Experimental Planning and Practical Skills in Marine Science

Practical skills are developed throughout the marine science course by conducting experiments and investigations that are directly linked to theoretical learning.
By the conclusion of the course, proficiency must be demonstrated in the following areas:
- Planning experiments.
- Presenting observations and data clearly.
- Evaluating both the experimental method and the quality of the data collected.
- Drawing appropriate scientific conclusions.
These specific skills are tested in Paper 2 and Paper 4 of the assessment.
Students are expected to apply these skills to both familiar practicals performed in class and entirely unfamiliar practical scenarios.
There are four core areas of confidence for the student:
- Planning.
- Presenting.
- Evaluating.
- Concluding.

Experimental planning follows the scientific method, which is an iterative process.
Ideas within the scientific method are subject to change in the future if new observations are made, even if a current hypothesis is supported.
Defining the problem is the first stage of planning a successful investigation. This requires clarity regarding the specific question the experiment aims to answer.
The planning process often begins with making observations. These initial observations are frequently qualitative (descriptive) rather than quantitative (possessing an amount or numerical value).
A hypothesis is formulated to explain an observation. It is defined as one possible answer to the question 'why?'.
A prediction is linked to the hypothesis and states what is expected to happen during the experiment. Predictions may need to be presented as a sketch of the expected shape of a graph rather than a written description.
The design of the experiment must produce quantitative data that can be used to either:
- Support the hypothesis.
- Refute the hypothesis (defined as submitting evidence that shows a hypothesis is not correct).

Variables are the conditions in an experiment that can be changed.
The independent variable is the specific condition that is changed by the experimenter during the investigation.
The dependent variable is the condition that is measured.
A control experiment is normally included to provide results for comparison. The control group is treated in the exact same manner as the experimental groups, with the exception of the independent variable, which is not changed.
To ensure valid results, all variables other than the independent variable must be kept constant. If more than one variable changes simultaneously, it is impossible to determine which one caused the changes in measurements.
Control variables are the variables kept the same because they could potentially affect the dependent variable. Key control variables to consider include:
- Temperature.
- Carbon dioxide concentration ( $CO_2$ ).
- Oxygen concentration ( $O_2$ ).
- pH.
- Light intensity.
- Light wavelength.
When using living organisms, identical subjects are difficult to obtain. To maintain consistency, experimenters should choose organisms of the same:
- Species.
- Age.
- Size.
- Sex.
- Origin (from the same place).

Laboratory-based experiments allow for tighter control over variables compared to field-based experiments.
In the field (e.g., a seashore), it is impossible to control factors like temperature or light.
To analyze results in field experiments, any variables that might affect the dependent variable should be measured and recorded at the same sampling sites. These are known as confounding variables.
While confounding variables are controlled in a lab to prevent them from affecting results, in the field they are measured so that their effects on the results can be identified.

Temperature Control:
- Often controlled using a water bath.
- Simple water baths are containers where hot or cold water is added manually.
- Thermostatically controlled water baths use heating units to maintain temperatures within programmed limits.
- A thermometer should always be used to monitor and ensure the temperature remains constant.
pH Control:
- Controlled using a buffer, which is a solution consisting of an acid and a base that remains at the same pH even if more acid or base is added.
Gas Concentrations ( $CO_2$ and $O_2$ ):
- These are often maintained in excess so they do not become limiting factors.
- Carbon dioxide excess is typically achieved using hydrogencarbonate solution.
- Oxygen can be bubbled into the solution using an air pump.
Light Control:
- Light intensity is controlled by maintaining an equal distance from the light source. Other sources of light should be removed.
- Light wavelength is controlled by using the same light source throughout the experiment. Because wavelength is difficult to measure, it is often just standardized and assumed to remain constant.

Selecting equipment that yields the most accurate results is vital.
Liquids:
- A measuring cylinder is standard, but the smallest appropriate size should be used for accuracy. For example, measuring $8\,cm^3$ in a $10\,cm^3$ cylinder is more accurate than using a $200\,cm^3$ cylinder.
- For volumes less than $10\,cm^3$ , a pipette or syringe is more accurate.
- Very small volumes (e.g., adding a stain to a slide) may require less than $1\,cm^3$ .
- Large volumes (e.g., filling a tank for living organisms) may be measured in liters ( $1000\,cm^3$ ).
Common Measurement Methods (Table P.1):
- Temperature: Thermometer (digital thermometers are most accurate).
- pH: Universal indicator or a pH probe.
- Light Intensity: Light sensor or approximated by distance from the light source.
- Volume: Measuring cylinder, pipette, or syringe.
- Mass: Balance (weighing scales).
- Time: Stopwatch.
- Distance: Ruler (for short distances in $mm$ ) or tape measure (for longer distances in $m$ ).

Safety involves assessing hazards and risks:
- A hazard is something that could cause harm or damage to health.
- A risk is the chance of that damage happening and the severity of the potential harm.
Ethics relates to the treatment of living organisms and the avoidance of causing them harm during investigations.
Communicating a plan clearly is essential for validity and reliability, ensuring another person could replicate the experiment and obtain the same pattern of results.
Effective communication includes:
- A labeled diagram of the apparatus, following scientific drawing rules.
- A logical, step-by-step written procedure.
Example Investigation: Snails in the littoral zone of a rocky shore.
- Independent Variable: Part of the littoral zone (varied by measuring in low, middle, and high tide zones).
- Dependent Variable: The abundance of the snails.