Productivity and ecosystems: exam questions

Answer: B – NPP = GPP − R = 15 000 − 6 000 = 9 000 kJ m⁻² year⁻¹.

• NPP = GPP − R = 9 800 − 2 600 (1)
• = 7 200 kJ m⁻² year⁻¹ (1)
• efficiency = 720 ÷ 7 200 × 100 (1) (accept error carried forward from NPP)
• = 10 % (1)

• some of the primary consumer is not eaten (for example bones, fur, teeth) (1)
• some of what is eaten is not digested and is lost as faeces (egestion) (1)
• some energy is lost in excretory products such as urea (1)
• energy is lost as heat from respiration, which is used for movement / maintaining body temperature / active transport (1)
• some primary consumers die of other causes and pass to decomposers (1)
• Max 4

• population: all the organisms of one species in the habitat at the same time (1)
• community: all the populations of different species living (and interacting) in the habitat (1)
• ecosystem: the community together with the abiotic (non-living) environment (1)
• suitable named example (for example a pond / woodland) used correctly (1)
• Max 3

• abiotic: the lower shore is covered by sea water for longer, so the limpets are less likely to dry out / less desiccation (1)
• abiotic: temperature / salinity is more stable (less extreme) on the lower shore (1)
• biotic: more algae / food on the lower shore (accept limpets are submerged for longer so have more time to graze) (1)
• biotic: less time exposed to predators that feed at low tide, such as birds (1)
• a clear link between each factor and the survival / reproduction / numbers of the limpets (1)
• Max 4 (max 2 for abiotic and max 2 for biotic)

• niche is the role of a species in its habitat / how it interacts with its environment (1)
• the two species have different niches / different feeding positions (1)
• so less interspecific competition for food (1)
• if niches were the same, one species would outcompete the other / be excluded (1)
• each population is controlled by the food available in its part of the habitat (accept intraspecific competition) (1)
• Max 4

• tape measure laid out at right angles to the path / along the line from the path into the wood (1)
• quadrats placed at regular intervals (for example every 2 m) along the line (interrupted belt transect) (1)
• in each quadrat record the abundance of the species / percentage cover / number of plants (1)
• use of the same size quadrat each time (accept 0.25 m²) (1)
• measure light intensity at each quadrat using a light meter, held at the same height and orientation (1)
• repeat the transect / use several transects and calculate means (1)
• plot a graph of abundance against distance and light intensity / carry out a correlation test (1)
• link: correlation does not prove causation (accept other factors such as soil moisture could vary) (1)
• Max 6

• area sampled = 12 × 0.25 = 3 m², so mean = 54 ÷ 3 = 18 per m² (1)
• population = 18 × 4 800 (1)
• = 86 400 (1) (no mark for the unit; accept 86 400 plants)

• pioneer species (for example lichens / mosses) colonise the bare rock (1)
• they tolerate harsh conditions / lack soil / photosynthesise (1)
• when they die and decompose they add organic matter, which forms soil / increases nutrients and water retention (1)
• the abiotic conditions become less hostile, so other species (grasses, shrubs) can colonise and outcompete the pioneers (1)
• diversity and biomass increase / food webs become more complex (1)
• eventually a stable climax community forms, with no further net change in species, in balance with the climate (1)
• Max 5