(1) According to the schematic diagram of the balanced diet pagoda, it can be seen that the food on the first floor of the balanced diet pagoda is rice, bread, potatoes and other foods, and the main nutritional component is starch. The digestion of starch begins in the mouth and is decomposed into maltose by salivary amylase and glucose in the small intestine. The food on the fifth floor is fat, grease, candy and other foods. The main nutrition is fat, and the digestion of fat starts from the small intestine.
(2) The small intestine is the place to digest food and absorb nutrition. This is because the small intestine is about 5 ~ 6 m long and contains various digestive juices such as intestinal juice, pancreatic juice and bile. There are annular folds on the inner wall of the small intestine, and there are small intestinal villi on the folds, which increases the area of digestion and absorption; There are capillaries and lymphatic capillaries in the villi of small intestine, which are composed of a layer of epithelial cells, which is beneficial to the absorption of nutrients.
The liver is the largest digestive gland in human body. Adult liver weighs about 65438±0.5kg, and most of it is located in the upper right part of abdominal cavity. Bile secreted by the liver has the function of emulsifying fat. Both the pancreas and the liver are located outside the digestive tract. Pancreatic juice secreted by the pancreas and bile secreted by the liver flow into the small intestine through the pancreatic duct and bile duct respectively, and participate in the digestion of food.
(3) protein is the basic substance that constitutes human cells; The growth and development of human body and the renewal of tissues are inseparable from protein; Teenagers are in a critical period of growth and development, so they should eat more food on the third and fourth floors of the Balanced Diet Pagoda, which is rich in protein.
(4) As shown in the figure, gingival bleeding is a disease caused by vitamin C deficiency. Long-term insufficient intake or diarrhea, vomiting, etc. It can cause vitamin C deficiency, prevent collagen from being synthesized normally, lead to cell connection disorder, increase capillary fragility, and lead to submucosal bleeding. It can be seen from the "balanced diet pagoda" that it is necessary to supplement the second layer of food, because there are more vegetables and fruits rich in vitamins and inorganic salts.
So the answer is: (1) sugar (or starch); ① Oral cavity; ④ Small intestine;
(2) small intestine; Bile; Pancreas;
(3) protein;
(4) 2.