Chapter 28, Problem 7A

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 7A

Correct answer:

The correct answer is option (C) jaws.

Explanation of Solution

Explanation/justification for the correct answer:

Option (C) jaws. Most of the fishes have jaws. The fish catch the prey with their teeth and instantly kill them with strong jaw muscles. Jaws also provide a biting defense against predators. So, the correct answer is option (C).

Explanation for incorrect answer:

Option (A) paired fins. Paired fins are paddle-shaped structure that is used for balance, steering, and propulsion. So, this is an incorrect option.

Option (B) placoid scales. The placoid scales are found in shark scales. These are made of tooth like materials and are rough and heavy. Scales reduce friction with the water and allow the fish to move easily. So, this is an incorrect answer.

Option (D) 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 answer.