A normal heartbeat is not set or initiated by the nervous system, which may be expected since the heart has electrical activity. If not the nervous system, then what actually regulates or initiates a normal heartbeat?
What will be an ideal response?
A region of muscle cells located in the upper portion of the right atrium (the sinoatrial node or pacemaker) can spontaneously become excited. This region also depolarizes at a faster rate than the surrounding cells, so the SA node initiates and sets the pace of electrical activity of the heart, and hence the heart rate.
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The group that probably gave rise to chloroplasts is the
A. cyanobacteria. B. green photosynthetic bacteria. C. purple sulfur bacteria. D. non-sulfur purple bacteria. E. methane bacteria.
Two groups of organisms can occupy the same exact niche
Indicate whether the statement is true or false
Which are main colors of light absorbed by rod
cells?
a. red, green, blue b. blue, yellow, red c. yellow, orange, brown d. green, blue, white e. none of these colors of light are absorbed by rod cells
Human actions have altered the global carbon cycle by ___
a. decreasing the number of photosynthetic organisms b. cutting down large numbers of trees c. inventing the internal combustion engine and burning fossil fuels d. developing and using drilling and mining methods that allow access to previously inaccessible fossil fuel deposits e. all of the above