Notes : 5.10 to 5.11 - Energy and Ecosystem

Question 1

What is gross primary productivty

Answer 1

The rate at which energy is incorporated into the plant biomass. Or the total energy fixed by photosynthesis.

Question 2

What are the units that GPP is measured in ?

Answer 2

biomass/area/time gm^-2 year^-1
or
energy/area/time kJm^-2 year^-1

Question 3

What is the net primary productivity calculation

Answer 3

• NPP=GPP-R
  (Gross primary productivity - Respiration losses)

Question 4

How does energy enter the food chain ?

Answer 4

Energy enters the food chain when producers absorb light energy and convert it into chemical energy during photosynthesis

Question 5

How much energy is passed on to the next tropic level ?

Answer 5

**40% but 10 % is converted into biomass and the remain 30 % is used in :
- Respiration
- Movement
- Maintaining body temp

Question 6

How is energy lost before it is passed on to the next tropic level ? for (produces - primary consumers)

Answer 6

• Plants can’t use all the energy that reaches their leaves : some is reflected, some passes straight through the leaves, some light will hit the non-photosynthetic parts of the plant (e.g. the tree trunk)., ** not all of it can be absorbed because it is the wrong wavelength (e.g. chlorophyll pigments are unable to absorb green parts of the visible spectrum, which is why they appear green to us).**
• Plants respires so energy is lost from there.

Question 7

How is energy lost before passed on to the next trophic level (primary producers to secondary producers)

Answer 7

• Not all part of the organism can be eaten (e.g bones, plants-cellulose, roots)
• Animals respire
• Excretion
• Movement
• Regulation of body temperature

Question 8

What is net primary productivity

Answer 8

the amount of energy
that’s available to the next trophic level. The flow of
energy transfer continues at the next trophic level

Question 9

How do we calculate net productive

Answer 9

Gross productivity - Respiratory loss
Note : Not the same as Net primary productivity

Question 10

How can we calculate the efficacy of energy transfers ?

Answer 10

Question 11

How can we measure energy transfers between trophic levels ?

Answer 11

1. Choose the area that you want to sample - e.g. a m2 area of woodland.
2. Calculate the amount of biomass in a sample of the organism by Dry the different organisms in the food chain in an oven until their mass becomes constant - at this point you can be sure that all the water has been removed and you’re left with only the dry mass (biomass).
3. Multiply the results of the sample by the size of the total area (e.g. to work out the biomass of that organism in 1500 m2 of woodland .
4. The difference in biomass between the trophic levels is the same as the amount of biomass transfer (or energy transfer) between the organisms.