The SA node exhibits automaticity; it can spontaneously generate action potentials without neural input. 

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#Id: 5324

#Unit 7. System Physiology – Animal

Isovolumetric Ventricular Relaxation

Closure of aortic valve producing the second heart sound (S2).

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#Id: 9928

#Unit 4. Cell Communication and Cell Signaling

There are 18 different antigenic subtypes for HA and 11 for NA.

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#Id: 7027

#Unit 11. Evolution and Behavior

Proximate causes - The subject of cell biology, neurobiology, and many other biological disciplines

Ultimate causes - Their historical causes, especially the action of natural selection

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#Id: 2821

#Unit 13. Methods in Biology

In Ion-exchange chromatography There are two types of ion exchanger, namely cation  and anion exchangers.

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#Id: 2315

#Unit 3. Fundamental Processes

The group I and group II introns have the remarkable ability to excise themselves from an RNA. This is called auto-splicing, or self-splicing. 

Group I introns are more common than group II introns.