Digestion and absorption

Question 1

What is digestion

Answer 1

The hydrolysis of large insoluble biological molecules into smaller soluble biological molecules so that they can be absorbed across the cell membrane

Question 2

What does the digestion system contain

Answer 2

Salivary glands
Oesophagus
Stomach
Liver
Gall bladder
Pancreas
Small intestine
Large intestine
Rectum

Question 3

What do the salivary glands do

Answer 3

Secretions contain amylase that hydrolyses starch into maltose

Question 4

What does the oesophagus do

Answer 4

Carries food from mouth to stomach by peristalsis and has thick muscular walls

Question 5

What does the stomach do

Answer 5

Food is mixed with acidic gastric juice killing microorganisms
Contains proteases which hydrolyses protein into amino acids

Question 6

What does the pancreas do

Answer 6

Gland that is attached between the stomach and the small intestine secretes pancreatic juice containing amylase, protease and lipases

Question 7

What does the small intestine do

Answer 7

Food is further digested here by enzymes the wall is folded into villi made of epithelial cells which have microvilli to increase the surface area for absorption. Membranes contain disaccharides which hydrolyse disaccharides into monosaccharides

Question 8

What does the large intestine do

Answer 8

Absorbs water from food turning the remains into faeces

Question 9

What does the rectum do

Answer 9

Stores faeces before periodical release via the anus

Question 10

What is the equation of the digestion of carbohydrates for starch

Answer 10

Starch + water —> Maltose+water—>glucose
amylase maltase
Salivary amylase produced in salivary glands and pancreatic amylase is produced in amylase

Question 11

What is the equation for the digestion of carbohydrates for maltose

Answer 11

Maltose+water—> Glucose+ glucose
maltase

Question 12

What is the equation for the digestion of carbohydrates for sucrose

Answer 12

Sucrose+water—>Glucose+fructose
sucrase

Question 13

What is the equation for the digestion of carbohydrates for lactose

Answer 13

Lactose+water—>Glucose+galactose
lactase

Question 14

Why is it useful to have membrane bound enzymes

Answer 14

Enzymes dont get removed in faeces
Monosaccharides and amino acids are close to transport proteins in the cell membrane for facilitated diffusion into the epithelial cells

Question 15

Where does absorption occur

Answer 15

In small intestine

Question 16

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

Answer 16

Microvilli increases 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 is one cell thick providing a short diffusion pathway

Question 17

How else is the small intestine adapted for the absorption of nutrients

Answer 17

The constant flow of blood creates a concentration gradient between the inside of the cello and the blood

Question 18

What are the stages of the co transport of glucose

Answer 18

1) Sodium ions are actively transported from the epithelial cells into the blood. This maintains the sodium ion concentration gradient between the lumen of the small intestine and the epithelial cells
2) Glucose and sodium ions are co transported from the lumen of the small intestine into the epithelial cells via a carrier protein. This is facilitated diffusion because sodium ions move down thei concentration gradient
3) The glucose molecules move into the blood via facilitated diffusion down their concentration gradient

Question 19

What are the 3 types of proteases

Answer 19

Endopeptidases
Exopeptidases
Dipeptidases

Question 20

What are endopeptidases

Answer 20

They hydrolyse peptide bonds in the middle of the polypeptide producing shorter polypeptides

Question 21

What are exopeptidases

Answer 21

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

Question 22

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

Answer 22

Because endopeptidases hydrolyse bonds in the middle of the polypeptide which creates more ends and more surface area for hydrolysis by exopeptidases

Question 23

What are dipeptidases

Answer 23

Hydrolyse dipeptides into amino acids
They are embedded in the membrane of the epithelial cells in the ileum like disacchiarides

Question 24

How would you answer how amino acids are being absorbed across the small intestine

Answer 24

You say the same stages for co transport but use amino acids instead of glucose

Question 25

What is the digestion of lipids

Answer 25

Lipids are hydrolysed into monoglycerides and fatty acids by lipase
Lipase is produced in the pancreas and secreted into the small intestine
Bile salts are produced by the liver and stored in the gall bladder
They emulsify lipids into smaller droplets
This increases the surface area for faster hydrolysis of lipids by lipases

Question 26

What are the stages for the absorption of lipids

Answer 26

1) Monoglycerides and fatty acids form a micelle with bile salts
2) Micelles make the fatty acids and monoglycerides more soluble in water
3)The micelles also carry fatty acids and monoglycerides to the epithelial cell membrane
4)Monoglycerides and fatty acids diffuse through phospholipid bilayer

Question 27

What are the stages for the absorption of lipids (2)

Answer 27

5) Monoglycerides and fatty acids reform triglycerides in the smooth ER and are encased in a vesicle
6) The golgi modifies the triglycerides by combining them with proteins forming chylomicrons
7) Chylomicrons are packaged into vesicles for secretion
8)Chylomicrons then enter the lymph vessels