Abiotic & biotic factors

Students investigated how many daisy plants were growing in a field at different distances from a tree.

This is the method used.

1. Place a 20-metre tape measure on the ground, with the tree at 0 metres.

2. Place a 1 m² quadrat on the ground every 4 metres along the tape measure.

3. Count the number of daisy plants in each quadrat.

4. Take a soil sample from each quadrat to find the percentage of water in the soil.

Figure 14 shows the tree and the tape measure.

This is the method used for finding the percentage of water in each soil sample (step 4):

5. Weigh an empty container.

6. Place the soil sample in the container and weigh again.

7. Heat the container of soil in an oven at 100 °C for several hours.

8. Allow the container of soil to cool and weigh again.

9. Repeat steps 7 and 8 until there is no further change in mass.

Suggest why the students repeated steps 7 and 8 until there was no further change in mass.

Table 6 shows the results.

Calculate percentage X in Table 6.

Give your answer to the nearest whole number.

Describe the effect of distance from the tree on the percentage of water in the soil between 4 metres and 16 metres.

Use Table 6.

A student concluded:

‘As the water content of the soil increases, so does the number of daisy plants.’

Describe two changes to the investigation that would increase the validity of the student’s conclusion.

The percentage of water in the soil is an abiotic factor.

Suggest three other abiotic factors that might have caused more daisy plants to grow further away from the tree.

Do not refer to water in your answer.

Students investigated how many daisy plants were growing in a field at different distances from a tree.

This is the method used.

1. Place a 20-metre tape measure on the ground, with the tree at 0 metres.

2. Place a 1 m² quadrat on the ground every 4 metres along the tape measure.

3. Count the number of daisy plants in each quadrat.

4. Take a soil sample from each quadrat to find the percentage of water in the soil.

Figure 2 shows the tree and the tape measure.

This is the method used for finding the percentage of water in each soil sample (step 4):

5. Weigh an empty container.

6. Place the soil sample in the container and weigh again.

7. Heat the container of soil in an oven at 100 °C for several hours.

8. Allow the container of soil to cool and weigh again.

9. Repeat steps 7 and 8 until there is no further change in mass.

Suggest why the students repeated steps 7 and 8 until there was no further change in mass.

Table 2 shows the results.

Calculate percentage X in Table 2.

Give your answer to the nearest whole number.

Describe the effect of distance from the tree on the percentage of water in the soil between 4 metres and 16 metres.

Use Table 2.

A student concluded:

‘As the water content of the soil increases, so does the number of daisy plants.’

Describe two changes to the investigation that would increase the validity of the student’s conclusion.

The percentage of water in the soil is an abiotic factor.

Suggest three other abiotic factors that might have caused more daisy plants to grow further away from the tree.

Do not refer to water in your answer.

Frogs are animals that lay their eggs in water. The eggs hatch as tadpoles.

Students investigated the number of tadpoles in a pond for 8 weeks.

This is the method used.

1. Collect 10 dm³ of pond water in a bucket.

2. Count the number of tadpoles collected.

3. Put the tadpoles back into the pond.

4. Repeat steps 1 to 3 another three times in different parts of the pond.

5. Repeat steps 1 to 4 at intervals for 8 weeks.

Suggest one improvement to the method.

Table 1 shows the results.

Value X is the number of tadpoles in sample 4, at 3 weeks.

Calculate value X.

Complete Figure 15 to show how the total number of tadpoles changed over the 8 weeks.

You should:

• label the x-axis

• use a suitable scale for the x-axis

• plot the data for the total numbers of tadpoles from Table 1

• draw a line of best fit.

After 0 weeks, no more tadpoles hatched in the pond.

Calculate the percentage of the tadpoles that would still be found in the pond at 4 weeks compared with 0 weeks.

Use information from Figure 15.

After 4 weeks many of the tadpoles had died.

Suggest two reasons why the tadpoles died.

Different species in a habitat may depend on each other for food.

Figure 3 shows a food chain.

