Biodiversity (AQA A Level Biology)

Compare species diversity with species richness.

Fertilizers are commonly used today by most farmers as they help to increase crop yield and profit. If it rains shortly after fertilizers are applied to a field then some of the fertilizer can enter nearby water sources as runoff. A conservationist investigated the effect that runoff fertilizer from a nearby farm had on the distribution of organisms living in a stream. At the point where fertilizer had entered the stream, she found a high density of specific organisms but a low index of diversity. 

Suggest how fertilizer contaminating the stream could explain their findings.

Predict how the index of diversity will change as the conservationist moves further away from the farm to take her sample. Justify your answer.

The conservationist wanted to use their findings to take action against the local farm. However, the farmer’s lawyer argued that the scientific methods of the conservationist were not rigorous enough to conclude that runoff fertilizer was affecting species richness in the nearby stream.  He demanded that more samples at random locations needed to be taken. 

Explain the importance of taking a large number of samples at random sites. 

A biology teacher investigated the different species of insects found in a grassy meadow and in a nearby farmed field. The insects were collected using traps at randomly chosen sites both in the grassy meadow and in the farmed field. Table 1 shows the data collected.

Table 1

Use the formula below to calculate the index of diversity for the insects caught in the farmed field.

d = index of diversity N = total number of organisms of all species

n = total number of organisms of each species

Show your calculations.

 Use the formula below to calculate the index of diversity for the insects caught in the farmed field.

Without doing any further calculations, predict whether the index of diversity for the grassy meadow will be higher or lower than the index of diversity for the farmed field. Explain your answer.

A student stated that the experiment suggested farming caused a reduction in species diversity. Evaluate this statement.

Farmers were offered money by an environmental agency to grow more than one plant species in their fields. Very few farmers agreed to this. Suggest why.

Describe what is meant by a community.

Researchers calculated the percentage of reptile species that had gone extinct on five islands in the last 150 years. The islands are made up of sandy beach and forest habitats. The forests have been declining in size over recent years. The researchers calculated the percentage of original forest floor area that remained on each island after 150 years. Figure 1 below shows their results.

Figure 1

Describe and explain the relationship between the percentage of original forest floor remaining and the percentage of reptile species that have gone extinct.

What two measurements would the researchers need to obtain in order to calculate the index of diversity of reptiles on each island?

It was later discovered that some of the reptile species living on the islands with less forest floor remaining had changed scale colour, from green/brown to brown/yellow. Explain how this is an adaptation to their environment.

There are ecological, ethical and economic arguments to be made for maintaining biodiversity. Suggest one of each.

Farmers can plant their crops at different times throughout the year. Traditionally crops were planted in April and harvested in September. However, in modern times farmers have switched to planting their crops in September and harvesting in June/July.

Scientists decided to investigate the effect that the change in planting time had on the number of farmland birds over 10 years. The scientists counted the number of farmland birds found within a 1km radius of farm X that plants its crops in April, and within a 1km radius of farm Y that plants its crops in September.

Figure 1 below shows the data they collected.

Figure 1

Describe the results seen in Figure 1.

In recent years, farmers have merged grazing fields together by removing hedgerows.This has resulted in a decline in the diversity of farmland birds. Explain why.

Organic farms do not use any chemical insecticides. Suggest what effect organic farming would have on the number of farmland birds. Explain your answer.

Conservationists investigated the effect of different types of animal grazing on the diversity and number of beetles. Traps were laid and used to measure both the number of different beetle species and the total number of beetles in cow grazed (field type 1), donkey grazed (field type 2) and sheep grazed (field type 3) fields.

Their results are shown in Figure 1 and Figure 2 below.

State which field is the most species rich. Explain your answer.

Explain what the standard deviations in Figure 2 suggest about the difference in total number of beetles between the differently grazed fields.

Suggest three considerations that should have been taken into account when planning the investigation to ensure reliable and fair testing.

Additional information on the total number of beetle individuals and the number of each beetle species for a cow grazed field (field type 1) is provided in Table 1 below. Calculate the index of diversity for this field using the equation shown.

Table 1

d = index of diversity N = total number of organisms of all species

n = total number of organisms of each species

Corn is a crop plant that produces seeds that are harvested for food. Some students investigated whether corn could be grown successfully using freshwater mixed with seawater. This would reduce the use of freshwater, which can be in short supply in certain countries. Seawater contains dissolved sodium chloride (salt). The students grew corn in plots of equal size in the same area of land. Each plot received one of four watering treatments:

The students measured the concentration of salt in the soil in each plot and the yield of corn seed harvested from each plot. Their results are shown in Table 1 below:  

Table 1

The same variety of corn was used in the four plots. Explain the importance of this.

Consider the data in Table 1. What was the effect of watering corn with a mixture of freshwater and seawater?

The students conclude that watering corn with diluted seawater might not be sustainable if this is repeated every year. Considering the data in Table 1, do these data support this conclusion?

For the investigation carried out by the students, state a dependent variable and explain what is meant by the dependent variable.

