7.2 Organisation of an Ecosystem

Higher Tier Only

Ecologists carried out a study into the effect of soil moisture level on the distribution of certain species of wildflower in a large meadow.

Figure 3 shows the meadow from the study, bounded by a river to the north and east and by farmland to the west and south.

The meadow slopes down to the river, with the south end of the meadow elevated approximately 10 metres above the north end. 

Figure 3

A quadrat study was carried out to determine the abundance and distribution of wildflowers in the meadow, alongside a measurement of soil moisture levels using a soil moisture probe of the sort shown in Figure 4.

Samples were analysed in four areas of the meadow, W, X, Y and Z as shown in Figure 3.

Figure 4

The data found by the ecologists is shown in Table 1.

Table 1

Area	Soil moisture level in % by mass	No of wildflower species identified in quadrats	Predominant species found
W	28	23	Succisa pratensis, Lychnis flos-cuculi, Centaurea nigra
X	13	15	Chrysanthemum segetum, Centaurea nigra
Y	31	21	Lychnis flos-cuculi, Silaum silaus
Z	41	26	Succisa pratensis, Lythrum salicaria

Suggest reasons for the differing soil moisture levels at W, X, Y and Z.

Higher Tier Only

Using the data in Table 1, assign a rank order 1 - 6 to each of the wildflower species named below in ascending order of being adapted to living in dry conditions. 

Species	Rank 1 - 6 6 = best adapted to dry conditions
Centaurea nigra
Chrysanthemum segetum
Lychnis flos-cuculi
Lythrum salicaria
Silaum silaus
Succisa pratensis

Higher Tier Only

Suggest why the answer you gave in part 3(b) may not be the the most accurate rank order of adaptation to dry conditions. 

Identify and explain two structural adaptations of wildflowers that would benefit the plant living in a dry soil environment.

The carbon cycle is built around the constant exchange of carbon between carbon dioxide (CO₂) in the air and carbon in other forms, including in biomass.

There is one other carbon-containing gas that plays an important role as it is exchanged between living organisms and the atmosphere.

Name this other gas.

Table 2 shows the approximate masses of carbon contained within carbon-containing compounds in various parts of the Earth's crust and atmosphere.

Table 2

Reservoir	Mass of carbon in gigatonnes
Sedimentary rocks (including fossil fuels)	50 000 000
Deep oceans	38 000
Soil	1 580
Surface oceans	970
Atmosphere	750
Land organisms	610
Ocean organisms	3

1 gigatonne is 1 billion (1 000 000 000) metric tonnes.

Calculate the total mass of carbon in carbon-containing compounds in all reservoirs except for sedimentary rocks. Give your answer in kg in standard form. 

Name one process by which carbon in sedimentary rock (the largest sink shown in Table 2) is returned directly to the atmosphere. 

Carbon transfers from the 'land organisms' sink to the 'soil' sink. Give two ways in which this transfer takes place. 

Recently, rules governing the disposal of waste in landfill sites have been introduced to separate food waste from general waste and from waste to be recycled.

Food waste is a valuable resource in the production of high-quality compost that can be used in gardens and on crops. 

State and explain one other advantage and one disadvantage of separating food waste from other waste streams during waste disposal. 

In-Vessel Composting (IVC) is an industrial process to manufacture compost from household food and garden waste. 

Figure 5 shows the typical process flow through an IVC factory manufacturing compost sold in garden centres and DIY stores. 

Figure 5

Suggest the source of the heat referred to in stage 4 of Figure 5.

Stages 2 and 3 in Figure 5 are for preparing the biomaterial for the composting stage.

Mixing involves making a blend of garden waste (grass cuttings, hedge trimmings etc) with food waste (uneaten food, peelings etc).

Shredding involves chopping all the pieces down to an average size of 10-15 mm and allowing all the pieces to drop from a height of about 4 metres onto a pile for composting.

Suggest the main reason for both stages 2 and 3 of the process. 

The type of compost made in a process such as the one described in Figure 5 is claimed to be 'peat free'.

Explain why it is important for commercially-available composts to be peat-free.

Microorganisms play a vital role in cycling nutrients through ecosystems.

Explain how.

Carbon in dead biomass is converted into carbon dioxide by the action of certain bacteria and fungi.

Name these microorganisms.

A gardener is attempting to create compost to spread on her flower beds. She uses dead plant biomass to create compost. List the three conditions that she should optimise in order to create the best quality compost that she can. 

A group of students investigated the abundance of daisies in a field behind their school.

The dimensions of the field were 200 metres × 100 metres.

The students:

• Chose areas where the daisies were growing
• Placed 20 quadrats in these areas where daisies were growing
• Counted the number of daisies in each of the 20 quadrats

Each quadrat was 0.25 × 0.25 metres in size.

Table 1 shows their results.

Table 1

Quadrat Number	Number of daisy plants	Quadrat number	Number of daisy plants
1	5	11	3
2	3	12	14
3	4	13	3
4	1	14	1
5	3	15	10
6	2	16	2
7	4	17	2
8	1	18	3
9	5	19	5
10	6	20	1

Using the students' results from Table 1, calculate the estimated number of daisy plants in the whole field.

It is unlikely that it is possible to calculate a valid estimate of the number of daisy plants in the field using the students' method. 

Suggest two improvements that could be made to the students' method.

For each suggested improvement, give a reason why your method would produce more valid results than the students' method. 

Explain how systematic sampling differs from random sampling in a quadrat study.

Figure 2 shows an outline of the carbon cycle.

Figure 2

Describe the role of living organisms in the cycling of carbon.

Suggest a consequence to the living world of substances such as carbon not being recycled. 

Microorganisms such as bacteria can produce methane gas.

Name the process that produces methane gas in microorganisms such as bacteria. 

Methane gas can be produced industrially using a biogas generator. 

Methane gas can be used as a fuel.

Table 2 below shows how the composition of biogas changed over the first three weeks of production. 

Table 2

Explain why it would not be advisable to collect biogas from the generator after longer than three weeks. 

Use data from Table 2 in your answer. 

Air from the atmosphere is present in the biogas generator when it is set up.

Suggest an explanation as to why the concentration of carbon dioxide changed over the course of three weeks. 

Higher Tier Only

Sulfur dioxide is one type of air pollutant.

About 99% of atmospheric sulfur dioxide in air comes from human activity. 

One source of sulfur dioxide pollution comes from burning fossil fuels contaminated with sulfur. 

A group of students decided to measure the distribution of two species of lichen growing on trees at increasing distances from a main road. 

One of the species of lichen they decided to study is sensitive to high levels of sulfur dioxide; the other is not. 

Describe how a group of scientists would investigate the distribution of the two lichens.

Higher Tier Only

Predict the results that might be expected from the experiment you described in part (a). 

Explain the reasoning behind your prediction.