The absorptive surface of the small intestine is greater than that of other human digestive organs because of its length and the presence of

A. alveoli

B. neurons

C. villi

D. nephrons

Answer Explanation:

C) villi

- Correct: The absorptive surface of the small intestine is greatly increased due to the presence of villi. Villi are finger-like projections that line the inner surface of the small intestine. These structures greatly increase the surface area available for absorption. Each villus contains capillaries and lacteals (lymphatic vessels) that absorb nutrients from digested food. The large surface area provided by the villi allows for more efficient absorption of nutrients such as carbohydrates, proteins, fats, vitamins, and minerals.

A) alveoli

- Incorrect: Alveoli are tiny air sacs in the lungs where gas exchange occurs during respiration. They are not found in the digestive system and do not contribute to the absorptive surface of the small intestine.

B) neurons

- Incorrect: Neurons are nerve cells that transmit signals throughout the body, including the digestive system. While neurons play a role in regulating digestion and other digestive processes, they do not directly contribute to the absorptive surface of the small intestine.

D) nephrons

- Incorrect: Nephrons are the functional units of the kidneys responsible for filtering blood and producing urine. They are not part of the digestive system and do not contribute to the absorptive surface of the small intestine.

Therefore, the Correct Answer is C.

Q #1: In humans, structures that release digestive secretions directly into the small intestine include both the

A. salivary glands and the pancreas

B. gall bladder and the lacteals

C. villi and the salivary glands

D. pancreas and the gall bladder

Answer Explanation

D) pancreas and the gallbladder

- Correct: Both the pancreas and the gallbladder release digestive secretions directly into the small intestine. The pancreas secretes pancreatic enzymes (such as amylase, lipase, and proteases) into the small intestine to aid in the digestion of carbohydrates, fats, and proteins. The gallbladder stores bile produced by the liver, which is released into the small intestine to aid in the emulsification and digestion of fats.

A) salivary glands and the pancreas

- Incorrect: While the pancreas releases digestive secretions directly into the small intestine, the salivary glands secrete saliva into the mouth, which contains enzymes (such as amylase) that begin the digestion of carbohydrates. Salivary glands do not release digestive secretions directly into the small intestine.

B) gall bladder and the lacteals

- Incorrect: The gallbladder stores bile produced by the liver, which is released into the small intestine to aid in fat digestion. Lacteals are lymphatic vessels found in the villi of the small intestine and are involved in the absorption of fats, but they do not release digestive secretions directly into the small intestine.

C) villi and the salivary glands

- Incorrect: Villi are finger-like projections in the small intestine that increase the surface area for absorption of nutrients but do not release digestive secretions directly into the small intestine. Salivary glands secrete saliva into the mouth to initiate the digestion of carbohydrates but do not release digestive secretions directly into the small intestine.
Q #2: Three days after an organism eats some meat, many of the organic molecules originally contained in the meat would be found in newly formed molecules of

A. glucose

B. protein

C. starch

D. oxygen

Answer Explanation

B) protein

- Correct: After an organism consumes meat, the organic molecules present in the meat, such as amino acids and lipids, are broken down through the process of digestion. These molecules are then absorbed into the bloodstream and transported to various cells throughout the body. In the cells, these molecules are used as building blocks for synthesizing new proteins. Proteins are essential macromolecules involved in numerous cellular functions, including structural support, enzymatic activity, and regulation of cellular processes. Therefore, many of the organic molecules originally contained in the meat would be found in newly formed molecules of protein within the organism's cells.

A) glucose

- Incorrect: Glucose is a simple sugar that is primarily derived from the digestion of carbohydrates. While some amino acids obtained from the digestion of protein can be converted into glucose through gluconeogenesis, the majority of amino acids are used for protein synthesis, not glucose production.

C) starch

- Incorrect: Starch is a complex carbohydrate found in plants. It is not typically present in meat, and it is not directly synthesized from the organic molecules obtained from meat consumption.

D) oxygen

- Incorrect: Oxygen is a gas essential for cellular respiration but is not synthesized from the organic molecules obtained from meat consumption. Oxygen is mainly obtained through breathing and is used in cellular respiration to generate ATP, the energy currency of the cell.
Q #3: What occurs during the digestion of proteins?

A. Specific enzymes break down proteins into amino acids.

B. Specific hormones break down proteins into simple sugars.

C. Specific hormones break down proteins into complex starches.

D. Specific enzymes break down proteins into simple sugars.

Answer Explanation

A) Specific enzymes break down proteins into amino acids.

- Correct: This is the correct answer. Proteins are broken down into their constituent amino acids by specific enzymes during the process of digestion. Enzymes like pepsin in the stomach and various proteases in the small intestine facilitate this breakdown.

B) Specific hormones break down proteins into simple sugars.

- Incorrect: Hormones are not directly involved in breaking down proteins into simple sugars. Hormones are signaling molecules that regulate various processes in the body, including metabolism, but they don't directly participate in the breakdown of proteins into sugars.

C) Specific hormones break down proteins into complex starches.

- Incorrect: Hormones do not break down proteins into complex starches. Proteins are broken down into amino acids by enzymes, not hormones. Starches are complex carbohydrates and are broken down into simple sugars by enzymes like amylase, not proteins.

D) Specific enzymes break down proteins into simple sugars.

- Incorrect: Proteins are not broken down into simple sugars. They are broken down into amino acids by specific enzymes. Simple sugars come from the breakdown of carbohydrates, not proteins.

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The absorptive surface of the small intestine is greater than that of other human digestive organs because of its length and the presence of

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