3.3.3 Digestion and Absorption

Question 1

What is the role of salivary glands?

Answer 1

+ connected to the mouth via a duct, through
which they secrete amylase

Question 2

What is the role of the stomach?

Answer 2

+ muscular sac whose inner layer produces
enzymes
+ contains HCl - breaks don large food

Question 3

What is the role of the ileum?

Answer 3

+ produces enzymes in its wall and has them
secreted in by glands
+ inner walls folded into villi, further folds called
microvilli

Question 4

What is the role of the pancreas?

Answer 4

+ produces pancreatic juice

Question 5

What is the role of the large intestine?

Answer 5

+ absorbs water

Question 6

What is the role of the rectum?

Answer 6

+ stores faeces until egestion occurs

Question 7

What is physical digestion?

Answer 7

+ occurs in mouth and stomach, breaks large
food molecules into smaller pieces by teeth to
provide a large SA for chemical digestion

Question 8

What is chemical digestion?

Answer 8

+ breaks down large insoluble molecules into
smaller using enzymes

Question 9

What is stage 1 in starch digestion?

Answer 9

1. Food is chewed to make molecules smaller
   and provide a larger SA for enzymes to work
   on

Question 10

What is stage 2 in starch digestion?

Answer 10

2. Saliva which is mixed in during chewing.
   Salivary amylase starts hydrolysing any starch
   to maltose
   Saliva also contains mineral salts to maintain a
   neutral pH

Question 11

What is stage 3 in starch digestion?

Answer 11

3. Food enters the oesophagus and passes down
   to the stomach using PERISTALSIS
   Stomach conditions are too acidic - denaturing
   the salivary amylase

Question 12

What is stage 4 in starch digestion?

Answer 12

4. Food is passed into the ileum where it mixes
   with pancreatic juice

Question 13

What is stage 5 in starch digestion?

Answer 13

5. Pancreatic juice contains pancreatic amylase
   and alkaline salts to maintain a neutral pH
   (optimum pH)

Question 14

What is stage 6 in starch digestion?

Answer 14

6. Muscles in the intestine wall push the food
   along the ileum
   Epithelial lining of the ileum produces maltose
   which remains a part of the cell-surface
   membrane of the epithelial cells ( MEMBRANE
   BOUND DISACCS)
   Maltose hydrolyses maltose into alpha-glucose

Question 15

What are the adaptations of the villi/ microvilli?

Answer 15

+ interface between the lumen of the small
intestine and the blood and tissues
+ increase SA for diffusion
+ thin walled, reducing distance for diffusion to
occur
+ good blood supply to carry away absorbed
materials - maintaining a diffusion gradient

Question 16

What are the stages of absorption of glucose (co-transport) ?

Answer 16

1. sodium ions actively transported out of
   epithelial cells into the capillary, whilst K+ are
   pumped in
2. this causes there to be a lower concentration
   of Na+ in the epithelial cell
3. there’s a high concentration of Na+ ions in the
   lumen of the ileum (from digested products)
4. Na+ use facilitated diffusion to diffuse into the
   epithelial cell
5. a glucose molecule is also brought into the
   epithelial cell along with the sodium
6. the glucose molecule (high conc. in the
   epithelial cell compared with capillary) is
   moved out of the epithelial cell into the
   capillary, via facilitated diffusion

Question 17

How is sucrose digested?

Answer 17

+ must be physically broken down by the teeth in
order to release it for digestion
+ this is becuase sucrose is stored within cells,
surrounded by a membrane
+ passes from the stomach to the small intestine
where the epithelial lining secretes sucrase
+ hydrolyses the single glycosidic bond in
sucrose to form glucose and fructose