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Digestion Textbook B Chp 11
Topics • • • •
Overview of Digestion Parts & Functions of Alimentary Canal Enzymes Food Tests
Overview • Big Idea: what happens when (& after) we eat food? • Why do we need to eat food in the first place? – For Energy – For growth – For maintenance (to remain healthy)
Processes of Eating 1. 2. 3. 4. 5.
Ingestion Digestion Absorption Assimilation Egestion
ALIMENTARY CANAL
Parts of the Digestive System 1. 2. 3. 4. 5. 6. 7.
Mouth Oesophagus Stomach Small Intestine Large Intestine Liver, Pancreas, Gall Bladder Rectum, Anus
Alimentary Canal
Video • Once Upon a Time…Life (Part 1) • https://www.youtube.com/watch?v=M1PuS2NVOw • Once Upon a Time…Life (Part 2) • https://www.youtube.com/watch?v=M4e6qf8r 8Tk • Once Upon a Time…Life (Part 3) • https://www.youtube.com/watch?v=QY5q4GJ OOgg
Mouth • Chewing breaks up food into smaller pieces – Increase surface area for digestion
• Saliva softens & moistens food (aid digestion) • Saliva contains the enzyme amylase – Amylase converts starch to maltose
Oesophagus • Carry food from mouth to stomach through the process peristalsis
Stomach • Many layers of muscle surround the stomach walls – mixes food by contraction and relaxation of muscles
• Contains hydrochloric acid (pH 1-2) – kills bacteria – provides an acidic environment for enzymes (proteases) to work
• Proteases convert protein to amino acids
Small Intestines • The small intestines are made up of three parts: duodenum, jejunum and ileum • Duodenum – contains several types of enzymes to digest food – amylase convert starch to maltose – lipase convert fat to fatty acid & glycerol – protease convert protein into amino acids
Small Intestines • While food is in the duodenum, different substances from other organs are also released into the duodenum to aid digestion – Bile • Produced from Liver, stored in Gall Bladder, and released to duodenum through the Bile duct • Bile emulsifies fat, making fat globules smaller and increasing surface area
– Pancreatic juice released from Pancreas • Amylase, protease and lipase
Small Intestines • The small intestines are very long so that there is large surface area to absorb digested food • The surface area is increased further by the presence of villi, fingerlike structures • Greater surface area allow for faster absorption of digested food
Other Parts • • • •
Large Intestine (colon) absorbs water and mineral salts Rectum stores undigested remains of food (faeces) Anus, where faeces is expelled from the body Did you know: colonoscopy
Physical vs Chemical Processes • Throughout digestion, there is a combination of physical and chemical processes • Physical processes involve breaking food down into smaller parts, but does not change the nature of the food (e.g. chewing, churning, emulsification) • Chemical processes involve breaking food down into different chemical components (e.g. work by enzymes)
ENZYMES
Enzymes • Recall: what is a chemical reaction? • An enzyme is a catalyst, something which speeds up chemical reactions (but is not “used up” in the process; remains unchanged) • The “raw material” which an enzyme works on is called the substrate, the “end product” is called the product • Enzymes are made of proteins • Enzyme activity is affected by temperature as well as pH (acidity)
Enzymes & Temperature • Recall in particulate model, we studied that at higher temperatures, molecules move faster • Enzymes and substrates collide with each other more frequently when temperature is raised, increasing rate of reaction • However, if the temperature becomes too high, the enzyme becomes denatured (i.e. changed in shape, become useless) • Optimum temperature around 40 °C
Enzymes & pH • pH is a measure of acidity • Neutral is pH7, less than 7 is acidic, more than 7 is alkali (or basic) • Stomach has around pH 1-2 (very acidic) due to the presence of hydrochloric acid produced by gastric juices • Enzymes have an optimum pH, depends on type of enzyme (stomach protease pH 2, salivary amalyse at pH 8, pancreatic lipase at pH 11)
Enzyme Summary Enzyme
Location
Substrate
Product
Amalyse
Mouth (from Starch Salivary Glands) & Duodenum (from Pancreas)
Maltose
Protease
Stomach, Duodenum (from Pancreas)
Protein
Amino Acids
Lipase
Duodenum (from Pancreas)
Fat
Fatty Acid + Glycerol
FOOD TESTS
Food Tests • There are 4 food tests you need to perform for your lab. These tests check if there are certain nutrients present in the sample. 1. Benedict’s test (for reducing sugars) 2. Iodine Test (for starch) 3. Emulsion Test (for fat/oil) 4. Biuret Test (for protein)
Food Test Summary Nutrient
Test Name
Starch
Iodine Test
Glucose/Malto Benedict’s Test se Protein Biuret Test Fat/Oil Ethanol Emulsion
Nutrient Present Blue-Black
Nutrient Absent Remains Brown Remains Blue
Red-Orange Precipitate Violet Solution Remains Blue White Remains Emulsion Colourless
Summary • • • •
Overview of Digestion Parts of Alimentary Canal Enzymes Food Test
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