All of the following are types of phloem or xylem cell except:

A. tracheid.
C. sieve tubes.
B. veins.
D. vessel cell.

How does secondary succession differ from primary succession?

With regard to enzymes, key is to lock as a) substrate is to activation energy eliminate b) product is to substrate. c) enzyme is to active site. d) substrate is to active site.

Crossing over is a method of (blank)?