Question

Snails were discovered in the Negev desert at night, harvesting the lichens that grew in the moist pores of the limestone and wearing down the desert more than abrasion from wind. They added mild acid to the snail feces and it foamed; this was an important test to detect that:

a. Snails have acidic digestive enzymes.
b. Snails secrete alkaline substances.
c. Snails produce ammonia as waste.
d. Snails possess carbonate-shelled skeletons.

Answer 1

The foaming when mild acid is added to snail feces indicates the presence of calcium carbonate, revealing that snails possess carbonate-shelled skeletons. The correct answer is option d.

Step-by-step explanation:

The foaming reaction mentioned in the student's question happens when the mild acid added to the snail feces reacts with a substance that must be present in the feces. In biology, we learn that many animals, including gastropods like snails, secrete metabolic wastes from digestion.

One such waste product is ammonia, which is alkaline. However, when it comes to tests involving acid and foam, such a reaction typically indicates the presence of carbonates. Since gastropod shells, including those of snails, are primarily made of calcium carbonate, the foaming is a result of the reaction between the calcium carbonate from the snail shells and the added acid, releasing carbon dioxide gas.

The correct answer to the test detecting is the presence of calcium carbonate in the snail's waste, confirming that snails possess carbonate-shelled skeletons.

Therefore, the correct option from the given choices is:

d. Snails possess carbonate-shelled skeletons.