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Structure of cellulose, the main macromolecule of the primary cell wall
Wood first appeared in plants called progymnosperms.
Spider's main organs
Structure of the trachea, which extends from the larynx above to the main bronchi below.
Photograph of the flea that transmits Yersinia pestis to cause bubonic plague, called the oriental r
Cancer cells can move to new locations in the body, a process called metastasis