Which of the following contributes most directly to the hardness of bones? 1) hydroxyapatite 2) periosteum 3) articular cartilage 4) osteoid

The correct option is number 1. Hydroxyapatite contributes most directly to the hardness of bones

Explanation:

Hydroxyapatite can be described as a naturally occurring biological molecule of high importance. It provides hardness the bones and teeth. Hence, option 1 is correct.

Periosteum can be defined as the outer layer of a bone which functions as an attachment site for the skeletal muscles. Osteoid is a structure that is made before a bone occurs in its mature form. Hence all the other options 2, 3 and 4 are false.

phylogenetic tree is the tree of life or evolution tree. it shows the different branches of evolution. the sequence goes like tissues - coelom - backbone - endoskeleton - segmentation

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.