodical release via the anus

Question 9

how is starch broken down in the body

Answer 9

(found in pancreas or salivary glands)
amylase maltase
starch + water ———-> maltose + water ———–> glucose

Question 10

why is it useful to have membrane-bound enzymes

Answer 10

• enzymes dont get removed in faeces
• monosaccharides and amino acids are close to transport proteins in the cell membrane for facilitated diffusion into epithelial cell

Question 11

how are cells of the small intestine adapted for the absorption of nutrients

Answer 11

• microvilli increase surface area for diffusion
• more channel and carrier proteins in membrane for facilitated diffusion or active transport
• many mitochondria to produce more ATP for active transport via aerobic respiration
• epithelial lining in one cell thick providing a short diffusion pathway
• constant flow of blood creates a concentration gradient between the inside of the cell and the blood

Question 12

describe the process of co-transporting glucose

Answer 12

• sodium ions are actively transported from the epithelial cells into the blood to maintain the sodium concentration gradient between the lumen of the small intestine and the epithelial cell
• glucose and sodium ions are co-transported form the lumen of the small intestine into the epithelial cell via a carrier protein, this is facilitated diffusion because sodium ions move down a concentration gradient
• the glucose molecules move into the blood via facilitated diffusion down the concentration gradient

Question 13

what do endopeptidases do

Answer 13

hydrolyse peptide bonds in the middle of the polypeptide producing shorter polypeptide chains

Question 14

what do exopeptidases do

Answer 14

hydrolyse peptide bonds at the end of the polypeptide chain to remove single amino acids

Question 15

where are exo/endopeptidases produced

Answer 15

stomach and pancreas

Question 16

why is the combined action of endopeptidases and exopeptidases more efficient than exopeptidases on their own

Answer 16

• endopeptidases hydrolyse bonds in the middle of a polypeptide which creates more ends and more surface area for hydrolysis from exopeptidases

Question 17

what are dipeptidases

Answer 17

enzymes which hydrolyse dipeptides into amino acids

Question 18

where are dipeptidases found

Answer 18

embedded in the membrane of epithelial cells in the ileum

Question 19

how are lipids digested

Answer 19

• hydrolysed into monoglycerides and fatty acids by lipase

Question 20

where is lipase produced

Answer 20

in the pancreas and secreted into small intestine

Question 21

describe the process of absorption of lipids

Answer 21

• monoglycerides and fatty acids form a micelle with the bile salts
• micelles make the fatty acids and monoglycerides more soluble in water
• micelles also carry fatty acids and monoglycerides to the epithelial cell membrane
• monoglycerides and fatty acids diffuse through phospholipid bilayer
• monoglycerides and fatty acids reform triglycerides in the smooth ER and are encased in a vesicle
• the golgi modifies the triglycerides by combining them with proteins forming chylomicrons
• chylomicrons are packaged into vesicles which fuses with cell surface membrane releasing chylomicrons by exocytosis
• chylomicrons then enter the lymph vessels