Why Do Living things need Energy?
Living things need energy for carrying out many activities that are important for the life. There are various biochemical reactions going on in our body which need energy. Some of the reactions directly need the energy components called ATP or NADH. Some reactions make use of enzymes that catalyze the reaction which are again energized in order to perform the catalysis. The metabolic reactions occur in the body to bring the growth and repair of the tissues. As growth and repair of the cells and tissues are very important and required by the body, the energy required to make these processes to occur also needs to be used.
The other biological processes that require energy are active transport of molecules across the cell membrane. The transport of nutrients, minerals and other necessary ions that are involved in many biochemical processes occur in the tissues. This active transport of molecules and ions makes use of energy to move them against the diffusion gradient. Passive transport of molecules occurs normally without the expense of energy and follows the diffusion gradient while the active transport uses the energy to balance the cell interior effectively.
The other biological process that involves energy is the movement of molecules from cytoplasm to the nucleus or from nucleus into cytoplasm. For the cells to divide, the chromosomes also replicate and the cells divide by generating a new cell membrane between the two cells. Energy is required in order to facilitate the chromosomes to move and the cells to divide. Apart from the movement of molecules inside the cell as well as from one cell to the other, the movement of the organism also requires energy while in plants it is not necessary as they are sedentary.
Warm blooded animals make use of energy to control the temperature in their body. Some organisms like electric eels make use of energy to generate light from their body parts. In all the above mentioned ways, energy is used up by the living organisms.