AQA GCSE Biology 2.1 Organisation: Digestion PDF

Head to www.savemyexams.com for more awesome resources AQA GCSE Biology 2.1 Organisation: Digestion Contents 2.1.1 Principles of Organisation 2.1.2 The Stomach 2.1.3 The Human Digestive System 2.1.4 Enzymes & Metabolism 2.1.5 Required Practical: Enzymes 2.1.6 Enzymes & Digestion 2.1.7 Required Pract...

Head to www.savemyexams.com for more awesome resources AQA GCSE Biology 2.1 Organisation: Digestion Contents 2.1.1 Principles of Organisation 2.1.2 The Stomach 2.1.3 The Human Digestive System 2.1.4 Enzymes & Metabolism 2.1.5 Required Practical: Enzymes 2.1.6 Enzymes & Digestion 2.1.7 Required Practical: Food Tests Page 1 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources 2.1.1 Principles of Organisation Your notes Organisation: Principles Page 2 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Multicellular organisms have many levels of organisation Cells are the basic building blocks of all living organisms Page 3 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Unicellular organisms are made from one cell, whereas multicellular organisms are made up of collections of cells In complex multicellular organisms, cells are specialised to carry out particular functions. These specialised cells form tissues, which form organs in organ systems In humans, the digestive system (provides the body with nutrients) and the respiratory system (provides the body with oxygen and removes carbon dioxide) are examples of organ systems that provide dissolved materials that need to be moved quickly around the body in the blood by the circulatory system Organisation table Page 4 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources 2.1.2 The Stomach Your notes The Stomach We can illustrate different levels of organisation by looking at the stomach: The role of the stomach is to start protein digestion To do this, the stomach produces proteases like pepsin, which digests proteins into amino acids. Acid produced by glandular tissue in the stomach aids protein digestion; it helps proteins unravel so that enzymes can break the bonds holding the amino acids together. It also inhibits many microorganisms that may be present in food, reducing the chance of infection The stomach is one of a number of organs that make up the digestive system The role of the digestive system is to break down large insoluble molecules into smaller, soluble food molecules to provide the body with nutrients Page 5 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Three types of tissue found in the stomach are muscular, epithelial and glandular. These tissues work together to allow the stomach to carry out its role Page 6 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources 2.1.3 The Human Digestive System Your notes Digestion: Basics 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 Page 7 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Tissues & Organs of the Human Digestive System The human digestive system is made up of the organs that form the alimentary canal and accessory organs The alimentary canal is the channel or passage through which food flows through the body, starting at the mouth and ending at the anus. Digestion occurs within the alimentary canal. Accessory organs produce substances that are needed for digestion to occur (such as enzymes and bile) but food does not pass directly through these organs The human digestive system includes the organs that form the alimentary canal, and accessory organs that aid the process of digestion Page 8 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Alimentary canal and accessory structures table Your notes Page 9 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Page 10 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes The Importance of Bacteria in Digestion The large intestine is home to hundreds of species of bacteria These bacteria form a microbial ecosystem (the microbiota, or gut flora) that play an essential role in human digestion of food by: Breaking down substances we can’t digest (like cellulose) Supplying essential nutrients Synthesising vitamin K Providing competition with any harmful bacteria to restrict their growth Taking antibiotics can disrupt the gut microbiota which can cause short-term problems with digestion Page 11 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources 2.1.4 Enzymes & Metabolism Your notes Enzymes & Metabolism Digestive enzymes work outside of cells; they digest large, insoluble food molecules into smaller, soluble molecules which can be absorbed into the bloodstream Metabolism is the sum of all the reactions happening in a cell or organism, in which molecules are synthesised (made) or broken down Enzymes are biological catalysts made from protein Enzymes speed up chemical reactions in cells, allowing reactions to occur at much faster speeds than they would without enzymes at relatively low temperatures (such as human body temperature) Substrates temporarily bind to the active site of an enzyme, which leads to a chemical reaction and the formation of a product(s) which are released Enzymes remain unchanged at the end of a reaction, and they work very quickly. Some enzymes can process 100s or 1000s of substrates per second Enzymes are biological catalysts that work in cells, so they randomly move about wherever they are in the cell. They don’t ‘choose’ to collide with a substrate – collisions occur because all molecules are in motion in a liquid Page 12 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Enzymes: How They Work Enzymes catalyse specific chemical reactions in living organisms – usually one enzyme catalyses one particular reaction: The enzyme catalase can bind to its substrate hydrogen peroxide as they are complementary in shape, whereas DNA polymerase is not