digestion and absorption

Question 1

digestion

Answer 1

getting food (fuel) so that respiration (combustion) can take to release energy (ATP+heat)

Question 2

autotrophs

Answer 2

self feeding = make their own food - mainly using light energy (photosynthesis)

• algae, plants

Question 3

heterotrophs

Answer 3

depend on autotrophs directly or indirectly

• they get large molecules / polymers - too large to cross membrane and enter cells
• therefore are digested (hydrolysed) into monomers, which are absorbed

Question 4

structure of digestion system

Answer 4

mouth - enzymes
oesophagus
stomach
liver - bile duct - duodenum pancreatic duct - pancreas
ideum (small intestine)
colon (large intestine)
rectum
anus

Question 5

mouth

Answer 5

mechanical digestion to increase surface area of food so enzyme have a larger area to work on

reaction
starch to maltose via hydrolysis of glycosidic bond

amylase
neutral pH

Question 6

stomach

Answer 6

mechanical digestion to increase surface area of food so enzyme have a larger area to work on

proteins - smaller polypeptide via hydrolysis of peptide bond

pepsin - endopeptidase

~2 pH - HCl

Question 7

duodenum

Answer 7

absorption of organic molecules

starch - maltose (amylase)
large - smaller peptides (trypsin is an endopeptidase)
triglycerides - monoglycerides and fatty acids (ester bond hydrolysed by lipase)

7 to 8 pH

HCl - neutralised with NaHCo3 from liver, pancreas and duodenum

Question 8

liver

Answer 8

secretes bile salts for lipid emulsification

Question 9

ileum

Answer 9

disaccharides - monosaccharides (maltase, sucrase, lactase)

short peptides - dipeptides - exopeptidases

dipeptides - amino acids - dipeptidases

neutral pH

Question 10

colon

Answer 10

large intestin

lots of bacteria - could secrete vitamins

Question 11

rectum

Answer 11

absorption of water and vitamins only

Question 12

process of digestion

Answer 12

ingestion - digestion and egestion

digestion leads to absorption - assimilation (using the molecule/breaking it down)

egestion (faeces)

The hydrolysis of larger molecules into smaller molecules.
To produce molecules small enough to be absorbed across the gut wall

Question 13

carbohydrate digestion

Answer 13

in the mouth - salivary amylase hydrolyses starch to maltose - released in solution in saliva from salivary glands (optimal pH 7 neutral)

from pancreas - released down pancreatic duct - acting in the small intestine - pancreatic amylase hydrolyses starch to maltose - pH 7

attached to the wall of the small intestine - maltase hydrolyses maltose to glucose (and other disaccharides) - pH7

Question 14

lipid digestion

Answer 14

pancreatic lipase - triglycerides to diglycerides and fatty acids to monoglycerides and fatty acids to glycerol and fatty acids

bile salts - made in the liver - stored in gall bladder - released down the bile duct - emulsify facts - this creates a larger surface area for lipase action

Question 15

protein digestion

Answer 15

pepsin (a type of protease) - stomach - polypeptides hydrolysed to shorter polypeptides
also called an endopeptidase as breaks peptide bonds in the middle of the polypeptide chain

released in solution in gastric juice from the wall of the stomach - released in an inactive form as pepsinogen

pepsinogen (inactive) -> HCl -> pepsin (active)

trypsin - pancreatic duct - hydrolyses polypeptides to shorter polypeptides
also called an endopeptidase as hydrolyses the peptide bonds in the middle of a polypeptide chain

released in solution in pancreatic juice - travels down the pancreatic duct - acts in the small intestine - released in an inactive form as trypsinogen

trypsinogen (inactive) -> trypsin (active)

exopeptidases - some break off one amino acid at a time, some break off two - all bound onto wall of small intestine
hydrolyse peptide bonds at end of the polypeptide chain

dipeptidases - hydrolyse the peptide bond in dipeptides to form amino acids

Question 16

absorption

Answer 16

occurs in the small intestine - ileum

The ileum is lined with finger-like processes called villi. Increases the SA for absorption.

Villi filled with capillaries, so there’s a short diffusion distance from the LUMEN of the gut (space inside the gut) into the blood.

