SARAH NICHOL: Hello, my name is Sarah Nichol.
And I am a Biology Teacher at Reddam House School.
Today, I am going to take you through a core
practical focused on investigating
the relationship between organisms
and their environment.
In this first part, we will investigate
the relationship between light intensity
and the distribution of an organism.
As you can see, there is a tree casting a shadow on the field.
We are going to see how a difference in light intensity
caused by this shadow affects the distribution
of an organism.
A transect is used to study the distribution of an organism
and how their distribution is affected by changes
in environmental conditions.
Today, we are going to use a belt transect where quadrats
are placed at regular intervals along the transect line
to count the number of organisms and take
readings of light intensity.
You will need the following things for this field work
investigation--
one 20 meter tape measure, light intensity meter, one quadrat,
and a clipboard.
Before you start, make sure that you've
chosen a flat area to study.
If you are working under trees, make
sure there are no unsafe branches
or roots you could trip over.
And wash your hands after you have finished.
Place the tape measure at the base of the tree
and stretch it into the open.
Place your quadrat at the very start of the tape measure
and count the number of organisms inside the quadrat.
Record this in your results table.
Take your light meter and record the light intensity.
To make your results valid, place the light meter
in the middle of the quadrat each time you take a reading.
Record your results.
Repeat this process at regular intervals
until you reach the end of your defined distance.
In our experiment, we covered 20 meters.
You now need to plot a scatter graph of your results,
putting your light intensity on the x-axis and the number
of organisms on the y-axis.
Use your data to make your own conclusions
between your own independent and dependent variable.
If you have time, you could test a different abiotic factor.
In the second part of this core practical,
we are going to use field work techniques to estimate
the number of a specific organism in our field work
area.
For this field work experiment, you
will need one quadrat, two 20 meter tape
measures, clipboards, and a random number table.
This is a quadrat.
Each side measures 50 centimeters.
We are going to use this to help estimate
the total number of organisms in a specific area.
First, we need to measure out our given area.
You could use two 20 meter type measures placed at right angles
or use a trundle wheel.
We then need a table of random numbers.
We will use this table of random numbers
to generate coordinates for our sampling.
For example, the first numbers on the table are 1 and 14.
Working in pairs is a good way to find your coordinate.
Count the number of your chosen organism
that are inside the quadrat and record
this in your results table.
Repeat this process by going back to your random number
table and choose your next set of coordinates
and start the process again.
The number of times you repeat this process
may be dependent on the amount of time you have.
Today, we have repeated the process 10 times.
The more repeats you have, the more accurate
your final result will be.
To estimate how many clover flowers there
are in total in the study area, we
will need to use this equation--
estimated population size equals the total number
of organisms in the sample times by the total area
of study divided by the total area of quadrats.
To do this, you will need to add up the total number of clover
flowers in each quadrat.
In this case, 63.
We then need to work out our total area of study, which
is 20 meters by 20 meters.
This gives us 400 meters squared.
The last thing we need is the total area of quadrats
that we used.
Our quadrats were 50 centimeters by 50 centimeters.
As we are using meters to work out the size of our study area,
we will convert centimeters to meters.
Therefore, our quadrats are 0.5 meters times by 0.5 meters,
giving us a total area of 0.25 meters squared
for each quadrat.
As we counted the clover flowers in 10 quadrats,
the total area of all the quadrats
is 0.25 meters squared times 10, which is 2.5 meters squared.
We now have all the data to put into our equation.
So 63 times by 400 meters squared
divided by 2.5 meters squared equals 10,080 clover flowers
in our 400 meter squared study area.
The results you obtain depend on the unique area
you will be studying.
If you have time, you may want to estimate
the population of another plant within your area of study
for comparison.