
Concept explainers
The oldest fossil eukaryote that can be resolved taxonomically is of
- A. a red alga that lived 1.2 billion years ago.
- B. a green alga that lived 635 million years ago.
- C. a
fungus that lived 2 billion years ago. - D. an Ediacaran that lived 550 million years ago.

Introduction:
Eukaryotic organisms need oxygen to survive. They are found in higher amounts in the atmosphere and are multicellular organisms.
Answer to Problem 1TYU
Correct answer:
The oldest fossil eukaryotic alga is a red alga that lived 1.2 billion years ago. Therefore, option (A) is correct.
Explanation of Solution
Reason for the correct statement:
The red alga lived 1.2 billion years ago and required oxygen for survival. This evidence suggests that oxygen was present to support the survival of the red alga.
Option (A) is given as “a red alga that lived 1.2 billion years ago”.
The oldest fossil eukaryote was determined taxonomically as a red alga, which lived 1.2 billion years ago. Hence, it is the right answer.
Hence, option (A) is correct.
Reasons for the incorrect statements:
Option (B) is given as “a green alga that lived 635 million years ago”.
A green alga belongs to the group of cyanobacteria, which is the group of prokaryotes and not eukaryotes. Hence, it is the wrong answer.
Option (C) is given as “a fungus that lived 2 billion years ago”.
A fungus that lived 2 billion years ago belongs to a different taxonomic group and was not an eukaryotic organism. Hence, it is the wrong answer.
Option (D) is given as “an Ediacaran that lived 550 million years ago”.
In the Ediacaran period, different shapes and sizes of organisms lived, but at that time there was no evidence of the presence of eukaryotes. Hence, it is the wrong answer.
Hence, options (B), (C), and (D) are incorrect.
The red alga is the oldest eukaryotic alga reported by fossil records. This eukaryotic organism requires oxygen to survive and they lived 1.2 billion years ago.
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