Abiotic & biotic factors

A group of students investigate the biodiversity in two fields, A and B. Field A is grazed by cattle and field B has no cattle.

Explain what is meant by the term biodiversity.

The students investigate the plant species in each field. They counted the number of each species in five 0.5 m × 0.5 m quadrats. They repeated this for each field. Table 1 shows their results.

Describe how the quadrats should be placed to obtain unbiased species numbers for each field.

For the most frequently occurring plant species in field B, calculate the number of plants in one square metre.

number of plants =_........

Name the species with the greatest variation in number of plants recorded in quadrats for field B.

Table 1 is repeated here.

The students conclude that grazing affects the species in field A. Using information in Table 1 and your own knowledge, discuss the students’ conclusion.

Many insect species damage crop plants. One such pest is the larvae of the Fall Armyworm moth. The photograph shows a larva of this moth feeding on a leaf of a maize plant.

(Source: © Alchemist from India / Shutterstock)

Explain how the larvae of the moth cause a reduction in the yield of the maize crop.

Biological control involves using a predator species to control the numbers of a pest species. Explain the advantages of using biological control rather than chemical pesticides to control a pest species.

A parasitic wasp is used as a biological control of the larvae of the Fall Armyworm moth. The wasp feeds off the moth larvae. The graph shows the change in the numbers of the larvae of the Fall Armyworm moth. It also shows the change in the numbers of the parasitic wasp.

Explain the relationship between the number of moths and the number of wasps during the 24-month period.

The range in moth numbers is the difference between the highest number of moths and the lowest number of moths. Use the graph to determine the maximum range in the number of moths in the period from 6 months to 24 months.

Suggest why some maize farmers choose not to use biological control to control the moth.

Scientists study the populations of plants in two fields, X and Y, in southern England.

They investigate the numbers of three different wildflower species, A, B and C, so that they can compare the biodiversity in each field.

(Source: © Dew_gdragon/
(Source: © Patrick Guenette/
(Source: © M_Morozova/ Shutterstock)
Alamy Stock Vector)
Shutterstock)

Species A
Species B
Species C

The table shows the numbers of plants of each species per m² counted in each field.

Calculate the mean number of plants of species B in Field Y.

mean number =_........ per m

Describe how the scientists could determine the number of each plant species per m² in each field.

Discuss what the results show about the distribution of species in each field and the difference in biodiversity between the two fields.

Name an abiotic factor that could affect the distribution of the plant species.

The diagram shows part of a food web from an ecosystem in a region of North America.

Which of these organisms in the food web is a primary consumer?

State what is meant by the term ecosystem.

Wolves were hunted in this region of North America until they became extinct in 1926.

The extinction of wolves damaged the ecosystem in these ways.

• the population of mice, hawks and beavers decreased

• the population of producer species decreased

Beavers are important in this ecosystem because they cut down old trees and create shelters that other organisms nest in.

Discuss why the extinction of wolves damaged the ecosystem.

In 1995, 14 wolves were reintroduced to this region.

The diagram shows the change in wolf population from 1996 to 2016.

Calculate the percentage change in the wolf population between 1996 and 2004.

Suggest why the wolf population changed between 2004 and 2012.

The reintroduction of wolves caused changes in the populations of some plant species.

Describe how the population size of a plant species in the region could be determined.

The plants in a woodland are eaten by mice and caterpillars. The mice also eat the caterpillars. The mice are eaten by birds called owls.

Draw a food web showing these feeding relationships.

Give the term that describes the trophic level of a caterpillar.

The woodland covered a total area of 5 km². A scientist investigates the number of mice and owls in the woodland. He counts the number of mice and owls on the same summer day each year for five years. The table shows the scientist’s results.

Year	Number of mice per km2	Number of owls in entire woodland
1	2103	10
2	2103	12
3	3103	12
4	5103	16
5	1103	14

Calculate the number of mice in the total area of woodland in year 3.

number of mice =_........

Suggest why there were more mice in year 4 than in the other years.

