Monitoring & Maintaining the Environment (OCR GCSE Combined Science A (Gateway): Biology)

A student investigates the effect of acid rain on seed growth.

• She soaks cotton wool in a solution with a pH value of 7.0.

• She puts 20 mustard seeds onto the cotton wool and places it inside a flask.

• She adds the same solution to the flask.

• She then repeats this four times using solutions with different pH values.

One of the flasks is shown in the diagram.

After 8 days she counts how many of the seeds are growing.

The table shows her results.

The student used 20 seeds in each flask.

Write down one other factor that the student should have kept the same in this investigation.

Describe what this investigation shows about the effect of acid rain on seed growth.

One way to compare the growth of seeds is to use a germination index (GI).

(i) For the seeds at pH 6.0, the mean root length was 5mm.

Calculate the GI for these seeds.

 Answer = ...................................[2]

(ii) Look at the equation for GI.

This is a better way of measuring the effect of acid rain on seed growth than just counting the number of seeds growing.

Explain why.

[1]

A salt marsh is a large, muddy area of land where a river joins the sea.

When the tide comes in, the salt marsh gets covered with seawater.

Suggest one reason why salt marshes are difficult places for plants to grow.

Student A and student B study the plants growing on a salt marsh.

They both sample the plants present by laying out two tape measures at right angles across the salt marsh.

They then place a square frame on the ground in different places and count the number of plants in the square, as shown below.

What is the name of the square frame that they use to sample the plants?

The diagrams show the position of each student’s samples across the salt marsh..

Each small square in the diagrams represents one sample.

(i) The whole salt marsh has an area of 2500m².

Each square frame has an area of 0.25m².

Calculate the percentage of the whole salt marsh that was sampled by student A.

Percentage = ................................ % [3]

(ii) Look at the two students’ sampling shown in the diagrams.

Explain which student is likely to get the most accurate estimate for the number of plants in the salt marsh.

student ...................................

explanation ...........................

[3]

(iii) Their teacher said that they should take care as there may be harmful bacteria in the salt marsh.

State two things that the students could do to reduce the risk of infection from the harmful bacteria.

1 ....................................
2 ....................................

[2]

In some salt marshes large sand banks have been built. These stop tides from entering the salt marsh. The level of soil on the salt marsh builds up and the marsh turns into dry land.

Local farmers want to turn salt marshes into dry land and other people want to leave it as a salt marsh.

Explain why. Use ideas about land use and biodiversity in your answer.

A student investigates the effect of acid rain on seed growth.

She dips some cotton wool in 20cm³ of water. She then puts 20 mustard seeds onto the cotton wool and places it inside a flask. The student puts the remaining water into the flask with the cotton wool. 

She repeats this four more times, each time using different solutions of water and dilute sulfuric acid.

One of the flasks is shown in the diagram.

After 8 days she counts how many of the seeds have germinated.

The table shows her results.

What is the dependent variable in this investigation?

State why the student changed the volume of water in each flask.

The student kept each flask at the same temperature during the experiment to make it a fair test.

Explain one other reason why she kept each flask at the same temperature.

Explain what this experiment shows about the effect of acid rain on seed germination.

The student used a formula to describe the germination of seeds called the viability index (VI).

(i) For the seeds in 20cm³ of sulfuric acid, the mean root length was 5mm and the mean shoot length was 2mm.

Calculate VI for these seeds.

Use the equation:

VI = mean root length × mean shoot length × percentage of seeds that germinated

Answer = ....................................... [2]

(ii) Using VI is a better way of comparing the effects of acid rain than just using the number of seeds germinated.

Explain why.

[2]

A salt marsh is a large muddy area of land where a river joins the sea. This is a rare habitat and some plants grow on salt marshes but nowhere else.

When the tide comes in the salt marsh gets covered with seawater.

Explain the effects of salt water on plant cells.

A student investigates the plants growing on a salt marsh. He uses a quadrat to sample the plants.

He puts down two long tape measures at right angles to each other across the salt marsh. He then picks numbers at random and uses them to decide where to place a quadrat.

The diagram shows the position of all his quadrats across the salt marsh.

(i) The salt marsh measured 50m × 50m.

Each quadrat measured 0.5m × 0.5m.

Calculate the percentage of the whole salt marsh that was sampled by the student.

Percentage = ............................... % [3]

(ii) A second student sampled by placing five quadrats close together in the centre of the salt marsh.

Evaluate the sampling method of the second student compared to the method of the first student.

 [3]

(iii) Suggest one factor that the students should consider in a risk assessment for their experiment.

 [1]

 In some salt marshes large sand banks have been built. This stops tides from entering the salt marsh.

The level of soil on the salt marsh builds up and the marsh turns into dry land.

This dry land shows a greater biodiversity of plants than a salt marsh.

Explain why some scientists want to limit the building of sand banks, even though they increase biodiversity.

The rock pocket mouse is a small grey coloured mouse that lives in Mexico.

• These mice are the main food for owls.

• Rattlesnakes also feed on these mice.

• The mice get most of their food from grass plants.

Complete the sentences about this food web.

The grass plants are producers in the food web.

Mice are primary ........................................ in this food web.

The group of mice living in this habitat is called a population.

All the organisms living in this habitat is called the ...................................

Scientists want to construct a pyramid of biomass for this food web.

They first need to estimate how many organisms there are in the area. They decide to do this using sampling.

(i) Describe how the scientists would sample an area and ensure that the sample was not biased.

[2]

(ii) To estimate grass cover and the number of animals, the scientists use a quadrat.

• Why do scientists use sampling when studying the organisms living in a habitat?

• Identify the limitations of this method and potential improvements that could be made to ensure that the estimated population size of plants and animals closely matches the actual value.

[6]