B5e: Digestion

Question 1

What is the importance of physical digestion(2)

Answer 1

to allow the food to pass more easily through the digestive system

to provide a larger surface area for chemical digestion

Question 2

Describe carbohydrates(what is it broken down by, where is it broken down, what is it broken down into)

Answer 2

carbohydrases

mouth (salivary glands release amylase) and small intestine

starch is broken down maltose, which is then broken down into glucose(a simple sugar) (by maltase)

Question 3

Describe fats(what is it broken down by, where is it broken down, what is it broken down into)

Answer 3

lipase

small intestine

fatty acids and glycerol

Question 4

Describe proteins(what is it broken down by, where is it broken down, what is it broken down into)

Answer 4

protease

stomach and small intestine

amino acids

Question 5

Where is bile made and what is its importance(3)

Answer 5

made in liver, stored in gall bladder, released into small intestine

alkaline; neutralises stomach acid to make the conditions right for enzymes in the small intestine to work

+rate of fat digestion by emulsifying fats (breaking it down into smaller droplets); +surface area for lipase enzymes to work on,
break down the fats faster

Question 6

Explain why the pH in the stomach is maintained at acidic levels, whereas the pH in the mouth and small intestine is alkaline or neutral (2)

Answer 6

acidic in stomach to kill any pathogens in food; to provide the optimum pH for protease enzymes to work; protease has low optimum pH

alkaline/neutral in mouth/small intestine to provide optimum pH for enzymes there to work; enzymes there have higher optimum pH

Question 7

Why do large molecules need to be broken down into small molecules?

Answer 7

so that they can diffuse through cell membranes in the gut wall and be absorbed into the blood or lymph

Question 8

How are glucose and amino acid molecules absorbed into the blood?

Answer 8

they are small enough so diffuse into the blood plasma across cell membranes from small intestine

Question 9

How are fat molecules absorbed into the blood?

Answer 9

too big to diffuse into blood plasma directly so diffuse out of small intestine and into lymph in the lymphatic system, where they’re
emptied into the blood

Question 10

How is the small intestine adapted for the efficient absorption of food? (5)

Answer 10

very long ­ enough time for digestion to complete and nutrients to be absorbed

large SA because its lining is folded and has small projections called villi

cells covering each villi have microvilli, +SA

villi have single permeable layer of surface cell, thin lining, short diffusion distance

constant blood supply to allow quick absorption