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January 15, 2018 | Author: Anonymous | Category: , Science, Biology, Nutrition, The Digestive System
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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


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) • • Once Upon a Time…Life (Part 2) • 8Tk • Once Upon a Time…Life (Part 3) • 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 • 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





Mouth (from Starch Salivary Glands) & Duodenum (from Pancreas)



Stomach, Duodenum (from Pancreas)


Amino Acids


Duodenum (from Pancreas)


Fatty Acid + Glycerol


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


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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