안녕하세요!

오! very good question!

you and I are essentially talking about the same thing, but the difference is in the scale of what we mean.

Chemistry is the study of reactions, therefore when we talk about reactions

we pay attention to individual energy steps as the reaction occurs.

When you say that breaking bonds is an endothermic process, what you are referring to is "activation energy" 

the energy required to break existing bonds in order for any reaction (exo or endothermic) to occur.

Whether something is described as endothermic or exothermic relies on the final end state of the product

if the overall energy level of the product is lower than the reactants, we say that the difference in energy has been released to the outside

therefore, energy has been released, aka "exothermic", 

and vice versa for "endothermic"

In biology, we are much more focused on this overall outcome of chemical reactions, not the individual steps.

So while the fact about activation energy still applies (remember the lectures about enzymes?),

we focus more on the final outcome, whether there is a net release or absorption of energy.

When two reactants react together to form a single product in biology

(such as binding amino acids together to form proteins, or binding phosphate groups to ADP)

more often than not, it is an endothermic reaction, 

meaning that there needs to be a "net input of energy from the outside" for the anabolic reaction to occur.

This "input of energy from the outside" can come from the breakdown of carbon bonds in carbohydrates,

(such as breaking glucose into 2x pyruvic acids)

where the energy released from the exothermic reaction of glycolysis can be harnessed

to complete the endothermic reaction of ATP formation.

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