Abiotic & biotic factors

A student investigates the effect of soil pH on the growth of dandelion plants.

They measure the height of different dandelion plants grown in soils with different pH.

The table shows their results.

Calculate the mean dandelion height for the soil at pH 10.

Write your answer in the table.

The student identifies an outlier in the results.

Tick (✓) one correct set of results to identify the outlier.

Soil pH
Dandelion height Outlier

Plot a graph of the student’s mean results. Choose appropriate scales.

Draw a curve of best fit.

What conclusions can be made from the student’s results?

Include data in your answer.

The moisture content in soil affects the growth of plants.

A student investigates the moisture content of different soils.

This is the method they use:

• Measure the mass of each soil sample.

• Place the soil samples in a warm oven to dry for 4 hours.

• Measure the mass of each soil sample again.

The table shows their results.

Calculate the change in mass for each soil sample.

Write your answers in the table. Give all answers to the same number of decimal places.

The student uses the changes in mass to conclude that soil sample B had the highest percentage moisture content.

Suggest why the student cannot make a fair comparison between the samples.

Describe two ways the student could improve their investigation to get a valid conclusion.

Explain how low moisture content in soil affects transpiration in plants.

Moisture content is one abiotic factor that affects plants.

State two other abiotic factors that affect plant growth.

The moisture content in soil affects the growth of plants.

Two students investigate the moisture content of different soils.

This is the method used by student X:

• Measure the mass of each soil sample.

• Place the soil samples in a warm oven to dry for 4 hours.

• Measure the mass of each soil sample again.

The table shows their results.

Calculate the percentage change in mass of soil sample C.

Give your answer to 3 significant figures. Write your answer in the table.

Soil sample A lost less mass than soil sample B.

Why is the percentage change in mass greater for soil sample A ?

The two students compare their results.

• Student Y used a similar method but left the soil in the oven for a different length of time.

• Student Y found the moisture content of soil sample C to be much higher than student X.

Explain why student Y found the moisture content of soil sample C to be higher than student X

What could both students do to check that the moisture content they measured is accurate?

Moisture content is one factor that affects plants.

The amount of microorganisms in the soil can also affect plant growth.

Explain why soil microorganisms are important for plant growth.

Why are microorganisms described as a biotic factor and soil moisture as an abiotic factor?

The graph shows the changing population of one species in a habitat.

Predict the years when this species had the highest availability of their food source.

A Between 1980 and 1990

B Between 1990 and 2000

C Between 2000 and 2010

D Between 2010 and 2020

The graph shows the changing population of one species in a habitat.

Predict the years when this species had the highest availability of their food source.

A Between 1980 and 1990

B Between 1990 and 2000

C Between 2000 and 2010

D Between 2010 and 2020

Lions hunt and eat antelopes.

Which row correctly describes lions in this relationship?

13* The pH of a soil will affect the crops that grow in the soil. When the soil pH is suitable, more crops will grow. This results in a higher yield (mass of crops).

The table shows data about the yield of four different crops, A, B, C and D, when grown in soils of different pH.

A farmer measures the pH of the soil in their field. The soil is pH 4.5.

Which crop should the farmer grow in the field?

Explain your choice and give reasons why pH 4.5 prevents growth in some crops. Include ideas about enzymes and their function in plants.

Which abiotic factor affects the growth of plants?

A Food

B Nitrogen gas

C Predators

D Soil pH

Two students investigate the population of daisies in a lawn. The diagram shows the lawn in front of a shed.

Complete these sentences about the method the students use to find the population of daisies.

Use the words in the list.

pooter quadrat random square

The lawn is sampled using a square frame called a........

Drop the square frame over one shoulder to provide a........ sample.

Count and record the number of daisy plants present in the square grid.

Repeat this process in 10 different areas of the lawn.

Table 16.1 shows their results.

Table 16.1

Estimate the population of daisies in the lawn.

• The students used a 0.5 m × 0.5 m frame to sample the lawn.

• The lawn size is 5 m × 3 m.

The students develop their investigation to show how the shed affects where daisies grow in the lawn.

Table 16.2 shows the results.

Table 16.2

Use the graph to determine the slope of the line.

Daisy plants require lots of light.

Explain the effect of the shed on the growth of daisies in the lawn.

Two students investigate the population of daisies in a lawn. The diagram shows the lawn in front of a shed.

Complete these sentences about the method the students use to find the population of daisies.

Use the words in the list.

pooter quadrat random square

The lawn is sampled using a square frame called a........

Drop the square frame over one shoulder to provide a........ sample.

