Question

Please explain why these choices are correct

* An organism that is mixotrophic can switch between being autotrophic and heterotrophic depending on its environment: False (Why is this false?)

* In photosynthesis, light energy is conserved as chemical energy.: True (I don't understand how this is true since light energy is converted to chemical energy, not conserved)

* Chemotrophic denitrifying bacteria can couple the oxidation of Fe2+ to the reduction of NO3- to N2 under anoxic conditions: True (Shouldn't it be under aerobic condition?)

Answer 1

*Mixotrophs are organisms that can be autotrophs and heterotrophs at the same time. It does not depend upon the environment to become specific. In the given sentence it is said that mixotrophs can switch between autotrophic and heterotrophic depending on its environment

*During photosynthesis, the light energy, which is sunlight, is converted into chemical energy in the form of ATP and NADPH through a series of biochemical reactions. Both ATP and NADPH are energy-producing molecules. This ATP and NADPH are stored in plants for further uses. So here we can say that in a way the light energy that falls on the leaves is converted and also at the same time conserved in plants.

*Basically denitrifying bacterias are anaerobic organisms. They require a very low oxygen concentration, less than 10%. Also reduction of NO3- to N2 occurs only in anaerobic conditions. This is because oxygen is a better electron acceptor than nitrogen. Thus terminal electron acceptor will be NO3- instead of oxygen. Here the electron comes from the oxidation of Fe2+ to Fe3+, which releases an electron. Thus in the absence of oxygen, the electron released will be taken by NO3- instead of oxygen. Because of all these reasons, the reactions occur in anoxic conditions