5.3 ENERGY TRANSFERS (GPP, NPP, PP, SP, BIOMASS, TROPHIC LEVELS)

WHERE DO PLANTS SYNTHESIS ORGANIC MOLECULES FROM?

• Atmospheric/aquatic CO2.

HOW ARE SUGARS SYNTHESISED BY PLANTS USED?

• Mostly as respiratory substrates.

• Some used as biological molecules - this forms biomass.

BIOMASS:

• Can be measured in terms of carbon mass (/dry tissue mass) per given area.

• Can estimate with calorimeter.

GPP:

• Chemical energy store in plant biomass in a given area/volume.

NPP:

• Chemical energy store in plant biomass AFTER respiratory losses have been taken into account.

• ::: NPP = GPP - R

WHAT IS NPP AVAILABLE FOR?

• Plant growth and reproduction.

• Other trophic levels in ecosystem, e.g. herbivores and decomposers.

NET PRIMARY PRODUCTION OF CONSUMERS FORMULA:

N = I - F - R

I = Chemicals ingested.

F = Faeces and urine.

PRIMARY AND SECONDARY PRODUCTIVITY:

• Productivity = Rate of production.

• Measured in biomass/area/year (KJ/m/year).

% EFFICIENCY OF ENERGY TRANSFER BETWEEN TROPHIC LEVELS FORMULA:

(Energy available before transfer) / (Energy available after transfer).

TROPHIC LEVELS:

• Position of an organism in a food chain.

• Energy flows through ecosystems from one trophic level to the next.

FARMIING PRACTICES THAT INCREASE EFFICIENCY OF ENERGY TRANSFER:

• Simplifying food webs to reduce losses to non-human food chains.

• Reducing R within a human food chain.

WHY ISN’T ALL OF LIGHT ENERGY USED IN PHOTOSYNTHESIS?

1. Does not strike chlorophyll.

2. Inappropriate wavelength.

3. Reflected/transmitted through leaf.

WHY IS ONLY A SMALL AMOUNT OF PHOTOSYNTHESIS ENERGY CONVERTED INTO CHEMICAL ENERGY OF GLUCOSE?

1. Some lost during very inefficient photosynthesis.

2. May be other limiting factors of photosynthesis.