While hiking after school one day, you came across several plants that you weren’t familiar with. You took a leaf sample from each, and went back to the lab and did a stomata density count. Using a 40x objective with a field diameter of 0.5 mm, you got the following counts: Sample 1: you counted 8 stomata Sample 2: you counted 42 stomata Calculate the stomata density for each of your samples
Sample 1: 41 stomata per mm^2
Sample 2: 214 stomata per mm^2
The density of the stomata on a leaf is the number of stomata on a leaf per leaf area. It is measured per unit area i.e. per square mm (mm^2).
The unknown leaf was taken to the laboratory and a microscope with a field diameter of 0.5mm was used. Since the density is measured per unit area, we need to find the area of the field of view.
To find the area, we use πr^2, which π= 3.142 and r= radius (diameter/2 i.e. 0.5/2 = 0.25mm)
Hence, using Area = πr^2
= 3.142 × 0.25 × 0.25
Therefore, the area of the field of view is 0.196mm^2
The stomata count for the samples are:
Sample 1: 8 counts
Sample 2: 42 counts
Area of field of view on microscope= 0.196mm^2
Therefore, the stomatal density of each sample of leaf in a single count is calculated by saying;
Number of stomata × 1/area
Sample 1= 8 × 1/0.196
= 8 ÷ 0.196
Approximately, we have 41 stomata per square mm as the density for sample 1
For sample 2: 42 × 1/0.196
= 42 ÷ 0.196
= 214. 2857
Approximately, we have 214 stomata per square mm as the density for sample 2.
from almost the creation of the first true maps of the earth, people started seeing how continents would be able to fit together. in particular, people noticed that south america fits almost exactly into africa.
you should be aware that while world maps were around early in the 1600’s and better defined by the end of the 1700’s, those maps were not ‘public’ but were treated as state secrets. and so it was not till much later that the broader ‘science’ community had access to good quality and accurate world maps.
get the whole story here…
it is now known that most of the major continental masses can be fit together in a jigsaw process. in fact we now know that the continents were indeed once all joined together as one land mass – the supercontinent of pangaea.
if you look at most world maps you will ponder how this is evidence, as the continents really don’t appear to ‘fit’ together very well. what you need to understand is that the vast majority of maps are drawn using a map projection that has the north and south poles (which are points) are a line the width of the map at the top and bottom. this means that the map distorts the true shape of the earth’s land and oceans as you love closer to the poles. some other map projections distort less, but have the map shape looking like segments of an orange. see here for a range of map projections. check out the way greenland changes size in each!
what is more remarkable, is the next piece of evidence when added to the shape of continents.
location of mountains and fossils
what is remarkable, when you reassemble all the continents together, the ancient mountain ranges (many now eroded to their cores) and the location of rock types and fossils all match up.