Chapter 23, Problem 1E

Summary Introduction

Introduction:

Pathogens are divided into five classes: bacteria, fungi, parasites, viruses and protozoa. Pathogens are the disease causing organisms and may invade human body through different pathways. Some are unicellular and some are multicellular based on complexity of their structure. Unicellular organisms are single celled organisms unlike multicellular organisms which have more than one cell. Unicellular are often called as prokaryotes.

Answer to Problem 1E

Solution:

The correct answer is option (b) bacteria.

Explanation of Solution

Explanation/justification for the correct answer:

Option (b) Bacteria. Bacteria are microscopically single celled organism with very simple cell structure. They are the unicellular prokaryotes which lack neatly packed DNA within a nucleus unlike prokaryotes; instead the DNA material is free floating. They also membrane bound organelles.

Explanation for incorrect answer:

Option (a) Virus. The viruses are composed of DNA/RNA fragments encapsulated within protein material. It has no organelles like any other cells and also lacks the capability of dividing.

Option (c) Fungi. The fungi are a member of eukaryotic group which are multicellular organisms. They have chitin in their cell wall that makes them different from other classes like plant or animal.

Option (d) Parasite. Parasites are the organisms that live in another organism called its host. They use host’s resources to live, generally by causing harm to its host. They may be microorganisms or may reach over 30 meters in length.

Option (e) None of these. Bacteria are the unicellular organisms among above options, hence this cannot be a correct option.

Conclusion

Bacteria are the unicellular organisms, made up of only one cell and having no defined organelles. Hence, the correct answer is option (b) Bacteria.