Science · Class 9 · Diversity in Living Organisms · Term 3

Phylum Chordata: Vertebrates (Pisces and Amphibia)

Begin your journey into the world of vertebrates, animals with a backbone. Explore the adaptations of the first two classes: Pisces (fishes) for aquatic life and Amphibia for their dual life in water and on land.

TL;DR:Let's dive into the world of animals with backbones, starting with the masters of the water and the pioneers of land.

• CBSE Learning Outcomes
• NCERT Class 9 Science: Chapter 7 - Diversity in Living Organisms

About This Topic

This topic introduces students to the Phylum Chordata, marking a significant transition from the study of invertebrates to vertebrates within the Class 9 curriculum, typically under the chapter 'Diversity in Living Organisms'. As per the NCERT framework, this section is crucial for building a foundational understanding of animal evolution and complexity. The focus on Pisces and Amphibia allows for a comparative study of the earliest vertebrate classes, highlighting the pivotal evolutionary step of moving from aquatic to terrestrial life. Teachers should contextualise this by emphasising the development of key features like the vertebral column, which replaced the notochord in most vertebrates, and the evolution of limbs and lungs. The comparison between the two-chambered heart of fish and the three-chambered heart of amphibians serves as an excellent entry point into the complexities of circulatory systems, a concept that will be elaborated upon in higher classes.

Key Questions

1. Identify the three fundamental characteristics of all chordates.
2. Compare the respiratory and circulatory systems of Pisces and Amphibia.
3. Explain the adaptations that allow amphibians to live both on land and in water.

Learning Objectives

• List the three fundamental characteristics of Phylum Chordata.
• Differentiate between Pisces and Amphibia based on their habitat, respiration, and circulatory systems.
• Describe specific adaptations of fish, such as gills, fins, and a streamlined body, for an aquatic life.
• Explain the adaptations of amphibians, like moist skin and limbs, that enable their dual life in water and on land.
• Provide at least two examples each for cartilaginous fish, bony fish, and amphibians.

Key Vocabulary

Notochord	A flexible, rod-shaped structure found in the embryonic stage of all chordates, providing skeletal support.
Vertebral Column	The backbone or spine, composed of a series of bones called vertebrae, that protects the spinal cord in vertebrates.
Poikilothermic	An organism whose internal temperature varies considerably, often matching the temperature of the immediate environment. Also known as cold-blooded.
Gills	The respiratory organ of most aquatic animals that allows them to breathe by extracting dissolved oxygen from water.
Metamorphosis	A profound transformation from a larval stage to an adult stage, as seen in amphibians like frogs (tadpole to adult frog).
Cutaneous Respiration	A form of respiration in which gas exchange occurs across the skin rather than through lungs or gills.

Watch Out for These Misconceptions

Common Misconception

All animals with fins that live in water are fish.

What to Teach Instead

While most fish have fins and live in water, some aquatic animals like whales and dolphins are mammals. They breathe air using lungs, not gills, and give birth to live young.

Common Misconception

Amphibians can breathe only through lungs, just like us.

What to Teach Instead

Amphibians have a unique ability to breathe through multiple surfaces. As adults, they use simple lungs on land, but they can also absorb oxygen directly through their moist skin, which is called cutaneous respiration. Their larvae, tadpoles, breathe through gills.

Common Misconception

The notochord and the vertebral column (backbone) are the same thing.

What to Teach Instead

The notochord is a flexible rod-like structure found in all chordates at some stage of their life. In vertebrates, this notochord is replaced by a bony or cartilaginous vertebral column during embryonic development, which provides better support.

Active Learning Ideas

Simulation Game

Comparative Chart Creation

Students work in small groups to create a large chart comparing Pisces and Amphibia across various features like habitat, respiration, circulation (heart chambers), reproduction, and body covering. They can use textbooks and diagrams to fill in the details.

40 min·Small Groups

Simulation Game

Observe and Infer

Using high-quality diagrams, models, or videos of a fish (like Rohu) and a frog, students identify and label key adaptive features. They then write a short paragraph inferring how each feature helps the animal survive in its environment.

30 min·Pairs

Simulation Game

Metamorphosis Storyboard

Individually, students create a simple six-panel storyboard illustrating the life cycle of a frog. They must label each stage (egg, tadpole, froglet, adult) and describe the changes in habitat, diet, and respiration.

25 min·Individual

Real-World Connections

• Fisheries and Aquaculture: Understanding fish biology is fundamental to India's large fishing industry, which is a major source of food and employment.
• Environmental Indicators: Amphibians are very sensitive to pollution and changes in their environment. Their population health is often used by scientists as an indicator of an ecosystem's health.
• Evolutionary Studies: Studying the transition from fish to amphibians helps us understand a major event in evolution: how life moved from water to land, which eventually led to the evolution of reptiles, birds, and mammals.
• Conservation in India: Knowledge of these groups is vital for conservation efforts for species like the Gharial (a fish-eating crocodile), the Ganges River Dolphin, and the unique Purple Frog of the Western Ghats.
• Medical Research: The regenerative abilities of some amphibians, like salamanders that can regrow limbs, are studied by scientists to understand tissue regeneration.

Assessment Ideas

Discussion Prompt

Conduct a 'Think-Pair-Share' where students are asked to identify one key adaptation of a fish and one of a frog, then discuss with a partner before sharing with the class.

Peer Assessment

Assign a short project where students create a detailed, labelled diagram of either a fish or a frog, annotating at least five adaptations and explaining their functions.

Quick Check

Provide students with a checklist of the learning objectives and ask them to rate their understanding of each concept on a scale of 1 to 3 (Not confident, Somewhat confident, Very confident).

Frequently Asked Questions

Why are frogs and other amphibians often found near water bodies?

Amphibians need to be near water for two main reasons. First, they lay their eggs in water as the eggs lack a protective shell and would dry out on land. Second, their skin must remain moist to help them breathe (cutaneous respiration), so they need a damp environment.

What is the difference between a cold-blooded and a warm-blooded animal?

Cold-blooded animals, or poikilotherms, like fish and amphibians, cannot regulate their internal body temperature. Their body temperature changes with the surrounding environment. Warm-blooded animals, like birds and mammals, can maintain a constant internal body temperature regardless of the outside temperature.

Are all chordates vertebrates?

No, not all chordates are vertebrates. Vertebrates (subphylum Vertebrata) are chordates where the notochord is replaced by a vertebral column. There are also simpler chordates, called protochordates (like Amphioxus), which have a notochord throughout their life but do not develop a backbone.