Which Statement About Precapillary Sphincters Is CORRECT

question 142

Multiple Choice

Which statement about precapillary sphincters is CORRECT?

• A) They contract when oxygen levels in the tissue are low.
• B) They can close off the capillaries by contracting.
• C) They are openings that allow large molecules and blood cells to leave the capillary.
• D) When the precapillary sphincters are open, blood flows only through the thoroughfare channels.
• E) They are voluntary.

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Definitions:

Anthocyanins

Class of red water-soluble plant pigments.

Petiole

The stalk that attaches the leaf blade to the stem in vascular plants, enabling nutrient and water transport between the leaf and the rest of the plant.

Abscission Zone

The area at the base of the petiole where the leaf will break away from the stem. Also known as the abscission layer.

Bundle Sheath

Bundle sheath cells are specialized cells surrounding the vascular bundles in plants; they play a crucial role in the C4 photosynthetic pathway by concentrating CO2 around the enzyme RuBisCO.