Define measurable variables and controls, present processed data with units, select the correct graph or test and judge validity from errors, repeats and uncertainty.
The photograph shows a fruit fly, Drosophila suzukii, on the skin of a fruit.
This species of fruit fly is endemic to southeast Asia but recently it has become an invasive species in Europe.
The female lays fertilised eggs under the skin of fruits.
The eggs hatch into larvae that feed on the fruit.
The larvae develop into pupae that become adult flies.
A student investigated the effect of using an organic pesticide, pyrethrum, on the hatching of eggs and the development of pupae.
Sixteen flasks containing a culture medium were prepared. Eight flasks had 0.5 g of pyrethrum added.
Each flask had one female fly that layed eggs for 24 hours. The fly was then removed and the eggs were allowed to hatch and develop into pupae.
The photograph shows fly pupae in one of the flasks.
After five days, the number of pupae in each flask was counted.
The results were:
Number of pupae from untreated culture medium ( A )
7268815643526064
Number of pupae from treated culture medium (B)
State a suitable null hypothesis for this investigation.
Draw a suitable table to display these data and the calculated means for the number of pupae from the flasks containing the untreated and treated culture medium.
Draw a suitable graph to show the mean number of pupae from the untreated culture medium and treated culture medium.
Include an indication of the variability of the data.
The student analysed the data with a t test using the formula:
where:
is the mean value for each treatment n is the number of samples for each treatment and
Calculate the value of t.
The table shows the critical values of t for different degrees of freedom. The number of degrees of freedom
Deduce the conclusions that can be drawn from this investigation.
Use the information in this table to support your answer.
Describe two ways this investigation could be extended to collect more data to either support or reject the hypothesis.
Pyrethrum is applied to fruit crops growing in fields.
Suggest two reasons why applying pyrethrum to fruit crops in fields might not reduce damage to fruits.
The photograph shows a young locust eating the leaves of a plant.
Locusts can breed in large numbers and destroy crops, such as sorghum, in East Africa. A scientist observed that some varieties of sorghum were more likely to be eaten by young locusts. The scientist collected the seeds of two varieties of sorghum (A and B) and grew them in trays. Locust eggs were collected and hatched into young locusts. Twenty young locusts were placed in a cage containing 100 g of fresh sorghum leaves of variety A. The cage was kept at . After 24 hours, the leaves were removed and the mass of leaves eaten was calculated. This method was repeated with fresh sorghum leaves of variety B. The method was repeated six times for these two varieties of sorghum leaves. The results: Mass of leaves eaten of variety A 17.317.217.517.016.716.9 Mass of leaves eaten of variety B 17.817.917.717.617.817.4
State a suitable null hypothesis for this investigation.
Draw a suitable table to display the data and your calculated means for the mass of leaves eaten for these varieties of sorghum.
Draw a suitable graph to show the mean mass of leaves eaten of variety A and variety B. Include an indication of the variability of the data.
The student analysed the data using the t test formula:
Where: is the mean value for each treatment n is the number of samples for each treatment and
Calculate the value of t.
The table shows the critical values of t for different degrees of freedom. The number of degrees of freedom . Describe the conclusions that can be drawn from this investigation. Use the information in the table to support your answer.
Describe how the student could extend this investigation to collect more data to either support or reject the hypothesis.
