required practical - sampling organisms

To estimate the total population of daisies in a field - using random sampling quadrats come in a rang of different sizes. We are going to use one that is 0.5 by 0.5 m

1) place two tape measures at right angles , these tape measure should be 20m in length.

2) then need to two bags and each bag contains the numbers 1 to 20.

3) In the practical students work in groups of three

4) the first student removes a number from the bag. Imagine the number is 8 , the student now moves to the 8 m point on one of the tape measures.

5) the second student now selects a number from their bag and moves to that point on the other tape measure.

6) imagine they’ve got the number 12 , now the third student places a quadrat on the ground at the 8m by 12m point like this,

7) the students now record the number of daises in the first quadrat.

8) the students now return their numbers back to the bags and then repeat the process nine more times for a total of ten samples.

9) imagine the students counted three hundred daises across the ten quadrats we now need to estimate the total population of daises in the whole field. To do that we use this equation

Total population size = total area / area sampled x number of organisms of that species counted in sample

In this case its: total population size = 400m² / area sampled x number of organisms of that species counted in sample.

This gives us an area sampled of 0.5 × 0.5 × 10 which is 2.5 m²

So total population size = 48,000

we also need to measure the effect of a factor on the distribution of a species in this required practical.

In this case, we are going to look at the effect of light intensity on the distribution of daises.

another field of daises but this field contains a large tree in this case we need to use a transect line to see how the number of daises changes from the tree outwards.

To do this we place a tape measure at the tree then use a quadrat to count the number of daises at the start of the transect, also need to record the light intensity at this point - to do this we can use a light meter or use an app- now move the quadrat 1m down the tape measure and repeat the measurements. And we continue doing this all the way down the tape measure. It is possible we will see a greater number of daises as we move further from the tree that is because under the tree there will be a lower light intensity. Remember plants need light in order to photosynthesise, however u also need to bear in mind that a tree will absorb a lot of water and minerals from the soil. So it might be that light intensity is not the only abiotic factor that is affecting the number of daises.