6.1

Define absorption

- Absorption is the process of taking in substances through cell membranes or layers of cells. - This occurs on the inner wall of the small intestine, which is made up of thousands of extensions called villi - Most of the molecules absorbed are taken in the capillary bed within each villus - All the absorbed molecules are taken to a wide variety of body cells by the circulatory system

Outline the function of the stomach

- Food is eaten in less time than it can be digested by the small intestine so it is stored in the stomach for a period of time - Once inside the stomach, the food is mixed with a variety of secretions known as gastric juice 1) Pepsin: a protease enzyme, begins the process of digestion by breaking down polypeptide into amino acids 2) Hydrochloric acid: Helps degrade and break down food and creates the acidic pH necessary for pepsin to be active; also kills bacteria in the food we eat 3) Mucus: lines the inside of the stomach wall to prevent stomach damage from the hydrochloric acid - The muscular wall of the stomach contracts in order to mix food with the gastric juice

Outline the function of the small intestine

- In the small intestine, three different accessory organs secrete juices to continue the digestive process. 1) Bile from the liver and gall bladder. Breaks droplets of fat into smaller droplets so the enzymes have larger surface area to act on 2) Pancreatic juices - These juices produce molecules that are then small enough to be absorbed. Also in the small intestine, lymphocytes detect pathogenic organisms in food and help in production of antibodies against them

Outline the function of the large intestine

- Indigestible matter, bacteria, water and mineral ions pass through into the large intestine. - The primary function of the large intestine is water and mineral ion absorption - Leaving the water in the alimentary canal as long as possible is beneficial because it keeps the moving food in a fluid environment. - Any undigested food is eliminated from the body as solid waste through anus

Explain why digestion of large food molecules is essential

- Most food molecules are large polymers and are insoluble - They must first be digested into their smaller soluble molecules, such as starch, proteins and lipids, before they can be absorbed into the bloodstream

Explain the need for enzymes in digestion

- The breakdown of carbohydrates, proteins and lipids is a slow process at body temperature - Enzymes lower the required activation energy and therefore increase the rate of digestion.

What are villi

- The inner wall of the small intestine is made up of thousands of finger like extensions called villi. - Each villus contains a dense network of blood capillaries and a lacteal - The function of the villi is to greatly increase the surface area for absorption of molecules

How do villi relate to their role in absorption and transport of the products of digestion

- The structure of villi are related to their role in absorption and transportation of the products of digestion - They increase the surface area of the small intestine wall for absorption x3 - Their outmost tissue is a single layer of epithelium cells, which are permeable to digested foods - There is also a layer of microvilli on the surface of the epithelium, further increasing the surface area x10 - Dense network of blood capillaries inside the villus absorb the end products of digestion from the epithelial cells - There is a branch of the lymphatic system in the centre of the villus called a lacteal. This absorbs fatty acids and lipoproteins, which are not easily absorbed into blood capillaries - Muscle fibres around the lacteal contract to make the villus shorter, squeezing fluid along the lacteal by peristalsis

Define assimilation

- This is the conversion of nutrients into fluid or solid parts of the organism - Assimilation can only occur after absorption has taken place - Within the body cell, the nutrient molecule may be used for energy (e.g glucose) or it may be used as a component to help build a larger molecule inside the cell - During assimilation, substances such as amino acids, fatty acids and glycerol, are built up into macromolecules, which then become a structural part of the body

State the source, substrate, products and optimum pH conditions for one lipase

Enzyme: Pancreatic lipase Source: Pancreas juice Substrate: lipids Product: Glycerol and Fatty acids pH: 7

State the source, substrate, products and optimum pH conditions for one protease

Enzyme: Pepsin Source: gastric juice Substrate: Proteins Product: amino acid pH: 2

State the source, substrate, products and optimum pH conditions for one amylase

Enzyme: Salivary amylase Source: Saliva Substrate: Amylose Product: Maltose pH: 7

Draw and label a diagram of the digestive system

Mouth, Esophagus, Liver, Stomach, Gall bladder, Pancreas, Small intestine, Large intestine, Anus