The grass needs energy to grow.

What is the source of energy for the grass?

Table 2 lists different types of feeding relationship.

Write the name of one organism from Figure 3 in each box in Table 2.

Each organism may be written in one box or in more than one box.

The first box has been completed for you.

Figure 4 shows the appearance of the snowshoe hare in the summer and in the winter.

Figure 4

Snowshoe hare in summer
Snowshoe hare in winter

The snowshoe hare has a different fur colour in the summer than in the winter.

Explain how the different fur colour increases the chance of survival of the snowshoe hare.

Figure 5 shows how the number of snowshoe hares and the number of lynx varied in one area between 1900 and 1935.

Figure 5 shows that the number of snowshoe hares and the number of lynx increase and decrease several times.

Suggest two reasons why the number of snowshoe hares increases.

The number of snowshoe hares increased and decreased four times between 1900 and 1935.

What effect does an increase in the number of snowshoe hares have on the number of lynx?

Suggest one reason why the number of lynx decreased from 1915 to 1919.

Use information from Figure 5.

When the snowshoe hare eats grass, about 90% of the biomass of the grass is lost.

Give two ways the biomass is lost.

Many different species can live together in the same habitat.

What name is given to all of the organisms living in the same habitat? Tick (✓) one box.

Figure 1 shows four species of bird from the same habitat in the UK.

Brambling (Fringilla montifringilla) Bullfinch (Pyrrhula pyrrhula)

Chaffinch (Fringilla coelebs) Goldfinch (Carduelis carduelis)

Which species of bird in Figure 1 do scientists think are most closely related? Tick (✓) one box.

Scientists think the brambling and the bullfinch belong to different species. What evidence is used by scientists to classify the brambling and the bullfinch as different species? Tick (✓) one box.

Four other species of bird (A, B, C and D) live in a habitat in the UK. Figure 2 shows how the numbers of each species of bird varied during one year.

Use information from Figure 2 to answer Questions 01.4 to 01.6

Describe what happens to the number of birds of species A during the year.

In June and July, a disease affected the populations of some of the species. Which species had the lowest resistance to the disease? Tick (✓) one box.

One species migrates between the UK and other countries. Which species migrates between the UK and other countries? Give a reason for your answer.

Rivers are sometimes polluted with untreated sewage. Figure 6 shows some changes that occurred when untreated sewage entered a river.

Which type of organism had the most rapid increase in numbers when sewage entered the river? Tick (✓) one box.

Protozoa are single-celled organisms. Describe two ways Figure 6 shows that the protozoa in the river feed on bacteria.

When sewage enters a river, the concentration of dissolved oxygen decreases. The decrease in oxygen concentration is caused by organisms in the water. What process in living organisms uses oxygen?

As the numbers of green algae in the river increase, the concentration of dissolved oxygen increases. Explain why the concentration of dissolved oxygen increases.

Scientists counted the numbers of five different animals in the river at sites A and B,

shown in Figure 6 on page 14. Table 2 shows the results.

Figure 7 shows some of the data from Table 2.

Complete Figure 7. You should use data from Table 2 for the sludge worm and the bloodworm.

The concentration of oxygen in the water at site A is much lower than at site B.

• Sludge worms live in places which have a low concentration of oxygen.

• Mayfly nymphs need a high concentration of oxygen.

Give evidence from Table 2 for the difference in oxygen concentration at sites A and B. Refer to sludge worms and to mayfly nymphs in your answer.

Earthworms:

• live in soil

• feed on dead and decaying plant matter

• have soft, moist skin

• exchange gases through their skin.

Give two abiotic factors and two biotic factors that could affect the size of an earthworm population. Abiotic factors

Biotic factors

Students investigated the populations of earthworms in the soil in two different areas:

• Area A: a grass lawn

• Area B: a farmer’s field.

Chemical X can be mixed with water and poured onto the soil. The mixture brings earthworms to the surface of the soil but does not harm the earthworms. Plan an investigation using chemical X to compare the number of earthworms per m² in areas A and B.

