Option G Ecology and Conservation:
G2 Ecosystems and Biomes
Define gross production, net production, and
biomass.
• Gross production is the total amount of organic material
produced by plants in an ecosystem.
• Net production of an ecosystem is gross production less the
material expended by the plants in respiration.
• Both of these are measured in kJ per squared meter per year
(Kj m-2 yr-1).
• Biomass is the dry weight of organic matter in organisms of an
ecosystem.
Calculate values for gross production and net
production and net production using the equation: gross
production – respiration = net respiration
• GP – R = NP
Discuss the difficulties of classifying
organisms into trophic levels.
• It is difficult due to the fact that some organisms can
be secondary, tertiary, and may be quaternary
consumers at the same time, such as humans. It is
difficult to place them on a certain level of the food
pyramid.
Cont’d
• For this reason, an alternate method of
classification - the food web - has been
developed. The food web displays
relationships not as a simple hierarchy but
rather a complex network, with the various
feeding relationships between species
existing as connections and the animals
themselves existing as the hubs.
Explain the small biomass and low number
of organisms in higher trophic levels
• There is a decreasing biomass of organisms in
the higher trophic levels because energy is lost
between levels in the form of heat (respiration),
waste, and dead material.
• Only around 10-15% of the energy proceeds on
to the next trophic level.
• Often referred to as the 10% rule
Construct a pyramid of energy,
given appropriate information
• The lowest bar of the pyramid of energy represents gross primary
productivity, the next bar is the energy ingested as food by primary
consumers, and so on. The arrows demonstrate the direction of
energy flow. The units are energy per unit area per unit time
Distinguish between primary and secondary
succession using an example for each
• 1o
• Ecological succession is the gradual change in the
composition of a community with time in an ecosystem. If
succession occurs in a lifeless area it is primary succession.
It can start after things such as volcanoes, fire or flood.
• The process is usually goes: lichen, moss, ferns, flowerings
plants, conifers.
• For example on the Volcan Osorno in south Chile after ash
covers the ground: mosses spread over the ash. Small herbs
and ferns arrive and through the activity of their roots, soil
formation starts to occur. Shrubs and bushes grow and
replace these. Then flowering trees grow, then conifers, and
other larger trees producing a forest.
2o succession
Secondary succession is the series of community
changes which take place on a previously
colonized, but disturbed or damaged habitat.
Examples include areas which have been
cleared of existing vegetation (such as after treefelling in a woodland) and destructive events
such as fires. Fallowed farm fields.
1o and 2o Succession images
Explain the effect of living organisms on the abiotic
environment, with reference to the changes occurring
during primary succession
• Help with soil development, as a plant grows,
their roots grow deeper down and break rock
into small particles, helping soil formation.
• Plants enrich the soil with minerals as they die
and decompose.
• The plant roots hold the soil particles together,
preventing soil erosion and retain nutrients.
• The water that evaporates from many plant
leaves condenses and comes down in the form
of rain.
Distinguish between biomes
and biosphere
Explain how rainfall and temperature
effect the distribution of biomes
Outline the characteristics of the
6 major biomes
• HOMEWORK…. You should include
precipitation averages, temp ranges,
examples of flora and fauna that can be
found in these biomes as well