Problem 220 - Objective Biology for NEET

Question

The following features belong to (1) Exoskeleton include hairs on body, horns and nail. (2) Pinna is present. (3) Heart is four chambered. (4) Warm-blooded (homoiotherm). (5) Thecodont and heterodont teeth. (a) Reptilians (b) Aves (c) Mammals (d) Amphibians

Step-by-Step Solution

Answer

The classification for the given features leads to the group Mammals.

Step 1: Identify Features of Mammals

We'll start by identifying the unique characteristics of mammals. Mammals are characterized by: having an exoskeleton that includes hairs on their body, presence of pinna (external part of the ear), a four-chambered heart, being warm-blooded (homoiotherm), and possession of thecodont (teeth embedded in sockets) and heterodont (different types of teeth for different functions) teeth.

Step 2: Match Characteristics with Mammals

Looking at the given characteristics, all points (1,2,3,4,5) explicitly describe the features of mammals. Therefore, this distinctive combination of characteristics belongs to mammals.

Step 3: Confirm with Other Groups

We can further confirm this by quickly reviewing the characteristics of other groups. Reptilians are cold-blooded and do not possess hairs. Birds (Aves) do have a four-chambered heart and are warm-blooded but lack thecodont teeth and have feathers instead of hairs. Amphibians are cold-blooded and do not have an exoskeleton with hairs, horns, or nails.

Key Concepts

Exoskeleton

In biological terms, an exoskeleton refers to a hard outer structure that provides support and protection. However, in the context of mammals, it is slightly different. Instead of a protective shell like insects, mammals have an exoskeleton that includes

• Hair on the body
• Horns
• Nails

These features serve various functions such as regulation of body temperature, and protection, and can even aid in different sensory functions. For mammals, hair is especially crucial, being part of their characteristic trait that distinguishes them from other animal classes.

Four-chambered heart

The four-chambered heart is a crucial feature of mammals. It consists of two atria and two ventricles.
This structure is highly efficient as it allows complete separation of oxygenated and deoxygenated blood.
Here’s the basic functioning:

• The right atrium receives deoxygenated blood from the body.
• It then sends it to the right ventricle, which pumps it to the lungs for oxygenation.
• The left atrium receives this oxygen-rich blood from the lungs.
• Finally, the left ventricle pumps the oxygenated blood to the rest of the body.

This arrangement is vital for high energy levels and metabolism common in mammals.

Thecodont teeth

Thecodont teeth are teeth that are embedded in sockets in the jawbone.
In mammals, this feature provides a strong anchorage making the teeth very stable.
Here are some benefits of thecodont teeth:

• They allow for a powerful bite force, which aids in processing various types of foods.
• This setup helps in preventing tooth loss and damage.

This characteristic is another distinctive feature that helps to set mammals apart from other animal groups.

Heterodont teeth

Heterodont teeth refer to having different types of teeth that are adapted for various functions. In mammals, you will typically find:

• Incisors for cutting
• Canines for tearing
• Premolars and molars for grinding

This differentiation in tooth structure allows mammals to efficiently process a wide range of foods.
Their heterodont dentition is crucial for their adaptability and survival, enabling them to thrive in diverse environments.

Warm-blooded (homoiotherm)

Being warm-blooded means that mammals can regulate and maintain a constant body temperature, regardless of the external environment.
This trait is also known as being homeothermic.
Benefits include:

• The ability to be active in various climates, whether cold or hot.
• Enhanced endurance which allows sustained periods of activity.
• The capability to inhabit diverse environments from polar regions to deserts.

This adaptability is one of the factors that enable mammals to exist across every continent and in various ecological niches.