Question

Step 1: If 75 kg of "Molecule Z" is distributed amongst 5,000 organisms that weigh 2 kg each on average, what is the concentration, by mass, of "Molecule Z"?

Step 2: Assuming that 70% of "Molecule Z" from above is lost between trophic levels, and the next trophic higher level consists of 10,000 individuals weighing 0.1 kg each, what will the concentration of "Molecule Z" be in this next higher trophic level? (Hint: remember that what is not lost is what is passed to the next trophic level).

Answer 1

1)75kg of molecule Z is distributed amongst 5,000 organisms that weigh 2 kg each on average.

The total weight of the organism = Number of organism *Average weight of the organism = 5000*2kg = 10000 kg

The concentration in terms of mass is = Weight of the molecule Z distributed /Weight of thepopulation = 75kg/10000kg = 0.0075.

2)From the above concentration of the molecule Z is lossed in between the trophic level.

So the next level containing a population of 10000 people of weigh 0.1kg recieve only 30% of the concentration of the Molecule Z

That is equal to contration of the molecule Z *30/100 =0.0075* 0.3 =0.00225.

If they asked about the mass of molecule Z distributed in teh next trophic level we should consider the mass of the 10000 population

Mass of molecule Z used = concentration of molecule Z in this trophic level * weight of the this population

                                   =0.00225*[10000*0.1]=2.25kg.

Conclusion

Here the concentration of molecule Z in the next trophic level is used so 0.00225.