Comparison of natural ecosystems and those based on modern intensive farming in terms of energy input and productivity. Net productivity as defined by the expression Net productivity = Gross productivity – Respiratory loss The ways in which productivity is affected by farming practices that increase the efficiency of energy conversion. These include • the use of natural and artificial fertilisers • the use of chemical pesticides, biological agents and integrated systems in controlling pests on agricultural crops • intensive rearing of domestic livestock. Candidates should be able to • apply their understanding of biological principles to present scientific arguments that explain how these and other farming practices affect productivity • evaluate economic and environmental issues involved with farming practices that increase productivity • consider ethical issues arising from enhancement of productivity

In natural ecosystems there is a relatively closed system in terms of energy input, nutrients and energy go around in a cycle from producers to consumers to decomposers with the main input being sunlight.

In modern day farming energy is introduced to a system via feeding, heat and artificial light; this increase in input makes for an increase in out put, a higher yield.

Productivity is the amount of chemical energy that plants make by photosynthesis. The net is calculated by the amount of energy produced from photosynthesis take away the amount that is used by the plant during respiration.

Net productivity= gross production - respiratory loss

In modern day farming farmers use any means possible to increase their yield, and therefore increase their profit.

Natural fertilisers include manure and animal bone; things that naturally contain nitrogen. Artificial fertilizers contain nitrogen made by the harbour process and extracted from rocks.

Pesticides are chemicals that are spread on crops to kill pests (things that are eating or damaging crops). Biological control is the introduction of an organism that will eat a pest. An integrated system is a series of techniques used to try and keep pest damage to a minimum, without disturbing the biodiversity of an area e.g. choosing areas with few pests, encouraging natural predators to be around, removing but not killing pests.

Eutrophication happens when water leeches nitrogen from soil and takes it into a water system: here the nitrogen helps algae to grow causing a bloom (large layer of algae); this blocks light for other organisms, like fish, and uses up their oxygen, causing them to die; decomposers increase as they feed on the dead, using up even more oxygen; oxygen is so low that no other organisms can survive.

Intensive farming also happens with livestock.

1 Slaughtered when still growing/before maturity/while young
 so more energy transferred to biomass/tissue/production;
2 Fed on concentrate /controlled diet /controlled
 conditions/so higher proportion of (digested) food
 absorbed/lower proportion lost in faeces / valid reason for
 addition;
3 Movement restricted so less respiratory loss / less energy
 used;
4 Kept inside/heating/shelter / confined so less heat loss / no
 predators;
5 Genetically selected for high productivity;