The electrical stimulus for each human heartbeat begins in the

A. right atrium at the sinoatrial node.
B. left atrium at the sinoatrial node.
C. right atrium at the atrioventricular node.
D. right ventricle at the atrioventricular node.
E. pulmonary trunk at the sinoatrial node.


A. right atrium at the sinoatrial node.

Biology & Microbiology

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Two principal organelles in eukaryotes that were apparently derived from different types of bacteria are the  

A.  microfilaments and microtubules. B.  mitochondria and chloroplasts. C.  rough ER and smooth ER. D.  plasma membrane and nuclear membrane.

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In which tissue system of plants would you expect to find the guard cells?

A. Vascular tissue system B. Ground tissue system C. Dermal tissue system D. Germ tissue system

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The oxygen released in photosynthesis comes

from

a. carbon dioxide. b. glucose. c. water. d. ATP. e. NADPH

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Most of an organism's DNA is carried by its __________.

A. mitochondria B. chromosomes C. nucleoli D. endoplasmic reticulum

Biology & Microbiology