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brittykitty · Oct 20, 2008, 01:23 PM

7. The tip of the stem of an oat leaf plant is covered with aluminium foil. A light source from one side will

A. cause the stem to bend toward the light source
B. cause the stem to bend away from the light source
C. cause the stem to wither an die
D. have no effect on the stem

I say that it's a but the aluminium foil might make it have no effect since light would be coming from both sides? Not to sure.. any thoughts?

Unknown008 · Oct 21, 2008, 04:35 AM

If it's like that:

{| |}
{| |}
{| |}
{| |}
{| |}
{| |}

Where the '{ }' are the aluminium foil, and the '| |' represent the stem, I would say that the aluminium foil will prevent light from reaching the stem, so D. It's only a suggestion, OK?

brittykitty · Oct 26, 2008, 04:32 PM

OK thanks :)

Credendovidis · Oct 26, 2008, 05:39 PM

Hello brittykitty

The ability of a plant to bend toward a light source is known as phototropism. The hormone in a plant stem auxin causes elongation. Light destroys auxin when it strikes the stem. Because auxin is still present on the shaded side of the stem, the cells on the darker side are able to elongate more than the cells on the lighted side, causing the plant to bend toward the light. Phototropism by sunlight is also called heliotropism.

The by foil covered tip of the stem receives no sunlight, so no bending will occure there.
The correct answer is D.

:)