Digestion of food involves both physical and chemical processes. Through digestion, large food particles are converted into smaller components that can be readily absorbed into the bloodstream. Show
Mechanical digestionFood is taken into the mouth where it is broken down into smaller pieces by the teeth. As the teeth grip, cut and chew the food, saliva is released and mixes with the smaller food particles. Saliva moistens and lubricates the food, allowing it to be worked into a small ball called a bolus, which can then be easily swallowed. This mechanical work on the food not only greatly increases its surface area but also allows it to be mixed with a digestive enzyme present in saliva. Chemical digestionMechanical digestion can only break up the food particles into smaller pieces. A chemical digestion process called enzymatic hydrolysis can break the bonds holding the molecular ‘building blocks’ within the food together. For example, proteins are broken down into their ‘building block’ amino acids. Once released, these small molecules can then be absorbed through the gut wall and into the bloodstream. An enzyme is a protein that can control the rate of biochemical reactions. In enzymatic hydrolysis reactions, an enzyme incorporates a water molecule across the bond, allowing it to break. CarbohydratesThe basic building blocks of carbohydrates are simple sugars like glucose and fructose. The bonds holding these sugars together are called glycosidic bonds. ProteinsThe basic building blocks of proteins are amino acids. The bonds that hold amino acids together are known as peptide bonds. To break the peptide bonds in a protein, a hydrolysis reaction is needed similar to that involved in breaking up carbohydrates. Enzymes known as proteases are needed to break up the protein. The following example shows how a peptide bond can be broken. A protease enzyme catalyses this step: Two amino acids are released – glycine and alanine. Note how the water molecule splits, with OH added to form glycine and the H added to form alanine. Fats and oilsThese macronutrients are formed from a combination of glycerol and 3 fatty acids. For example, part of the saturated fat found in common foods like meats and dairy products is known as glyceryl tristearate. It has the following structure: To convert it into a form that can be absorbed into the bloodstream, the bonds indicated with ~ need to be broken. This involves an enzyme called a lipase as well as water molecules. The products from this reaction are shown below. Fatty acids are either saturated or unsaturated:
b. add a water molecule to break bonds.
The mammalian trachea and esophagus both connect to thea. pharynx.b. stomach.c. large intestine.d. rectum.
Which of the following organs is incorrectly paired with its function?a. stomach—protein digestionb. large intestine—bile productionc. small intestine—nutrient absorptiond. pancreas—enzyme production
b. large intestine—bile production
Which of the following is not a major activity of the stomach?a. storageb. HCl productionc. nutrient absorptiond. enzyme secretion
If you put the following events in the order they occur in the human digestive system, the third event in the series would bea. Cells in gastric pits secrete protons.b. Pepsin activates pepsinogen.c. HCl activates pepsinogen.d. Partially digested food enters the small intestine.
b. Pepsin activates pepsinogen.
After surgical removal of the gallbladder, a person might need to limit his or her dietary intake ofa. starch.b. protein.c. sugar.d. fat.
If you were to jog 1 km a few hours after lunch, which stored fuel would you probably tap?a. muscle proteinsb. muscle and liver glycogenc. fat in the liverd. fat in adipose tissue
b. muscle and liver glycogen
Essential amino acids are _____.a. all of the amino acids required to make proteinsb. those that cannot be made in the bodyc. those that contain nitrogend. obtained only by eating plantse. obtained only by eating animals
b. those that cannot be made in the body
A complete digestive tract, or alimentary canal, differs from a gastrovascular cavity in that only the complete tract a. permits extracellular digestionb. has teeth and tentacles to help with ingestion c. uses its surface area for nutrient absorptiond. has specialized compartments e. allows elimination of undigested wastes
d. has specialized compartments
In humans, the first opportunity for ingested food to undergo enzymatic hydrolysis is in the _____.a. mouthb. stomachc. liverd. small intestinee. large intestine
Hydrochloric acid in the stomach _____.a. splits polypeptides into amino acidsb. splits fats into fatty acids and glycerolc. activates pepsinogen into pepsin d. initiates the development of stomach ulcerse. inhibits the production of epithelial cells
