exchange systems
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what is digestion
large biological molecules are hydrolysed into smaller moleciles that can be absorbed across cell membranes
what enzymes are needed for the digestion of carbohydrates
amylase membrane bound disaccharidases e.g sucrase and lactase
where is amylase produced
amylase is produced by the pancreas and salivary glands- it hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds
where are carbohydrates hydrolysed
begins in the mouth continues in the duodenum completed in the ileum
what enzymes are needed to digest proteins
endopetptidases exopeptidases membrane bound dipeptidases
what do endopeptidases do
hydeolyse peptide bonds between amino acids in the middle of a polymer chain
what do exopeptidases do
hydrolyse peptide bonds between amino acids at the end of a polymer chain
what do membrane bound dipeptidases do
hydrolyse peptide bonds between two amino acids
where are proteins hydrolysed
starts in the stomach continues in the duodenum fully digested in the ileum
what are lipids digested by
lipase and the action of bile salts
where is lipase made and what does it do
made in the pancreas and it can hydrolyse the ester bond in triglycerides to form monoglycerides and fatty acids
what are bile salts and where are they made
made in the liver and stored in the gallbladder emulsify lipids to form small droplets called micelles which increases the surface area for lipase to act on
what are the two stages of lipid digestion
physical (emulsification and micelle formation) chemical (lipase)
describe physical digestion of lipids
lipids are coated in bile salts which have been released from the gallbladder after being made in the liver theyre covered in the bile salts which causes them to split into smaller droplets called micelles- this process is called an emulsion
why is micelle formation an advantage
many small droplets of lipids provides a larger surface area which enables lipase to hydrolyse the lipids faster
describe chemical digestion of lipids
lipase hydrolyses lipids into glycerol and fatty acids and some monoglycerides
what are micelles
water soluble vesicles formed of the fatty acids, glycerol, mologlycerides and bile salts
what do micelles do
deliver the fatty acids, glycerol and monoglycerides to the epithilial cells of the ileum for absorption fatty acids and glycerol can move into the epithilial cells by diffusion
where are products of digestion absorbed
across the cells lining the ileum
describe the structure of the ileum wall
the ileum wall is covered in villi which have thin walls surrounded by a network of capillaries and epithilial cells which have even smaller microvilli
how do features of the ileum wall make it adapted for absorption
they maximise absorption by increasing the surface area, decreasing the diffusion distance and maintaining a concentration gradient
how are amino acids and monosaccharides absorbed
by co transport or facillitated diffusion
how are lipids absorbed
when the micelles encounter the ileum epithilal cells, due to the non polar nature of the fatty acids and monoglycerides, they can simply diffuse across the cell surface membrane, into the epithilial cells once in the cell, these will be modified into triglycerides inside the endoplasmic reticulum and golgi body
what is transpiration
the loss of water vapour from the stomata by evaporation