Count and record the number of daisy plants present in the square grid.

Repeat this process in 10 different areas of the lawn.

Table 11.1 shows their results.

Table 11.1

Estimate the population of daisies in the lawn.

• The students used a 0.5 m × 0.5 m frame to sample the lawn.

• The lawn size is 5 m × 3 m.

The students develop their investigation to show how the shed affects where daisies grow in the lawn.

Table 11.2 shows the results.

Table 11.2

Plot a line graph of the results from Table 11.2. Draw a straight line of best fit.

Use the graph to determine the slope of the line.

Daisy plants require lots of light.

Explain the effect of the shed on the growth of daisies in the lawn.

Complete these sentences about different factors that affect the ecosystem.

Use the words or phrases in the list.

abiotic biotic carbon dioxide food oxygen

pH in soil predators temperature

Living organisms affecting the ecosystem are known as........ factors.

Physical factors that affect living organisms are described as........ factors.

Physical factors that can directly affect the rate of photosynthesis include

........ and........ concentration.

A student investigates the relationship between bean plants and the bacteria that live in the roots of the bean.

They think the bacteria live inside root nodules.

Fig. 12.1 shows root nodules on a bean plant.

Fig. 12.1

The student takes a thin section of the nodule and looks at it under a light microscope.

Fig. 12.2 shows bacteria inside the root nodule.

Fig. 12.2

Describe how to take a thin section of the nodule and prepare it to view under a light microscope.

The bacteria were not visible clearly using a light microscope.

The student found an image taken using a different type of microscope.

Fig. 12.3 shows this image.

Fig. 12.3

The maximum resolution of a light microscope is 200 nm.

What type of microscope is used to take this image?

The bacteria live inside the bean plant cells in root nodules. The bacteria are able to take nitrogen gas from the air and turn it into nitrates. The plants use nitrates to make amino acids.

Explain the relationship between the bacteria and the bean plant. Include ideas about photosynthesis in your answer.

What is the independent variable in this investigation?

Put a tick (✓) in the correct box.

Write down two changes that would improve the accuracy of these acid rainwater measurements.

Acid rain forms due to the emission of sulfur dioxide and nitrogen oxides when fossil fuels are burnt. These gases react with water, oxygen and other chemicals in the atmosphere.

The science club used sulfuric acid to represent acid rain.

Suggest why this is not a true representation of acid rain.

Suggest how the investigation could be developed to better represent acid rain.

This is a graph of the results, produced using computer software.

Estimate the range of acidity that by day 14 causes the sunflower plants to be reduced in height by about 50% compared to the sunflower plants in pot A.

Put a tick (✓) in the correct box.

Describe the impact of acid rain on biomass production.

Materials are cycled in the environment.

Complete these sentences about cycled materials.

Choose words from this list. You can use each word once, more than once or not at all.

decomposition condensation nutrition

photosynthesis translocation transpiration

Plants remove carbon from the atmosphere by the process of........

Plants return water to the atmosphere by the process of........

Nitrogen is returned to the soil by the process of........

Describe two ways that the water cycle is important to humans.

Abiotic and biotic factors can affect ecosystems.

Which two are biotic factors?

Tick (✓) two boxes.

The diagram shows a weather chart over 3 days.

The 24-hour rainfall for Sunday April 3 is ~1 mm.

Explain what is meant by the term ~1 mm.

Plants are an important part of ecosystems.

Which day would plants be most likely to take up water from the soil at the fastest rate?

Tick (✓) one box.

Explain your answer.

White clover plants have two variants.

Cyanogenic variants produce a toxin when their cells are damaged. Acyanogenic variants do not produce a toxin.

The cells of clover plants can be damaged by freezing temperatures or by snails eating the leaves. The toxin kills snails but also damages the plant.

Table 11.1 shows growing regions of the two variants.

Complete the hypothesis to link each variant to the region it is most often found.

Acyanogenic variants are found in colder climates because........

Cyanogenic variants are found in warmer climates because........

To investigate a hypothesis a field study is needed.

Sampling techniques are used to estimate the population size of each variant in different areas.

Why are sampling techniques used instead of counting the total number of individual plants in each area?

Two students investigate the variant plants living at altitudes of 0–250 metres.

The students use random sampling as a starting point of their investigation. They then go on to complete a transect.

Explain how random sampling differs from a transect.

Explain why using a transect would develop and improve their investigation.

Fig. 11.1 shows the number of cyanogenic variant plants found in a total clover population of 200 at different altitudes.

What conclusion can be made about the effect of altitude on the distribution of cyanogenic clover?

