There are many types of crabs in the sea. most of them have shells made from chitin, which is different from calcium carbonate (it's actually the same stuff that your fingernails are made of). however, hermit crabs live in shells that are made from calcium carbonate. where do these "houses" come from? do the crabs make them?

Which of the following sex and generation combinations directly produces the pollen tube of angiosperms? a) male gametophyteb) female gametophytec) male sporophyted) female sporophyte

The carbon cycle is best defined as a process in which a. carbon changes from inorganic forms to organic forms and back b. carbon is changed into other elements such as oxygen or nitrogen c. carbon is continually created from the sun’s energy by plants d. carbon is consumed and regenerated from other elements such as oxygen and nitrogen

Amines amides and amino acids are categories of