The world contains a variety of environments, which are mainly created by
a.
natural disasters, like volcanic explosions.
b.
a wide diversity of physical conditions.
c.
similar species of plants and animals.
d.
natural selection and selective breeding.

The microscope is an instrument used to see the smaller objects clearly. The microscope has different adjustment of lens  and can enlarge the image upto 100X.

The green cells has 4X objective and covers  1/8th of the width. The cell will approximately has the diameter of around 500-600 micrometers. This will accounts for its variability and the inaccuracies. The cells has size more than this diameter cannot be seen by the microscope.