NEET Biology Plant Growth And Development Based Practice Questions & Answers with Viewers Discussion and Detailed Explanation

Answer: (c)

Auxin bioassay is a quantitative test as it measures concentration of auxin to produce the effect and the amount of the effect. Avena curvature is based upon experiments of Went (1928). 10° curvature is produced by auxin concentration of 150 mg/litre at 25°C and 90% relative humidity. The test can measure auxin upto 300 mg/litre. Auxin from a shoot tip or any other plant organ is allowed to diffuse in a standard size agar block (generally 2 × 2 × 1 mm). Auxin can also be dissolved directly in agar. 15– 30 mm long oat coleoptile grown in dark is held vertically over water. 1 mm tip of coleoptile is removed without injuring the primary leaf. After 3 hours a second decapitation is carried out for a distance of 4 mm. Primary leaf is now pulled loose and agar block supported against it at the tip of decapitated coleoptile. After 90–110 minutes, the coleoptile is found to have bent. The curvature is measured. It can also be photographed and the curvature known from shadow graph.