Problem 102 - Objective Biology for NEET

Question

The following features belong to which option? I. Epidermis may bear trachoma and few stomata. II. Cortex is divided into three sub-zones. III. Hypodermis is made up of collenchymas starch sheath. IV. Pericycle above phloem is in the form of semilunar patches of sclerenchyma. (a) Dicot root (b) Dicot stem (c) Monocot root (d) Monocot stem

Step-by-Step Solution

Answer

The answer is (d) Monocot Stem. All the features listed can be found in a monocot stem.

Step 1 Identify Features

First, understand what each feature from I to IV means. These features are different characteristics found in plant structures. There are differences between the structures of dicots and monocots, and between roots and stems. It's important to use scientific understanding of plant anatomy to understand what these features indicate.

Step 2 Match Features with Options

Next, match each feature to a possible option. For example, the feature I: 'Epidermis may bear trachoma and few stomata' is a characteristic of a monocot stem. Similarly, understand which characteristic relates to each plant structure for features II to IV.

Step 3 Draw Conclusion

Finally, after all features have been matched, draw a conclusion. Analyze the provided options and check which option covers all the identified features. For this task, each feature points to a specific option, hence the option that contains all features is the correct answer.

Key Concepts

Dicot vs Monocot Differences

Understanding the differences between dicot and monocot plants is essential for students preparing for exams like the NEET. These two types of plants show distinct structural variations that can be observed in their roots, stems, leaves, and flowers.

Dicots, or dicotyledons, are plants that have two embryonic seed leaves, or cotyledons, while monocots, or monocotyledons, have only one. This distinction is critical as it leads to different developmental patterns. For instance, dicot stems typically show a vascular tissue arrangement in a ring, while monocots have scattered vascular bundles. Similarly, dicot roots have a central core of xylem in the form of an 'X' with phloem between each arm, contrasting with the ring of xylem and phloem found in monocot roots.

• Leaves: Dicot leaves usually have a branched network of veins, whereas monocot leaves display parallel veins.
• Flowers: The flower parts of dicots generally come in multiples of four or five, while monocots are typically in multiples of three.
• Roots: Dicots often form a taproot system, while monocots tend to have a fibrous root system.
• Stems: When it comes to stems, the presence of a cambium layer in dicots allows them to grow in thickness (secondary growth), which is generally absent in monocots.

By identifying these characteristics, one can often predict whether a plant is a dicot or a monocot before examining it under a microscope for more detailed features.

Plant Tissue Structure

The intricacy of plant tissue structure is another fundamental topic for students studying botany or preparing for competitive exams like NEET. Plants have specialized structures to perform different functions, and understanding the composition and role of each type of plant tissue is key.

Plant tissue is categorized into two main types: meristematic and permanent. Meristematic tissue is responsible for the growth of plants and can be found at the tips of roots and shoots. On the other hand, permanent tissue has cells that have reached their final size and shape. Permanent tissue is further divided into simple and complex tissues.

Simple Tissues

Simple tissues are made of similar types of cells and include parenchyma, collenchyma, and sclerenchyma:

• Parenchyma: These are the most common cells, which are adaptable and can store food or become the site of photosynthesis.
• Collenchyma: These cells provide flexibility and mechanical support; they are typically found in the hypodermis of stems and leaves.
• Sclerenchyma: Composed of thickened, toughened cells, they provide rigid support to the plant, seen in nuts and seed coats.

Complex Tissues

Complex tissues consist of different types of cells that work together. Xylem and phloem are the most prominent, being responsible for the transportation of water, minerals, and food throughout the plant.

• Xylem: Conducts water and dissolved minerals upward from the roots to other parts of the plant.
• Phloem: Transports sucrose and other organic compounds from the leaves to the rest of the plant.

Each tissue type has a specific structure and function that contribute to the overall physiology of the plant.

Plant Epidermis Function

The plant epidermis serves as the outermost layer of tissue and plays a crucial role in the protection and interaction of plants with their environment.

The epidermis is made up of tightly packed cells that create a barrier against the external world. It helps prevent water loss and provides defense against pathogens and physical damage. Stomata, or tiny openings found in the epidermis of leaves, permit gas exchange and transpiration, which is the evaporation of water from the plant's surface.
In addition to stomata, the epidermis may bear specialized cells such as trichomes and various glands. Trichomes can reduce water loss and reflect excess light or serve as defense structures by secreting substances that deter herbivores.

• Protection: It acts as a shield against mechanical injury, UV radiation, and pathogens.
• Control of Gas Exchange: Stomata control both the intake of carbon dioxide for photosynthesis and the loss of oxygen and water vapor.
• Water Conservation: The epidermis can have a waxy layer known as the cuticle, which helps to further reduce water loss.

Understanding how the plant epidermis functions is integral to studying plant biology and ecology, as well as in practical horticulture and agriculture where controlling these factors can be key to plant health and yield.