How many degrees does the Earth's axis tilt from perpendicular?
A) 10°
B) 90°
C) 23.5°
D) 0°
C
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One double-stranded DNA molecule combined with proteins form ____________________, which is visible as clumps or threads in the cell nucleus
Fill in the blank(s) with correct word
Prokaryotes ____
a. lack a nucleus b. are generally larger than eukaryotes c. are found only in certain niches d. have a narrow range of metabolic activities e. have a smaller biomass than plants
Breathing helps move blood from lower parts of the body toward the heart by which of the following mechanisms?
A) Inhalation decreases pressure in the abdominal cavity, which opens veins and pushes blood toward the heart. B) Inhalation increases the size of the thoracic cavity and increases pressure in the abdominal cavity. C) Inhalation increases the size of the thoracic cavity, which reduces pressure and draws blood toward the heart. D) Breathing does not help return blood to the heart.
If each human lung contains about 300 million alveoli with a summed total surface area for gas exchange of 40 square meters, what is the approximate surface area of a single alveolus?
A. 750 square micrometers B. 133 square millimeters C. 7.5 square micrometers D. 7.5 square millimeters E. 0.133 square micrometers F. 1.33 square micrometers