Chapter 34: Digestive Systems and Nutrition

Transcription

1 Chapter 34: Digestive Systems and Nutrition AP Curriculum Alignment In order to maintain homeostasis, each cell of a living organism must have the correct surface area to volume ration to move nutrients into the cell and waste products out of the cell. This concept is explained in Big Idea 2. Chapter 34 discusses how the lining of the intestines has an increased surface area for absorption of nutrients due to enfolding of the intestinal lining to form villi which are then covered with microvilli. These structures are illustrative examples and can provide students with information about maintenance of homeostasis within the limitations of cell size. Any biological system needs to obtain nutrients and Chapter 34 explains how this need is met among very simple animals that are filter feeders through the human digestive system. The complex interactions between the human stomach and intestines are fully explained in Chapter 34. These interactions are illustrative examples in Big Idea 4 of the contribution of organs interactions to the well-being of the organism. The specialization of organs and their associated functions, such as those contained in the digestive system, contributes to the overall well-being of an organism. Big Idea 4 also acknowledges as an illustrative example the contribution that bacteria make to the digestion of food for some animals, such as ruminates. Chapter 34 goes into great detail about the anatomy of ruminates and their interaction with bacteria and other microorganisms in order to obtain nutrients. ALIGNMENT OF CONTENT TO THE CURRICULUM FRAMEWORK Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce, and to maintain dynamic homeostasis. Enduring understanding (EU) 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter. Essential knowledge (EK) 2.A.3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization. b. Surface area-to-volume ratios affect a biological system s ability to obtain necessary resources or eliminate waste products. Evidence of student learning is a demonstrated understanding of each of the following: 1. As cells increase in volume, the relative surface area decreases and demand for material resources increases; more cellular structures are necessary to adequately exchange materials and energy with the environment. These limitations restrict cell size. To foster student understanding of this concept, instructors can choose an illustrative example such as: Root hairs Cells of the alveoli Cells of the villi Microvilli 484

2 Enduring understanding (EU) 2.D: Growth and dynamic homeostasis of a biological system are influenced by changes in the system s environment. Essential knowledge (EK) 2.D.2: Homeostatic mechanisms reflect both common ancestry and divergence due to adaptation in different environments. a. Continuity of homeostatic mechanisms reflects common ancestry, while changes may occur in response to different environmental conditions. b. Organisms have various mechanisms for obtaining nutrients and eliminating wastes. To foster student understanding of this concept, instructors can choose an illustrative example such as: Gas exchange in aquatic and terrestrial plants Digestive mechanisms in animals such as food vacuoles, gastrovascular cavities, one-way digestive systems Respiratory systems of aquatic and terrestrial animals Nitrogenous waste production and elimination in aquatic and terrestrial animals Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties. Enduring understanding (EU) 4.A: Interactions within biological systems lead to complex properties. Essential knowledge (EK) 4.A.4: Organisms exhibit complex properties due to interactions between their constituent parts. a. Interactions and coordination between organs provide essential biological activities. To foster student understanding of this concept, instructors can choose an illustrative example such as: Stomach and small intestines Kidney and bladder Root, stem and leaf Enduring understanding (EU) 4.B: Competition and cooperation are important aspects of biological systems. Essential knowledge (EK) 4.B.2: Cooperative interactions within organisms promote efficiency in the use of energy and matter. a. Organisms have areas or compartments that perform a subset of functions related to energy and matter, and these parts contribute to the whole. Evidence of student learning is a demonstrated understanding of each of the following: 1. At the cellular level, the plasma membrane, cytoplasm and, for eukaryotes, the organelles contribute to the overall specialization and functioning of the cell. 2. Within multicellular organisms, specialization of organs contributes to the overall functioning of the organism. To foster student understanding of this concept, instructors can choose an illustrative example such as: Exchange of gases 485

3 Circulation of fluids Digestion of food Excretion of wastes 3. Interactions among cells of a population of unicellular organisms can be similar to those of multicellular organisms, and these interactions lead to increased efficiency and utilization of energy and matter. To foster student understanding of this concept, instructors can choose an illustrative example such as: Bacterial community in the rumen of animals Bacterial community in and around deep sea vents Concepts covered in Chapter 34 also align to the learning objectives that provide a foundation for the course, an inquiry-based laboratory experience, class activities, and AP exam questions. Each learning objective (LO) merges required content with one or more of the seven science practices (SP), and one activity or lab can encompass several learning objectives. The learning objectives and science practices from the Curriculum Framework that pertain to the digestive system and nutrition are shown in the table below. Note that other learning objectives may apply as well. LO 2.6 The student is able to use calculated surface area-to-volume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion. LO 2.7 Students will be able to explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination. LO 2.8 The student is able to justify the selection of data regarding the types of molecules that an animal, plant or bacterium will take up as necessary building blocks and excrete as waste products. LO 2.9 The student is able to represent graphically or model quantitatively the exchange of molecules between an organism and its environment, and the subsequent use of these molecules to build new molecules that facilitate dynamic homeostasis, growth and reproduction. LO 4.18 The student is able to use representations and models to analyze how cooperative interactions within organisms promote efficiency in the use of energy and matter. Key Concepts Summary Digestive system evolution Digestion contributes to homeostasis by provided all the nutrients to sustain life A digestive system includes all of the organs, tissues, and cells involved in ingestion and breaking down food into smaller pieces for adsorption. A digestive system: o Ingests food; o Breaks food down into small molecules that can cross plasma membranes; 486

