A botanist discovers a plant that lacks the ability to form starch grains in root cells,yet the roots still grow downward.This evidence refutes the long-standing hypothesis that
A)falling statoliths trigger gravitropism.
B)starch accumulation triggers the negative phototropic response of roots.
C)starch grains block the acid growth response in roots.
D)starch is converted to auxin,which causes the downward bending in roots.

Question

Quizplus · Accepted Answer

Starch grains in plant cells, particularly in specialized plastids called statoliths, are thought to play a crucial role in gravitropism—the growth or movement of plants in response to gravity. The statoliths are believed to settle under the influence of gravity to the lower sides of cells, which helps the plant detect the direction of gravity. This detection mechanism then triggers a series of responses that lead to growth in the direction of gravity (downward for roots, known as positive gravitropism, and upward for shoots, known as negative gravitropism). If a plant lacks the ability to form starch grains yet its roots still grow downward, it suggests that the presence of starch grains (and their role as falling statoliths) is not essential for the detection of gravity or the initiation of gravitropic responses. This evidence challenges the hypothesis that falling statoliths (which would require starch grains) are necessary to trigger gravitropism.

A Botanist Discovers a Plant That Lacks the Ability to Form