The calvin cycle and the krebs cycle are referred to as cycles of chemical reactions because they occur inside organelles. start over continually. are part of the carbon cycle. allow energy to flow in ecosystems.

b. the carbon cycle ensures living things have a source of hydrogen

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.