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Why do very small seeds such as lettuce fail to germinate in the dark?
ATheir embryos need a cold period before growth
BTheir coats must be abraded by soil particles
CTheir phytochrome stays in the inactive Pr form
DTheir reserves are digested by soil microbes
Answer & Solution
Correct answer: C. Their phytochrome stays in the inactive Pr form
1. In seeds the phytochrome system is used simply to detect whether there is any light at all.
2. In the dark phytochrome sits in the inactive Pr form and the seed will not germinate.
3. On exposure to light, Pr is converted to Pfr and germination proceeds.
4. This matters most for very small seeds such as lettuce, which have few food reserves.
5. A seedling from such a seed that germinated a centimetre below the surface would run out of fuel before reaching sunlight.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 30 "Plant Form and Physiology", section 30.6 Plant Sensory Systems and Responses_
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