Biology Homework Chapter 21: The Digestive System

Homework

• Reading Preparation
• WebLecture
• Study Activity
• Preparation work for chat
• Online Quiz
• Lab Instructions

Reading Preparation

Textbook assignment: Chapter 21: Digestion and Nutrition, sections 1-13.

Study Notes

• 21.1 Animals are distinguished by what they eat and how they injest it. Herbivores eat plants, carnivores eat meat, omnivores eat both. Suspension feeders filter food from water, substrate feeders live in their food source and eat their way through it, fluid feeders suck fluids from either plants or animals, bulk feeders take in relatively large pieces of food. Regardless of feeding processes, all animals must filter food through cells, which means exchanges of nutrition and waste occur through the membrane mechanisms we studied in chapter 5: osmosis, diffusion, active and passive transport.
• 21.2 The four main steps carried out by the digestive system are ingestion, digestion, absorption, and elimination. Digestion always involves hydrolysis to break down polymers of carbohydrates, fats, nucleic acids and proteins into their monomer components.
• 21.3 Because strong acids are required to break down nutrient molecules found as building blocks of proteins and organelles in all cells, the chemical reactions of digestion must be confined to those specialized compartments that make up the digestive system. Animals with gastrovascular cavities have only one opening. Animals with alimentary canals have a mouth, esophagus, stomach, intestine and anus, and may have additional pouches such as a crop or gizzard to perform additional digestive functions.
• 21.4 The Human Digestive System The human digestive system includes the organs of the alimentary tract plus the liver, gallbladder, pancreas, and salivary glands, each of which produces important catalysts or reactants that help break down different nutrients.
• 21.5 The first stage of digestion, ingestion, occurs in the mouth, with preliminary mechanical breakdown of all food by grinding, and chemical digestion of starches by salivary amylase. Food is swallowed as a small ball or bolus.
• 21.6 The bolus passes from the mouth through the pharynx to the esophagus, where the esophageal sphincter prevents food from slipping into the trachea. (Failure or mistiming of this sphincter may lodge food in the bronchial tubes, causing the victim to choke). The esophagus pushes the bolus from the pharynx to the stomach using waves of muscle contraction called peristalsis.
• 21.7 Connection: Heimlich maneuver This simple first aid technique is used to force food trapped in the trachea out of the respiratory system.
• 21.8 Stomach: Digestion The stomach uses hydrochloric acid to convert pesinogen to pepsin, which can break down polypeptides (proteins). Gastrin hormones use negative feedback to control the release of gastric juices and prevent hyperacidic conditions in the stomach. When broken down, acid chyme is releastedinto the intestines. No absorption of nutrients occurs in the stomach.
• 21.9 Connection: Ulcers If bacterial infections survive the gastric juices in the stomach, they can attack and create raw areas in the stomach and instestinal linings that result in ulcers or irritation of the esophagus (GERD).
• 21.10 Small Intestines: Absorption In the small intestines, pancreatic amylase breaks down the remaiining starches to maltose, which maltase and other enzymes can break into monosaccharides; typsin and chymotrypsin break polypeptides into smaller chains, with other enzymes breaking these into amino acids; nucleases break down DNA and RNA into nucleotides, and then into nitrogenous bases, phosphates, and sugars; and bile salts break fat globules into smallar particles, with lipase completing the transition to fatty acids and glycerol. From these raw materials, the cell can reconstruct what it needs.
• 21.11 Liver: Filtering The liver filters the absorbed nutrients, isolating and detoxifying harmful substances, and using the urinary system to excrete them from the body. It also manufactures critical proteins, blood clotting factors, nad lipoproteins.
• 21.12 In the large intestine (colon), wastes are filtered for water and compacted into feces, while bacteria such as E. coli (good strains) make vitamins. Feces leave via the rectum after bypassing the appendix.
• 21.13 Many animals have digestive systems that have been optimized to make use of their available diet. Ruminants (grass eaters) have even more elaborate digestive systems than humans. Extra chambers allow cows, horses, and deer to break down vegetative matter with high cellulose content.

Web Lecture

Read the following weblecture before chat: Nutrition and Digestion

Take notes on any questions you have, and be prepared to discuss the lecture in chat.

Study Activity

Perform the study activity below:

Chat Preparation Activities

• Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

Chapter Quiz

• No quiz yet: the Chapter Quiz opens when we finish the chapter.

Lab Work

Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.

• Lab Instructions: Vitamin C

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