1. Nutrition (H) B1: Humans as Organisms

2. Nutrition The digestive system digests (breaks down) food and absorbs the products of digestion into the blood stream. Digestion is the breakdown of large, complex, insoluble, non-diffusible food substances into small, simple, soluble, diffusible food substances so that they can be absorbed. In mechanical digestion the food is broken down by the chewing action of the teeth (mastication). In chemical digestion the food is broken down by the actions of the enzymes.

3. Glucose molecules Amino acids Absorption is the transfer of the products of digestion into the bloodstream (or lymphatic system). Fatty Acids and Glycerol Fats Starch Protein digestion absorption Blood plasma Lymph Nutrition

4. Below is a partly labelled diagram of the human digestive system present in the abdominal cavity. The digestive system includes the gullet (oesophagus), the stomach, the liver, the pancreas, the small intestine and the large intestine. Add these structures to the diagram using the empty labels shown. (Click to check your answers). Liver Gullet Stomach Pancreas Small intestine Large intestine Gall bladder Diaphragm Rectum Anus Appendix

5. Nutrition The digestion of starch, proteins and lipids (fats and oils) is speeded up by the actions of enzymes. These are present in the digestive juices. Simple sugars, for example, glucose. Amino acids. Fatty acids and glycerol. Products of digestion Where it acts Substrate (What it acts on) Where produced Enzyme Amylases (Enzymes which digest carbohydrates). Salivary glands, pancreas and small intestine. Starch and other complex carbohydrates such as glycogen. Saliva acts in the mouth cavity. Pancreatic and intestinal juices act in the small intestine. Proteases (Enzymes which digest proteins). Stomach, pancreas and small intestine. Proteins. Gastric juice containing proteases acts in the stomach. Pancreatic and intestinal juices act in the small intestine. Lipases (Enzymes which digest fats/oils). Pancreas and small intestine. Fats and oils. Pancreatic and intestinal juices act in the small intestine.

6. Nutrition The oesophagus carries food to the stomach from the mouth cavity, where it has been chewed into smaller pieces by teeth (mastication) and mixed with saliva to start chemical digestion of starch. The muscular wall of the oesophagus (and other parts of the gut) contract in a wave-like motion (peristalsis) to move the food along. Bacteria also reach the stomach in swallowed mucus, wafted up the wind pipe from the lungs, by the action of cilia lining the respiratory tract. The stomach: produces hydrochloric acid which: kills most bacteria taken in with food; provides the best (optimum) conditions for the stomach enzymes to work.

7. Can you think why emulsification of fats allows faster lipase action? Smaller droplets of fat have a larger surface area relative to volume than large droplets of fat. A larger surface area means there is a greater area upon which lipases can act, thus, faster digestion. The liver produces bile which is stored in the gall bladder. It is released into the small intestine when food enters after digestion in the stomach. Neutralises the acid from the stomach. Provides alkaline conditions which are optimum for the pancreatic and intestinal enzymes to work efficiently. Emulsifies fats (breaks the large fat droplets down into smaller fat droplets). This enables faster breakdown by lipase enzymes. Bile has the following functions. Nutrition

8. The gall bladder collects and stores bile secreted by the liver. When the stomach empties its contents into the small intestine, the gall bladder contracts and empties the bile into the small intestine. Bile contains: water which acts as a solvent for digested foods and digestive juices, and bile salts, for example, sodium hydrogen carbonate. Sodium hydrogen carbonate neutralises the acidity from the stomach so that the small intestine contents are alkaline. This provides optimum conditions for the pancreatic and intestinal enzymes to operate well. The bile salts also lower the surface tension of fats. This emulsifies fats. This means that large fat droplets break into many minute fat droplets. This increases the surface area of the fat relative to its volume and so lipase enzymes can act faster. This means that fat can be digested and absorbed more readily.

9. Nutrition Simple sugars, amino acids, fatty acids and glycerol. These will be mixed up with undigested carbohydrate, protein and fat. The contents of the small intestine remain there for about 36 hours while being churned by muscular action and subjected to enzyme digestion. Absorption of most of the simple sugars, amino acids, water, salts and vitamins occurs through the small intestine wall into the blood stream. Fatty acids and glycerol are absorbed into the lymph. Indigestible material, for example, fibre, and undigested starch, protein and fat remain in the large intestine, and form faeces. These are eventually pushed into the rectum and released to the outside via the anus. This is called “defaecation”. What do you think will be in these intestinal contents?

