What is the source of the carbon that make up our biomolecules?

Answer 1

Most of it is a part of the closed carbon cycle, in which CO2 taken up by plants enters the food chain, and after death plant and animal bodies gradually break down biologically and chemically, yielding CO2 again.
A tiny amount of biocarbon is carbon-14, an isotope produced by fission of atmospheric nitrogen due to cosmic ray collisions (see ref.). The C-14 combines with atmospheric oxygen to form CO2, and enters the food chain. C-14 spontaneously reverts to "normal" carbon C-12 with a half-life of about 5700 years. There is an almost constant proportion of C-14 to C-12 in the CO2 and in living biological material. (This is the proportion at which the production and decay rates of C-14 are equal.) When an organism dies, it no longer takes in carbon, so its C-14/C-12 ratio gradually declines. Thus by measuring this ratio in an ancient biological sample, radiocarbon dating can establish its age over a span of about 100,000 years.

Answer 2

Source: carbon in the air (same place trees get it)

then into plants which we eat

or

Then into animal bodies and we cook and eat the animals

Answer 3

Plants absorb carbon dioxide and produce oxygen.
Animals eat the plants with the carbon and digest it.
We eat plants or animals, using their generous supply of carbon molecules.
Our body metabolizes these and convert to molecules we use.

Answer 4

The ultimate source? Nuclear reactions in stars billions of years ago.

Answer 5

The CO2 in the air, and the C's from the food you eat! Both!

Answer 6

most of the things you eat have carbon in them.

Answer 7

Ultimately CO2 via photosynthesis.....