Model answer and comments on how to write a planning answer for 6B. by Stafford Valentine Redden. www.staffordeducationalservices.com

Coconut palms are trees often found growing close to the sea. A student formed the hypothesis that the yield of coconuts from each tree would decrease as the distance from the sea became less because the salt levels in the soil might inhibit growth. Plan an investigation to test this hypothesis. Your answer should give details under the following headings. (a) A consideration of what sampling techniques might be appropriate to this investigation and any safety or ethical issues you would need to consider. Since there are hundreds of coconut trees running inland away from the beach, it would not be possible to include each and every tree in the investigation. So, we need an unbiased mechanism to select a few trees that would be used in the study. Two ropes are tied parallel to each other and drawn inland away from the beach for a distance of 150m. Any coconut tree found at intervals of 15m, within the belt, will be chosen for the experiment. This is a form of systematic sampling called the belt transect The risks include the danger of coconuts falling and injuring students. Climbing up the trees to harvest the coconuts for measuring the yield could be risky, as coconut trees are quite tall. Poisonous snakes, spiders, beetles and other insects usually inhabit the coconut trees and could cause fatal bites. Care must be taken to minimise disturbance to the habitat, which may be the breeding ground for birds and other organisms. (b) Suggestions for preliminary work that you might undertake to ensure your proposed method would provide meaningful data. To ensure that the method will work, a survey of the area could be carried out to determine whether the 15m interval for sampling of trees is feasible or not. An assessment of variables like competition, pests, light intensity, mineral content of the soil, salt content, etc must be carried out and we must decide on exactly which variables to control or monitor. A reliable way of measuring the yield of coconuts (dependent factor) would be to measure the mass of coconuts from each of the trees, as other parameters are difficult to measure accurately.

(c) A detailed method explaining exactly how you would carry out this investigation and how important variables are to be controlled or monitored. Sampling of coconut palms belt transect Extend two ropes from the water edge towards the coconut palms for a distance of 150m inland. The two ropes should be parallel to each other with a gap of 2m between them. Select 10 coconut trees that lie within the two ropes at regular intervals of 15m. Variables to be controlled Independent variable the distance from the sea shore The independent variable in this experiment is the distance from the sea shore. There are ten values for this variable ranging from 0 to 150m from the seashore, assuming that the first coconut tree lies at the water edge. Light intensity and competition There could be many other plants around the coconut trees. These will absorb nutrients from the soil and compete with the coconut palms, reducing the yield. If the plants are as tall as the coconut palms and are clustered too close then the light intensity may be reduced and could influence the yield. So we need to monitor the light intensity for all the ten plants to ensure that it is almost the same. Water content of soil The water content of the soil can be monitored at each site by taking a homogenised soil sample and finding its initial mass. The sample is then heated till its mass becomes constant and the water content is calculated by the difference in mass. Preferably the water content should be the same for all sites. Salinity of soil The soil can be dug up to a depth of 15cms in each site and 200g of homogenised soil can be suspended into 500cm3 of distilled water. A salinity meter can then be used to test the salinity of the soil at each site. Measuring the dependent variable the yield of coconuts

Commented [SVR1]: Either random or systematic sampling (Line transect or Belt transect)

Commented [SVR2]: Systematic sampling is used to investigate changes as we travel from one point in the habitat to another region. Changes in the yield of coconuts as we move away from the shore.

Commented [SVR3]: Risk assessment will vary from question to question. However, look for any factor that could cause harm to the experimenter or damage to the habitat. Do not hesitate to include any thought that may pass through your mind, however silly it may seem, as there is no negative marking and only the right answers will be marked.

Commented [SVR4]: There may not be an ethical issue always. So, if you cannot think of any issue then move on and ponder over it as you write. Do NOT get stuck at a question for a long time as time management is a major factor in this paper.

Commented [SVR5]: Some students have a tendency to quote the marking scheme points and thereby end up making vague statements. Instead relate marking scheme information to the context of the question and make a clear indication of what exactly you are going to do as preliminary work. Remember to state the variables and any other relevant information.

Commented [SVR6]: Identify the independent and dependent variables and state these variables.

Commented [SVR7]: Even though there is no specified format for writing this section, it is useful to write under sub headings, as it encourages elaboration of points and also helps to acquire the marks for organisation and sequence of writing.

Commented [SVR8]: State the independent variable, dependent variable and all other variables that can influence the dependent variable.

Commented [SVR9]: Give a detailed explanation about how each variable is to be controlled or monitored and a brief consequence of variations in these variables. Quote approximate values wherever possible, instead of making statements like a known amount, or a fixed distance, or specific volume, etc.

Commented [SVR10]: Describe at least five variables that are to be controlled. It is always better to state more variables than the marking schemes normally have. Remember when you are writing the experiment you are not sure which variables will be awarded marks so it is better to play safe and describe many variables, however take the time management into account. Give full practical details of how each variable may be controlled or monitored.

Commented [SVR11]: The dependent variable is to be measure to give you data for final analysis. Choose a method that can be measured accurately. It should also provide reliable data.

Model answer and comments on how to write a planning answer for 6B. by Stafford Valentine Redden. www.staffordeducationalservices.com

The yield of coconuts can be measured in different ways, like mass of coconuts, number of coconuts, diameter of coconuts, etc. However measurement of mass can be done most accurately. So, all the coconuts are plucked and the mass of coconuts from each tree is measured. Repeat the entire procedure at three different transects and find the mean.

(d) A clear explanation of how your data is to be analysed in order to make conclusions concerning this hypothesis. The data can be recorded in the table shown below and the results can be plotted on a scatter diagram as shown below.

Distance from the sea / m

Mass of coconuts per tree / kg

Transect 1 Transect 2 Transect 3 Mean

0

15

30

45

60

75

90

105

120

135

150

Hypothetical graph

A correlation coefficient can be used to analyse the data and draw a valid conclusion. Null hypothesis: there is no significant relationship between the distance from the sea and the mean mass of coconuts produced. If the calculated value is greater than the critical value, at the 5% significance level, then the null hypothesis must be rejected and we must conclude that there is a significant relationship between the two variables.

(e) The limitations of your proposed method.

It is difficult to standardise the measurement of yield as factors like water content of coconuts can vary with ripeness. Older coconuts are dry and hence lighter. It is difficult to harvest coconuts as they grow high on the palm. Some coconuts may fall of due to strong winds and these will not be measured, resulting in inaccurate measurements. It is difficult to control all abiotic factors affecting the yield, as the factors change as we move inland. It may also be difficult to sample the trees as they are not evenly arranged.

Analyse the model plans that follow and write a few plans on your own. Ask your teacher to give you a feedback.

Commented [SVR12]: Repeating helps us to check the reliability by giving us and idea of the variation if repeated experiments.

Commented [SVR13]: Table should have columns with appropriate headings and units. It should match the method used in the plan.

Commented [SVR14]: A hypothetical graph should label the axes appropriately and state the units. It may also show the trend of the expected results if the hypothesis is proven to be true.

Commented [SVR15]: State the statistical test used to analyse the data.

Commented [SVR16]: The statistical test will test the validity of the null hypothesis.

Commented [SVR17]: State the rule for acceptance or rejection fo the null hypothesis.

Commented [SVR18]: State the significance level or probability level used

Commented [SVR19]: Limitations will be genuine sources of error that cannot be controlled. Warning: do not deliberately ignore factors that must be controlled and state them as limitations.