In order to make ATP, food is broken down via ingestion, digestion, and absorption. This can occur intracellularly (within vacuoles fused with lysosomes) as in sponges or protists or extracellularly utilizing a gastrointestinal digestive tract. Human digestive systems have two openings, one for ingestion and one for excretion. Food goes into the pharynx via the oral cavity and then proceeds down the esophagus into the stomach and small intestine where the food is digested. Food is absorbed in the large intestine and then excreted. Accessory organs include the liver, gall bladder, and pancreas. Starch is first broken down in the mouth by amylose, while proteins are broken down by pepsin in the stomach. Fats are emulsified by bile and digested by lipases in the small intestine.
The mouth is a site of both
mechanical and chemical digestion. The salivary glands secrete
amylase, an enzyme that hydrolyzes starch into polysaccharides and
The rhythmic contractions of
the esophagus, called peristalsis, move food into the stomach.
Gastric glands in the stomach
secrete gastric juices, which contain hydrochloric acid and pepsin.
Pepsin breaks proteins down into polypeptides.
Digestion of starches, proteins
and fats takes place in the small intestine. The pancreas secretes
bicarbonate and enzymes into the duodenum. Additional enzymes are
produced by the epithelial cells of the small intestine.
The villi and microvilli of the
small intestine provide a large surface area for the digestion and
absorption of nutrients.
The liver produces bile, which
is stored by the gall bladder and secreted into the duodenum. Bile
emulsifies fat, facilitating the breakdown of fat by lipases.
The large intestine consists of
the cecum, colon and rectum. Major functions of the large intestine
are the absorption of water and minerals and the storage of waste.
Digestion is regulated by the
hormones gastrin, secretin and cholecystokinin (CCK).
The Digestive System
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
The book and CD package include two full length practice exams that are presented with all questions answered and explained. The author also presents detailed reviews of all test topics and includes multiple-choice and free-response questions with answers at the end of each topic's chapter.
This book includes a review of the AP Biology exam format and scoring, proven strategies for answering multiple-choice questions, and hints for tackling the essay questions. The practice tests include answers and explanations and there is also proven test-taking strategies for both the multiple choice and essay parts.