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Assessment Statements
6.1.1 Explain why digestion of large food molecules is 6.1.1 Explain why digestion of large food molecules is essential.essential.
6.1.2 Explain the need for enzymes in digestion.6.1.2 Explain the need for enzymes in digestion. 6.1.3 State the source, substrate, products and 6.1.3 State the source, substrate, products and
optimum pH conditions for one amylase, one protease optimum pH conditions for one amylase, one protease and one lipase.and one lipase.
6.1.4 Draw and label a diagram of the digestive 6.1.4 Draw and label a diagram of the digestive system.system.
6.1.5 Outline the function of the stomach, small 6.1.5 Outline the function of the stomach, small intestine and large intestine.intestine and large intestine.
6.1.6 Distinguish between 6.1.6 Distinguish between absorptionabsorption and and assimilationassimilation.. 6.1.7 Explain how the structure of the villus is related 6.1.7 Explain how the structure of the villus is related
to its role in absorption and transport of the products to its role in absorption and transport of the products of digestion.of digestion.
Series of events
1.1. IngestionIngestion
2.2. DigestionDigestion
3.3. AbsorptionAbsorption
4.4. TransportTransport
Why digestion of large molecules is essential
Large molecules are too big to pass Large molecules are too big to pass across any cell membraneacross any cell membrane
Any food we eat must be chemically Any food we eat must be chemically digested to a suitable sizedigested to a suitable size
Molecule type Molecular form ingested
Molecular form after digestion
Protein Protein Amino acids
Lipids Triglycerides Glycerol and fatty acids
Carbohydrates Polysaccharides monosaccharides
Nucleic acids DNA, RNA nucelotides
Digestion allows you to turn molecules into ‘your own’
Example:Example: You eat an eggYou eat an egg The egg white (albumin) The egg white (albumin)
contains an amino acid contains an amino acid called serinecalled serine
Your stomach/small Your stomach/small intestine digests the intestine digests the albuminalbumin
Serine diffuses through Serine diffuses through the cells of the small the cells of the small intestine and then into a intestine and then into a capillarycapillary
Serine is enters a Serine is enters a pancreas cellpancreas cell
The cell uses the genetic The cell uses the genetic code of your DNA to build code of your DNA to build serine into insulinserine into insulin
Benefits of Benefits of digestion:digestion: Serine is able to Serine is able to
leave the albumin leave the albumin and enter the and enter the bloodstreambloodstream
Serine helps to Serine helps to synthesize your synthesize your own protein under own protein under the control of your the control of your DNADNA
Need for enzymesTo lower activation energyTo lower activation energy
Enzymes are protein Enzymes are protein molecules which act as molecules which act as catalysts for reactionscatalysts for reactions
They lower the activation They lower the activation energy of the reactions energy of the reactions that they catalyzethat they catalyze
Reactions occurring with Reactions occurring with an enzyme can occur with an enzyme can occur with a lower input of energy a lower input of energy than the same reaction than the same reaction without the aid of an without the aid of an enzymeenzyme
To catalyze hydrolysis To catalyze hydrolysis reactionsreactions Converts large Converts large
macromolecules to smaller macromolecules to smaller molecules that can be molecules that can be absorbed and then usedabsorbed and then used
Amylase puts stress on Amylase puts stress on bonds of glucose held bonds of glucose held together in a starch together in a starch moleculemolecule
Surrounding thermal Surrounding thermal energy provides molecular energy provides molecular motion to break the bondsmotion to break the bonds
Examples of digestive enzymes
Salivary amylase
Pepsin (a protease)
Pancreatic lipase
Source Salivary glands
Stomach cells Pancreas cells
Substrate Amylose (starch)
Proteins Lipids
Products Maltose/glucose
Amino acids Glycerol/fatty acids
Optimum pH Neutral (pH 7) Acidic (pH 3) Neutral (pH 7)
Digestive system
Any foods you Any foods you ingest must ingest must eithereither be be digested and digested and absorbed for use absorbed for use by the body by the body oror remain remain undigested and undigested and be eliminated as be eliminated as solid waste solid waste (faeces)(faeces)
