Evidence for the impact of environmental changes - Higher

Temperature

As you climb up a mountain the temperature reduces. This reduction, together with other abiotic and biotic factors, determines what species of plant are found at different elevations.

Two students set up a transect up a mountain. Every one hundred metres of altitude they recorded the number of different species found. This is called species richness. They also recorded the temperature.

Height above sea level (m)4005006007008009001000110012001300
Temperature (°C)16.815.915.515.114.613.913.51312.612.1
Quadrat 17564342111
Quadrat 261159412121
Quadrat 357811321110
Quadrat 47556435111
Mean plants per quadrat6.3767.53.52.52.511.250.8
Question

Describe what happened to temperature as the students climbed the mountain.

Use data to support your answer. [1 mark]

As the students climbed higher up the mountain the temperature decreased from 16.8°C at 400 metres to 12.1°C at 1300 metres. [1 mark]

Question

Describe how temperature affects the number of different species of plants growing. Use data to support your answer. [2 marks]

As temperature decreases the mean number of different plant species decreases [1 mark]. At the highest temperature of 16.8°C it was at its maximum of 6.25 per quadrat and at the lowest temperature of 12.1°C the fewest species per quadrat were seen [1 mark].

Question

What limitations might there be in drawing these conclusions? [4 marks]

The two students only recorded two abiotic factors (height and temperature) [1 mark]. The recording of additional quadrats would allow them to be more confident in their conclusions [1 mark]. We cannot say whether the decrease in plants per quadrat was caused by the height, temperature or some other factor such as moisture and light [1 mark]. Without further investigation, such as sampling at a different site with similar altitude but different temperatures, we can only say that that they are linked [1 mark].

Availability of water

All life on Earth needs water. Too much and some species will drown or rot. Too little and all species die. Two students set up a transect from the edge of a river running into a nearby field. They placed quadrats every metre and recorded the percentage cover of each plant species in their quadrats. Their results are below.

Distance from river bank (m)12345678910
Nettles00000510301520
Grass10202535959090708575
Cow parsley90757560000000
Unknown species0505550005
Question

Suggest how the availability of water affects the growth of each plant.

Use data to support your answer. [4 marks]

Nettles grow in higher numbers further away from the river bank/no nettles are seen closer than six metres to the bank [1 mark]. Nettles prefer a drier environment/low water availability [1 mark]. Grass also increases in number further away from the bank but is seen at all distances/grass can grow in both wet and dry environments [1 mark]. Cow parsley is seen in higher numbers closer to the river bank/cow parsley prefers to grow in a wetter environment/high water availability [1 mark].

Question

What limitations might there be in drawing these conclusions? [3 marks]

The two students only completed one transect up the river bank [1 mark]. Additional transects would allow them to be more confident in their conclusions [1 mark].

We cannot say whether the distribution in plants was caused by the water availability or some other factor such as light [1 mark].

Atmospheric gases

Human activities, such as burning fossil fuels, are a source of polluting gases.

Sulfur dioxide is a polluting gas that can cause environmental and health problems.

Lichen are plant-like organisms that can grow on trees. Some species of lichen are very sensitive to sulfur dioxide in the air. Bushy lichens will not grow if levels of sulfur dioxide are high.

Students counted the number of bushy lichens on trees found growing at various distances from a busy motorway. Their results are shown below.

Distance from motorway (m)Number of bushy lichen growing on the trunk of one tree
500
1002
2005
3005
Question

Write a conclusion from these results.

Use data to support your answer. [3 marks]

There is a general trend in the number of bushy lichen growing on the trunks of trees as you go further away from the motorway. [1 mark] For example, at 50 m away there was no lichen but at 300 m away there was 5 lichens [1 mark]. This indicates that as you move away from the motorway the level of sulfur dioxide in the air decreases [1 mark].

Question

Evaluate the method used by the students.

Suggest improvements they could have made. [6 marks]

They only choose one tree at each distance [1 mark]. It would have been better to choose many trees and calculate a mean number of lichen [1 mark].

The trees could have been different sizes, so have more space for lichens to grow [1 mark]. This variable should have been controlled so they only choose trees of the same size [1 mark].

They should have used more distances [1 mark] so a clearer pattern in the results would have been seen [1 mark].