The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s) Enzymes have specific three-dimensional shapes because they are formed from protein molecules Proteins are formed from chains of amino acids held together by peptide bonds The order of amino acids determines the shape of an enzyme If the order is altered, the resulting three-dimensional shape changes The lock & key model The ‘lock and key theory’ is one simplified model that is used to explain enzyme action The enzyme is like a lock, with the substrate(s) the keys that can fit into the active site of the enzyme with the two being a perfect fit Page 13 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Your notes Page 14 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Diagram showing the lock and key model 1. Enzymes and substrates move about randomly in solution 2. When an enzyme and its complementary substrate randomly collide – with the substrate fitting into the active site of the enzyme – an enzyme-substrate complex forms, and the reaction occurs 3. A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions The induced-fit model Another model that explains enzyme activity is the ‘induced-fit theory’ In reality when a substrate(s) binds to the active site of the enzyme, the active site and substrate change shape slightly to fit more perfectly together This makes it easier for bonds within the substrate to break and new bonds to form, producing product(s) Page 15 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Enzymes: Temperature & pH The effect of temperature Your notes The specific shape of an enzyme is determined by the amino acids that make the enzyme The three-dimensional shape of an enzyme is especially important around the active site area; this ensures that the enzyme’s substrate will fit into the active site enabling the reaction to proceed Enzymes work fastest at their ‘optimum temperature’ – in the human body, the optimum temperature is around 37⁰C Heating to high temperatures (beyond the optimum) will start to break the bonds that hold the enzyme together – the enzyme will start to distort and lose its shape – this reduces the effectiveness of substrate binding to the active site reducing the activity of the enzyme Eventually, the shape of the active site is lost completely and the enzyme is described as being ‘denatured’ Substrates cannot fit into denatured enzymes as the specific shape of their active site has been lost Page 16 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Denaturation is largely irreversible – once enzymes are denatured they cannot regain their proper shape and activity will stop Increasing temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction This means that low temperatures do not denature enzymes, but at lower temperatures with less kinetic energy both enzymes and their substrates collide at a lower rate Page 17 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Page 18 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources This graph shows the effect of temperature on the rate of activity of an enzyme The effect of pH Your notes The optimum pH for most enzymes is 7 but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9) If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop If pH is increased or decreased away from the optimum, then the shape of the enzyme is altered Page 19 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes This graph shows the effect of pH on the rate of activity of an enzyme from the duodenum Page 20 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources 2.1.5 Required Practical: Enzymes Your notes Enzyme Rate Aim: To investigate the effect of pH on the rate of reaction of amylase You will: Use the enzyme amylase to breakdown starch at a range of pH values, using iodine solution as an indicator for the reaction occurring Use a continuous sampling technique to monitor the progress of the reaction Amylase is an enzyme that digests starch (a polysaccharide of glucose) into maltose (a disaccharide of glucose) Starch can be tested for easily using iodine solution Iodine can be used qualitatively to indicate the presence or absence of starch from a sample Method Place single drops of iodine solution in rows on the tile Label a test tube with the pH to be tested Page 21 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Use the syringe to place 2cm3 of amylase in the test tube Add 1cm3 of buffer solution to the test tube using a syringe Use another test tube to add 2cm3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette After 10 seconds, use a pipette to place one drop of the mixture on the first drop of iodine, which should turn blue-black Wait another 10 seconds and place another drop of the mixture on the second drop of iodine Repeat every 10 seconds until iodine solution remains orange-brown Repeat experiment at different pH values – the less time the iodine solution takes to remain orangebrown, the quicker all the starch has been digested and so the better the enzyme works at that pH Page 22 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Your notes Page 23 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Investigating the effect of pH on enzyme activity Improvements to method The above method can be adapted to control temperature by using a water bath at 35℃ All solutions that need to be used (starch, amylase, pH buffers) should be placed in a water bath and allowed to reach the temperature (using a thermometer to check) before being used A colorimeter can be used to measure the progress of the reaction more accurately; with a solution containing starch being darker and glucose light (as a result of the colour-change of iodine) – this will affect the absorbance or transmission of light in a colorimeter Exam Tip Describing and explaining experimental