The traditional practice of coppicing involves repeatedly felling certain species of tree at their base and allowing re-growth over a period of 15-25 years, in order to provide a regular supply of timber. Coppicing yields narrow, straight stems for use in fencing, tool making and construction. Explain one ecological advantage and state one disadvantage of this practice over the felling of mature trees for timber. 

The numbers of various woodland invertebrates were estimated in two areas of woodland. Area A was an area of coppiced woodland, whereas Area B was an area of fast-growing coniferous woodland plantation managed by the logging industry. Both areas were in the same Northern European country with a temperate climate. Table 1 shows the numbers of each organism counted in the two woodland areas. 

Table 1

Use the equation provided to calculate the index of diversity (d) in both Area A and Area B in Table 1 and comment on the difference. 

Calculate the species richness of woodland invertebrates from the data shown in Table 1 for Areas A and B. Suggest why this measure of species richness might have limited usefulness in analysing ecological relationships in these two areas. 

Explain how use of the index of biodiversity adds clarity into the analysis of biodiversity in two contrasting areas like those described in part c), over species richness. 

The farming industry has been accused of prioritising productivity over sustainability. Recent initiatives have attempted to restore biodiversity to farms. Outline one such initiative in an arable (crop farming) setting and give the reasons for its expected success. 

A group of students carried out a comparison between two areas of an agricultural field growing barley. Samples of soil were taken from two areas; (i) directly beneath the barley crop, and (ii) from beneath a 5 m wide field margin around the edge of the barley crop. The soil samples were hand sorted for 30 minutes each and all the animals from the soil were collected and counted. Figure 1 shows the findings. The error bars represent a range of ± 2 standard deviations.

Figure 1

Explain why an index of diversity would not be able to be quantified from the data in Figure 1

Using the data provided in Figure 1, assess the effectiveness of the practice of leaving field margins for promoting biodiversity. Outline other investigative work that could provide more information on the effect of field margins on biodiversity. 

Suggest an explanation for the difference in the number of woodlice observed in Figure 1.

Species differences can be measured by using the approaches set out in Table 1. 

Table 1

In the table, rank these approaches 1-5 in increasing order of effectiveness, with 1 being the most rudimentary approach and 5 being the most sophisticated. Explain your choice of the rank order. 

Some students carried out an analysis on the effect of sunlight on the growth of privet leaves on a hedge in the school grounds. Prior to the hedge being cut, they sampled 108 leaves at random from the north-facing side of the hedge and measured the leaves’ lengths. Their data is shown as grouped data in Table 2.

Table 2

Use the midpoints of each group of leaf lengths to calculate the mean length of the leaves in this sample. Give your answer to 2 significant figures.

The Human Genome Project was the first piece of research to establish the entire DNA sequence of a human. Explain how DNA sequencing has led to a better understanding of biodiversity. 

One gene that is often selected for DNA sequencing analysis for comparison of biodiversity is the gene that codes for pyruvate kinase (PKM), an important enzyme in the biochemical pathway glycolysis, which is the first stage of cellular respiration. Suggest why this gene is selected for this purpose. 

Read the following passage:

Deduce a food chain for Yellowstone based on the information contained in the passage.

Sketch a graph on the axes shown in Figure 1 of the biodiversity index of Yellowstone over time, based on the information in the passage. 

Figure 1

Use your knowledge of biodiversity to explain the term ‘unbalanced’ as used in line 10 of the passage provided in part a). Make reference to the changes to biodiversity that you have sketched in part b).

Some years after the successful introduction of wolves to Yellowstone, biologists examined the genetic diversity of the elk population. They found that the elk population had a more advantageous range of alleles compared to those from the 1980s, prior to the reintroduction of wolves. 

Suggest and explain why this was the case. 

Explain why biological sampling of an ecosystem must be free of bias, and how this can be achieved. 

Figure 1 shows a thistle plant growing in a field periodically grazed by sheep. 

 Figure 1

A piece of UK upland that has been grazed by sheep has, in the last ten years, been left ungrazed. Design an investigation to estimate the population density of thistle plants that have colonised the area since grazing has been discontinued. Include how your investigation will give a result in thistle plants per hectare (1 hectare (Ha) = 10 000 m²).

With around 72% of land in the UK being used for agriculture, the role of farming in promoting biodiversity is crucial. In an age when farming productivity has increased substantially, organic farming has emerged as a means of halting the loss of biodiversity. Two techniques, closed-loop farming and rotational silage have been used with some success. Silage is grass or other green plant material, allowed to decay partially and stored in an airtight tank or wrapped in airtight polythene, and used as animal feed during winter. 

Using this information and your knowledge of farming practices, suggest how these two systems might operate. 

Mob grazing is another farming technique designed to increase biodiversity. In this technique, a whole herd of grazing animals is moved on every few days to another field, allowing the previous grazing area to remain undisturbed for a period of time. Suggest and explain two benefits that this technique could bring to biodiversity.