Which part of a seed acts as the food source for the seed as it grows underground? roots
seed coat
embryo
endosperm

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".