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. Ingestion2. Digestion3. Absorption4. Assimilation5. Egestion

ALIMENTARY CANAL

Parts of the Digestive System

1. Mouth2. Oesophagus3. Stomach4. Small Intestine5. Large Intestine6. Liver, Pancreas, Gall Bladder7. Rectum, Anus

Alimentary Canal

Video• Once Upon a Time…Life (Part 1)• https://www.youtube.com/watch?v=M-1PuS2

NVOw• 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

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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, finger-like 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 SummaryEnzyme Location Substrate ProductAmalyse Mouth (from

Salivary Glands) & Duodenum (from Pancreas)

Starch 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 SummaryNutrient Test Name Nutrient

PresentNutrient Absent

Starch Iodine Test Blue-Black Remains Brown

Glucose/Maltose

Benedict’s Test Red-Orange Precipitate

Remains Blue

Protein Biuret Test Violet Solution Remains BlueFat/Oil Ethanol

EmulsionWhite Emulsion

Remains Colourless

Summary

• Overview of Digestion• Parts of Alimentary Canal• Enzymes• Food Test