Author: Philip Colls
Document comments: Created by the \'abHTML to RTF .Net\'bb 5.8.2.9

Energy in Ecosystems booklet revision questions     NAME:
Q1. Yield can be determined by measuring the dry mass of plants.
(a)     Suggest how you could determine the dry mass of a sample of plant material.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(b)     What is the advantage of using dry mass and not fresh mass to compare the yield of plants?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________(2)  (Total 4 marks)
Q2. The diagram shows the transfer of energy through a cow. The figures are in kJ × 10^6 year^–1.
 
Key:       A = energy absorbed from the gut
C = energy consumed in food
F = energy lost in faeces
P = energy used in production of new tissue
R = energy lost by respiration
U = energy lost in urine
(a)     (i)      Complete the following equation for the energy used in the production of new tissue. Use only the letters C, F, R and U.
P = _________________________________________________________(1)
(ii)     Calculate the value of P.

P = ____________________ kJ × 10^6 year^–1  (1)
(b)     It has been estimated that an area of 8100 m^2 of grassland is needed to keep one cow. The productivity of grass is 21 135 kJ m^–2 year^–1. What percentage of the energy in the grass is used in the production of new tissue in one cow? Show your working.

 
 
Answer ____________________ %   (2)
(c)     Keeping cattle indoors, in barns, leads to a higher efficiency of energy transfer.
Explain why.
___________________________________________________________________
_________________________________________________________________(1)
(Total 5 marks)
Q3. Scientists investigated the effect of a mycorrhizal fungus on the growth of pea plants with a nitrate fertiliser or an ammonium fertiliser. The fertilisers were identical, except for nitrate or ammonium.
The scientists took pea seeds and sterilised their surfaces. They planted the seeds in soil that had been heated to 85 °C for 2 days before use. The soil was sand that contained no mineral ions useful to the plants.
(a)     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.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(b)     Explain why it was important that the soil contained no mineral ions useful to the plants.
___________________________________________________________________
_________________________________________________________________(1)
The pea plants were divided into four groups, A, B, C and D.
•        Group A – heat-treated mycorrhizal fungus added, nitrate fertiliser
•        Group B – mycorrhizal fungus added, nitrate fertiliser
•        Group C – heat-treated mycorrhizal fungus added, ammonium fertiliser
•        Group D – mycorrhizal fungus added, ammonium fertiliser
The heat-treated fungus had been heated to 120 °C for 1 hour.
(c)     Explain how groups A and C act as controls.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
After 6 weeks, the scientists removed the plants from the soil and cut the roots from the shoots. They dried the plant material in an oven at 90 °C for 3 days. They then determined the mean dry masses of the roots and shoots of each group of pea plants.
(d)     Suggest what the scientists should have done during the drying process to be sure that all of the water had been removed from the plant samples.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
The scientists’ results are shown in the table below.

Treatment

Mean dry mass / g per plant
( standard deviation)

| Root | Shoot

A – heat-treated fungus and nitrate fertiliser

0.40
(±0.05)

1.01
(±0.12)

B – fungus and nitrate 
fertiliser

1.61
(±0.28)

9.81
(±0.33)

C – heat-treated fungus and ammonium fertiliser

0.34
(±0.03)

0.96
(±0.26)

D – fungus and ammonium fertiliser

0.96
(±0.18)

4.01
(±0.47)

(e)     What conclusions can be drawn from the data in the table about the following?
The effects of the fungus on growth of the pea plants.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
The effects of nitrate fertiliser and ammonium fertiliser on growth of the pea plants.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(4)
The scientists determined the dry mass of the roots and shoots separately. The reason for this was they were interested in the ratio of shoot to root growth of pea plants. It is the shoot of the pea plant that is harvested for commercial purposes.
(f)     Explain why determination of dry mass was an appropriate method to use in this investigation.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(g)     Which treatment gave the best result in commercial terms? Justify your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(Total 15 marks)

Q4.
In some countries, pigs are reared in intensive units in which the temperature is controlled. Agricultural scientists investigated the effect of temperature on pig growth and on the efficiency with which the pigs converted food to biomass.
(a)     (i)      In the investigation, the scientists used pigs of the same breed, with similar genotypes.
Explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
____________________________________________________________(2)
(ii)     The pigs were allowed to eat as much food as they wanted.
How could this have decreased the reliability of any conclusions drawn from the
investigation?
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
____________________________________________________________(2)
The table shows the results of this investigation.

