WJEC GCSE Biology - 1.3 Digestion & the Digestive System in Humans

Sep 5, 2026

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WJEC GCSE Biology revision notes explain why digestion is needed and how the digestive system breaks down large, insoluble food molecules into smaller, soluble products that can be absorbed into the bloodstream. The materials cover the digestion products of carbohydrates, proteins and fats, and link them to energy release and building molecules for growth, repair and function. It also introduces practical food tests for starch, glucose and protein and describes how digestive enzymes act as biological catalysts.

LanguageEnglish

CategoryExam

FormatPDF

Pages30

Reading Time1 h 16 min

AccessFree to download

The Need for Digestion

The Products of Digestion

Food Tests

Test for Starch using Iodine Solution

Test for Glucose using Benedict's Reagent

Test for Protein using Biuret Solution

Enzymes in Digestion

Carbohydrases

Proteases

Lipases

Head to www.savemyexams. com for more awesome resources WJEC GCSE Biology 1 .3 Digestion & the Digestive System in Humans Contents The Need for Digestion Food Tests Enzymes in Digestion The Human Digestive System Peristalsis Function of Bile Absorption of Substances in the Small Intestine The Products of Digestion Diet & Energy Content of Food Investigating the Energy Content of Foods © 2015 − 2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams. com for more awesome resources The Need for Digestion The Need for Digestion The digestive system is an example of an organ system in which several organs work together to digest and absorb food Digestion is a process in which relatively large, insoluble molecules in food (such as starch, proteins) are broken down into smaller, soluble molecules that can be absorbed into the bloodstream and delivered to cells in the body These small soluble molecules (such as glucose and amino acids) are used either to provide cells with energy (via respiration) , or with materials with which they can build other molecules to grow, repair and function The products of digestion Some examples of how these food molecules are broken down during digestion are: Insoluble fats are broken down to the soluble products of one glycerol molecule and three fatty acid chains Insoluble proteins are broken down to soluble amino acids Large insoluble carbohydrates, such as starch, can be broken down to soluble simple sugars An example of a simple sugar is glucose Your notes © 2015 − 2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams. com for more awesome resources Food Tests Testing for the Presence of Starch, Glucose & Protein Preparing a sample Before you can carry out any of the food tests described below, you may need to prepare a food sample |rst (especially for solid foods to be tested) To do this: Break up the food using a pestle and mortar Transfer to a test tube and add distilled water Mix the food with the water by stirring with a glass rod Filter the mixture using a funnel and |lter paper, collecting the solution Proceed with the food tests Test for starch using iodine solution We can use iodine solution to test for the presence or absence of starch in a food sample Add drops of iodine solution to the food sample A positive test will show a colour change from orange/brown to blue/black The iodine solution test for the starch diagram Your notes © 2015 − 2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams. com for more awesome resources In the presence of starch, the iodine solution will turn from brown to blue/black Test for glucose We can use Benedict's reagent to test for the presence or absence of simple reducing sugars, such as glucose, in a food sample Add Benedict 's reagent to the sample solution in a test tube Heat in a boiling water bath for 5 minutes Take the test tube out of the water bath and observe the colour A positive test will show a colour change from blue to brick red Benedict's test for glucose diagram Your notes © 2015 − 2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams. com for more awesome resources The steps to carryout Benedict 's test for glucose Test for protein We can use biuret solution to test for the presence or absence of protein in a food sample Add drops of Biuret solution to the food sample A positive test will show a colour change from blue to violet The biuret test for protein diagram Your notes © 2015 − 2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams. com for more awesome resources The steps to carryout the biuret test for protein Food test results table | Food test | | P

FAQs

Why is digestion necessary in humans?

Digestion breaks down large, insoluble food molecules into smaller, soluble molecules that can be absorbed into the bloodstream and delivered to body cells.

What are the main digestive products of carbohydrates, proteins and fats?

Starch is broken down into simple sugars like glucose, proteins are broken down into amino acids, and fats are broken down into glycerol and fatty acid chains.

How can you test for starch, glucose and protein in food samples?

Starch is tested using iodine solution, glucose using Benedict's reagent (heated in a water bath), and protein using biuret solution. Each has a characteristic colour change for a positive result.

Sep 5, 2026

Upload by Jake