All questions of April for NEET Exam

Root Systems in Monocotyledonous Plants
Monocotyledonous plants, commonly known as monocots, exhibit a characteristic root system known as the fibrous root system. Understanding this root structure is crucial for grasping the differences between monocots and dicots.
Characteristics of Fibrous Root System
- Structure: The fibrous root system consists of numerous thin, branching roots that spread out horizontally from the base of the plant. These roots are generally similar in size and are formed from the base of the stem.
- Absorption: This extensive network of roots is highly efficient in absorbing water and nutrients from the upper layers of soil, making monocots well-adapted to various environments.
- Stability: The fibrous roots help stabilize the plant in the soil, which is particularly important for tall grasses and cereal crops.
Comparison with Other Root Systems
- Taproot System: Found in dicots, the taproot system features a main central root that grows deeper into the soil, providing stability but often making the plant reliant on deeper water sources.
- Adventitious Root System: While some monocots may develop adventitious roots, this system is more common in certain plants that require additional support or have unique growth conditions.
- Aerial Root System: Primarily seen in climbing plants and epiphytes, these roots grow above ground and are not typical in monocots.
Conclusion
In summary, the fibrous root system is a defining feature of monocotyledonous plants, enabling them to thrive in diverse habitats. Understanding this root structure provides insight into the ecological roles and adaptations of monocots in the plant kingdom.

Introduction to Angiosperms and Gymnosperms
Angiosperms and gymnosperms are two major groups of seed-producing plants. The primary distinction between them lies in their reproductive structures and seed development.
Key Differences
- Enclosed Seeds in Fruits:
- Angiosperms, commonly known as flowering plants, produce seeds that are enclosed within a fruit. This fruit develops from the ovary wall after fertilization and serves to protect the seeds and aid in their dispersal.
- Naked Ovules:
- In contrast, gymnosperms have naked ovules that are not enclosed by an ovary. Their seeds are exposed on cone scales, making them vulnerable compared to the protected seeds of angiosperms.
- Presence of Vascular Tissues:
- Both angiosperms and gymnosperms possess vascular tissues (xylem and phloem), which are essential for nutrient and water transport. Thus, vascular tissues are not a distinguishing factor between the two groups.
- Lack of Flowers:
- Angiosperms are characterized by their flowers, which are the reproductive structures that facilitate pollination. Gymnosperms, on the other hand, do not produce flowers but reproduce through cones.
Conclusion
The defining feature of angiosperms, which sets them apart from gymnosperms, is the presence of enclosed seeds within fruits. This adaptation not only provides protection but also enhances the chances of successful seed dispersal, making angiosperms the most diverse group of plants on Earth.

Uniparous cyme is characterized by lateral branches ending in a flower one after another, with an acropetal arrangement of flowers.

Understanding the Taxonomic Hierarchy
In biological classification, the organization of living organisms is structured in a hierarchical manner. Here, we identify the relationships between different taxonomic ranks.
X - Order
- The term "X" refers to an Order.
- An Order is a higher taxonomic rank that groups together families that share certain characteristics.
Y - Similar
- The "Y" characters are described as similar.
- Families within the same Order exhibit shared traits or characteristics, which is why they are grouped together.
Z - Different
- The "Z" characters are indicated as being less in number and different.
- Within a family, there can be multiple genera that exhibit a variety of distinct traits, leading to more diversity at the genus level compared to the overarching family.
Conclusion
Thus, the correct answer is:
- X - Order
- Y - Similar
- Z - Different
This classification highlights how organisms are systematically categorized based on shared and differing characteristics, aiding in the study of biodiversity and evolutionary relationships.

Thomson's Model could not explain the phenomenon of radioactivity because it did not include the concept of the nucleus, which is central to understanding radioactive decay.

Leaf spine modification involves the development of pointed spines on leaves or leaflets for defense purposes.

