Which organism possesses a three-chambered heart?
a. human
b. amphibian
c. arthropod
d. bird
e. fish
b
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The branch points on a cladogram represent ____
a. the species' extinction b. derived characters c. related clades d. a common ancestor of two lineages e. mass extinctions
Transcription starts at a region of DNA called a(n)
a. sequencer. b. promoter. c. activator. d. terminator. e. transcriber.
A model is used by ecologists to
A) prove how nature works by demonstrating cause-and-effect relationships. B) analyze data that have been collected during an experiment. C) make predictions about how nature works using a set of explicit assumptions. D) observe how nature works in an experimental setting.
Helper T cells secrete ________ to stimulate the proliferation of B-cells.
A. antigens B. antibodies C. MHC proteins D. cytokines