Answer:
1. Before: carbon dioxide After: Oxygen
2. Oxygen
3. Chloroplast
It's the concentration of sense organs, nervous control, etc., at the anterior end of the body, forming a head and brain, both during evolution and in the course of an embryo's development.
The body needs calcium and phosphorous because phosphorus works with calcium to help build bones
Isotopes
Atoms of the same element; number of protons remain the same, number of neutrons vary. Chemical properties remain the same. Atomic mass varies.
Na sodium with 11 neutrons = atomic mass of 22
With 22 neutrons the mass is 23.
Both have 11 protons in the nucleus.