Suggest why the number of owls was fairly constant each year.

Suggest a method you would use to estimate the number of mice in the woodland.

The diagram shows a food chain in the Antarctic ocean.

Which term describes the trophic level of the krill?

Draw a labelled pyramid of biomass to represent this food chain.

The microscopic plants float in seawater, but also grow on the lower surface of ice.

The krill feed on the microscopic plants.

They remove microscopic plants from the lower surface of the ice at a rate of 1.6 cm² per second.

Calculate the time taken for the krill to remove microscopic plants from one square metre of ice.

Give your answer in minutes.

time taken =_........ minutes

A student investigates the rate that krill feeding removes microscopic plants floating in seawater.

Suggest how the student could do this investigation in a laboratory.

Krill obtain most of their food from microscopic plants growing on the lower surface of ice.

Explain how global warming could affect the whale population in the Antarctic ocean.

Deforestation is the cutting down of trees.

After deforestation many dead leaves are left on the forest floor.

A student investigates the decomposition of these leaves.

This is her method.

● collect four samples of dead leaves each with a mass of 6.0 kg

● label the samples P, Q, R and S

● cut sample P into small pieces and keep at 10 °C

● cut sample Q into small pieces and keep at 20 °C

● do not cut sample R and keep at 10 °C

● do not cut sample S and keep at 20 °C

● measure the mass of each sample after three months

The graph shows her results.

Explain the results obtained by the student.

Calculate the difference between the rate of decomposition in sample P and the rate of decomposition in sample Q.

Give your answer in kg per month.

difference =_........ kg per month

The student needs to control biotic variables in her investigation.

Give two biotic variables she should control.

A scientist investigates the effect of growth hormone (GH) on the body mass of rats.

This is his method.

● give one rat a GH solution every day for 500 days

● give another rat a control solution every day for 500 days

● measure the mass of each rat each week for 500 days

The graph shows his results.

Suggest how the control solution differs from the GH solution.

Calculate the average rate of growth of the rat given GH solution from 100 days to 500 days.

Give your answer in g per day.

rate of growth =_........ g per day

The scientist controlled all the variables in his investigation.

Suggest two abiotic variables he controls.

The scientist repeats his investigation using more rats.

Explain why using more rats improves his investigation.

GH increases transcription in cells.

Explain why this affects the growth of rats.

Suggest what is meant by the term sustainable (line 3).

Explain why having a developed root system makes regrowth quicker (lines 4 to 5).

Coppiced wood can be used as a biofuel (lines 8 to 9).

Give similarities and differences in the use of biofuel compared with the use of fossil fuels.

New growth in woodland is often destroyed by species such as deer (lines 5 to 6).

Suggest one way to protect woodland from this damage.

Coppicing increases biodiversity in woodland ecosystems (line 17).

Describe a method to investigate the effect of coppicing on the biodiversity of plants in a woodland.

Coppicing increases the number of insects in woodland.

A farmer owns a field next to a coppiced woodland.

Give one reason why more insects in the woodland might be an advantage for the farmer.

Give one reason why more insects in the woodland might be a disadvantage for the farmer.

Explain why a range of different light levels in a woodland leads to an increase in plant biodiversity (lines 23 to 24).

Scientists investigate the effect of pollution on the growth of plant shoots. This is their method.

• expose a sample of 500 seeds to pollution

• leave another sample of 500 seeds free from pollution

• allow the seeds to germinate and produce shoots

• after one day, squash 100 shoots from each sample

• using a microscope, count the number of cells in each shoot

The scientists squash 100 shoots from each sample every day for five days. The table shows their results.

Plot a line graph of this data on the grid. Use a ruler to join the points with straight lines.

What is the dependent variable in this investigation?

The scientists conclude that pollution reduces the growth of shoots by affecting cell division.

Name the type of cell division affected by pollution in this investigation.

To make sure their conclusion is valid, the scientists control abiotic variables while the seeds are germinating. Discuss two abiotic variables that the scientists control.

State one biotic factor that the scientists should control.