According to OpenStax College. (2013), electron plays important role to generate energy in the form of ATP in oxidative phosphorylation by electron transport chain. In electron transport chain NADH and FADH2 is oxidized and release electrons, the electrons then transported through electron transporters embedded in inner membrane of mitochondria and some of energy released which facilitate proton transport from mitochondria to the intermembrane space. This electrochemical gradient is then used by the ATP synthase to produce ATP by adding a phosphate onto the ADP. So electrons plays profound importance in the transfer of energy in living systems in the form of ATP.
Electrons also plays vital role to generate energy in plant , in photosynthesis sunlight is utilized in photosystem II to extract electron from water molecule and electrons then transferred from one molecule to another molecule to photosystem I and released energy . Some of this energy used to transfer protons across the membrane. In photosystem 1, electrons get excited again by the light energy which reduces NADP+ to NADPH. The breakdown of water molecule and electron transportation through this electron transport chain accumulated proton into the thylakoid lumen. This electrochemical gradient is then used by the ATP synthase to produce ATP by adding a phosphate onto the ADP. So electrons plays profound importance in generation of energy in the form of ATP. The ATP, NADPH and along with the CO2 finally produce Sugar through photosynthesis.
Image: The Light-Dependent Reactions of Photosynthesis," by OpenStax College, Biology (CC BY 4.0)\
Plant stores glucose produced by photosynthesis, Human, animals intake plant’s store food. This food then undergoes cellular metabolism to give energy. In glycolysis one glucose molecule gives 2 molecule of pyruvate and 2 molecule of ATP and 2 molecule of NADH. 2 molecule of pyruvate goes into krebs cycle and produce 8 molecule of NADH, 2 molecule of ATP and 2 molecule of FADH2. Then NADH, FADH2 goes into electron transport chain and each NADH molecule produce 3 ATPs and FADH2 gives 2 ATPs. So ultimately one molecule of Glucose give 38 ATPs by cellular metabolism.
So, we can say that electron plays the most important role in generation of energy both in plant and animal kingdom.