10. Nutrition The small intestine is adapted to achieve maximum absorption of water, salts, vitamins and digested foods. It has a folded inner surface to increase its surface area for absorption. It has its surface developed into millions of small finger-shaped projections called villi. It has many blood capillaries to absorb food into. The absorbed food is then carried in the blood directly to the liver. fat droplets and partly digested fat is absorbed into special ducts called lacteals. These carry lymph (a type of tissue fluid) which is eventually returned to the blood. Columnar epithelium Dense capillary network (A) Lacteal (B) Artery from heart Vein to liver List, (1)digested foods absorbed into A, (2)non-digested substances absorbed into A and (3)substances absorbed into B.. (1). Simple sugars, amino acids, fatty acids and glycerol. (2). Water, salts, vitamins. (3). Fat droplets and partly digested fat. Vertical section of a villus

11. Test questions on the digestive system 1. Try to complete the following table: SubstanceActionWhere found Digests starch to simple sugars Protease Hydrochloric acid Digests fats to fatty acids and glycerol Amylase Saliva, pancreas, small intestine Digests proteins to amino acids Stomach, pancreas, small intestine Kills bacteria, provides an acid medium for enzymes to work Stomach LipasePancreas and small intestine 2. Think of three functions of bile in the small intestine. 3. What substances in the human diet do not require digesting? Neutralises stomach acid, provides an alkaline medium for the enzymes to work, emulsifies fats. Water, mineral salts, vitamins. Nutrition

12. The chemical reactions inside cells are controlled by enzymes. An enzyme is a biochemical catalyst which can increase the rate of a biochemical reaction. An enzyme works faster as the temperature rises, up to a maximum called the optimum temperature. Above this temperature, because they are made of protein, they are broken apart (denatured) and no longer work. Enzyme action is also affected by the surrounding pH. They work best at their optimum pH.. Enzymes are also found outside cells, although they will have been made in cells and then secreted. Thus digestive enzymes are found in the digestive juices in the digestive system. Nutrition

13. The graph shows the effect of temperature on the rate of enzyme action. Rate of enzyme action Temperature Mean body temperature (37 o C) In view of this graph why is it important to maintain body temperature close to its mean value? Because the enzymes in the body work best at the mean body/optimum temperature. Any deviation from the mean reduces the efficiency of enzyme action.

14. Nutrition Under suitable conditions, a protease enzyme will digest the gelatine of exposed developed film so that the black deposits of silver salts will fall off the film and form a deposit at the bottom of the test tube. This can be used as a tool to investigate the effects of temperature, or pH, or enzyme concentration, on the action of protease enzymes. A developed film was cut into 1 cm squares and each piece was immersed in 5cm 3 of a pH 4.0 buffer solution. The test tubes were placed in ice and waterbaths at 10 o C, 20 o C, 30 o C, 35 o C, 40 o C and 50 o C to acclimatise. 5cm 3 of temperature acclimatised 1% protease solution was then added to each tube and the contents mixed. Controls were also set up and temperature acclimatised. 5cm 3 of distilled water was added to the controls instead of protease solution. The tubes were left to incubate for 10 minutes and then observed for black deposits of silver salts. Try to complete the table of results on the next slide.

15. Nutrition No digestion because no enzyme is present. Enzyme activity has ceased due to enzyme denaturation. At temperatures above the optimum the rate of enzyme action decreases. Enzyme action tends to be greatest near the optimum temperature. As temperature is increased the rate of enzyme action increases and so progressively more deposit is formed and the film becomes clearer. Temperature too low to enable enzyme activity. Film black, no deposit. Film showing some clear areas, medium deposit. Film completely clear, biggest deposit. Film showing mostly clear, large deposit. Film showing a few clear areas, small deposit. Film black, trace of deposit. Film black, no deposit. ExplanationClarity of film/amount of deposit All controls 50 40 35 30 20 10 0 Temperature o C

16. Food Tests: Iodine test for starch – starch turns iodine blue/black. Add some drops of brown iodine solution to the food. If it contains starch the iodine will turn blue/black. Nutrition

17. Then add some dilute copper sulphate solution. Food Tests: Biuret test for protein – turns purple. Add some sodium hydroxide (NaOH) solution and shake with care. If the pale blue colour turns purple there is protein present. Nutrition

18. Food Tests Benedict’s test for simple sugars – an orange precipitate. Add blue Benedict’s solution to food in test tube. HEAT Orange precipitate indicates food contains simple sugars. Put into a water bath Do not heat directly!