energy ecosystem and nutrient cycles

Question 1

Suggest one way in which an increase in the uptake of phosphate could
increase plant growth.

Answer 1

used to produce atp or phospholipids

Question 2

Explain why an increase in shoot biomass can be taken as a measurement
of net primary productivity.

Answer 2

represents dry mass of carbon
represents gross production minus resp losses

Question 3

suggest how the mass of
carbon in the wood of a plantation of trees of a particular species could be estimated.
Start with measuring the diameter of a large number of trees.
Assume that the dry biomass of a tree consists of biological molecules that
contain carbon.

Answer 3

Calculate a mean diameter
determine the mean fresh biomass of trees; Use the percentage water content to find the dried biomass;
Use the dried density to calculate the mass of tree;
estimate the number of trees in plantation and multiply by
(mean) carbon content (to find total carbon);

Question 4

Explain why the scientists sterilised the surfaces of the seeds and grew them in soil
that had been heated to 85 °C for 2 days.

Answer 4

To kill any fungus on surface of seeds
So only the added fungus has any effect.

Question 5

Describe the role of microorganisms in producing nitrates from the remains of
dead organisms.

Answer 5

Saprobiotic microorganisms break down remains
ammonium ions into nitrite and then into nitrate
By Nitrifying bacteria

Question 6

Explain why the scientists measured the rate of production of oxygen in this
investigation.

Answer 6

Oxygen produced in light-dependent reaction;
The faster (oxygen) is produced, the faster the light-dependent reaction.

Question 7

why is there a decrease in gross productivity as woodland matures

Answer 7

Less light / more shading / more competition for light
Reduced photosynthesis.

Question 8

Use your knowledge of succession to explain the increase in biomass during the
first 20 years.

Answer 8

Pioneer species;
Change in abiotic conditions less hostile more habitats / niches;
Increase in diversity of species

Question 9

why’s net productivity decreasing when gross is

Answer 9

Net productivity = gross productivity minus respiratory loss;
Decrease in gross productivity
increase in respiration.

Question 10

Applying very high concentrations of fertiliser to the soil can reduce plant growth.
Use your knowledge of water potential to explain why.

Answer 10

Soil has low(er) water potential
not enough water taken up by osmosis