# energy flow

• July 3rd, 2014, 01:44 PM
ioa
energy flow
The amount of solar energy falling on the surface of the sea in the English
Channel is 2.1 × 10^6 kJ m−2 y−1. Photosynthetic phytoplankton in the water
assimilate energy from sunlight to generate a gross primary production
(GPP) of 6.3 × 103 kJ m−2 y−1 and a net primary production (NPP) of
5.0 × 103 kJ m−2 y−1. Herbivorous zooplankton consume phytoplankton
biomass equivalent to 4.0 × 103 kJ m−2 y−1 of energy and the rest of the
phytoplankton die and sink to the bottom, so that 1.0 × 103 kJ m−2 y−1
passes to detritivores and decomposers. Zooplankton convert
7.1 × 10^2 kJ m−2 y−1 of the phytoplankton they consume to biomass, which
then passes to numerous predators that feed on the zooplankton. The waste
products of the zooplankton, equivalent to 4.9 × 102 kJ m−2 y−1, sink to the
bottom and are consumed by detritivores and decomposers..

(i) Calculate the percentage of the solar energy falling on the surface of the
water that is lost and does not pass into the food chain of this
ecosystem.
(ii) Calculate how much energy is lost from this ecosystem through
zooplankton respiration.
• July 3rd, 2014, 01:46 PM
PhDemon
No one here is going to do your homework for you.
• July 3rd, 2014, 01:54 PM
ioa
i didnt post it here in order for someone to do my homework. i just need directions on how to deal with this exercise
• July 3rd, 2014, 01:58 PM
PhDemon
• July 3rd, 2014, 01:59 PM
Zwirko
Draw a diagram. Should be straightforward once you can see where everything is going.
• July 3rd, 2014, 02:06 PM
ioa
i. 1.3*10^3 diFFErence GPP-NPP

SO ANSWER 0.06 % AS %*SOLAR ENERG=RESPIRATION (1.3*10^3)
• July 3rd, 2014, 05:56 PM
Zwirko
I never enjoyed this sort of biology, so I'm very rusty on this stuff, so take anything I say with a pinch of salt.

I don't really understand your notation, but it seems to me as if you have calculated losses from GPP due to respiration, rather than the percentage of solar energy not utilised by the food chain. I would expect to see a number well over 90% since photosynthetic efficiency is quite low anyway.
• July 3rd, 2014, 11:24 PM
Lynx_Fox
Ya notation can be messy and I think the original question lost quite a bit of the meaning when it was copy pasted.

My preference by a long shot is simply use "E" notional instead of the cluttering up things with the x10 power terms.

--
Look at the first part. You appear to be looking for % amount lost between solar and GPP. That's not a simple ration between solar and GPP but a difference between solar and GPP divided by solar * 100.
• July 4th, 2014, 03:30 AM
ioa
I see. so for part 1
SO I WILL DO
2.1 E^6 - (6.3 E^3)=2.09 E^6

2.09 E^6 / 2.1E^6 =0.99
0.99*10
SO 99%?????
• July 4th, 2014, 05:44 AM
Zwirko
Radiant energy from the sun falls on the sea surface and is absorbed by phytoplankton. This energy is "converted" in to biomass (GPP). The synthesis of that biomass required energy (R). What's left, primary productiony (NPP) is available to the trophic level below (NPP = GPP - R). Energy lost to the foodchain at the top would have to include R. In other words, I think you should be looking at NPP rather than GPP.

It'll still be a very large percentage though.
• July 4th, 2014, 12:29 PM
ioa
I can not get it. I found really difficult to understand which equations to use
• July 7th, 2014, 05:53 AM
ioa
so I will do

((1.2 E ^6) -(6.3 E^3))/(1.2 E^6) =0.99

.99*100=99???
• July 7th, 2014, 08:00 AM
Zwirko
NPP/solar = percentage of solar energy that is incorporated into the food chain. The phytoplankton had to use energy (i.e. respiration) to help make the gross primary production, so we can't use the GPP figure. We need to look at the net primary production instead (NPP).

5.0 × 103 kJ m-2 y-1 / 2.1 × 106 kJ m−2 y−1

So, 99.761% is lost.

I admit that this figure looks scarily wrong since it's just a cat's whisker away from being a total loss. However, the number falls within the acceptable range of values one would expect to see since the efficiency of the conversion of solar energy into the energy contained in carbon compounds is very, very low - often below 1%.
• July 7th, 2014, 08:15 AM
ioa
Thank you!! For my second query i did so far

4 e^3 - 7.1e^2- 4.9 e^2=2800"

is this wrong too?
• July 7th, 2014, 08:27 AM
exchemist
Quote:

Originally Posted by Zwirko
NPP/solar = percentage of solar energy that is incorporated into the food chain. The phytoplankton had to use energy (i.e. respiration) to help make the gross primary production, so we can't use the GPP figure. We need to look at the net primary production instead (NPP).

