Quick questions on Energy flow, food webs and trophic efficiency (QCE Biology Unit 3)

Producers fix energy from an abiotic source into chemical energy in organic molecules.

Consumers obtain energy by eating other organisms.

A food chain is a single linear path of energy transfer. Example: grass to kangaroo to dingo. Useful as a diagram but rarely the full picture.

Biomass is the total mass of living organic matter (dry mass, in g or kg) per unit area or volume.

Productivity is the rate at which producers fix energy (or organic matter) per unit area per unit time.

On average, only around 10 per cent of the energy at one trophic level is incorporated into biomass at the next level. The other 90 per cent is lost as:

Suppose a Queensland savanna has:

The compounding effect of the 10 per cent rule means each added trophic level captures a tenth of the energy of the level below. After four or five transfers, the residual energy is too small to support a population of mobile predators. Productive ecosystems (estuaries, reefs) can support longer chains; unproductive ones (deserts, deep ocean) sustain shorter chains and fewer top predators.

Three pyramid forms appear in QCAA stimulus.

Arrows in food webs follow energy flow, from prey to predator.

GPP is total photosynthesis; NPP is what is left after plant respiration. Only NPP is available to herbivores.

It is an average. State it as approximate, and use it where the question specifies.

Biomass can invert in plankton systems; energy cannot.

Decomposers receive energy from every trophic level (through dead matter and waste) and return inorganic nutrients to the abiotic pool. They appear in any complete food web.