Productivity: GPP and NPP

A student determined the dry mass of lettuce leaves. The equipment used was an oven and a weighing balance.

Describe how the student could use this equipment to determine the dry mass of lettuce leaves.

The student then used a calorimeter to determine the chemical energy stored in a sample of lettuce leaves with a dry mass of 1.50 g

The 1.50 g sample was fully combusted in a calorimeter.

The volume of water in the calorimeter was 150 cm³

The increase in temperature of the water was 18.2 °C

4.18 J of heat energy are required to increase the temperature of 1 cm³ of water by 1 °C

Use this information to calculate the heat energy released, in kJ g^–1, of dry mass of lettuce leaves.

Show your working.

Biomass can be measured as the dry mass of tissue per given area. Some crop plants are grown in large greenhouses (glasshouses) where optimum growing conditions can be maintained.

Growing crop plants at higher temperatures than their optimum temperature can decrease their biomass.

Use your knowledge of net primary production to explain why.

In the following passage, the numbered spaces can be filled with biological terms.

An ecosystem supports a certain size of population of a species, called

Write the correct biological term beside each number below that matches the space in the passage.

Suggest two reasons for conserving rainforests.

Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem.

In the following passage the numbered spaces can be filled with biological terms.

carbon, such as carbohydrates, lipids and proteins. Most of the sugars synthesised

per given time. The chemical energy store in dry biomass can be estimated

Write the correct biological term beside each number below, that matches the space in the passage.

Describe the light-independent reaction of photosynthesis.

I represents the chemical energy store in ingested food F represents the chemical energy lost to the environment in faeces and urine R represents the respiratory losses to the environment.

In the UK, some female cattle are only used for breeding. This female breeding herd has dairy cows and beef cows.

Table 1 shows data on dairy cows and beef cows in the UK female breeding herd in December 2013 and December 2017.

In December 2017, the female breeding herd was 48% of all female cattle in the UK. Use Table 1 to calculate the percentage of all female cattle that were beef cows in the UK in December 2017.

Use Table 1 to calculate the increase in the number of dairy cows in the UK female breeding herd between December 2013 and December 2017.

Show your working.

Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain why.

Scientists investigated the effect of full sun and shade on the rate of photosynthesis in a species of shade-tolerant tree.

To estimate the rate of photosynthesis, the scientists measured uptake of carbon dioxide by trees in a forest. They measured uptake of carbon dioxide during two parts of the day:

• 08.30 – 09.40 hours

• 11.40 – 13.15 hours.

Figure 8 shows the scientists’ results.

Figure 8

Figure 8 not reproduced here due to third-party copyright restrictions

Calculate the total uptake of carbon dioxide between 11.40 and 13.15 hours in trees exposed to full sun in a forest that is 12 000 m² in area.

Give your answer in standard form. Show your working.

Figure 8 shows there is a small difference in the mean uptake of carbon dioxide between 08.30 and 09.40 hours by trees in full sun and by trees in the shade. When the scientists performed a statistical test on these data, they calculated P > 0.5

State what this P value tells you about this difference.

Explain your answer using the words probability and chance.

In this species of tree, very high light intensities can inhibit the release of electrons from chlorophyll.

Suggest how this could explain the results shown in Figure 8 for 11.40 to 13.15 hours.

Tomato plants grow best in high light intensities. To increase the yield of tomato plants, a farmer uses LED lightbulbs to provide additional light.

The increase in dry mass (D) produced when using additional light can be calculated using this equation.

Where L = light used in photosynthesis F = GPP to NPP conversion factor for tomato plants

Table 5 shows some of these values for LED lightbulbs.

Use the equation and Table 5 to calculate the increase in dry mass produced when using LED lightbulbs.

Give your answer in standard form and give the units.

Mature leaves from slow-growing, shade-tolerant plants produce poisonous chemicals that are a defence against being eaten by herbivores.

Suggest how this benefits slow-growing, shade-tolerant plants.

Scientists measured the concentration of poisonous chemicals produced by

shade-tolerant plant species in six taxa. They compared this with the mean concentration of poisonous chemicals produced by all plants and the phylogenetic relationships between the six taxa.

Figure 9 shows the scientists’ results.

A journalist published the following summary of these results.

‘The more recently a shade-tolerant plant species evolved, the greater the concentration of poisonous chemicals it produces.’

Do the data in Figure 9 support this summary? Justify your answer.

Freshwater marshes have one of the highest rates of gross primary production (GPP and net primary production (NPP) of all ecosystems.

Carbon use efficiency (CUE) is the ratio of NPP:GPP. Freshwater marshes have a high CUE.

Use your knowledge of NPP to explain why freshwater marshes have a high CUE and the advantage of this.

Do not refer to abiotic factors in your answer.

Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions.

Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions.

A student investigated the growth rate of a freshwater marsh plant.

The growth rate (R) of a plant can be determined using this equation.

