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 unit of the living organisms. Basically, all the cells that exist on the Earth can be categorized into two different kinds, namely prokaryotes and eukaryotes.

Answer to Problem 1SQ

Correct answer:

Prokaryotic cells lack the double membrane structures, whereas eukaryotic cells possess double membrane–bound organelles such as the nucleus. Therefore, option b. is correct.

Explanation of Solution

Reasons for the correct statement:

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

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

Option b. is given as “a nucleus”.

The statement, “the nucleus is the structure 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”.

A cell wall is a structure surrounding the cell and it provides the structural support to a cell. It is present in most of the prokaryotes and in some eukaryotes, including algae, fungi, and plants. Hence, it is a wrong answer.

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

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

Option d. is given as “ribosomes”.

Ribosomes are the structures that are composed of ribonucleic acid (RNA) and proteins. Ribosomes play role in the synthesis of proteins. Prokaryotes have 70S (sedimentation coefficient) ribosomes, whereas eukaryotes have 80S ribosomes. Hence, it is a wrong answer.

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

Conclusion

The nucleus is present only in the eukaryotic cells and this double membrane–bound organelle is absent in prokaryotic cells. Thus, the presence of a nucleus can be utilized as a distinguishing feature to determine whether the unknown cell viewed under a microscope is prokaryotic or eukaryotic.