MCQ 11 Mark
Assertion $(A):$ The earliest organisms that appeared on the earth were non$-$green and presumably anaerobes.
Reason $(R):$ The first autotrophic organisms were the chemo-autotrophs that never released oxygen.
Reason $(R):$ The first autotrophic organisms were the chemo-autotrophs that never released oxygen.
- ✓Both $A$ and $R$ are true and $R$ is the correct explanation of $A.$
- BBoth $A$ and $R$ are true but $R$ is not the correct explanation of $A.$
- C$A$ is true but $R$ is false.
- D$A$ is false but $R$ is true.
Answer
View full question & answer→Correct option: A.
Both $A$ and $R$ are true and $R$ is the correct explanation of $A.$
Primitive earth was devoid of oxygen. So, only those organisms that we're able to survive within anaerobic conditions developed. All these were heterotrophic organisms $($taking nutrients from outside$).$ Then after autotrophic organisms were developed that used inorganic sources such as $\ce{H_2S, NH_3, CH_4}$ as the principal sources of energy. These organisms are called chemo$-$autotrophs.