Earthworms:

• live in soil

• feed on dead and decaying plant matter

• have soft, moist skin

• exchange gases through their skin.

Give two abiotic factors and two biotic factors that could affect the size of an earthworm population. Abiotic factors

Biotic factors

Students investigated the populations of earthworms in the soil in two different areas:

• Area A: a grass lawn

• Area B: a farmer’s field.

Chemical X can be mixed with water and poured onto the soil. The mixture brings earthworms to the surface of the soil but does not harm the earthworms. Plan an investigation using chemical X to compare the number of earthworms per m² in areas A and B.

A student estimated the percentage cover of buttercup plants in a field. The student used a quadrat. The quadrat was divided into 25 equal squares. Figure 10 shows the quadrat.

This is the method used.

1. Place the quadrat on the ground.

2. Record how many squares in the quadrat contain buttercup plants.

3. Place the quadrat in a new position in the field.

4. Record how many squares in the quadrat contain buttercup plants.

5. Repeat steps 3 and 4 another three times.

What method should the student have used for placing the quadrat?

Tick (✓) one box.

The student calculated the percentage cover of buttercup plants for each quadrat. Table 1 shows the student’s results.

Calculate mean value X in Table 1.

Table 1 shows that quadrat 1 and quadrat 5 each had 40% cover of buttercup plants.

Figure 11 shows the results for quadrat 1 and quadrat 5.

The student’s method of estimating the percentage cover of buttercup plants is not accurate. How does Figure 11 show this?

Tick (✓) one box.

The student wanted to get a more valid estimate of the percentage cover of buttercup plants in the field. Suggest two improvements to the method to make the results more valid.

Give three environmental factors that would affect the growth of buttercup plants in a field.

3 9

The growth of daisy plants on a lawn is affected by biotic factors and by abiotic factors.

Table 2 shows six factors. Tick () one box in each row to show whether the factor is biotic or abiotic.

Figure 8 shows a plan of a garden.

A student estimates the number of daisy plants growing on the lawn. The student places a quadrat at 10 different positions on the lawn. The quadrat measures 50 cm 50 cm. The student counts the number of daisy plants in each quadrat.

How should the student decide where to place the quadrat? Give the reason for your answer.

The mean number of daisy plants in each quadrat is 6. Calculate the number of daisy plants on the lawn. Give your answer to 3 significant figures.

Number of daisy plants on the lawn =

Using the mean from this investigation to calculate the number of daisy plants on the lawn may not be accurate. Give two reasons why.

Figure 8 shows when two mammals existed in Asia.

Determine the number of years both Andrewsarchus and Brontotherium existed together.

The oldest fossils of human ancestors found in this area are 700 000 years old. Andrewsarchus was a carnivore and Brontotherium was a herbivore. Suggest how the extinction of Andrewsarchus could have resulted in the extinction of Brontotherium.

Information about extinct animals is often not clear because the fossil record is incomplete. Give three reasons why the fossil record is not clear for older species.

Figure 9 shows the percentage (%) survival of large mammal species in four areas of the world. The time at which humans first appeared in each of the four areas is also shown.

A mass extinction is a rapid decrease in biodiversity on Earth.

A student stated: ‘The data in Figure 9 shows that humans caused mass extinctions.’ Evaluate the student’s statement.

Give one disadvantage and one advantage of mass extinction events. Answer in terms of evolution.

Figure 14 shows a food chain in a pond.

Which term describes the Daphnia in this food chain?

Tick (✓) one box.

Draw a pyramid of biomass for the food chain.

Label each trophic level.

Give one reason why the total biomass of the Daphnia in the pond is different from the total biomass of the algae.

Students investigated the size of the population of Daphnia in the pond.

This is the method used.

1. Collect 1 dm³ of pond water from near the edge of the pond.

2. Pour the water through a fine net.

3. Count the number of Daphnia caught in the net.

4. Repeat steps 1–3 four more times.

Table 3 shows the results.