results for enzyme experiments is a common type of exam question so make sure you understand what is happening and, for a 7, 8 or 9, can relate this to changes in the active site of the enzyme when it has denatured, or if it is a low temperature, relate it to the amount of kinetic energy the molecules have. Page 24 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources 2.1.6 Enzymes & Digestion Your notes Chemical Digestion The purpose of digestion is to break down large, insoluble molecules into smaller, soluble molecules that can be absorbed into the bloodstream Large insoluble molecules, such as starch and proteins, are made from chains of smaller molecules which are held together by chemical bonds. These bonds need to be broken Enzymes are biological catalysts – they speed up chemical reactions without themselves being used up or changed in the reaction There are three main types of digestive enzymes – carbohydrases, proteases and lipases Carbohydrases Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch into maltose, which is then broken down into glucose by the enzyme maltase Amylase is made in the salivary glands, the pancreas and the small intestine Diagram showing the digestion of starch Proteases Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine Protein digestion takes place in the stomach and small intestine, with proteases made in the stomach (pepsin), pancreas and small intestine Page 25 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Diagram showing the digestion of proteins Lipases Lipases break down lipids (fats) to glycerol and fatty acids. Lipase enzymes are produced in the pancreas and secreted into the duodenum Diagram showing the digestion of lipids Exam Tip The pancreas is an accessory organ in the digestive system. Food does not pass directly through it, but it has a key role in producing digestive enzymes as well as the hormones that regulate blood sugar (insulin and glucagon). Page 26 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources The Role of Bile Cells in the liver produce bile which is then stored in the gallbladder Bile production and secretion Bile has two main roles: It is alkaline to neutralise hydrochloric acid from the stomach. The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach It breaks down large drops of fat into smaller ones, increasing surface area. This is known as emulsification. The alkaline conditions and larger surface area allows lipase to chemically break down fat (lipids) into glycerol and fatty acids faster (the rate of fat breakdown by lipase is increased) Exam Tip Emulsification is the equivalent of tearing a large piece of paper into smaller pieces of paper. Page 27 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Products of Digestion The products of digestion are used to build new carbohydrates, lipids and proteins required by all cells to function properly and grow Some glucose released from carbohydrate breakdown is used in respiration to release energy to fuel all the activities of the cell Amino acids are used to build proteins like enzymes and antibodies The products of lipid digestion can be used to build new cell membranes and hormones Page 28 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources 2.1.7 Required Practical: Food Tests Your notes Food Tests Aim: To use qualitative reagents to test for a range of carbohydrates, lipids and proteins. To include: Benedict’s test for sugars, Iodine test for starch, the emulsion test for lipids and the Biuret reagent for protein You will: Use qualitative reagents to test for the presence of key biological molecules in a range of foods Safely use appropriate heating devices and techniques including the use of a Bunsen burden and a water bath A qualitative food test indicates if a substance is present or absent in a sample (although it doesn’t tell you how much is present) Observations are essential in this practical; you are looking for colour changes in particular which can indicate if a substance is present or absent: Food test colour changes table Use this image Preparing a sample Page 29 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Before you can carry out any of the food tests described below, you may need to prepare a food sample first (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 filter paper, collecting the solution Proceed with the food tests Use this image Page 30 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Your notes Use this image Page 31 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Use this image Page 32 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Your notes Use this image It is important that you carry out the tests methodically, recording your observations carefully Important hazards Whilst carrying out this practical you should try to identify the main hazards and be thinking of ways to reduce harm: Page 33 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Head to www.savemyexams.com for more awesome resources Biuret solution contains copper (II) sulfate which is dangerous particularly if it gets in the eyes, so always wear goggles Iodine is also an irritant to eyes (wear goggles) Sodium hydroxide in biuret solution is corrosive, if any chemicals get onto your skin wash hands immediately Ethanol is highly flammable; keep it away from the Bunsen burner used in the Benedict’s test (you should turn the Bunsen off completely) And of course, the Bunsen itself is a hazard! Page 34 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes Head to www.savemyexams.com for more awesome resources Use this image Be prepared to explain what molecules are or are not present in a food sample – make sure you know the positive and negative results for each test Page 35 of 35 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers Your notes