Task: Class Definition Understanding (ontology: Earth_Environment/OBOE)

Which of the following definitions best describes 'MicromolePerKilogram'?

A. An einstein is a unit used in irradiance and in photochemistry. One einstein is defined as one mole of photons, regardless of their frequency. Therefore, the number of photons in an einstein is Avogadro's number, 6.022×1023.

Quantum flux of Photosynthetically active radiation (PAR) is usually reported in microeinsteins per second per square meter, one microeinstein being one-millionth of an einstein.

Irradiance might be measured in einsteins per square metre per second, if the source is monochromatic. (note: If the optical frequency is not well defined this is a sloppy misuse of the term irradiance, which is defined in terms of power per unit area, and p.


The einstein is used in studies of photosynthesis since the light requirement for the production of a given quantity of oxygen is a fixed number of photosynthetically active photons (about nine photosynthetically active einsteins per mole of oxygen formed).

It is named in honor of Albert Einstein, who in a 1905 paper explained the photoelectric effect in terms of light quanta, now called photons, an idea introduced by Max Planck.
B. The the concept is the unit of force derived in the SI system; it is equal to the amount of net force required to accelerate a mass of one kilogram at a rate of one meter per second per second. 
1 N = kg  m  s-2
C. Unit of concentration often used for gasses (e.g., oxygen, or O2) because it is related to solubility measurements.
D. Conductivity is the reciprocal (inverse) of electrical resistivity, ρ, and has the SI units of siemens per metre (S·m-1). "siemens" is used for both singular and plural.

Answer: Unit of concentration often used for gasses (e.g., oxygen, or O2) because it is related to solubility measurements.