Where ln = natural logarithm t = duration of the investigation in days W₁ = plant biomass at the start of the investigation W₂ = plant biomass at the end of the investigation

The student used the equation above; however, she substituted height for biomass. This was because she did not want to destroy the plants to measure their biomass.

State the assumption the student has made and suggest why this assumption might not be valid.

At the end of the investigation, the student noted the freshwater marsh plant had grown 268 mm in height, and now measured 387 mm. She calculated the rate of

Use this information and, substituting height for biomass, use the equation to calculate the duration of the student’s investigation.

Give your answer to the nearest full day. Show your working.

Figure 2 shows one type of calorimeter.

A calorimeter can be used to determine the chemical energy store of biomass. A known mass of biomass is fully combusted in a calorimeter. The heat energy released from this combustion increases the temperature of the water in the calorimeter. The increase in the temperature of a known volume of water is recorded.

Other than the thermometer, explain how two features of the calorimeter shown in Figure 2 would enable a valid measurement of the total heat energy released.

A 2 g sample of biomass was fully combusted in a calorimeter.

The volume of water in the calorimeter was 100 cm³

The increase in temperature recorded was 15.7 °C

4.18 J of energy are needed to increase the temperature of 1 cm³ of water by 1 C

Use this information to calculate the heat energy released in kJ per g of biomass.

Show your working.

Plants and algae produce fuels called biofuels. Scientists have used Chlorella to produce biofuel. Chlorella is a genus of single-celled photosynthetic alga. Chlorella can be grown in open ponds and fermenters.

In natural ecosystems, most of the light falling on producers is not used in photosynthesis.

Suggest two reasons why.

The light absorbed by chlorophyll is used in the light-dependent reaction.

Name the two products of the light-dependent reaction that are required for the light-independent reaction.

Chlorella cells can divide rapidly. A culture of 2000 Chlorella cells was set up in a fermenter. The cells divided every 90 minutes.

You can assume that there were no limiting factors and that no cells died during the 24 hours.

Calculate the number of cells in the culture after 24 hours.

Give your answer in standard form.

Show your working.

A scientist investigated the effects of different fertilisers on the growth of spinach plants. The scientist:

• set up a large sample of identical pots of soil

• added different masses of different fertilisers to selected pots

• did not add fertiliser to the control pots

• planted the same number of young spinach plants in each pot

after 20 days, determined the biomass of spinach plants in each pot.

The results the scientist obtained after 20 days are shown in Figure 4.

Calculate how many times greater the mean growth rate per day was using 37.5 g potassium nitrate than using 37.5 g ammonium sulfate.

Assume the mean biomass of the spinach plants at the start of the investigation was 0.5 g per pot.

Using all the information, evaluate the effect on plant growth of adding the different fertilisers to the soil.

The scientist determined the dry mass of the spinach plants. First, he heated each sample at 80 C for 2 hours.

Suggest what the scientist should do to ensure that he has removed all the water from the sample.

Succession occurs in natural ecosystems. Describe and explain how succession occurs.

Figure 1 shows percentages of energy transferred from sunlight to a zebra in a grassland ecosystem.

Use Figure 1 to calculate the percentage of sunlight energy that would be transferred into the faeces and urine of a zebra. Give your answer to 3 significant figures.

In this ecosystem the net productivity of the vegetation is 24 525kJ m² year¹

Use this information and Figure 1 to calculate the energy stored in new tissues of the

Scientists investigated the process of succession on sand dunes. They measured the percentage cover of different species of plants on sand dunes of different ages. Some of the results the scientists obtained are shown in Figure 5.

Describe how you would determine the mean percentage cover for beach grass on a sand dune.

The scientists concluded that the results shown in Figure 5 were due to succession taking place.

Use Figure 5 to explain why the scientists reached this conclusion.

The scientists also investigated how the proportion of sunlight reaching the ground changed during succession. Some of the results the scientists obtained are shown in Figure 6.

Use Figure 5 to explain the results in Figure 6.

Using evidence from Figure 6, what can you conclude about the net primary productivity (NPP) in the sand dunes that are older than 1000 years?

Explain your answer.

Arbuscular mycorrhiza fungi (AMF) are fungi which grow on, and into, the roots of plants. AMF can increase the uptake of inorganic ions such as phosphate.

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

Suggest one way in which AMF may benefit from their association with plants.

Scientists investigated the effects of different AMF species on the productivity of the plant community of a prairie grassland ecosystem when growing in/on soil containing different phosphate concentrations.

The scientists set up identical plots of prairie grassland soil containing seeds of the plant species found in the ecosystem. The scientists added different AMF species and different concentrations of phosphate to particular plots. Control plots without AMF species were also set up. After 20 weeks the scientists determined the shoot biomass for each plot.

The results the scientists obtained are shown in Figure 5.

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

Using the data from Figure 5, evaluate the effect on plant productivity of adding AMF species and adding phosphate to the soil.

Using the e^x button on your calculator, determine the rate of shoot biomass production in grams per day for the control plot in soil with normal phosphate concentration.