4 o Absorbs these nutrient molecules; o Eliminates indigestible remains. Sponges have no digestive system and are filter feeders with specialized cells that break down food and make nutrients available to other cells. An incomplete digestive tract has one opening for food to enter and waster to leave. A complete digestive tract contains a mount and an anus and food moves in one direction through the digestive system. Animals may be herbivores (eat only plants), carnivores (eat only other animals), or omnivores (eat plants and animals). Dentition, types and placement of teeth, of animals aids their digestion and may indicate the type of diet pursued by a particular animal. Human digestive system The human digestive tract is a complete digestive system that requires the cooperation of many other systems. The human digestive tract organs are the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus. The accessory organs include the salivary glands, liver, gall bladder and pancreas. It has two major stages: mechanical digestion and chemical digestion. o Salivary glands secrete amylase which starts chemical digestion in the mouth where mechanical digestion also starts. o The muscular walls of the stomach contract vigorously and mix food with gastric juices, hydrochloric acid (HCl) and pepsin that are secreted whenever food enters the stomach. The stomach has a ph of around 2 which is low enough to kill most bacteria and microorganisms that enter the system. Marshall and Warren were awarded the Nobel Prize in Medicine in 2005 for discovering that stomach ulcers can be caused by an acidresistant bacterium, Helicobacter pylori. o When the sphincter between the stomach and the intestines relaxes, a small amount of partially digested food, chime, moves from the stomach into the intestines. The first part of the small intestines is the duodenum and receives bile from the liver and gall bladder and pancreatic digestive enzymes. Pancreatic juice contains sodium bicarbonate (NaHCO3), which neutralizes chyme. o Food digestion is completed in the small intestines. The surface area of the small intestines is increased by fingerlike projections called villi, and each villi has thousands of microscopic extensions called microvilli. Sugars and amino acids enter the blood. Starches are broken down into glucose molecules that are actively transported across the microvilli cell membranes into blood vessels. 487

5 Proteins are broken down into amino acids that are actively transported across the villi cell membranes into blood vessels. Fat droplets are broken down into fatty acids that diffuse scross the villi membranes into lymph vessels. o After nutrients are absorbed, they are eventually carried to all the cells of the body by the bloodstream. Undigested material then passes into the large intestines which includes the caecum (with the appendix), colon, rectum, and anus. o Water is reabsorbed in the large intestines. o Up to 400 different species of bacteria live in the large intestines and help prevent pathogenic bacteria from residing there. Key Terms bile bolus chyme complete digestive tract dentition duodenum gallbladder incomplete digestive tract lacteal liver microvilli mucosa pancreas peristalsis radula rumen ruminates salivary amylase salivary glands sphincters villi Teaching Strategies Class time: Two 45-minute class periods Day 1: Lecture on the human digestive system 25 minutes Activity 1 on digestive enzymes 20 minutes Day 2: Activity 2, investigating the effect of ph on amylase 45 minutes 488

6 Suggested Approaches The best approach to teaching the digestive system and nutrients is to focus on the mechanical and chemical breakdown of food into molecules that can be utilized by the animal. The mechanical activity increases the surface area for the enzymatic activity to chemically complete the breaks down of food into molecules that can be used by the animal. Interactions between the stomach, which mechanically and chemically digest food, and the intestines which primarily conduct chemical digestion should be an area of focus. Call attention to the evolutionary trends that are present in lower invertebrates such as a two-way digestive tract and trace the development of the one-way digestive tract. Student Misconceptions and Pitfalls Students may not realize that accessory organs, such as salivary gland, the liver, the gallbladder, and the pancreas, are not part of the passage that food takes through the human body. These accessory organs produce the enzymes that are largely responsible for digestion. The actual path that food takes through the body should be a focus point so that students will completely understand the interactions between all of the digestive organs. 489

7 Suggested Activities Activity 1: Digestive Enzymes 1. Have students make draw the digestive pathway through which food passes in the human body. 2. Students should then add the accessory organs to their drawing. 3. All of the digestive enzymes that are produced and their substrates should be added to this drawing. Activity 2: Investigating the effect of ph on amylase activity Amylase solution and iodine solution are low hazard once made up. Wear eye protection when handling iodine solution. In this activity, students will measure how much time it takes for amylase, a digestive enzyme, to completely break down starch. Find complete directions and student worksheet at: 490