Temperature / °C

Mean growth rate /
kg per day

Efficiency of conversion of
food to biomass /%

0 | 0.54 | 19
10 | 0.80 | 42
20 | 0.85 | 48
30 | 0.45 | 37
35 | 0.31 | 37
(b)     (i)      Describe the effect of temperature on mean growth rate.
______________________________________________________________
______________________________________________________________
____________________________________________________________(1)
(ii)     A student concluded from these data that the mean growth rate of the pigs was fastest at 20 °C.
Do you agree with this conclusion? Explain your answer.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(c)     (i)      Pigs can survive at temperatures above 35 °C. Use the data to suggest why scientists did not carry out any investigations at temperatures higher than 35 °C.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii)     The efficiency of conversion of food to biomass is lower at 0 °C than it is at 20 °C.
Suggest an explanation for the lower efficiency.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(d)     Pigs require a mixture of fibre and protein in their food. The greater the ratio of fibre to protein, the less the food costs.
Scientists took five large groups of pigs. They fed each group a different high-fibre food. Each of the foods contained fibre from different plant species, but they all had the same energy content. The scientists fed a control group of pigs a low-fibre food with the same energy content. After 10 days, the scientists compared the masses of the pigs fed on high-fibre food to those fed on low-fibre food.
The graph shows the results of the investigation. The bars represent ±2 standard errors of the mean.
 
A farmer saw these results and concluded that he should replace his pigs’ usual food with food B.
Evaluate this conclusion.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________ (4)
(Total 15 marks)
Q5. Ecologists developed a method for estimating the biomass of trees in a plantation.
The plantation consisted of trees of the same species.
They collected samples of wood from trees. For each sample they:
•        determined the density of the freshly cut wood
•        dried the wood in an oven at 103 °C for 24 hours
•        determined the volume of the dried wood sample
•        determined the density of the dried wood.
The table below shows data about one wood sample.

Volume of freshly cut wood sample
/ dm^3

Density of freshly cut wood
/ g per dm^3

Volume of dried wood sample
/ dm^3

Density of dried wood sample
/ g per dm^3

1.345 | 993.0 | 1.125 | 769.0
(a)     The loss of mass of the wood sample was due to loss of water. Water has a density of 1 g per cm^3.
Use the data in the table to calculate the percentage of water in the freshly cut wood sample. Show your working.
Percentage of water = __________________________________
(2)
(b)     The ecologists dried the samples in an oven at 103 °C for 24 hours. Describe how the ecologists could have determined whether or not this drying removed all the water from a sample of wood.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(c)     Ecologists then investigated the relationship between the diameter of the trunk of the trees and their biomass.
The graph below shows their results. Each point is the result for one tree.
 
What does the graph show about the relationship between the diameter of the trunk of the trees and their biomass?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(d)     Plantations of trees are often created to remove carbon dioxide from the atmosphere, to help to balance the carbon dioxide released by burning fossil fuels.
For different species of tree, information is available for:
•        the relationship between diameter of trunk and freshly cut biomass
•        the percentage of water in fresh-cut wood
•        the mean dried density of wood.
Using only the information provided in part (c), 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.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(4)
(Total 10 marks)

Q6. Introduction. Resource A – D relate to a single investigation.
Scientists investigated the effect of supplying extra carbon dioxide on the yield of tomatoes growing in a glasshouse. They compared the mean yield of tomatoes from 1995 to 1997 when no extra carbon dioxide was supplied with the mean yield of tomatoes from 1998 to 2000 when extra carbon dioxide was supplied.
Resource A Tomato plants were grown in two glasshouses, each with an area of 2000 m^2. Figure 1 shows the mean number of hours of sunshine per month during fruit production.
Figure 1
 
| 1995 - 1997 (no extra carbon dioxide) | 1998 - 2000 (extra carbon dioxide)

Mean number of hours of 
sunshine per month

148.91

147.00

•        The scientists used heating to maintain the tempera ture inside the glasshouses above 18 °C. They opened the windows to keep the tempera ture below 30 °C.
•        From 1998 to 2000 they maintained the carbon dioxide concentration between 0.06 % and 0.08 % when the windows were closed and between 0.04 % and 0.05 % when the windows were open.
•        The carbon dioxide concentration in the air outside the glasshouse was 0.04 %.
Resource B
Figure 2 shows the mean difference between the yield of tomatoes with extra carbon dioxide and the yield with no extra carbon dioxide for each week during the harvesting period. If the yield is greater when extra carbon dioxide is supplied, the difference in yield is shown as an increase. If the yield is lower when extra carbon dioxide is supplied, the difference is shown as a decrease. Figure 2
 
Resource C
Figure 3 shows the relationship between the time when the tomatoes were harvested and the yield.
Figure 3

