AQA AS Bio unit 1:The Digestive System

Includes digestion, proteins, enzymes and carbohydrates.

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  • Created on: 27-05-13 18:09
Preview of AQA AS Bio unit 1:The Digestive System

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The 4 stages of the digestive system
Food enters through the mouth and down the oesophagus.
Food gets broken down with enzymes in the stomach and the colon.
Food gets absorbed through the epithelial cells all around the digestive system.
Waste material gets ejected from the anus after being stored in the rectum.
The Digestive system
Salivary Glands
Saliva is produced which contains amylase
Amylase breaks down starch into maltose
Saliva lubricates food making it easier to pass through the oesophagus
Saliva is pH7 for the optimum pH of amylase.
Relatively large circular and longitudinal muscle layer as peristalsis (the squeezing movement
of the oesophagus to push food) is needed to push food down.
Used only for transportation.
Only mucus producing cells to protect the lining.
Muscular walls and enzymes help with digestion
Pepsin is secreted here
There are no villi
Mucus layer to prevent self digestion
Secretes enzymes: protease, lipase, amylase
Pancreatic juice also contains pancreatic salts to neutralise acidity from the stomach

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

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Amino acids join together by a condensation reaction to form Dipeptides. A peptide bond is
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 in a polypeptide chain the complete properties of the
molecule can be changed
The structure of proteins
1. Primary structure
The sequence of amino acids that make up a polypeptide chain.
2.…read more

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

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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 after there aren't enough active sites to fit the substrate molecules into at the
same time.
4.…read more

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Glucose + Galactose = Lactose
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 bonds
o Amylopectin
Amylopectin is more branched. It contains 1-6 and 1-4 glycosidic bonds.
Starch contains both of these which intertwine together which makes it compact as heck.
Starch is also insoluble.…read more


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