Stomach
Food brought to Food brought to stomach by stomach by oesophagusoesophagus
When you swallow, the When you swallow, the food is forced down to food is forced down to your stomach by your stomach by peristalsisperistalsis
Once in the stomach, Once in the stomach, the food is held for a the food is held for a period of time in order period of time in order to mix it with a variety to mix it with a variety of secretions of secretions collectively known as collectively known as gastric juicesgastric juices
PepsinPepsin – a protease – a protease enzyme most active in enzyme most active in acidic pHacidic pH
Hydrochloric acidHydrochloric acid – – helps degrade and helps degrade and break down foods and break down foods and creates the acidic pH creates the acidic pH necessary for pepsin to necessary for pepsin to be activebe active
MucusMucus – lines the – lines the inside of the stomach inside of the stomach wall to prevent stomach wall to prevent stomach damage from the damage from the hydrochloric acidhydrochloric acid
The muscular wall The muscular wall of the stomach of the stomach creates a churning creates a churning motion in order to motion in order to mix the food with mix the food with the gastric juicethe gastric juice
After a period of After a period of time, a valve at the time, a valve at the lower end of the lower end of the stomach opens and stomach opens and the food enters the the food enters the small intestinesmall intestine
What are you eating in a day?
How to read food labels Record the nutrition facts for all of Record the nutrition facts for all of
the food that you consume in one the food that you consume in one mealmeal
Small intestine
11stst portion is called the portion is called the duodenumduodenum Secretions are emptied here in Secretions are emptied here in
order to continue the digestive order to continue the digestive process:process: Bile from liver and gall bladderBile from liver and gall bladder Trypsin (a protease), lipase, amylase Trypsin (a protease), lipase, amylase
and bicarbonate from the pancreasand bicarbonate from the pancreas
Small intestine villi
Molecules are produced that are Molecules are produced that are small enough to be absorbedsmall enough to be absorbed
Inner wall of small intestine is made Inner wall of small intestine is made up of thousands of finger-like up of thousands of finger-like extensions called extensions called villivilli which functions which functions to increase surface area for to increase surface area for absorptionabsorption
Each villus contains a capillary bed Each villus contains a capillary bed and a and a lacteallacteal (a small vessel of (a small vessel of lymphatic system)lymphatic system)
AbsorptionAbsorption Molecules taken into Molecules taken into
capillary bed and capillary bed and lacteallacteal
Taken to a wide Taken to a wide variety of body cellsvariety of body cells
Used for energyUsed for energy
AssimilationAssimilation Molecules taken into Molecules taken into
capillary bed and capillary bed and lacteallacteal
Taken to a wide Taken to a wide variety of body cellsvariety of body cells
Used for building Used for building larger moleculeslarger molecules
Large intestine
Vast majority of food is absorbed in SI
What remains is undigested
Much of the water we drink or that is found within food is still present
Escherichia coli and other naturally occurring bacteria are mutualists
We provide nutrients, water, and a warm environment
They synthesize vitamin K and maintain and overall healthy environment
Any undigested food is eliminated from the body as solid waste or faeces
Vitamin K
Vitamin K is essential in humans and most animals as we cannot synthesize the compound ourselves
vitamin K is used by the liver to synthesise prothrombin, which in turn is processed to form the enzyme thrombin; a key enzyme involved in the blood clotting process
there is increasing evidence that vitamin K has additional roles in maintaining in bone health
There are two forms of vitamin K vitamin K1 – comes from our diet and is found in soybean
oil and dark green veggies vitamin K2 - which can come from the bacteria in the gut
and indeed E. coli can synthesise menaquinone because it uses it during respiration. As E. coli lives and dies in the gut, the dead cells release vitamin K2, which can then, theoretically, be absorbed and utilised by the body.
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