Chapter 6, Problem 1Q

Which descriptors are likely to have applied to the earliest microbes on the planet?

1. a. chemoautotrophic
2. b. thermophilic
3. c. chemoheterotrophic
4. d. two of the above

Summary Introduction

Introduction:

The different factors that affect the existence of various life forms present on the Earth are such as, temperature, oxygen, pH, osmotic pressure, radiations. Several other factors also affected the earliest life form that existed on the planet Earth.

Answer to Problem 1Q

Correct answer:

The descriptors most likely to have applied to the earliest microbes on the planet were chemoautotrophic and thermophilic. Hence, the option (d) is correct.

Option (d) is given as “two of the above”.

Explanation of Solution

Justify reason for the correct statement:

The first organisms required energy for their survival and in order to meet the requirement they had raw chemicals as substrate and no ready-made energy source, hence, they converted these chemicals into food and generated energy.

The temperature of the Earth was high during the initial days of development, and only organisms that could have survived in that temperature where thermophiles. Also the earliest fossils obtained are that of cyanobacteria, which support the existence of thermophiles as the earliest life forms.

Hence, option (d) is correct.

Justify reasons for the incorrect statements:

Option (a) is given as “chemoautotrophic”.

It is true that the earliest life-form that existed was chemoautotrophic but it is not the only correct answer as these were also thermophilic in nature. Hence, it is a wrong answer.

Option (b) is given as “thermophilic”.

It is true that the earliest life-form that existed was thermophilic but it is not the only correct answer as these were also chemoautotrophic in nature. Hence, it is a wrong answer.

Option (c) is given as “chemoheterotrophic”

The earliest cells had only raw chemicals and not the prepared food they converted these chemical molecules to generate food. Hence, it is a wrong answer.

Hence, options (a), (b), and (c) are incorrect.

Conclusion

The earliest life form that originated on Earth were chemoautotrophic and thermophilic as the early Earth condition only supported this type of physiology.