The mechanisms of reproductive isolation prevent the reproduction of two individuals from different species. The prezygotic mechanisms disrupt the stages of reproduction before the forming of the zygote or prevent the mating at the start, and the postzygotic mechanisms affect the stages of reproduction after the forming of the zygote.
So, the first and the third example (the urchins and the grasshoppers) show the prezygotic mechanism, as the two individuals are not able to mate or form a zygote.
The second and the fourth example ( zonkey and the death of a zygote) show the working of the postzygotic mechanisms, as the zygote is formed, but it seems to be inviable, and the zonkeys are sterile, preventing the individual to reproduce.
Some individuals are more likely to survive and reproduce than others because they are fit and easily adapting. This idea is called 'survival of the fittest'.
1st the periostneum which is the outside of the bone and a thin but dense layer that has nerves and blood vessels
2nd compact bone. It is very smooth and very hard
3rd and lastly Cancellous, this looks a little like a sponge but much harder.
Answer: sand particles, small pebbles and weathered rock
Sedimentary rocks are the rocks that are formed by various physical, chemical, and biological processes. It is formed by the withered remains of the other rocks, biological wastes liberated by the living beings. These rocks are formed when the fine sand particles, stones, small pebbles and biological residues of living beings becomes cluster and attains compaction due to the effect of exerted pressure and temperature.