Number of weeks from 
beginning of year

Mean yield per week with 
extra carbon dioxide / kg m^–2

Mean yield per week without 
extra carbon dioxide / kg m^–2

13 – 19 | 1.25 | 0.83
20 – 25 | 1.62 | 1.47
26 – 48 | 1.23 | 1.06
The commercial price for tomatoes varies with the time of year. The highest price is paid for tomatoes between weeks 13 and 19. The lowest price is paid between weeks 26 and 48.
Resource D
Whiteflies are an important insect pest of tomatoes. The adults can fly from plant to plant. Their young do not have wings. The adults and young feed on the plant sap and introduce viruses into the tomato plants. Feeding and the introduction of viruses both reduce the yield of tomatoes. The scientists controlled the number of whitefly in the glasshouses by releasing parasitic wasps. The wasps lay their eggs in the young of the whitefly. The wasp eggs hatch and feed on the young whitefly, killing them.
(a)     (i)      An increase in carbon dioxide concentration affected the yield of tomatoes in week 35. Use Figure 2 to describe how.
______________________________________________________________
____________________________________________________________(1)
(ii)     There was a decrease in yield when extra carbon dioxide was supplied during some weeks of the year. Use information from Resource A to suggest why.
______________________________________________________________
____________________________________________________________(1)
(b)     Using Figure 3, calculate the percentage increase in yield when extra carbon dioxide was added for weeks 13 to 19. Show your working.

 
 
Percentage increase ____________________
(2)
(c)     Additional information is required for tomato growers to decide whether it is economically profitable to add extra carbon dioxide to produce very early tomatoes.
Give two pieces of information that the growers would require.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
(2)
(d)     Adding extra carbon dioxide during the summer (weeks 24 – 36) is unlikely to be profitable. Use data from the resource sheet explain why.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(e)     The control experiment in this investigation was when data were collected with no extra carbon dioxide added. Some scientists said this control experiment was not satisfactory. Explain how you could improve the control experiment.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(Total 10 marks)
Q7. 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.
(a)     Suggest one way in which an increase in the uptake of phosphate could increase plant growth.
___________________________________________________________________
___________________________________________________________________
(1)
(b)     Suggest one way in which AMF may benefit from their association with plants.
___________________________________________________________________
___________________________________________________________________
(1)
(c)     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 the graph.
 
Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(d)     Using the data from the graph in part (c), evaluate the effect on plant productivity of adding AMF species and adding phosphate to the soil.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________ (4)
(e)     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.
Answer = ____________________ g day^−1
(2)
(Total 10 marks)