Understanding the Exclusive Characteristic of Living Things
The question revolves around identifying a unique trait that distinguishes living organisms from non-living entities. Let’s break down the options to highlight why option 'C' is the correct answer.
Isolated Metabolic Reactions (Option A)
- Living organisms have metabolic processes, but isolated reactions can occur in vitro (in a controlled environment outside a living organism) and do not exclusively define life.
Increase in Mass from Inside Only (Option B)
- While living organisms grow and develop, the increase in mass is not exclusively from internal processes. Nutrients are absorbed from the environment, indicating that growth can occur from both internal and external sources.
Perception and Memory (Option C)
- This option highlights the ability of living organisms to perceive their surroundings and retain memories.
- Key Points:
- Perception: Living organisms respond to stimuli (e.g., light, sound, temperature).
- Memory: Many organisms, especially animals, exhibit behaviors based on past experiences, showcasing a level of cognitive function.
- This characteristic is unique to living beings, as non-living entities do not possess awareness or memory.
Increase in Mass by Accumulation (Option D)
- Similar to Option B, while living organisms do accumulate mass, this process involves both external absorption and internal growth, thus not being exclusive to the characteristics of life.
Conclusion
In summary, option 'C' is the only aspect that encapsulates a definitive characteristic of living organisms— the ability to perceive their environment and remember experiences, setting them apart from non-living matter. This cognitive ability is vital for survival and adaptation in a dynamic world.

Seed Habit in Plants
The seed habit is a crucial evolutionary development in the plant kingdom. It provides several advantages for survival and reproduction.
Origin of Seed Habit
- Gymnosperms: The first group of plants to develop seeds are gymnosperms. This group includes conifers and cycads, which appeared during the Mesozoic era.
- Characteristics: Gymnosperms produce seeds that are not enclosed in an ovary. Instead, they develop on the surface of scales or leaves, typically in cones.
Importance of Seeds
- Protection: Seeds provide a protective covering for the embryo, ensuring its safety from environmental hazards and predation.
- Nutrient Supply: Seeds contain stored food, which supports the embryo during its early growth stages.
- Dispersal Mechanisms: Seeds can be dispersed by wind, water, or animals, allowing plants to colonize new areas effectively.
Comparison with Other Groups
- Pteridophytes: These plants reproduce via spores, lacking seeds altogether. Their reproductive mechanisms are less efficient than those of seed plants.
- Cycadofilicales: This is an extinct group, part of the gymnosperms, and while they had seed-like structures, true seeds were fully developed only in later gymnosperms.
- Angiosperms: Although angiosperms (flowering plants) are the most advanced in seed development, they evolved after gymnosperms.
Conclusion
In conclusion, the seed habit was first established in gymnosperms, making option 'D' the correct answer. This evolutionary development marked a significant leap in plant adaptation and success on land, leading to the diverse flora we see today.

Understanding Bohr's Model
Bohr's model of the atom describes the behavior of electrons in hydrogen-like systems. The energy levels of an electron in these orbits are quantized and can be calculated using specific formulas.
Energy Levels Formula
The energy of an electron in the nth orbit is given by the formula:
- E_n = - (13.6 eV) / n²
where:
- E_n is the energy level of the nth orbit.
- n is the principal quantum number (1, 2, 3, ...).
Calculating Potential Energy
In Bohr's model, the potential energy (U) of an electron is related to its total energy (E) by the relation:
- U = 2E
Since the total energy in the nth orbit is negative, the potential energy will also be negative.
Energy in the Second Orbit
For the second orbit (n=2):
- E_2 = - (13.6 eV) / 2²
- E_2 = - (13.6 eV) / 4
- E_2 = -3.4 eV
Now, using the relation for potential energy:
- U = 2E_2
- U = 2 * (-3.4 eV)
- U = -6.8 eV
However, it's important to note that for hydrogen-like atoms (like He+), the calculations vary slightly. For He+, the total energy is modified due to the increased nuclear charge.
Potential Energy in He+
For He+:
- The potential energy in the second orbit can be recalculated as follows:
- U = 2 * E_2 = 2 * (-13.6 eV) / 4 = -27.2 eV
Hence, the correct potential energy of an electron in the second orbit of helium ion (He+) is -27.2 eV, which corresponds to option 'D'.