Chapter 19, Problem 27A

Summary Introduction

Introduction :

The given figure is of Euglena gracilis . They are single-celled algae of the genus Euglena. They are usually found in freshwater and have characteristics of both animals and plants. They have secondary chloroplasts for the process of photosynthesis which is a characteristic of plants, but they lack a cell wall which is a characteristic of animals. They are mixotrophs that mean they can feed themselves by the process of photosynthesis or by phagocytosis.

Answer to Problem 27A

Correct answer :

The correct answer is option (C) flagella.

Explanation of Solution

Explanation/justification for the correct answer :

Option (C) flagella. Euglena has an elongated cell body that lacks the cell wall. It is a unicellular organism and has one nucleus and a thin plasma membrane that encloses the cell organelles and the cytoplasm. Euglena possesses emergent long flagella that are used for the movement towards the food or light. The surface of flagella is covered by the very fine filaments known as mastigonemes. Flagella are found in euglena mainly for movement (swimming). So, the correct answer is option (C).

Explanation for incorrect answer :

Option (A) cilia. Cilia are tiny hair-like structures found in different types of organisms and cells. The organisms that contain cilia are known as ciliates. Cilia are mainly involved in the process of locomotion but they also participate in mechanoreception. Euglena don’t have cilia because they have flagella for the locomotion. So, this is an incorrect option.

Option (B) contractile vacuole. The contractile vacuole is a star-like structure found towards the posterior side of the euglenoid cell. Contractile vacuole helps the euglena to remove the excess water from their cell body. If euglena doesn’t have the contractile vacuole then they could take a large quantity of water in their cell body and would burst. So, this is an incorrect answer.

Option (D) pseudopod. Pseudopods are found filled with the cytoplasm. They contain actin filaments, intermediate filaments, and microtubules. They are used for the movement and ingestion. Pseudopods are usually found in amoebas but not in euglena. So, option (D) is also incorrect.