Answer:
<em>Light of wavelength 550 nm is least effective at promoting photosynthesis.</em>
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<em>-</em><em>-</em><em>></em><em> </em><em><u>L</u></em><u><em>ight</em><em> intensity</em></u><em><u>:</u></em><em><u>-</u></em>
<em>Without enough light, a plant cannot photosynthesise very quickly - even if there is plenty of water and carbon dioxide and a suitable temperature. Increasing the light intensity increases the rate of photosynthesis, until some other factor - a limiting factor - becomes in short supply.</em>