Predict the altitude where you would expect to find mostly acyanogenic clover plants. Explain why most clover plants are acyanogenic at that altitude.

Use the theory of natural selection to explain how the cyanogenic variant of white clover plant could have developed.

The flowchart in Fig. 12.1 shows bacteria involved in cycling nitrogen.

Identify which of the bacteria in Fig. 12.1, if present in large amounts, would make the soil poor for plant growth.

Tick (✓) one box.

Explain why large amounts of these bacteria would make the soil poor for plant growth.

Abiotic and biotic factors can affect the bacterial communities.

Which is a biotic factor?

Tick (✓) one box.

Plants are an important part of any community.

Fig. 12.2 shows the effect of abiotic factors on the rate of photosynthesis by plants.

Explain why lines X, Y and Z level out at different rates of photosynthesis.

Which of these is a biotic factor that can affect an ecosystem?

A Acidity of soil

B Bacterial levels in a river

C Carbon dioxide levels in the atmosphere

D Oxygen levels in a river

Algae can photosynthesise and grow rapidly in lakes during the summer.

The growth of algae is affected by abiotic factors.

An experiment measured the dry mass of algae at different temperatures for 25 days. Light intensity was kept constant.

Table 13.1 shows the results for 25 °C and 35 °C.

Describe the trends shown in the graph.

Table 13.2 shows the dry mass of algae on day 25 for all the temperatures measured in the experiment.

In some lakes, algae are the main producers.

One year, water temperatures in a lake did not rise above 20 °C.

Use data from Table 13.2 to explain how this might affect the community of organisms living in the lake.

The algae produce a toxin. High levels of toxins can kill fish in the water.

Suggest why scientists are concerned about the effects of global warming on algae growth.

The picture shows a mealybug insect.

This mealybug is a pest for orange tree growers.

The scientists compared the number of mealybugs found on two trees, tree A and tree B.

For each tree they:

• Collected a sample of mealybugs from the tree

• Counted the number of mealybugs in each sample

• Marked the mealybugs

• Released the mealybugs back onto the tree they were collected from.

The next day another sample was collected from each tree.

Describe how the scientists should collect and mark the mealybugs.

Include the equipment they need to use.

You may include a diagram with your answer.

Write down three precautions that should be taken when deciding how to mark the mealybugs.

The table shows the results for tree A.

Estimate the population size of mealybugs on tree A.

Use the formula:

When using this method to estimate population, the scientists make several assumptions.

One assumption is that there was no immigration of mealybugs between day 1 and 2.

Suggest two other assumptions they would make.

The number of mealybugs on each tree may be affected by the light intensity.

The scientists measured the light intensity for each tree at midday on day 1 of their investigation. Light intensity is measured using a light meter.

Tree B had an estimated population of 250 mealybugs at the end of the investigation. Tree B had a higher light intensity reading than tree A.

Read this statement.

The mealybugs are thought to breed rapidly in low light conditions.

Do the results for the two trees support this statement?

Use the information above and your answer to (c)(i).

Explain your answer.

Errors can occur when taking light meter readings.

Explain how errors occur and write down one way to take more precise readings.

The picture shows a mealybug insect.

This mealybug is a pest for orange tree growers.

The scientists compared the number of mealybugs found on two trees, tree A and tree B.

For each tree they:

• Collected a sample of mealybugs from the tree

• Counted the number of mealybugs in each sample

• Marked the mealybugs

• Released the mealybugs back onto the tree they were collected from.

The next day another sample was collected from each tree.

Describe how the scientists should collect and mark the mealybugs.

Include the equipment they need to use.

You may include a diagram with your answer.

Write down three precautions that should be taken when deciding how to mark the mealybugs.

The table shows the results for tree A.

Estimate the population size of mealybugs on tree A.

Use the formula:

When using this method to estimate population, the scientists make several assumptions.

One assumption is that there was no immigration of mealybugs between day 1 and 2.

Suggest two other assumptions they would make.

The number of mealybugs on each tree may be affected by the light intensity.

The scientists measured the light intensity for each tree at midday on day 1 of their investigation. Light intensity is measured using a light meter.

Tree B had an estimated population of 250 mealybugs at the end of the investigation. Tree B had a higher light intensity reading than tree A.

Read this statement.

The mealybugs are thought to breed rapidly in low light conditions.

Do the results for the two trees support this statement?

Use the information above and your answer to (c)(i).

Explain your answer.

Errors can occur when taking light meter readings.

Explain how errors occur and write down one way to take more precise readings.