DIGESTION AND ABSORPTION

Question 1

digestion

Answer 1

digestion can be defined as a biological process in which large biological molecules are hydrolysed into smaller biological molecules to be absorbed across the cell membrane.

Question 2

digestion of carbohydrates needs

Answer 2

1. Amylases
2. Membrane bound disaccharidases

Question 3

digestion of carbohydrates

Answer 3

• amylase is produced by pancrease and salivary gland. amylase hydrolyses the polysaccharides into disaccharide maltose by hydrolysing the glycosidic bonds.
• once the digestion of carbohydrates occurs in the mouth, it passes down to the stomach through oesosphagus. the hydrochloric acid in the stomach inactivates the amylase.
• the next step of digestion occurs in the duodenum. pancreatic amylase is secreted by pancrease which continues the breakdown of starch and glycogen to disaccharides which are then broken down into monosaccharides by enzymes lactase, maltase and sucrase. these are then absorbed across the intestinal epithelium into the blood stream to be transported to different cells in the body.

SUCRASE AND LACTASE are the membrane bound enzymes which hydrolyses the disaccharide sucrose and lactose into monosaccharides.

Question 4

peristalsis

Answer 4

the rhythmic contraction of the circulatory muscles in the gut is known as peristalsis.

Question 5

digestion in mouth ( mastication )

Answer 5

• food is chewed by the teeth which increases the surface area . salivary glands produce saliva. salivary amylase is secreted and catalyses the breakdown of carbohydrates ( starch) into some disaccharides.

Question 6

swallowing

Answer 6

the tongue presses against roof of the mouth . the soft palate closes the nasal cavity and the epiglottis closes the trachea.

Question 7

enzymes in protein digestion

Answer 7

• endopeptidases
• exopeptidases
• membrane bound dipeptidases

Question 8

digestion of protein

Answer 8

• protein digestion begins in the lumen of the stomach. protein are large molecules that are broken down by the enzymes; endpeptidases, exopeptidases and membrane bound dipeptidases.
• endopeptidases hydrolyses the peptide bonds between amino acids in middle of the polymer chain and exopeptidases hydrolyses peptide bond in the end of the polymer chain. dipeptides are produced as aresult which are then hydrolysed by membrane bound dipeptidases enzymes to amino acids which is then released in cytoplasm.

Question 9

enzymes in carbohydrate digestion

Answer 9

• salivary amylase and membrane bound disaccharidases

Question 10

substances required in lipid digestion

Answer 10

lipase and bile salts

Question 11

digestion of lipids

Answer 11

it occurs in two stages : physical digestion ( emulsification ) and chemical digestion ( lipase)

Question 12

physical digestion ( emulsification)

Answer 12

bile salts are produced in liver. lipids are coated into bile salts to create an emulsion. emulsification is a process where lipids are broken down into tiny droplets (micelles) these tiny droplets increases the s.a enabling a faster hydrolysis rxn for lipase.

inc s. a —- more enzymes can be attatcged — more enzyme substrate complex — faster rxn

Question 13

chemical digestion ( lipase )

Answer 13

lipase is an enzyme produced in pancrease which hydrolyses the ester bonds between tiglycerides to form monoglycerides and fatty acids.

Question 14

micelles ( tiny droplets)

Answer 14

micelles are water soluble vesicles made up of monoglycerides, fatty acids, glycerol and bile salts.

micelles deliver the fatty acids, monoglycerides and glycerol in the epithelial cells of ileum for absorption.

Question 15

where does absorptio occur

Answer 15

epithelium cells lining the ileum

Question 16

villi and micro villi . how do they help in digestion

Answer 16

thesw are the finger like projections.

1.increases the s. a – more space for transport
2. made of single layer of cells – shorter diffusion distance for transport
3. good blood supply - maintains a conc. gradient
4. lacteal - lymphatic system - absorption of lipids

Question 17

absorption of glucose and amino acids

Answer 17

through co transport and active transport.

it is because the concentration is higher in the epithelial cells than the lumen so co transport is used. if it would have been vice versa, facilitated diffusion would have been used.