5.0 × 103 kJ m-2 y-1 / 2.1 × 106 kJ m−2 y−1

So, 99.761% is lost.

I admit that this figure looks scarily wrong since it's just a cat's whisker away from being a total loss. However, the number falls within the acceptable range of values one would expect to see since the efficiency of the conversion of solar energy into the energy contained in carbon compounds is very, very low - often below 1%.

Assuming the original "5.0 x 103" in the OP was a typo and meant 5.0 x 10^3, and given the the quoted figure for incident solar energy, then the amount converted is clearly around 0.25%, so yes ~99.75% is not converted. Mind you I think the term "lost" is an oddly loaded one in this context, as I can't see why anyone would expect that plankton in the sea would be expected to capture more than a tiny fraction of the incident solar energy. If they captured it all then the sea would not warm and cool and there would be nothing to drive the weather systems of the planet!
• July 7th, 2014, 08:43 AM
Zwirko
I don't know why terms like "lost" and "efficiency" are used either, as they make plants look they have failed in some regard. Only a fraction of the incident solar radiation gets incorporated into the food chain, so maybe the rest is erm "lost"?

Perhaps those who started studying these things in depth from an energetics perspective were trained primarily in thermodynamics and got carried away with their metaphors or something...
• July 7th, 2014, 08:45 AM
ioa
Thank you!! For my second query i did so far

4 e^3 - 7.1e^2- 4.9 e^2=2800"

is this wrong too?
• July 7th, 2014, 09:03 AM
Zwirko
temporary deleted. back in a moment.
• July 7th, 2014, 09:19 AM
Zwirko
Any sort of biology that happens on a scale larger than a few micrometers is really not my area of expertise. So, bearing that in mind, I'd suggest the following (which could be wrong):

There are two respiration values we need to look for.

1) The phytoplankton respiration value can be found by subtracting NPP from GPP.

GPP = 6.3 × 103 kJ m−2 y−1
NPP = 5.0 × 103 kJ m−2 y−1

So, losses due to respiration here = 1.3 × 103 kJ m−2 y−1

2) The zooplankton consume the equivalent of = 4 x 103 kJ m−2 y−1
Of this, they convert = 7.1 X 102 kJ m−2 y−1 to biomass.
Respiration will be difference.

So, losses due to zooplankton respiration = 3.29 × 103 kJ m−2 y−1

Adding them both gives 4.59 x 103 kJ m−2 y−1

Maybe. Anyone think that makes sense?
• July 7th, 2014, 07:49 PM
ioa
http://www.thescienceforum.com/image...quote_icon.png Originally Posted by Zwirko http://www.thescienceforum.com/image...post-right.png NPP/solar = percentage of solar energy that is incorporated into the food chain. The phytoplankton had to use energy (i.e. respiration) to help make the gross primary production, so we can't use the GPP figure. We need to look at the net primary production instead (NPP).

5.0 × 103 kJ m-2 y-1 / 2.1 × 106 kJ m−2 y−1

So, 99.761% is lost.

how we came to this solution? when I divide them I get 2.38 E^-3
• July 7th, 2014, 08:07 PM
Lynx_Fox
Quote:

Originally Posted by ioa
how we came to this solution? when I divide them I get 2.38 E^-3

What is 2.39E-3 in %?

multiply by 100, so it's 0.239%

So

100% - 0.239% = 97.762%

You'll need to become more comfortable with %s.
• July 8th, 2014, 11:56 AM
ioa
Quote:

Originally Posted by Zwirko
Any sort of biology that happens on a scale larger than a few micrometers is really not my area of expertise. So, bearing that in mind, I'd suggest the following (which could be wrong):

There are two respiration values we need to look for.

1) The phytoplankton respiration value can be found by subtracting NPP from GPP.

GPP = 6.3 × 103 kJ m−2 y−1
NPP = 5.0 × 103 kJ m−2 y−1

So, losses due to respiration here = 1.3 × 103 kJ m−2 y−1

2) The zooplankton consume the equivalent of = 4 x 103 kJ m−2 y−1
Of this, they convert = 7.1 X 102 kJ m−2 y−1 to biomass.
Respiration will be difference.

So, losses due to zooplankton respiration = 3.29 × 103 kJ m−2 y−1

Adding them both gives 4.59 x 103 kJ m−2 y−1

Maybe. Anyone think that makes sense?

why do i have to find phytoplankton respiration?? and where do we find 3.29 x10^3?
• July 8th, 2014, 01:40 PM
Zwirko
You're right. I misread the question thinking it was referring to zoo- and phyto- for some reason.
• July 8th, 2014, 01:45 PM
ioa
Quote:

Originally Posted by Zwirko
You're right. I misread the question thinking it was referring to zoo- and phyto- for some reason.

so what is the way to find only zooplankton espiration? it says that In your calculation, show your working, usingword equations that describe the relationships between respiration,
biomass consumption, energy assimilation and energy lost as waste