8 Student Edition Chapter Review Answers Answers to Assess Questions 1. d; 2. d; 3. a; 4. d; 5. a; 6. b; 7. c; 8. a; 9. a; 10. c; 11. Test tube 1: no digestion (as a control); Test tube 2: some digestion (enzyme but no acid); Test tube 3: no digestion (no enzyme); Test tube 4: digestion (both enzyme and acid are present); 12. d; 13. b; 14. c Answers to Applying the Big Ideas Questions 1. The small intestine mixes chime with digestive enzymes for final breakdown, absorbs nutrient molecules into the body, and secretes digestive hormones into the blood. a) Describe the specialized structures of the villi and microvilli of the intestine. b) Explain how cell size and shape affect the overall rate of nutrient absorption and waste elimination. Essential Knowledge Science Practice Learning Objective 2.A.3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization. 6.2: The student can construct explanations of phenomena based on evidence produced through scientific practices. 2.7: Students will be able to explain how cell size and shape affect the overall rate of nutrient intake and the rate of waste elimination. 3 points maximum. Explanations for how cell size and shape affect the overall function of the intestine may include: Descriptions of villi and Explanation of related function microvilli (1 point each) The wall of the small intestine contains fingerlike projections called villi. The vessels of a villus contain blood capillaries and a lymphatic capillary, called a lacteal. (1 point each) By projecting from the intestinal wall The surface of the small intestine is increased. Essential molecules (e.g. sugars and amino acids) from digested materials enter the capillaries of a villus. Each villus has an outer layer of columnar epithelial cells, and each of these cells has thousands of microscopic extensions called microvilli. Microvilli contain intestinal enzymes. More microvilli means more enzymes that complete the process of food digestion, which means a greater rate of food digestion. 491

9 2. Organisms exhibit complex properties due to interactions between their constituent parts. Cooperation between the stomach and small intestine ensures an effective digestive process. a) Describe the mechanism by which the food from the stomach enters the small intestine. b) Predict the effect on the digestive process if something were to malfunction in the action of the pyloric sphincter which separates the stomach from the duodenum. Essential Knowledge Science Practice Learning Objective 4.A.4: Organisms exhibit complex properties due to interactions between their constituent parts. 6.4: The student can make claims and predictions about natural phenomena based on scientific theories and models. 4.9: The student is able to predict the effects of a change in a component(s) of a biological system on the functionality of an organism(s). 3 points maximum. Predicted effects of a change in a component of the digestive system may include: Description of mechanism Predicted effects of change (1 point each) (1 point each) The connection between the stomach If the sphincter is unhealthy and not and the duodenum of the small contracting when needed, food may intestine is regulated by the actions reenter the stomach from the intestines of a sphincter (pyloric sphincter can (also known as reflux or regurgitation). be retrieved from the prompt) which If the sphincter is unhealthy and not contracts and relaxes. contracting when needed, food may In the stomach, food mixes with enter the intestines before digestion is gastric juices to become chyme. The fully completed. opening and closing of the sphincter If the sphincter thickens, it can block slows the flow of chyme into the the channel, preventing the passage of small intestine, which allows for more food (chyme) from the stomach to the thorough digestion. In other words, small intestine, blocking the absorption when the sphincter is contracted, it of nutrients into the capillaries of the holds food in the stomach, allowing villi. digestion to continue to process. 492

10 Answers to Applying the Science Practices Questions Think Critically 1. Percent difference = (actual mass - label mass)/actual mass 100 cereal, bran flakes = 28%; cereal, toasted grains = 42%; cookie = 15%; mini danish = 22%; mini donut = 14% 2. All actual masses were greater than the label masses. Cereals have the highest percent difference. 493

11 Additional Questions for AP Practice 1. Describe the interactions between the human stomach and the human intestines. 2. Explain the importance of villi and microvilli to the human digestive system. 494

12 Grid-In Questions 1. The American and Canadian Dietetic Associations recommend that athletes should consume grams of protein per kilogram of body weight per day. What is the minimum amount of protein a 180 pound athlete should aim to consume during one week? 495

13 Answers to Additional Questions for AP Practice 1. The human stomach provides mechanical breakdown of food. The HCl and pepsin also induce chemical breakdown of the food. A sphincter separates the stomach and the intestines and will open to allow small portions of partially digested food to pass into the duodenum of the intestines for further completion of digestion. The partially digested food has been reduced to small particle that allow the digestive enzymes of the intestine ample surface area to complete the digestive process. 2. The wall of the small intestine has folds that bear fingerlike projections called villi.the surface of each villi is further folded into microvilli. The increased surface area provided by this enfolding allows for quicker digestion of food and absorption of nutrients. The products of digestion are absorbed into the blood capillaries and the lacteals of the villi by microvilli, which project from the villi. Answers to Grid-In Questions ; 180 lll 0.45 kk lll = 81.6 kk 1 g 7 dddd = 567 ggggg/wwww ddd 1 wwww 496