AQA A-Level Biology - Energy & Ecosystems

Vocabulary flashcards covering biomass measurement, primary production (GPP & NPP), energy transfer efficiency, agricultural efficiency practices, and nutrient cycles.

Biomass

The total mass of living material in a specific area.

Dry Mass

The mass of an organism measured after all water has been removed, providing a more consistent comparison because water content varies.

Calorimetry

A procedure used to calculate stored chemical energy by burning a dry sample and measuring the temperature rise of a known volume of water.

Gross Primary Production (GPP)

The total chemical energy stored in plant biomass in a given area and time, representing energy fixed by photosynthesis.

Net Primary Production (NPP)

The chemical energy remaining in plant biomass after plant respiration, calculated as $NPP = GPP - R$, which is available for growth, reproduction, and transfer to higher trophic levels.

Respiratory Losses ($R$)

The energy used by an organism for its own life processes or lost as heat from respiration.

Producers

Organisms such as plants and algae that occupy the first trophic level and fix energy through photosynthesis.

Primary Consumers

Herbivores that occupy the second trophic level and feed on producers.

Secondary Consumers

Carnivores that occupy the third trophic level and feed on herbivores.

Tertiary Consumers

Top carnivores that occupy the fourth trophic level.

Consumer Net Production ($N$)

The net energy calculated for a consumer using the formula $N = I - (F + R)$.

Energy Ingested ($I$)

The total energy contained in the biomass eaten or ingested by a consumer.

Energy Lost in Faeces and Urine ($F$)

The energy lost by a consumer through undigested matter in faeces and metabolic excretion in urine.

Energy Transfer Efficiency

The efficiency percentage of energy transferred between trophic levels, calculated as \text{Efficiency (\frac{\text{Energy available after transfer}}{\text{Energy available before transfer}})} \times 100.

Simplifying Food Webs

An agricultural practice of removing pests and weeds to reduce energy lost to non-crop species, leaving more energy available for human consumption.

Battery Farming

An intensive livestock method that increases efficiency and reduces cost by restricting movement and controlling temperature, but creates animal welfare concerns and disease risks.

Pesticides

Chemical substances used to reduce competition or crop poisoning, which carry risks of eutrophication, bioaccumulation, and harming beneficial species.

Nitrogen Fixation

The process converting $N_2$ gas into ammonia, carried out by bacteria such as Rhizobium in root nodules and free-living Azotobacter.

Nitrification

An oxidation process converting ammonia to nitrites and then to nitrates, carried out sequentially by Nitrosomonas and Nitrobacter.

Assimilation (Nitrogen Cycle)

The process where plants absorb nitrates from soil water to synthesize proteins and nucleic acids.

Ammonification

The process where decomposers break down nitrogenous organic matter from dead organisms and waste into ammonia.

Denitrification

The conversion of nitrates into $N_2$ gas by bacteria under anaerobic conditions, such as in waterlogged soil.

Phosphorus Cycle

A nutrient cycle lacking a gas phase, in which phosphorus is stored in sedimentary rocks, released by weathering as phosphate ions, absorbed by plants to synthesize ATP, DNA, and phospholipids, and recycled by decomposers.