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Digestion
The 4 stages of the digestive system
Ingestion

Food enters through the mouth and down the oesophagus.

Digestion

Food gets broken down with enzymes in the stomach and the colon.

Absorption

Food gets absorbed through the epithelial cells all around the digestive system.

Egestion

Waste material gets ejected from…

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Duodenum
The lining is folded into villi with many microvilli to increase surface area for
absorption.

Ileum
Villi with microvilli
Epithelial cells have many mitochondria to provide energy for active transport
Rich blood supply to remove absorbed molecules away quickly, maintaining a
diffusion gradient
Each villus contains a lymph vessel…

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Dipeptides
Amino acids join together by a condensation reaction to form Dipeptides. A peptide bond is
formed.




Polypeptides
Made by adding more amino acids
Each polypeptide has its own unique sequence of amino acids. This is known as the primary
structure of the protein
By changing just one amino acid…

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The biuret test
The biuret test is a test for proteins. You add sodium hydroxide and copper sulphate to the sample, if
the test turns lilac, protein is present.


Enzymes
Enzyme action
Enzymes are biochemical catalysts
They catalyse reactions by reducing the activation energy required for a specific reaction.

Mechanism…

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In high pH conditions, OH- molecules will disrupt the bonds maintaining the tertiary structure
The optimum pH varies from enzyme to enzyme
3. Substrate concentration
The higher the substrate concentration, the more active sites which are filled at any point in
time so the higher rate of reaction
This plateaus…

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Glucose + Galactose = Lactose

Starch
Starch is the main food storage molecule in plants.
It is made of many -glucose molecules which are arranged in two types of polysaccharides.
o Amylose
Amylose is coiled into a spiral which is held by hydrogen bonds. It is made
with 1-6 glycosidic…

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