Organisation of an Ecosystem (AQA GCSE Biology: Combined Science)

The intertidal zone is the area along a coast which is underwater at high tide and above water (exposed) when the tide is low.

A group of students on a field trip in Asia wanted to investigate the distribution of two species of seaweed (C. racemosa and C. microphysa) along a rocky shore to establish whether they could live at certain positions. 

Seaweeds are multicellular algae that produce glucose. 

(a)

Describe the role that seaweeds play in an ecosystem as producers.

[3 marks]

(b)

Describe and explain a method that the students could use to investigate the distribution of the two species of seaweed along the rocky shore using a quadrat and a tape measure. 

You should explain how the students would collect valid data.

[6 marks]

(c)

How could the students alter their method if they wanted to investigate the abundance of each type of seaweed along the coastline by measuring percentage cover?

[4 marks]

(d)

Another group of students carried out the same investigation the year before.

Their results are shown in Figure 1 below.

Figure 1

Suggest and explain a conclusion that the students could draw from their results using information from Figure 1.

[3 marks]

(a)

Microorganisms play a vital role in cycling nutrients through ecosystems.

Explain how.

[3 marks]

(b)

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

Name these microorganisms.

[1 mark]

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

(a)

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

[4 marks]

(b)

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. 

[2 marks]

(c)

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

[2 marks]

Figure 2 shows an outline of the carbon cycle.

Figure 2

(a)

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

[6 marks]

(b)

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

[2 marks]

It has been found, through DNA sequencing, that many extremophile organisms share a higher-than-normal proportion of guanine and cytosine (G and C) in their DNA.

Guanine and cytosine are joined by 3 hydrogen bonds across a molecule DNA, whereas the other two bases (adenine and thymine) are joined by just 2 hydrogen bonds. 

Suggest and explain the property that having a high G-C content gives those organisms. 

[2 marks]

List three extreme conditions that extremophile microorganisms have been found in and for each one, describe the adaptations that allow the microorganisms to survive in those extreme conditions.

[3 marks]

One group of extremophile microorganisms are the barophiles.

Which extreme condition of A - D is the one to which barophiles are well-adapted? 

[1 mark]

Figure 2

[2 marks]

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

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

[2 marks]

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. 

[3 marks]

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. 

[2 marks]

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

[2 marks]

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.

[1 mark]

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

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. 

[3 marks]

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

[1 mark]