Chapter 14, Problem 1TQ

Summary Introduction

An organism that contains only one cell is known as unicellular organism. Unicellular organism falls under two categories and they are prokaryote and eukaryote. Some of the unicellular organisms are seen in large colonies. For example, algae, bacteria, amoebas, and planktons. These single-celled organisms can be seen using a microscope.

Answer to Problem 1TQ

The single-celled organisms on earth first appeared about 3.7 billion years ago as evidenced by the fossil record.

Therefore, option (c) is correct. 

Explanation of Solution

Justify the reasons for the correct statement:

The solar system and earth is formed 4.6 billion years ago. The structures that are similar to cell have been found in sedimentary rocks (as layered mounds) known as stromatolites. They were formed 3.7 billion years ago. The DNA analysis supports a concept that life appeared on earth during this era.

Option (c) is given as, “3.7 billion years ago”.

Hence, the option (c) is correct.

Justify the reasons for the incorrect statements:

Option (a) is given as, “3,700 years ago”. 

According to fossil record and DNA analysis, single-celled organisms on earth first appeared about 3.7 billion years ago and not 3700 years ago. Hence, it is a wrong answer.

Option (b) is given as, “3.7 million years ago”. 

According to fossil record and DNA analysis, single-celled organisms on earth first appeared about 3.7 billion years ago and not 3.7 million years ago. Hence, it is a wrong answer.

Option (d) is given as, “We have no idea when the first life on earth appeared”. 

According to the fossil record and DNA analysis, we have an idea that first life on earth has occurred about 3.7 billion years ago. Hence, it is a wrong answer.

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

Conclusion

The first life or single-celled organism on Earth probably evolved 3.7 million years ago. This data is given based on evidences.