Biology AQA AS Unit 1 Topic 2: Digestion

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Digestion Key Terms
· Digestion is the process in which large insoluble
molecules are hydrolysed by enzymes into small
molecules which can be absorbed and assimilated.
· hydrolysis ­ splitting up of molecules by adding water
to the bonds that hold them together.
· Ingestion- taking in food
· Absorption- taking soluble molecules into the body
· Egestion- removal of undigested food, bacteria, and
dead cells from the gut as faeces
· Assimilation- incorporating absorbed molecules into
body tissues…read more

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Major Parts of the digestive system
· Oesophagus ­ carries food from mouth to
stomach. Thick muscular wall.
· Stomach ­ muscular sac with inner layer
producing enzymes to digest protein. Stores and
digest food. Mucus produced to stop being
digested by own enzymes.
· Small intestine ­ long muscular tube. Enzymes
secreted from walls. Inner wall folded to villi->
gives large s.a. Further increased by microvilli on
epithelial cells of each villus. Purpose is to absorb
products of digestion to bloodstream.…read more

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Major Parts Continued.
· Large intestine ­ absorbs water. Food
therefore increases in consistency and forms
faeces.
· Rectum ­ faeces stored. Egested.
· Salivary glands ­ produce enzyme amylase to
break starch to maltose.
· Pancreas ­ large gland. Secretes protease to
break down proteins, lipase to digest lipids
and amylase to digest starch.…read more

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What is digestion?
· 2 stages: physical and chemical
· Physical: teeth chew. Increase surface area. Churned
by stomach wall muscles to break it up.
· Chemical: carried out by enzymes hydrolysing bonds.
· Carbohydrates monosaccharides (Carbohydrases)
· Lipids glycerol and fatty acids (lipases)
· Proteins amino acids (proteases)
· After being hydrolysed, they are absorbed into blood,
carried to parts of the body and built up into large
molecules which are incorporated into body tissues or
used in body processes.…read more

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Carbohydrate Digestion
· Carbohydrates are polymers made up of
monomers.
· Monosaccharides are sweet-tasting
monomers with the formula (CHO) e.g.
Glucose.
· Monosaccharide + monosaccharide =
disaccharide
· Disaccharide + disaccharide = polysaccharide…read more

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