6.1

Question 1

Explain why digestion of large food molecules is necessary

Answer 1

large food molecules must be broken down into smaller molecule so that they can be absorbed across small intestine wall into blood

Question 2

function of mouth

Answer 2

ingestion
- where food is taken into the body
- food is physically broken down by teeth (mechanical digestion)
- starch is broken down into sugars by salivary amylase (chemical digestion)

Question 3

esophagus

Answer 3

• muscular tube which connects the mouth to the stomach
• moves food by peristalsis

Question 4

stomach

Answer 4

• HCl provides acid condition (pH 2) which kills bacteria on food and provides optimum pH for stomach enzymes (eg. pepsin)
• pepsin breaks down proteins into amino acids
• mucus lining protects the stomach wall from autolysis (self-digestion)

Question 5

liver

Answer 5

• produces bile

Question 6

gall bladder

Answer 6

• stores bile

Question 7

pancreas

Answer 7

• produces enzymes and secretes them into the small intestine
  e.g. amylase, lipase

Question 8

small intestine

Answer 8

• emulsification of lipids & neutralisation of stomach acids by bile
• chemical digestion of food by enzymes
• absorption of small soluble molecules into the blood

Question 9

large intestine

Answer 9

• absorption of water (by osmosis) & minerals into the blood

Question 10

rectum

Answer 10

• stores faeces

Question 11

anus

Answer 11

• where faeces are secreted by process called egestion

Question 12

draw & label digestive system

Answer 12

Question 13

peristalsis

Answer 13

• the gut is made of smooth muscle which is not under conscious control & contracts rhythmically
• peristalsis is waves of muscle contractions which help move food along the gut
• contraction of circular muscles behind food help prevent it from being pushed backwards
• contraction of longitudinal muscles help move food forwards
• a special type of peristalsis in the small intestine called segmentation helps mix food with digestive enzymes

Question 14

enzymes on digestion

Answer 14

• enzymes digest most macromolecules in food into monomers in the small intestine
• the pancreas secretes three types of enzyme into the lumen of the small intestine: amylase, lipase, endopeptidase

Question 15

how do the three enzymes secreted by pancreas break down products into monomers

Answer 15

Question 16

membrane bound digestive enzymes

Answer 16

• some enzymes catalyse hydrolytic reactions by mixing with the ingested food, however, as food moves continuously through the alimentary canal, the enzymes are either digested or lost in the faeces
• some enzymes are not mixed with the ingested food but are produced by and remain in the cells lining the small intestine, such as maltase
• maltase is produced by epithelial cells in the small intestine
• it remains bound to the plasma membrane on microvilli
• it catalyses the hydrolysis of maltose to glucose
• this means that maltase isn’t lost as food moves along the small intestine and it means that glucose is produced in the right location for absorption

Question 17

cellulose digestion

Answer 17

• although humans can digest starch, glycogen, lipids, and nucleic acids, we cannot digest cellulose as we don’t have the enzymes cellulase or any cellulose-digesting bacteria
• however it is still an important component to our diet (even though we gain no energy from it)
• it is what we call fibre and it provides bulk to the food in the digestive system and it also aids the movement of food through the alimentary canal by peristalsis as it gives the smooth muscle of the gut something to push against

Question 18

identify the tissue layers in the transverse section of small intestine to

Answer 18

Question 19

absorption in small intestine (features)

Answer 19

microvilli/villi:
- greatly increase the surface area over which absorption takes place

epithelium:
- only one cell thick, reduces distance over which absorption takes place

capillaries:
- close to epithelium to reduce distance for absorption

lacteals (absorb lipids);
- close to epithelium today reduce distance for absorption

length:
- about 6m
- increases surface area and provides enough time for absorption to take place

Question 20

different methods of absorption

Answer 20

simple diffusion
- substances can move b/w phospholipid molecules
facilitated diffusion
- involves channel proteins which lets solutes pass OR involves specific carries proteins that change shape to let solutes pass

active transport
- particles collide with protein pump
- protein pump is activated by ATP, which causes a shape change
- particles are released on föhr side of membrane
- ADP & Pi are released which reverts protein pump back to original shape
- occurs against a concentration gradient

endo- & exocytosis
- endo: the bulk transport of materials/large molecules into the cell
- exo: the bulk transport of materials/large molecules out of the cell

Question 21

describe how fructose & glucose is absorbed

Answer 21

fructose is absorbed into epithelial cells by facilitated diffusion

glucose is absorbed by the sodium glucose co-transport mechanism

both are then absorbed into blood by facilitated diffusion

Question 22

describe how amino acids are absorbed

Answer 22

di peptides and tripeptides are hydrolysed by membrane bound proteases into amino acids which are then actively transported into epithelial cells

they then diffuse into the blood

Question 23

describe how lipids are absorbed

Answer 23

fatty acids and glycerol are absorbed into epithelial cells by simple diffusion because they are non polar and can pass through hydrophobic membrane into the blood

Question 24

dialysis tubing model

Answer 24

• can model the digestion of the small intestine
• dialysis tubing is semi-permeable (to small molecules but not to large ones)
• the medium outside represents blood into which digested products are absorbed
• the movement of glucose mimics absorption via epithelial cells as the glucose moves from an area of high glucose concentration (inside tubing) to low glucose concentration (in beaker) = positive results
• if it was starch the result would be negative as starch is too large to diffuse through the dialysis tubing