1. DIGESTION
Topic 6.1
IB Biology
Miss Werba

2. NERVOUS & ENDOCRINE SYSTEMS
TOPIC 6 - PHYSIOLOGY
6.1
DIGESTIVE SYSTEM
6.2
CIRCULATORY SYSTEM
6.3
IMMUNE SYSTEM
6.4
RESPIRATORY SYSTEM
6.5
NERVOUS & ENDOCRINE SYSTEMS
6.6 REPRODUCTIVE SYSTEM
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3. THINGS TO COVER Importance of digestion Need for digestive enzymes
Optimum conditions of digestive enzymes
Diagram of the digestive system
Function of the digestive organs
Absorption vs assimilation
Structure of the villus
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4. IMPORTANCE OF DIGESTION
6.1.1
IMPORTANCE OF DIGESTION
Digestion: breaking large, insoluble food molecules into smaller, soluble molecules
Food is composed of large, insoluble molecules:
eg. carbohydrates, proteins, lipids
Humans need to break these molecules down into smaller units to:
Makes it soluble & able to be absorbed
Generates usable building blocks
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5. NEED FOR ENZYMES Digestion is a slow process
6.1.2
NEED FOR ENZYMES
Digestion is a slow process
Enzymes allow digestion to occur at a faster rate at body temperature
Enzymes lower the activation energy for the reactions of chemical digestion to occur
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6. 6.1.2
NEED FOR ENZYMES
Specific digestive enzymes are required for each type of substrate.
They can be classified into groups depending on their action:
Carbohydrases (or amylases)
work on carbohydrates
Proteases
work on proteins
Lipases
work on lipids
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7. NEED FOR ENZYMES Command term: STATE
6.1.3
NEED FOR ENZYMES Command term: STATE
Name of Enzyme
Where it is made (Source)
Where it works
What it works on
(Substrate)
What is made
(Products)
Optimum pH
Amylase
Salivary amylase
Salivary Glands
Mouth
Starch
Maltose 7
Protease
Pepsin
Wall of the stomach
Stomach
Protein
Polypeptides
1-2
Lipase
Pancreatic lipase
Pancreas
Small Intestine
Lipids
Glycerol
&
3x Fatty Acids 8
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8. THE DIGESTIVE SYSTEM Command terms: DRAW and LABEL
6.1.4
THE DIGESTIVE SYSTEM Command terms: DRAW and LABEL
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9. THE DIGESTIVE SYSTEM Command terms: DRAW and LABEL
6.1.4
THE DIGESTIVE SYSTEM Command terms: DRAW and LABEL
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10. THE DIGESTIVE SYSTEM Command terms: DRAW and LABEL
6.1.4
THE DIGESTIVE SYSTEM Command terms: DRAW and LABEL
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11. 6.1.4
THE DIGESTIVE SYSTEM
The digestive system can be broken into two parts:
Alimentary canal:
a continuous tube running from the mouth  anus
Accessory structures:
lie outside the alimentary canal
either produce or store secretions which aid in digestion of food
eg. salivary glands, liver, gall bladder & pancreas
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12. THE DIGESTIVE SYSTEM: The Stomach
6.1.5
THE DIGESTIVE SYSTEM: The Stomach
Temporary food storage
Mechanical digestion:
Peristalsis of the stomach wall mixes the food into a paste called chyme
Chemical digestions:
Glands in the stomach wall produce gastric juices containing pepsin and acid
Pepsin - proteins  soluble polypeptides
Hydrochloric acid - provides the optimum pH for pepsin and kills microbes
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13. THE DIGESTIVE SYSTEM: The Small Intestine
6.1.5
THE DIGESTIVE SYSTEM: The Small Intestine
Entry point for pancreatic juice and bile:
Pancreatic juice – produced in pancreas; alkaline; contains enzymes
Bile – produced in liver; stored in gall bladder; emulsifies fats to break them into tiny droplets
Lined with villi to increase the SA:Vol ratio
Intestinal crypts aid digestive process
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14. THE DIGESTIVE SYSTEM: The Small Intestine
6.1.5
THE DIGESTIVE SYSTEM: The Small Intestine
Primary site of food breakdown
Intestinal wall also produce a number of enzymes:
Protease – peptides  amino acids
Lipase - lipids  3x fatty acids & glycerol
Carbohydrase - carbohydrates  simple sugars
Nuclease – nucleic acids  nucleotides
Absorption of nutrients (aided by high SA:vol ratio established by presence of villi & microvilli)
