At the end of this lesson, you should be able to:

Digestion

Learning Objectives At the end of this lesson, you should be able to: Enzymes Explain enzyme action in terms of the lock and key hypothesis Explain the effects of temperature and ph on the rate of enzyme catalyzed reactions Digestive Process Explain the importance of the digestive system Identify the main parts of a digestive system and how they work together to perform a function Describe how a digestive system helps in digestion of food and the part played by enzymes in digestion (Only classes of enzymes such as amylase, protease and lipase are needed. Specific names of enzymes not required.)

Why EAT? We need to eat because Our body needs NUTRIENTS CARBOHYDRATES PROTEINS FATS Types of Nutrients the Body Needs

Why EAT? CARBOHYDRATES PROTEINS FATS Types of Nutrients the Body Needs

Why DIGESTION?

Why DIGESTION? Digestion is necessary - to break down large insoluble molecules into smaller molecules - so that the body can absorb the nutrients required for its functioning DIGESTION is the process whereby large, insoluble food molecules are broken down into smaller, soluble food molecules

Large Complex Insoluble Molecules Small Simple Soluble Molecules DIGESTION Starch carbohydrase Glucose Proteins protease Amino Acids Fats lipase Glycerol Fatty Acids

DIGESTION Glucose Small simple soluble molecules are used for the following purposes: Growth of new cells and tissues Amino Acids Provide energy for growth, movement and for keeping warm Repair damaged tissues Glycerol Fatty Acids Keep us healthy

FOOD TESTS STARCH test Add about 5 drops of iodine solution to the sample to be tested. If starch is present, the iodine will turn dark blue If starch is absent, the iodine will remain brown

ENZYMES A A enzyme Enzymes are biological catalysts. Catalysts are substances that speed up the rate of reactions, but themselves remain chemically unchanged at the end of the reaction. A A A A enzyme enzyme

Lock & Key Hypothesis Substrate A Enzyme Enzyme Substrate B Enzyme Enzyme

ENZYMES- Mechanism substrate Enzyme products LOCK and KEY hypothesis Specificity: One enzyme binds to only one substrate Reusable: They are chemically unchanged at the end of the reaction Required in minute amounts Sensitive to temperature and ph Enzyme

ENZYMES- Mechanism substrate Enzyme Enzyme-substrate complex products Enzyme

Lock & Key Hypothesis

Rate of Enzyme Activity ENZYMES- Factors Enzymes work best at their optimum temperature. At low temperatures, enzymes are inactivated. At high temperatures, enzymes are denatured. Temperature/ C

Rate of Enzyme Activity ENZYMES- Factors Enzymes work best at their optimum ph. At extreme ph, enzymes are denatured. ph

LEARNING OBJECTIVES You should now know how to: - identify the main organs in the human digestive system - describe the process of digestion within the human body in detail

DIGESTIVE SYSTEM Associated (accessory) organs

The PROCESS Mechanical Digestion Biting Tearing Slicing Chewing (Masticating) Chemical Digestion Acid Enzymes

Mouth 1. Mechanical Digestion Food is broken down into smaller pieces by the chewing, tearing, slicing and biting action of the teeth 2. Enzymatic Digestion Starch is broken down into maltose by amylase in saliva No digestion of proteins and fats in the mouth Starch Maltose

Oesophagus Partially digested food is pushed down from the mouth into the stomach by muscles in the oesophagus that alternately contract and relax. (peristalsis) NO enzymes are present in the oesophagus.

Stomach Complex Proteins Simpler Proteins Complex proteins are broken down into simpler proteins by proteases (pepsin) found in gastric juices secreted by the stomach. No digestion of carbohydrates or fats occur in the stomach.

Small Intestines Simpler Proteins Amino Acids Maltose Glucose Fats Glycerol + Fatty Acids Three digestive juices are secreted into the small intestines to complete digestion: 1. Bile from the Liver This breaks fats into small droplets for easier digestion 2. Pancreatic Juice from the Pancreas 3. Intestinal Juice from the Small Intestines Both juices contain carbohydrase, protease and lipase.

Large Intestines Undigested food that reaches the large intestines will be passed to the rectum and anus for removal by the body as faeces. As it passes through, a lot of water is absorbed by the large intestines and taken back into the body.

INQUIRY time! Some obese people have had part of their small intestines removed. Suggest with reasons the effects of such a surgery? Proteins are digested in the stomach. The stomach wall consists of cells which are made of protein. So why does the stomach wall not get digested?

ABSORPTION Small Intestine Villi cells Blood Capillary

ABSORPTION Absorption is the movement of digested food molecules through the walls of the small intestine into the blood stream. Small Intestine By what process do the food molecules move through the intestinal walls? Blood Capillary Why does food molecules move into the blood stream but not move out?

ABSORPTION Digested food molecules move through the walls of the small intestine via diffusion. Undigested food molecules are too large to move through the walls of the small intestine. Small Intestine Blood Capillary

ABSORPTION How is the rate of absorption made faster in the small intestine? 1. Finger-like projections (called villi) in the wall of the small intestine provide a large surface-area for absorption of digested food molecules. Small Intestine Blood Capillary 2. The small intestine is long and convoluted, thus increasing the surface area for quicker absorption.

ABSORPTION Small Intestine How is the rate of absorption made faster in the small intestine? 3. The wall of the small intestine is only one-cell thick, shortening the distance between the wall and blood vessels so absorption can be faster. 4. A constant flow of blood ensures a low concentration of food molecules in the capillary, so rate of diffusion of digested food molecules into the blood is increased. Blood Capillary