Published on July 24, 2013
MAKING SENSE OF DIGESTION AND ENZYMES IGCSE Biology 2.2 Food and Digestion Brought to you by MrExham.com Image © Depositphotos.com/[julos #4371007]
• Can you label a diagram of the digestive system and explain the functions of the mouth, oesophagus, stomach, small intestine, large intestine and pancreas? • Can you explain what the following terms mean: ingestion, digestion, absorption, assimilation and egestion? • What is peristalsis? • Can you explain how digestive enzymes are used to break down starch, protein and fat? • Where is bile produced and stored? What are its roles? • How do villi aid absorption in the small intestine?
• Digestion is the chemical and mechanical breakdown of food. • It converts large insoluble molecules into small soluble molecules, which can be absorbed into the blood.
mouth liver gall Bladder duodenum ileum appendix anus rectum colon pancreas stomach oesophagus salivary gland Small intestine Large intestine
• Chemical digestion occurs when the enzyme in the saliva breaks down starch into . • Mechanical digestion occurs as the teeth break the food down into smaller chunks. This gives a larger surface area for the enzymes to work.
• The chewed lump of food passes from the mouth into the stomach via a tube called the oesophagus or gullet. Oesophagus
• The food is held in the stomach for several hours. • Mechanical digestion occurs as the muscular stomach wall churns up the food. • The stomach wall secretes which kills bacteria to protect us from food poisoning. • A protease enzyme called breaks down protein in the stomach into amino acids. • A sphincter holds the food in the stomach until it is ready to be released into the first part of the small intestine called the duodenum.
• Several enzymes are added into the duodenum by the pancreas in the form of a liquid called pancreatic juice. • These include: , and . • Also added at this stage is . • Bile is made in the liver and stored in the . • Bile is not an enzyme. It’s function is to large lipids. • This means they become small fat droplets which increases the surface area for the enzyme lipase to work. • Bile and pancreatic juice are both alkali in order to neutralise the food covered in stomach acid.
• Food moves along the gut by a process called . • The gut has two layers of muscle, one is and the other is . • They work together to push the food along like a squeezing wave. Boumphreyfr on wikimedia
• By this stage the food has been broken down fully into small enough molecules to be absorbed into the blood. • The ileum is adapted for this process. • It has a very large surface area due to and . Sunshineconnellyaten.wikibooks
• Each villus contains a network of blood vessels and a . • The blood vessels join up to form the which leads to the liver. • The lacteals absorb the products of fat digestion into the system. • The food molecules get transported in the blood to the tissues where they get into cells. http://www.flickr.com/photos/wellcomeimages/
• The first part of the large intestine absorbs water. • This is called the . • All that is left is indigestible fibre which is called faeces. • This is stored in the rectum and expelled through the anus. This is called .
Term Definition Ingestion Food is taken into the mouth. Digestion Food is broken down from large insoluble molecules to small soluble molecules. This can be done mechanically and chemically. Absorption Molecules diffuse into the blood. Assimilation Molecules are used by the body for various processes such as building or repairing cells. Egestion Undigested food leaves via the anus.
Enzyme Location Breaks down Into Amylase Saliva/Small Intestine Starch Maltose Pepsin Stomach Protein Amino Acids Trypsin Pancreatic Juice Protein Amino Acids Maltase Small Intestine Maltose Glucose Lipase Pancreatic Juice Lipids Glycerol and Fatty Acids
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