Question

life requires energy to exist, but is not able to produce energy. explain this apparent contradiction

Answer 1

Life requires energy in order to circulate water and also to continue all life processes. Living organisms utilize energy for all anabolic processes. Basic processes of metabolism, forming cell and tissues in multicellular organism, reproduction all require inputs of energy. ATP is the major energy rich molecule that provides this input of energy in microorganism, plants and animals including humans. Hydrolysis of ATP releases energy that can be used for these metabolic purposes. However, although ATP is in general said to be a source of energy, it is only a storage form of energy. It stores the energy in the high energy phosphate bond is generated when inorganic phosphate binds to ADP.

Plants produce glucose from the carbon dioxide and water in presence of light energy it harvests from the sunlight. Thus, sunlight is the source of energy for plants, which is then stored in glucose, a high energy molecule. This energy is transferred to ATP when glucose is broken down during cellular respiration. Plants merely convert solar energy to the chemical form of energy, in form of glucose. Sunlight contains UV rays, visible light and infra-red light. Ultraviolet light and longer wavelength infra-red light are absorbed by ozone layer surrounding the earth. Half of visible light is absorbed while half is reflected back. This visible light is used by plants for photosynthesis.

Animals obtain energy when they consume carbohydrates and fats from diet. Proteins are low sources of energy. Carbohydrates are primary sources of energy which are broken down in digestive tract and metabolized to release energy. Fats are also rich source of energy which his released upon digestion and beta oxidation pathways. In case of microorganism, energy is produced from either organic or inorganic compounds, well of which have their energy source as sunlight. Thus, ultimately, sunlight is the main source of energy for all lives present on earth. This energy is stored in different compounds and then can be harvested by living organism for use for its metabolic pathways and other requirements. Energy is harvested from energy rich molecules by living organism and then used for their bioprocesses. Thus, life can utilized energy but does not produce energy. It just converts one form of energy to another form of energy that can be utilized by it. Without energy, life cannot exist as all metabolic and anabolic processes will cease to exist. Anabolic processes in living organism are non-spontaneous chemical reactions, that require energy to take place. They have positive Gibbs free energy values and thus, require input of energy to occur. If no energy is present, there chemical reactions will take place and hence, life will cease to exist.