Chapter 4, Problem 1SQ

You look into a microscope and view an unknown cell. What might you see that would tell you whether the cell is prokaryotic or eukaryotic?

1. a. a rigid cell wall
2. b. a nucleus
3. c. a plasma membrane
4. d. ribosomes

Summary Introduction

Introduction:

The cell can be defined as the functional, structural and building block of the living organisms. Basically, all the cells existing on the earth can be categorized into two different kinds, namely- prokaryotes and eukaryotes.

Answer to Problem 1SQ

Correct answer: The prokaryotic cells lack the double membrane structure including the nucleus. The eukaryotic cells have double membrane-bound organelles. Therefore, option b. is correct.

Explanation of Solution

Reasons for the correct statement:

All the cells have the DNA (deoxyribonucleic acid) as the genetic material. The DNA in the prokaryotic cells is confined to a small region known as the nucleoid. The nucleoid is not membrane-bound.

The eukaryotes have double membrane-bound structures including the nucleus, whereas the prokaryotes lack any double membrane-bound structure. The membrane surrounding the nucleus is known as the nuclear membrane. Majority of the genetic material is confined inside the nucleus.

Option b. is given as "a nucleus".

As, “the nucleus is the only structure in the cells which is present in the eukaryotes and not in the prokaryotes”, is the right answer.

Hence, option b. is correct.

Reasons for the incorrect statements:

Option a. is given as “a rigid cell wall”.

The cell wall is the structure which surrounds some of the cells and provides structural support to the cell. It is present in most of the prokaryotes and some eukaryotes including algae, fungi, and plants. So, it is a wrong answer.

Option c. is given as “a plasma membrane”.

The plasma membrane is the selectively permeable structure, which separates the exterior of the cell from the interior. The prokaryotes and eukaryotes have the plasma membrane. So, it is a wrong answer.

Option d. is given as “ribosomes”.

The ribosomes are the structures comprised of RNA (ribonucleic acid) and proteins. They help in the synthesis of proteins. The prokaryotes have 70S (sedimentation coefficient) ribosomes, whereas the eukaryotes have 80S ribosomes. So, it is a wrong answer.

Hence, the options a, c, and d are incorrect.

Conclusion

The nucleus is present only in the eukaryotic cells; the prokaryotic cells lack any double-membrane-bound organelle. So, it is the distinguishing feature of the prokaryotic and eukaryotic cell.