Using field-work techniques

In a nutshell

Quadrats are square frames that enclose a given area, they can be used to investigate the distribution of small organisms in an area. You can also investigate changes in distribution using lines called transects. Sampling along the length of a transect using a quadrat is known as a belt transect. You will first measure the population size of a common species in a habitat and then use sampling techniques to investigate the effect of an abiotic factor on the distribution.

Equations

You need to know this equation for these experiments.

$estimated\space population\space size ={{total\space area \over area\space sampled} \times total\space number\space of \space plant\space species\space counted }$

Equipment list

The following equipment can be used to investigate the distribution of small organisms in an area.

Equipment	Use
$1\space m^2$ Quadrats	To measure distribution in a given area.
$30\space m$ Tape measures	To measure your survey area.
Light meter	To measure light intensity.

Experiment 1: Estimating the population size of a chosen plant species in a given area using a quadrat

Experimental variables

Every experiment will have an independent, dependent and control variable. The independent variable is the variable that you change. The dependent variable is the variable which depends on the independent variable, therefore it is the one you measure. The control variable is the variable that is kept the same during the experiments.

Independent variable	$The \space sampling \space area.$
Dependent variable	$Number \space of \space your \space chosen \space plant \space species.$
Control variable	$The \space surveying \space area.$

Safety precautions

When performing experiments, it is important you consider safety precautions. However, in this experiment there are no significant risks.

Method

These are your instructions on how to complete the experiment.

Biology; Biology practicals; KS4 Year 10; Using field-work techniques — A quadrat.

1.	Using two tape measures, lay out a $10\space m \times 10\space m$ surveying area in your chosen habitat.
2.	Use a random number generator to generate a set of coordinates.
3.	Place the quadrat at this position.
4.	Count the number of your selected plant species in this area.
5.	Repeat steps 2-4 for $10$ different points in your surveying area.

Analysis

This is how you will use your data to form conclusions.

Use the formula to estimate population size of your chosen plant species in the surveying area:

$estimated\space population\space size ={{total\space area \over area\space sampled} \times total\space number\space of \space plant\space species\space counted }$

Conclusion

You can compare your estimated population size with your classmates to see how similar your results are.

Evaluation

If your results are very different compared to your classmates, it is important that you consider why. One common error may be miscounting the number of species in the quadrat, next time you may choose to count the species twice. You should identify any anomalous quadrat recordings and exclude them from your results.

Experiment 2: Investigating the effect of light intensity on the distribution of your chosen plant species using a transect line.

Experimental variables

Every experiment will have an independent, dependent and control variable. The independent variable is the variable that you change. The dependent variable is the variable which depends on the independent variable, therefore it is the one you measure. The control variable is the variable that is kept the same during the experiments.

Independent variables	$The\ sampling\ area\ and\ light\ intensity.$
Dependent variables	$Number\ of\ your\ chosen\ plant\ species.$
Control variable	$The\ surveying\ area.$

Safety precautions

When performing experiments, it is important you consider safety precautions. However, in this experiment there are no significant risks.

Method

These are your instructions on how to complete the experiments.

Biology; Biology practicals; KS4 Year 10; Using field-work techniques — Your experiment set up.

1.	Place the $30\space m$ tape measure in a line from the base of a tree to an open area of ground. This is the transect line.
2.	Put the quadrat at $0\space m$ and count the number of your chosen plant species.
3.	You should also record the light intensity using the light meter. *Note:* Abiotic factors are non-living factors, in this experiment light intensity is the abiotic factor.
4.	Repeat steps 2 and 3 every $5\space m$ along the transect line.
5.	Record your results in a suitable table.

Analysis

This is how you will use your data to inform conclusions.

1.	Plot a graph with appropriate scales. The dependent variable (number of plant species) should be on the $y$ -axis and the independent variable (light intensity) should be on the $x$ -axis. Draw a line of best fit, label your axes and add a suitable title. *Note*: Your line of best fit should past through the origin.
2.	Write a sentence explaining the relationship between the two variables as demonstrated by your graph.

Conclusions

Your graph should show a positive correlation between plant abundance and light intensity. This means as the light intensity increases, the abundance of plant species also increases. This makes sense as plants require light for photosynthesis which is the process they use to make food for growth.

Biology; Biology practicals; KS4 Year 10; Using field-work techniques — A: Number of plant species, B:Light intensity in units.

Evaluation

If your results were unexpected, you must consider why. Ask yourself questions about your techniques and assess the equipment you used. You may need to edit the method or surveying area next time. One error may be misidentifying the plant species. This would lead to miscounting and inaccurate results.