Calculate the mean number of Daphnia in 1 m³ of pond water.

The pond was a rectangular shape, measuring:

• length = 2.5 metres

• width = 1.5 metres

• depth = 0.5 metres.

Calculate the estimated number of Daphnia in the pond.

Use your answer from Question 07.4.

Give your answer in standard form.

Rainfall can cause fertiliser to be washed from farmland into a pond.

The students investigated the effect of fertiliser on the population of Daphnia in water from the pond.

• The students put 20 Daphnia in each of five different concentrations of fertiliser.

• The students counted the total number of Daphnia in each concentration of fertiliser after 2 weeks.

Figure 15 shows the results.

A concentration of 5.0 mg/dm³ of fertiliser caused a large increase in the population of Daphnia.

Explain why.

Figure 14 is repeated below.

The population of Hydra will decrease when 20 mg/dm³ of fertiliser is added to the pond.

Explain why.

Figure 1 shows a food chain in a pond.

Which term describes the Daphnia in this food chain?

Tick (✓) one box.

Draw a pyramid of biomass for the food chain.

Label each trophic level.

Give one reason why the total biomass of the Daphnia in the pond is different from the total biomass of the algae.

Students investigated the size of the population of Daphnia in the pond.

This is the method used.

1. Collect 1 dm³ of pond water from near the edge of the pond.

2. Pour the water through a fine net.

3. Count the number of Daphnia caught in the net.

4. Repeat steps 1–3 four more times.

Table 1 shows the results.

Calculate the mean number of Daphnia in 1 m³ of pond water.

The pond was a rectangular shape, measuring:

• length = 2.5 metres

• width = 1.5 metres

• depth = 0.5 metres.

Calculate the estimated number of Daphnia in the pond.

Use your answer from Question 01.4.

Give your answer in standard form.

Rainfall can cause fertiliser to be washed from farmland into a pond.

The students investigated the effect of fertiliser on the population of Daphnia in water from the pond.

• The students put 20 Daphnia in each of five different concentrations of fertiliser.

• The students counted the total number of Daphnia in each concentration of fertiliser after 2 weeks.

Figure 2 shows the results.

A concentration of 5.0 mg/dm³ of fertiliser caused a large increase in the population of Daphnia.

Explain why.

Figure 1 is repeated below.

The population of Hydra will decrease when 20 mg/dm³ of fertiliser is added to the pond.

Explain why.

Figure 1 shows a food chain in a river.

Draw one line from each scientific term to the correct organism in the food chain.

Organism Scientific term

Table 1 shows the biomass of the organisms at each stage in the food chain.

Calculate the percentage of the biomass of the invertebrate animals that is transferred to the large fish.

Use the equation:

A large amount of biomass is lost from the food chain.

Complete the sentences.

Choose answers from the box.

When the small fish eat the invertebrate animals, not all of this material is

Materials absorbed from the gut may enter the body cells of the small fish.

These materials are broken down into carbon dioxide and

The carbon dioxide and other waste materials from the body cells are removed

A disease kills many of the small fish.

Why does the number of invertebrate animals increase?

Some students investigated the size of a population of dandelion plants in a field.

Figure 5 shows the field.

The students:

• placed a 1 m x 1 m square quadrat at 10 random positions in the field

• counted the number of dandelion plants in each quadrat.

Table 2 shows the students’ results.

Why did the students place the quadrats at random positions?

Estimate the total number of dandelion plants in the field.

Calculate your answer using information from Figure 5 and Table 2.

Give your answer in standard form.

Quadrats 5, 7 and 8 were each placed less than 10 metres from the woodland.

These quadrats contained low numbers of dandelion plants.

The students made the hypothesis:

‘Light intensity affects the number of dandelion plants that grow in an area.’

Plan an investigation to test this hypothesis.

Light is an environmental factor that affects the growth of dandelion plants.

Give two other environmental factors that affect the growth of dandelion plants.