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15. THE DIGESTIVE SYSTEM: The Large Intestine
6.1.5
THE DIGESTIVE SYSTEM: The Large Intestine
The caecum and the appendix are found at the join of the small and large intestine
no digestive function
Produces no digestive enzymes
Absorbs water & dissolved minerals
Secretes mucous to lubricate GI tract from abrasion by faeces
Semi-solid faeces eliminated via anus
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16. ABSORPTION & ASSIMILATION
6.1.6
ABSORPTION & ASSIMILATION
Digest
Absorb
Assimilate
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17. ABSORPTION & ASSIMILATION
6.1.6
ABSORPTION & ASSIMILATION
Digestion :
breaking down large molecules into smaller ones
Absorption :
small molecules are taken up from the digestive system into the blood stream
Assimilation :
when these molecules are incorporated into tissues of the body
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18. THE VILLUS Create high TSA for absorption:
6.1.7
THE VILLUS
Create high TSA for absorption:
Small intestine surface folded into villi
Villi surface folded into microvilli.
Thin epithelium (one cell layer) for easy absorption.
Protein channels in the microvilli membranes - allow rapid absorption by diffusion and active transport.
Dense capillary network – for rapid absorption of molecules.
A lacteal in the centre of the villus - carries away fats after absorption.
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19. 6.1.7
THE VILLUS
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20. THE VILLUS Remember: MR SLIMM
6.1.7
THE VILLUS
Remember: MR SLIMM
Microvilli – ↑ SA:Vol ratio for absorption
Rich capillary network – more efficient transport
Single-layer epithelium – short diffusion distance
Lacteals – absorption of lipids
Intestinal crypts – secretes juice to aid absorption
Membrane proteins – facilitated diffusion
Mitochondria in epithelium – active transport
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21. Sample questions Q1
Celiac disease causes the destruction of the villi cells. Which of the following is most likely to happen to people with celiac disease?
Incomplete digestion of fats
Poor absorption of calcium
Increased levels of glucose in blood
Damage in the esophagus caused by increase in acid content of the stomach
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22. Sample questions Q2
Researchers extracted an enzyme from the human digestive system and tested its activity at different pH values on proteins extracted from the blood of cows. The results are shown in the graph below.
Deduce from where in the human digestive system this enzyme was extracted. [1]
Outline the need for enzymes in the digestive system. [2]
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23. Sample questions A1 B A2 stomach 1max
enzymes speed up the digestive processes; (chemical) break down of food/food particles/large molecules; make soluble products/molecules small enough to be absorbed;
2 max
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24. Sample questions Q3
Explain how the structure of a villus in the small intestine is related to its function.
[7]
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25. Sample questions A3
To achieve [1] answer must name the structure and relate it to its function.
the villus has a large surface area to volume ratio;
microvilli increase surface area for absorption;
thin surface (epithelial) layer so products of digestion can pass easily through;
channel proteins located in plasma membrane used for facilitated diffusion;
network of capillaries inside each villus (so only short distance) for movement of absorbed products;
capillaries transport absorbed nutrients/sugars and amino acids away from small intestine;
blood flow in capillaries maintains concentration gradient;
central lymph vessel/lacteal to transport absorbed fats/fatty acids away from small intestine;
large number of mitochondria provide ATP needed for active transport;
protein pumps in membrane (of microvilli) carry out active transport;
pinocytosis occurs at surface (epithelial) layer;
Accept any of the points above shown in a drawing. 7 max
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