What percentage of water absorbed by plant roots is lost to the air via transpiration?

Correct answer: About 99%

Direct answer: B, about 99%. Roots absorb water from the soil, and that water travels through the plant’s conducting tissues toward leaves. At leaf surfaces, especially through stomata, most of the water escapes as water vapour; this loss is called transpiration. In the commonly taught school-level estimate, approximately 99% of absorbed water is lost through transpiration, while only a very small fraction is retained or used in metabolic processes and growth. A, C and D are much lower than the accepted approximate value for this question. The figure is an estimate, not a universal constant: it can vary with plant species, humidity, temperature, wind, soil water and stomatal behaviour. Do not confuse transpiration with evaporation from open water; transpiration is specifically water loss from plant surfaces. Cue: plants absorb much water but use only a tiny fraction internally.