c. activates pepsinogen into pepsin
The bile salts function in fat digestion by _____.a. hydrolyzing fat molecules to glycerol and fatty acidsb. separating individual fat molecules from each otherc. dissolving fats in waterd. dispersing big droplets of fats to small dropletse. triggering the secretion of pancreatic lipase
d. dispersing big droplets of fats to small droplets
A fatty acid absorbed into an intestinal cell _____.a. is hydrolyzed to smaller fragmentsb. enters a lacteal vessel as a carbohydratec. becomes part of a chylomicrond. is bound to bile saltse. exits the cell to directly enter the blood
c. becomes part of a chylomicron
Glucagon, a pancreatic hormone, functions to _____.a. stimulate hungerb. inhibit activity in the small intestinec. increase fat storage in fat cellsd. reduce glucose levels in the bloode. stimulate the liver to release glucose
e. stimulate the liver to release glucose
Increased appetite is the typical result of increased levels in the blood of _____.a. leptinb. PYYc. ghrelind. insuline. secretin
Increased glucose levels in blood, after a meal, trigger _____.a. glucagon release from the pancreasb. insulin release from the pancreasc. secretin release from the duodenumd. cholecystokinin release from the pancrease. activation of amylase in the blood
b. insulin release from the pancreas
In which of the following structures does absorption of water, vitamin K, and salt occur?a. large intestineb. small intestinec. liverd. stomache. pancreas
Which of the following organisms is most likely to have an extremely large cecum?a. carnivoreb. ruminant herbivorec. nonruminant herbivored. insectivore
What is a lacteal? a. a vessel within each villusb. part of the vertebrate immune systemc. a type of liver sinusoidd. a globule containing phospholipid, cholesterol, and protein
a. a vessel within each villus
Ninety-five percent of the bacterial DNA sequences obtained from stomachs of individuals infected with the bacterium Helicobacter pylori were found to be H. pylori (phylum Proteobacteria). A conclusion that may be drawn from this finding is _____.a. Actinobacteria, Firmicutes, Bacteroidetes, and Fusobacteria do not cause ulcersb. Actinobacteria, Firmicutes, Bacteroidetes, and Fusobacteria are bacterial symbionts required for human healthc. H. pylori outcompetes compete resident bacterial species in infected individualsd. Uninfected individuals have less resident Fusobacteria than infected
c. H. pylori outcompetes compete resident bacterial species in infected individuals
The primary reason the hepatic portal vein delivers blood containing the products of digestion directly to the liver is in order to _____.a. recover excess water and ionsb. store glucose as glycogenc. detoxify foreign molecules and metabolic wastesd. allow toxic substances to circulate broadlye. conduct blood from the gastrointestinal tract to the heart
c. detoxify foreign molecules and metabolic wastes
A simple change contributed to the improvement of human health by reducing the risk of neural tube defects. This change was the _____.a. iodination of table saltb. consumption of massive doses of vitamin supplementsc. recommendation that the shift from breast milk to solid foods be delayedd. supplementation of soils with phosphoruse. addition of folic acid to grain products
e. addition of folic acid to grain products
Which of the following cell types is incorrectly matched with its function?a. parietal—pumps sodium ions into the stomach lumenb. chief—releases pepsinogen into the stomach lumenc. epithelial—within villus, contains projections that face the intestinal lumend. alpha—makes glucagone. beta—makes insulin
a. parietal—pumps sodium ions into the stomach lumen
Which of the following statements correctly describes non-insulin-dependent (type 2) diabetes?a. It is body weight and exercise independent.b. It usually appears during childhood.c. Immune cells destroy pancreatic insulin-producing islets.d. Stem cell research is under investigation for a cure.e. Blood glucose levels may be improved with regular exercise and a healthy diet.
e. Blood glucose levels may be improved with regular exercise and a healthy diet.
Which of these statements about the role of the human microbiome in health and disease is not correct?a. Microbiome differences may aid in the development of therapies for certain diseases.b. Microbiome changes may play a role in some abnormal conditions or disease states.c. Brain function or mood may be affected by digestive system microorganisms.d. Human mutualistic colon bacteria contain hydrolytic enzymes for digesting cellulose to simple sugars.e. Intestinal development and immune function are regulated by intestinal bacteria.
d. Human mutualistic colon bacteria contain hydrolytic enzymes for digesting cellulose to simple sugars.
