The cholera bacterium produces a toxin. The toxin causes the secretion of chloride ions into the lumen of the small intestine. Why does this cause diarrhoea?
A) The water potential in the lumen of the small intestine decreases and water moves into the small intestine by osmosis.
B) The water potential in the lumen of the small intestine increases and water moves into the small intestine by osmosis.
C) The water potential in the lumen of the small intestine decreases and water moves out of the small intestine by osmosis.
D) The water potential in the lumen of the small intestine increases and water moves out of the small intestine by osmosis.
▶️ Answer/Explanation
Ans: A
The cholera toxin increases chloride ion (\(Cl^-\)) secretion into the intestinal lumen. This raises the solute concentration, decreasing the water potential in the lumen. As a result, water moves from the higher water potential in intestinal cells into the lumen by osmosis, leading to excessive fluid accumulation and diarrhoea.
Options B and D incorrectly state that water potential increases, while C wrongly describes water moving out of the intestine. Thus, the correct answer is A.
The cholera bacterium produces a toxin which affects humans. What is an effect of this toxin on the human body?
A) the secretion of chloride ions from the blood into the lumen of the large intestine
B) the secretion of chloride ions from the blood into the lumen of the small intestine
C) the secretion of chloride ions from the lumen of the large intestine into the blood
D) the secretion of chloride ions from the lumen of the small intestine into the blood
▶️ Answer/Explanation
Ans: B
The cholera toxin disrupts ion transport in the small intestine, causing excessive secretion of chloride ions (Cl⁻) from the blood into the intestinal lumen. This leads to water loss via osmosis, resulting in severe diarrhea.
Options A and C incorrectly mention the large intestine, while D reverses the direction of ion movement. Since cholera acts on the small intestine and causes outward Cl⁻ secretion, the correct answer is B.