Energy & Light

[MedPR]

Chlorophyll absorbs maximally in red and blue wavelengths. Consider a genetically modified plant which expresses an enzyme that emits red and blue light using energy from the conversion of ATP to ADP. If the plant were placed in complete darkness, would it be able to grow from the light energy emitted by the enzymes?

A. No, because the amount of energy absorbed by the plant must be greater than or equal to the energy involved in the metabolism of the plant, impossible under the described conditions since the light energy emitted must be less than the energy involved in the metabolism of the plant.

B. No, because the amount of energy absorbed by the plant must be less than or equal to the energy involved in the metabolism of the plant, yet the energy emitted by the enzymes is greater than the the energy involved in the metabolism of the plant.


Answer is A.

The first part of the answer makes sense. But don't normal chlorophyll emit green light? And green light is higher energy than red and blue light. So isn't the second half of the answer incorrect?

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[milski]

The first part of the answer makes sense. But don't normal chlorophyll emit green light? And green light is higher energy than red and blue light. So isn't the second half of the answer incorrect?

Normal chlorophyl does not emit any light, that's easy to confirm by putting a plant in the dark. It absorbs red and blue light. Under white light, it will reflect anything else. Looking at the spectrum, anything else happens to be green. That gives the typical green color of plants.

 

[MedPR]

Normal chlorophyl does not emit any light, that's easy to confirm by putting a plant in the dark. It absorbs red and blue light. Under white light, it will reflect anything else. Looking at the spectrum, anything else happens to be green. That gives the typical green color of plants.

Oh, right. It reflects the green, not emits it. Thanks.

 

[ljc]

Also, green light is not higher energy than blue light.

Remember the acronym:
ROYGBIV - red orange yellow green blue indigo violet

with R being the lowest energy light, and V being the highest. The way I remember which is which is I always think "ultraviolet" is just after violet, and it's ULTRA high energy. So that means red is low energy, blue/violet are high energy. Green is in the middle.