Requirement of energy for metabolic processes
The first reaction is catabolism. It does require some energy input in the beginning ("energy investment" of glycolysis) but ultimately leads to net energy release through "energy payoff" of glycolysis, citric acid cycle, and finally electron transport chain and oxidative phosphorylation.

The final result is oxidation of glucose, and reduction of oxygen.. At various points, electrons transfer to NAD+ and FAD. Then, the reduced forms of these 2 electron carriers (NADH &amp; FADH2) go to the electron transport chain, where electrons transfer to oxygen at the end (reduction of oxygen). Meanwhile, protons were pumped into the intermembrane space to create the proton gradient that drives ATP synthesis.

The second reaction is anabolism. The Calvin Cycle requires energy from ATP and NADPH to create the necessary bonds to build up sugars.

In terms of bioenergetics, degradation of a molecule is exergonic. This is favorable if you think about the second law of thermodynamics: there is more entropy when there are multiple, separate sub-units, while there is more order when one molecule made up of those sub-units. Synthesis of a molecule is endergonic (requiring energy). It IS favorable in the sense that we get sugar to eat and burn in the future.

In summary:


Breaking down a molecule = catabolism = release energy from chemical bonds
Building up a molecule = anabolism = absorb energy to FORM chemical bonds (think of the resources needed to construct a new building)


Note my answer leaves out specific details about the processes, but I hope this is basic enough to answer your question!

Source: Lehninger Principles of Biology, David Nelson &amp; Michael Cox