Problem 74 - Objective Biology for NEET

Question

Which of the following is a common feature of category 'insecta'? (a) Presence of ostium (b) Presence of coxal gland for excretion (c) Three pair of jointed legs in thoracic region (d) Exoskeleton of cutin

Step-by-Step Solution

Answer

The common feature of category 'insecta' is (c) Three pair of jointed legs in the thoracic region.

Step 1: Understanding the Choices

Assess each option (a) to (d) individually and in relation to Insecta characteristics.(a) Ostium are heart openings seen in certain Arthropods, but it is not specific to Insects.(b) Coxal glands are excretory organs in some Arthropods such as spiders. Insects do not possess coxal glands.(c) Three pair of jointed legs in the thoracic region is a defining feature of Insects.(d) While Insects do have exoskeleton, it is made of chitin, not cutin.

Step 2: Eliminate Incorrect Choices

Based on the above understanding, eliminate (a), (b) and (d) as these are not features common to Insecta. Their exoskeleton is not composed of cutin, and they neither have coxal gland for excretion, nor ostium.

Step 3: Confirming the Correct Choice

The feature that remains is (c) Three pair of jointed legs in the thoracic region. Search for confirming information that this is indeed a common characteristic of Insecta.

Step 4: Conclude the Answer

After confirming (c) as a common characteristic of Insecta, it is safe to conclude that this is the answer to the question.

Key Concepts

Arthropod Anatomy

Arthropods are a diverse and fascinating group of animals that include insects, crustaceans, and arachnids. Understanding their anatomy is essential for students preparing for exams such as NEET. One of the defining features of arthropods is their segmented bodies, which are typically divided into three regions: the head, thorax, and abdomen. The thorax is particularly interesting as it bears the appendages, including legs and wings in the case of insects.

For example, in the insect category 'Insecta', one can observe the presence of three pairs of jointed legs specifically in the thoracic region. This feature aligns with the fundamental arthropod body plan but is uniquely characteristic of insects among arthropods. It's importance for locomotion and interaction with the environment makes it a key point for students to note when studying arthropod anatomy, especially for high-stakes exams where such distinctions can be crucial.

Excretory System in Arthropods

In the realm of arthropods, the excretory system varies significantly among different groups, which is crucial for students to understand for comparative anatomy subjects. In general, arthropods use various organs to filter out waste from their hemolymph (the equivalent of blood). For instance, insects utilize Malpighian tubules for excretion, distinguishing them from other arthropods that may possess structures like coxal glands, as seen in spiders and some other chelicerates.

The Malpighian tubules work by absorbing waste from the hemolymph and converting it into a form that can be easily excreted with minimal water loss. This system is highly efficient for terrestrial life, which is why it is prevalent among insects. Understanding the nuances of the arthropod excretory system, especially differences such as these, is vital for competitive exams where a single detail can be the difference between a correct and incorrect answer.

Exoskeleton Composition

The exoskeleton of arthropods is not only a defining trait but also a critical area of study for students, particularly those interested in biology and zoology. Unlike vertebrates, arthropods have an external skeletal structure that provides support and protection. The composition of this exoskeleton is one such detail that cannot be overlooked. In insects, the exoskeleton is primarily made of a complex carbohydrate called chitin. Chitin is a sturdy yet flexible material that allows for protection without compromising mobility.

Contrary to some misconceptions, the insect exoskeleton is not composed of cutin, which is found in plants. Chitin, combined with various proteins and sometimes minerals, forms a tough outer layer that also plays a role in water resistance. This intricacy in the composition of the exoskeleton is not just a trivial fact; it is pivotal for students to understand as it relates to the physiology and ecological adaptations of these creatures.