Has a structure called a LACTEAL running up the centre into which fats are absorbed. This a branch of the LYMPH SYSTEM, which is a system of tubes that fills your body.

ileum is lined with columnar epithelial cells - villi - increase surface area

Question 17

carbohydrate digestion - shanti

Answer 17

polymers - starch (long and branches)

starch - amylase (salivary and pancreatic) - maltose (ileum) - glucose (monosaccharides)

lactose - lactase (ileum) glucose and galactose

sucrose - sucrase (ileum) - glucose and fructose

hydrolysis reactions in which the glycosidic bond is broken using water

Question 18

protein digestion - shanti

Answer 18

proteins - endopeptidases - smaller polypeptides - exopeptidases - dipeptides + AA - dipeptidases - AA

hydrolysis of peptide bond using water

endopeptidases - pepsin, trypsin - hydrolyse the peptide bond in the middle of the chain to make more ends available

exopeptidases - aminopeptidases and carboxypeptidases
- hydrolyse the peptide bond at the ends of the chain to release amino acid and dipeptides in the duodenum and ileum

dipeptidase hydrolyse the dipeptides to amino acids - ileum

Question 19

transport in small intestine

Answer 19

villi and microvilli to increase surface area of the lumen of the small intestine - intestinal epithelial cell

membrane bound enzymes which allow for a short diffusion distance for glucose and amino acids

capillary - circulation of blood maintains the concentration gradient

the intestinal epithelial cells complete the hydrolysis reaction using membrane-bound enzymes and absorb the monomers and pass them into the capillary

water soluble monomers into the capillary

Question 20

co-transport of glucose / amino acids with Na+

Answer 20

1. There is a higher concentration of glucose inside the epithelial cell than in the lumen.
   
   2. There is a lower concentration of Na+ inside the epithelial cell than in the lumen.
   3. The co-transport / carrier protein has two binding sites, one for glucose and one for Na+.
   4. When both glucose and Na+ bind to the carrier protein, the protein changes its tertiary structure to transport them into the cell. (Na+ move down the concentration gradient, while glucose is transported against the concentration gradient.)
   5. Glucose enters the capillary from the epithelial cell by facilitated diffusion through a carrier protein.
   6. The low concentration of Na+ within the ep cell is maintained by the Na+/K+ pump, which actively transports 3 Na+ out of the cell and 2 K+ into the cell using energy from ATP hydrolysis.
   7. For aa, there are several different co-transport proteins (for aa with different types of side chains).

Question 21

lipid digestion - shanti

Answer 21

• are not polymers
• insoluble in water to form droplets

in the duodenum - liver secretes bile salts, which emulsify the large lipid droplets into smaller droplets increasing surface area

lipase - from the pancreas - attaches to the small droplets - hydrolysis of ester bond
TG + 2H2O = monoglyceride + 2FA
triglycerides + 3H2O = glycerol + 3 FA

micelle formation
- phospholipids also combine with the digested droplets to form a micelle
- forms a phospholipid monolayer on the outside with monoglyceride, fatty acid ect inside
- micelles transport the monoglyceride, fatty acid to the epithelial cell
- monoglyceride and fatty acids enter the epithelial cell via simple diffusion through the phospholipid biplayer

triglycerides are re-synthesised in the epithelial cell in the smooth endoplasmic reticulum
proteins get added to the triglyceride in the golgi apparatus to form chylomicrons

chylomicrons enter the lymph vessel or lacteal

Question 22

lipid digestion - summary

Answer 22

• emulsification by bile
• enzymatic digestion by pancreatic lipase
• absorption of products of fat digestion depend on size

short and medium chain fatty acids and glycerol absorb into blood via capillary

long chain fatty acids and monoglycerides form into triglycerides by fatty acid linking and are transported in chylomicrons into lymph vessels

Question 23

villi

Answer 23

villus - folding of intestine

epithelial cells line the villi
microvilli - folding of the cell membrane

intestinal villi - lumen
lacteal and blood capillar

water soluble monomers - glucose and amino acids enter the blood capillaries
these capillaries join into the hepatic portal vein - carries monomers to the liver, where they are used / stored

lipids (water insoluble) enter the lymph - a slow moving fluid in the lymph vessels containing white blood cells
the lymph joins the blood circulation at the carotid duct

Question 24

define digestion

Answer 24

the hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes

Question 25

which molecules require co-transport

Answer 25

amino acids and monosaccharides

Question 26

explain how sodium ions are involved in co-transport

Answer 26

sodium ions are actively transported out of the cell into the lumen, creating a diffusion gradient

nutrients are then taken up into the cells along with the Na+ ions

Question 27

why do fatty acids and monoglycerides not require co-transport

Answer 27

the molecules are nonpolar, meaning they can easily diffuse across the membrane of the epithelial cells