For Many Years Scientists Believed That Almost All Animal Lineages

question 17

Multiple Choice

For many years scientists believed that almost all animal lineages burst into being during the Cambrian era (just after the end of the Precambrian super eon) .However,there have been many recent findings of animal-like fossils and "trace fossils" (fossils of an animal-like organisms movement) from the late Precambrian.Which of the following best explains why it took so long to realize there was animal-like life in the Precambrian?

• A)There were no animals in the Precambrian.
• B)Animals from the late Precambrian had soft bodies.
• C)There were many hard-shelled animals in the Cambrian.
• D)The global climate was such that there was poor fossilization in the Precambrian.
• E)There were very few animals during this period.

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Definitions:

Enzyme-linked Receptors

A class of cell surface receptors that initiate a cellular response upon binding a specific ligand, often leading to a series of enzymatic reactions inside the cell.

Ion Channel-linked Receptors

Proteins that span a cell membrane and open to allow ions such as Na+, K+, Ca2+, and Cl- to pass in response to the binding of a chemical messenger.

G Protein-linked Receptors

Proteins that transmit signals from outside the cell to the inside by binding with G proteins, initiating various cellular processes.

Second Messenger

Intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules.