Chapter 28, Problem 5A

Summary Introduction

Introduction:

Fishes live in aquatic habitats like lakes, seas, rivers, ponds, etc. Some fishes live in complete darkness at the bottom of the deep ocean whereas others live in the freezing water of the Polar Regions and have special proteins in their blood to keep the blood from freezing. There are about 24,600 species of living fishes found.

Answer to Problem 5A

Correct answer:

The correct answer is option (D) pelvic fins.

Explanation of Solution

Explanation/justification for the correct answer:

Option (D) pelvic fins. The given structure labelled B is called pelvic fins. These fins are located on the ventral surface of fish. These fins help the fish to balance and keep it in level. These fins also reduce the chance of rolling to the side and allow for better steering during swimming. So, the correct answer is option (D).

Explanation for incorrect answer:

Option (A) gills. The fish's gills absorb oxygen from the water and help the fish breathe. The fish get oxygen as the water that reaches their mouth passes through their gills. Gills are made up of thin filaments lined with a tightly folded, plate like lamellae. So, this is an incorrect option.

Option (B) swim bladder. The swim bladder is an internal organ. It is filled up with gas. The swim bladder regulates the buoyancy of many bony fishes. So, this is an incorrect answer.

Option (C) ventricle. Ventricle is a chamber of heart in fish. The ventricle is responsible for the generation of the blood pressure. So, this is an incorrect answer.