Mark schemes
Q1.
(a)     Heat at 100°C / heat to temp to evaporate water;
Value which would not burn material
Weigh and heat until no further change in mass;
2
(b)     Amount of water present will vary;
This will affect fresh mass / will not affect dry mass;
2
[4]
Q2.
(a)     (i)      P = C – R – U– F  /   C – (R + U + F) / eq;
1
(ii)     3.74;
1
(b)     Correct answer: 2.18
(Accept 2.19 or 2.2)
/ correct for candidate’s (a)(ii) ;;                       = 2 marks
Correct use of data but wrong answer:
                                             = 1 mark
2
(c)     Less energy lost as heat / in maintaining body
temperature / in movement
1
[5]
Q3.
(a)     1.      To kill any fungus / bacteria on surface of seeds or in soil;
2.      So only the added fungus has any effect.
2
(b)     So that only nitrate or ammonia / type of fertiliser affects growth.
1
(c)     1.      So that effects of nitrate or ammonium alone could be seen;
2.      So that effects of fungus can be seen.
2
(d)     1.      Weigh samples at intervals during drying;
2.      To see if weighings became constant (by 3 days).
2
(e)     With live fungus – showing effects of the fungus:
1.      Fungus increases growth of roots and shoots in both;
2.      Produces greater growth with nitrate.
With heat-treated fungus – showing effects of fertiliser:
3.      Similar dry masses for roots and shoots;
4.      (Probably) no significant difference because SDs overlap.
4
(f)     1.      Dry mass measures / determines increase in biological / organic material;
2.      Water content varies.
2
(g)     1.      Fungus with nitrate-containing fertiliser gave largest shoot: root ratio;
2.      And largest dry mass of shoot;
3.      6.09:1 compared with ammonium-containing fertiliser 4.18:1
2 max
[15]
Q4.
(a)     (i)      1.      Same breed so similar alleles;
1.  Allow different alleles have different effects
2.      Controls / removes variable / so genes not a factor / only temperature affects results / rate of growth affected by genes;
2. Accept idea worded in such terms as inherited.
2
(ii)     1.      Different growth rates / gained different biomass / grew different amount;
Allow “more food for growth”
Ignore references to efficiency of conversion.
2.      Not due to temperature / the independent variable;
2
(b)     (i)      Rise then fall with peak at 20 C;
Do not accept 0.85 as alternative to 20.
1
(ii)     1.      Temperature may be between 10 and 30 / 10 and 20 / 20 and 30;
No mark for yes or no.
2.      Intervals are 10°C / large / not small / should be smaller / should be intermediates;
2
(c)     (i)      1.      Growth rate decreasing / conversion staying same / decreasing;
2.      (Scientists would be) looking for high growth rate / conversion / data shows unlikely to improve growth / yield;
3.      Wastes time / resources / would not relate to farming conditions;
3. Ignore cruelty to pigs
2 max
(ii)     1.      Will lose more heat / not as much energy used to maintain body temperature;
1. Must be a comparative statement
Accept energy as equivalent to heat in the context of this question
2.      Heat resulting from respiration / more respiration;
2. Do not credit answers relating to energy made in respiration 
3.      More food used in respiration;
2 max
(d)     In support
Read standard deviation as standard error
1.      Food B produces greater mass than control / greater than 100%;
1. Must refer to control
But
2.      Error bars for B mean B could be no better / not different from control;
3.      Overlap of error bars for B and A;
4.      A no better than / not different from B;
4. Neutral: “Results not significant”. Mark must compare A to B
Experimental limitations
5.      Experiment only ran for 10 days;
6.      Experimental conditions / breed of pig may not be the same as on the farm;
7.      No information about cost;
4 max
[15]
Q5.
(a)     1.      35.22 or 35.23% = 2 marks;
Award 1 mark if only fresh and dry masses correct, 1335.59 and 865.13 g;
2
(b)     (After 24 hours)
1.      Record mass and reheat;
Accept return to oven = reheat
2.      Until constant mass recorded;
2
(c)     1.      Positive correlation (between diameter and biomass);
2.      Not linear / geometric / exponential / gradient gets steeper;
2
(d)     1.      Calculate a mean diameter;
2.      (Use this to) estimate / determine the mean fresh biomass of trees;
3.      Use the percentage water content to find the dried biomass;
4.      Use the dried density to calculate the mass of tree;
5.      Count / estimate the number of trees in plantation and multiply by (mean) carbon content (to find total carbon);
4 max
[10]
Q6.
(a)     (i)      Yield increases by 0.6 kg m^–2 (when extra carbon dioxide present);
1
(ii)     Temperature / light intensity so could be lower in these weeks (as temperature / light insensity not fully controlled / monitored) (over period 1998 – 2000);
1
(b)     Two marks for correct answer of 50.6%;;
One mark for incorrect answer in which candidate has shown clearly that calculation based on an increase / 0.42 and original mass / 0.83
2
(c)     Cost of supplying carbon dioxide;
Price of (very early) tomatoes;
2
(d)     Lowest price paid for tomatoes;
Some carbon dioxide lost as windows open in summer;
Little / no mean increase in yield in summer;
2 max
(e)     Grow with extra carbon dioxide in one glasshouse and without carbon dioxidein other glasshouse at same time;
So all environmental conditions / light and temperature same for experiment and control;
2
[10]
Q7.
(a)     Used to produce named phosphate compound in cells;
e.g. ATP / ADP / phospholipids / DNA / RNA / RuBP / TP /GP etc.
1
(b)     Example of a carbon-containing biological compound e.g. carbohydrate / amino acid / vitamin;
Accept: sugars / organic (compounds).
Ignore: products of photosynthesis.
Ignore: starch.
1
(c)     1.      Represents dry mass / mass of carbon;
2.      Represents gross production minus respiratory losses;
2.      Accept: NPP = GPP −R.
2.      Accept: Chemical energy minus respiratory losses.
1 and 2. Chemical energy store minus respiratory losses = 2 marks.
2
(d)     1.      For the control an increase in phosphate increases (plant) growth;
2.      For Entrophospora an increase in phosphate reduces (plant) growth;
3.      Scutellospora reduces (plant) growth (compared to control);
4.      Entrophospora and Glomus increases (plant) growth (compared to control);
5.      No SD / statistical test to determine significance;
6.      Only 20 weeks of growth;
7.      Underground / root growth not known;
5.      Accept: no error bars.
7.      Accept: only shows shoot growth.
4 max
(e)     1.      Answer in range 0.07 to 0.09 = 2 marks;
2.      Answer in range 9.97 to 12.2
OR
Shows division by 140 or 20 × 7 = 1 mark;
2
[10]