In the Malpighian tubules of an insect (blind, threadlike excretory tubule attached to the gut of an insect), salt molecules are actively transferred from body fluids to the inside of the tubule. This transfer of salt molecules would result in
A) water being "pulled" by osmosis into the Malpighian tubule.
B) an increase in the salt concentration of the body fluids.
C) an increase in the water concentration of the body fluids.
D) the Malpighian tubules becoming isotonic to the body fluids.
E) the tubules becoming hypotonic to the body fluids.

Question

Quizplus · Accepted Answer

When salt molecules are actively transferred from body fluids to the inside of the Malpighian tubule, the salt concentration inside the tubule increases. This creates a concentration gradient, which results in water being "pulled" by osmosis into the Malpighian tubule from the body fluids. This means that choice A is the correct answer. Option B is incorrect because the transfer of salt molecules from body fluids to the inside of the tubule will result in a decrease in the salt concentration of body fluids, not an increase. Similarly, option C is incorrect because the concentration of water in body fluids will decrease due to the osmotic movement of water into the Malpighian tubule. D and E are also not correct because the Malpighian tubules will become hypertonic to the body fluids due to the accumulation of salt molecules.

In the Malpighian Tubules of an Insect (Blind, Threadlike Excretory