The tryptophan operon is a repressible operon that is turned off whenever tryptophan is added to the growth medium. turned on only when tryptophan is present in the growth medium. turned on only when glucose is present in the growth medium. permanently turned on.

The table shows dates and appearance of index fossils. which rock layers can be dated most precisely? a) a layer containing both a fossil 4 and a fossil 3 b) a layer containing both a fossil 2 and a fossil 3 c) a layer containing both a fossil 1 and a fossil 4 d) a layer containing both a fossil 1 and a fossil 2

Which of the following is a macronutrient? carbohydrates lipids amino acids all of the above

Draw the structure of dna nucleotide with adenine as nitrogenous base