BSC 1407 Ch. 46

(a)   is a carbohydrate monomer that is absorbed from the digestive tract.

Answer explanation

In an omnivore, most carbohydrates are typically polysaccharides (starch and cellulose from plants and glycogen from animals), while some are monosaccharides and disaccharides.

Digestion of carbohydrates:

Some polysaccharide digestion occurs in mouth (salivary amylase), but most takes place in small intestine by pancreatic amylase, producing maltose.

-Maltose and other disaccharides are broken down by enzymes on the brush border of the small intestine.

-Monosaccharides, such as glucose, are transported across intestinal epithelium into the blood.

Once food is digested, the nutrients must be absorbed by the epithelial cells that line the specialized portions of the alimentary canal. Small, hydrophobic molecules can diffuse down concentration gradients across the membrane. What types of molecules would require ACTIVE TRANSPORT in order to get across?

• Minerals

• Water

• Monoglycerides

• Amino acids

• Salt

Birds store food in a modified portion of the lower esophagus called the

• Crop

• Epiglottis

• Gizzard

• Alimentary canal

• Pharynx

Answer explanation

The crop is a storage organ where there is little or no digestion. It is found in most birds and some invertebrates.

- Size is dependent on diet

- Provides material regurgitated by birds for their young.

Tags

NGSS.MS-LS1-7

In the mammalian digestive system, what is the primary site of nutrient absorption?

• Pharynx

• Stomach

• Small intestine

• Large intestine

• Pancreas

Answer explanation

Nearly all digestion of food, and absorption of food and water, occurs in the small intestine.

-Hydrolytic enzymes found on apical surface of epithelial cells or secreted by pancreas into lumen.

-Products of digestion are absorbed across epithelial cells and enter blood.

-Vitamins, minerals and water are also absorbed.

In the stomach, food processing continues and secretions from stomach glands aid the initial digestion of

• Carbohydrates

• Lipids

• Nucleic acids

• Proteins

• Vitamins

Answer explanation

Proteins are broken down to polypeptide fragments by pepsin in the stomach and by proteases such as trypsin in small intestine.

The pancreas secretes enzymes as inactive precursors that become activated in the small intestine.

Small intestine enzymes complete digestion of proteins into amino acids, that are then transported into intestinal cells and into blood stream.

Cows are able to survive on a diet consisting almost entirely of cellulose because

• cows are autotrophic.

• cows can manufacture all 20 amino acids out of sugars in the

  liver.

• unlike humans, the saliva the cow produces has enzymes

  capable of digesting cellulose.

• cows have cellulose-digesting, symbiotic microorganisms in

  their rumens.

Answer explanation

Ruminants, such as sheep, goats, llamas, cows, lack the enzymes needed to digest cellulose, but have the ability to digest cellulose due to the help of microorganisms living in digestive tract.

Tags

NGSS.HS-LS2-6

What is peristalsis?

• a process of fat emulsification in the small intestine

• voluntary control of the rectal sphincters regulating defecation

• the transport of nutrients to the liver through the hepatic portal

  vein

• loss of appetite, fatigue, dehydration, and nervous disorders

• smooth muscle contractions that move food through the

  alimentary canal

Answer explanation

Swallowing begins in the pharynx as a voluntary action and continues in esophagus by involuntary peristalsis

Most nutrients are absorbed across the epithelium of the

• Colon

• Stomach

• Esophagus

• Small intestine

• Large intestine

Answer explanation

The small intestine is specialized to carry out the bulk of digestion and absorption.

-Mucosal infoldings

-Villi ( finger-like projections). Each villus has a

• Capillary – nutrients other than fat absorbed into blood

• Lacteal (part of lymphatic system) – allows for larger fat

particles to enter, eventually dumped into blood

-Specializations increase surface area 600-fold & Increases likelihood of a food particle encountering a digestive enzyme and being absorbed.

The small intestine releases the hormone secretin in response to acid.

• True

• False

Answer explanation

Fats packaged in chylomicrons pass directly from epithelial cells to the bloodstream.

Fats packaged in chylomicrons pass directly from epithelial cells to the bloodstream.

• True

• False

Answer explanation

Chylomicrons are released by exocytosis from epithelial cells and enter lacteals. The fluid from the lacteals eventually empties into a large vein and from there into the blood circulation.