What change would result for a land snail that had a mutation interfering with chitin formation?

Question

A.  It would have a soft, demineralized shell.
B.  It would have difficulty feeding.
C.  It could not form its exoskeleton.
D.  Molting would not be possible.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content
· What do you already know about mollusk feeding and shell formation?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  It would have difficulty feeding.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses mollusk feeding and shell formation.
· What type of thinking is required?
        o This question is asking you to take what you already know and apply it to this unfamiliar situation.

Gather Content
· What do you already know about mollusk feeding and shell formation?
        o Gastropods are a type of mollusk – they are the snails and slugs.
        o Mollusks feed using the radula – a rasping, tonguelike structure.
        o The radula consists of dozens to hundreds of microscopic, chitinous teeth arranged in rows on an underlying membrane and lies in a chamber at the anterior end of the gut.
        o The radula can be protruded through the mouth and move something like a sanding belt over what is being rasped. Benthic mollusks use their radulae to scrape up algae and other food materials.
        o One of the best-known characters of the mollusk phylum is the shell, which protects against predators and adverse environmental conditions.
        o A mollusk shell is secreted by the outer surface of the mantle.
        o A typical mollusk shell consists of two layers of calcium carbonate, which is precipitated extracellularly. The outer layer consists of densely packed crystals. In some species, the inner layer is pearly in appearance, and is called mother-of-pearl or nacre.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Without chitin, would a snail have a demineralized shell? No, the hard, mineral component of a mollusk shell is calcium carbonate, not chitin.
        o Without chitin, would a snail fail to form its exoskeleton? Well, yes, but that is because mollusks do not have an exoskeleton – arthropods do.
        o Without chitin, would a snail be unable to molt? Again, technically yes, but, mollusks never molt – arthropods and nematodes do.
        o Without chitin, would a snail have difficulty feeding? Yes. The main structure in a snail that is composed of chitin is the radula – the hard, rasping tongue-like structure with which mollusks feed.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o The question required you to take what you already know and apply it to thisunfamiliar situation.
        o Did you recognize that the radula of a mollusk is made of chitin?