Investigating species distribution A Level Biology
In this investigation, students are to measure the distribution of dandelions in an area of lawn. There is some advance preparation to be considered here. An area of lawn within the school grounds should be selected prior to the required practical period. Science staff should liase with the school Site Manager and Premises Team well in advance of the practical session to select an appropriate area of lawn that can be used for this required practical.
Weed Killer is required. A 20M x 20M area should suffice which needs to be marked out. The area needs to be away from a path. Half of the lawn needs to be treated with normal commercial weed killer approximately 2 weeks before the investigation.
Subject: Biology | Level: A Level |
You will need:
• Grid quadrat 100 squares
• Tape measure, 30M
• 2 bags each containing the numbers 1 to 10
Method
Students need to generate 10 sets of 2 random numbers which will be used as co-ordinates during the investigation. They can do this using two bags, each containing the numbers 1 to 10. Students select one number from each bag to make a pair of co-ordinates. The co-ordinates generated should be organised into a results table.
Students then approach the marked area that has been treated using the herbicide. They use the co-ordinates to identify the area they are to place the quadrat. One student in the group walks along the bottom edge of the area, using the first number of the co-ordinates to dictate how many metres they are to walk along the edge of the area. The second student in the group walks along the vertical edge of the area, using the second number of the co-ordinates. The two students then walk towards the middle of the area so that they meet in the middle. The third member of the group then places the quadrat on the ground.
Students then count the number of squares which have dandelions present inside the area of the quadrat to obtain a cover ratio. This number is noted in the table.
The process is repeated until the students have results for each of the 10 sets of co-ordinates that they prepared for both the area treated with weed killer and the side which is untreated.
Percentage cover is then calculated using the following equation:
Percentage Cover = Number of Quadrat Squares containing Dandelions x100
Total Number of samples
Technician tips
The more advance notice the better: a lot of advanced planning is required for this required practical. An appropriate area needs to be located, preferably in the school grounds, away from a path. The technical team will need to work closely with the school premises team in order to facilitate the treatment of an area in order for this practical to take place.