Which of the following organs or structures is not part of the large intestine?a. cecumb. colonc. appendixd. jejunume. rectum
The following table shows the contents of a multivitamin supplement and its percentage of recommended daily values (%DV).Table.The most likely reason that some of the vitamins and minerals in this supplement are found at less than 100% is that ___.a. it is dangerous to overdose on fat-soluble vitamins such as A and Kb. these vitamins and minerals are too large in size to reach 100%c. it is too easy to overdose on minrals such as phosphorous and calciumd. it would be chemically impossible to add more
a. it is dangerous to overdose on fat-soluble vitamins such as A and K
Animals that migrate great distances would obtain the greatest energetic benefit of storing chemical energy as ___.a. proteinsb. carbohydratesc. mineralsd. fats
Lysine is an essential amino acid for animals. If an animal did not consume lysine in its diet, you might expect that the animal ___.a. could not effectively make many necessary proteinsb. was a carnivorec. would make lysine from other amino acidsd. would be very healthy
a. could not effectively make many necessary proteins
Three groups of cyclists consumed three different types of diets: high-carbohydrate; a diet mixed in carbohydrates, fat, and protein; or a diet higher in protein and fat. The average time each group could spend cycling over a six-hour period is shown in the accompanying graph. What conclusion from the data would help an athlete or trainer improve performance?Figurea. An early 50 percent drop in blood glucose is associated with improved endurance.b. Diet is not at all related to endurance.c. Maintaining elevated blood sugar improves performance.d. Endurance is entirely related to diet.
c. Maintaining elevated blood sugar improves performance.
Ticks are parasites that obtain nutrients by ingesting blood from a host animal. Ticks would be classified as ___.a. substrate feedersb. fluid feedersc. filter feedersd. bulk feeder
Because the foods eaten by animals are often composed largely of macromolecules, animals need to have mechanisms for ___.a. regurgitationb. demineralizationc. dehydration synthesisd. enzymatic hydrolysis
Fat digestion yields fatty acids and glycerol, whereas protein digestion yields amino acids; both digestive processes ___.a. use water molecules when breaking bonds (hydrolysis)b. require adenosine triphosphate (ATP) as an energy sourcec. require the presence of hydrochloric acid to lower the pHd. are catalyzed by the same enzyme
a. use water molecules when breaking bonds (hydrolysis)
Mechanical digestion, the process of breaking down large chunks of food into smaller pieces, is important because smaller pieces of food ___.a. are more easily stored in the stomach than are larger pieces of foodb. do not taste as good as larger pieces of foodc. have more surface area for chemical digestion than do larger pieces of foodd. are easier to excrete than are larger pieces of food
c. have more surface area for chemical digestion than do larger pieces of food
Stomach cells are moderately well adapted to the acidity and protein-digesting activities in the stomach by having ___.a. a high level of secretion of enzymes by chief cellsb. a thick, mucous secretion and active mitosis of epithelial cellsc. a cell wall impermeable to acidd. a sufficient colony of H. pylori
b. a thick, mucous secretion and active mitosis of epithelial cells
Upon activation by stomach acidity, the secretions of the parietal cells ___.a. initiate the chemical digestion of protein in the stomachb. initiate the chemical digestion of lipids in the stomachc. delay digestion until the food arrives in the small intestined. initiate the mechanical digestion of lipids in the stomach
a. initiate the chemical digestion of protein in the stomach
Over-the-counter medications for acid reflux or heartburn block the production of stomach acid. Which of the following cells are directly affected by this medication?a. parietal cellsb. goblet cellsc. smooth muscle cellsd. chief cells
Cattle are able to survive on a diet consisting almost entirely of plant material because cattle ____.a. are autotrophicb. manufacture all fifteen amino acids out of sugars in the liverc. re-ingest their fecesd. have cellulose-digesting, symbiotic microorganisms in chambers of their stomachs
d. have cellulose-digesting, symbiotic microorganisms in chambers of their stomachs
A zoologist analyzes the jawbones of an extinct mammal and concludes that it was an herbivore. The zoologist most likely came to this conclusion based upon the ___.a. angle of the teeth in the mouthb. size of the mouth openingc. shape of the teethd. position of muscle attachment sites
If you found a vertebrate skull in the woods and the teeth were sharp and scissor-like, what type of food would you expect this animal to eat?a. flesh of another animalb. nectarc. bloodd. grass
a. flesh of another animal
What benefit is gained by intestinal bacteria living in a mutualistic relationship with an animal?a. The bacteria can avoid the animal's immune system.b. The bacteria are provided with a regular source of nutrients.c. The bacteria can easily infect the animal's intestinal cells.d. Temperature is always regulated.
b. The bacteria are provided with a regular source of nutrients.
