A physical change is... —
1. when a substance changes its appearance or form, but not its identity.

2. when a substance changes into a new substance.

3. when a substance catches on fire.

4. when a substance reacts with another substance.

1. when a substance changes its appearance or form, but not its identity.

Explanation:

It basically applies makeup but you're still same person

thymine. in rna, thymine is replace by uracil

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.