When used appropriately, antibiotic treatment can effectively reduce bacteria populations and help fight infections. However, antibiotic treatments can have unintended effects. What is one concern when using antibiotics?a. Antibiotics also damage animal cells, so they can be more harmful than a bacterial infection.b. Antibiotics may also kill the beneficial bacteria of the microbiome, thereby disrupting digestive health.c. Antibiotics cause viruses to become more effective at infecting cells.d. Each antibiotic is only effective against one type of bacteria, so effects on infection are limited.
b. Antibiotics may also kill the beneficial bacteria of the microbiome, thereby disrupting digestive health.
In a healthy person, after a carbohydrate-rich meal, the production of ___ will increase, causing the uptake of ___ from the blood into liver cells.a. glucagon; proteinb. glucagon; glucosec. insulin; glucosed. insulin; glucagon
If there is a strong genetic link for type II diabetes mellitus in your family, how might you minimize your risk of developing the disorder?a. maintain a healthy weight, eat a balanced diet, and exerciseb. monitor your blood glucose levels dailyc. eat complex carbohydrates like starch instead of sweetsd. take oral insulin daily
a. maintain a healthy weight, eat a balanced diet, and exercise
Choose the list that presents the four stages of food processing in the order in which they naturally occur.a. ingestion → digestion → absorption → eliminationb. ingestion → absorption → elimination → digestionc. ingestion → digestion → elimination → absorptiond. digestion → ingestion → absorption → eliminatione. absorption → digestion → ingestion → elimination
a. ingestion → digestion → absorption → elimination
The gastrovascular cavity differs from the alimentary canal in that only the gastrovascular cavity _____. a. has only a single openingb. functions in digestion but not absorptionc. absorbs food molecules but does not produce hydrolytic enzymesd. stores food but does not digest ite. is capable of extracellular digestion
a. has only a single opening
Choose the correct anatomical sequence that presents the order in which food in the digestive system passes through.a. esophagus → stomach → pharynx → small intestineb. pharynx → stomach → esophagus → small intestinec. pharynx → small intestine → large intestine → stomachd. esophagus → pharynx → stomach → small intestinee. pharynx → esophagus → stomach → small intestine → large intestine
e. pharynx → esophagus → stomach → small intestine → large intestine
For ingested foods, the first opportunity for enzymatic digestion occurs in the _____.a. stomachb. large intestinec. pancreasd. small intestinee. mouth
The lower esophageal sphincter surrounds the upper opening into the stomach. If this sphincter failed to properly constrict, there might be a problem with _____. a. too rapid emptying from the stomach into the small intestineb. the movement of swallowed food into the trachea rather than into the esophagusc. regurgitation of acidic stomach contents into the esophagus, commonly called "heartburn"d. too rapid emptying of the small intestine into the large intestinee. the control of defecation
c. regurgitation of acidic stomach contents into the esophagus, commonly called "heartburn"
Different types of food are eaten by various groups of animals, but it is usually true that _____. a. the teeth of herbivores tend to be sharper than the teeth of carnivoresb. animals typically produce enzymes that hydrolyze cellulosec. the intestines of carnivores tend to be longer than the intestines of herbivores of similar overall body sized. many carnivorous vertebrates house large populations of symbiotic bacteria and protists in special fermentation chambers in their stomachse. cellulose digestion in ruminant mammals occurs before the ingested foods reach the small intestine
e. cellulose digestion in ruminant mammals occurs before the ingested foods reach the small intestine
Among humans, increased interest in food intake normally occurs _____.a. via chemical signals related to the amount of protein stores in the liverb. via chemical signals related to the amount of glucose stored in the liver and muscle cellsc. only after the production of glucose in the liver can no longer meet metabolic needsd. when fewer calories are taken in than are expended, but only after the body depletes its reserves of fat in the livere. via chemical signals released when the stomach is empty
e. via chemical signals released when the stomach is empty
Consider the interior surface of the human stomach and its secretions, shown in the figure. Why doesn’t gastric juice, composed of hydrochloric acid and a protease called pepsin, digest the cells that line the stomach?a. Chief cells release pepsin in an inactive form. HCl in the stomach converts pepsin to an active form of the enzyme called pepsinogen by clipping off a small portion of the molecule to expose its active site.b. Digestion doesn’t begin until the small intestine.c. The stomach lining secretes mucus, a mixture of glycoproteins, cells, salts, and water.
c. The stomach lining secretes mucus, a mixture of glycoproteins, cells, salts, and water. |
For ingested foods, the first opportunity for mechanical digestion occurs in the _____.
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