Problem 155 - Objective Biology for NEET

Question

Assertion: Parallel venation is the characteristics of most of monocots. Reason: In parallel venation veins run parallel to each other with in a leaf lamina.

Step-by-Step Solution

Answer

Both the assertion and the reason are correct, and the reason accurately explains the assertion. Parallel venation is indeed a characteristic of most monocots, and this leaf structure is correctly described in the reason clause.

Step 1: Verify the Assertion

Parallel venation refers to the arrangement of veins (vascular bundles) in a leaf where they run parallel to each other from the base to the tip of the leaf. This is a characteristic mostly seen in monocotyledonous (or simply, monocots) plants, which are one of the two major groups of flowering plants. Therefore, the assertion is correct.

Step 2: Verify the Reason

The given reason is a definition of parallel venation. It correctly explains that in parallel venation, veins run parallel to each other within a leaf lamina. This structural attribute is present in the leaves of most monocots. Therefore, the reason given is accurate.

Step 3: Connect the Assertion and Reason

Now we must see if the reason correctly explains the assertion. Since the assertion is that parallel venation is a characteristic of most monocots, and the reason explains the concept of parallel venation, we can conclude that the reason accurately validates the assertion.

Key Concepts

monocots

Monocots, short for monocotyledons, are a group of flowering plants that have a single embryonic leaf, or cotyledon, in their seeds. Unlike dicotyledons (dicots), which have two cotyledons, monocots are known for several distinctive features. Some of the most notable traits include:

• Parallel venation in their leaves, where the veins run side by side.
• Flower parts that often come in multiples of three.
• Fibrous root systems rather than a central taproot.

Monocots include a variety of plants such as grasses, lilies, orchids, and palms. Their unique characteristics, especially parallel venation, make them easily distinguishable from dicots. This venation pattern is well-suited for their typical growth environments, allowing efficient transport of water and nutrients across the leaf surface.

leaf lamina

The leaf lamina, also known as the leaf blade, is the broad, flat part of the leaf. It’s the main site of photosynthesis, where plants convert sunlight into energy. In monocots, the leaf lamina often has a uniform, elongated shape, which complements the parallel venation pattern. This design facilitates efficient absorption and distribution of light across the leaf.
The structure of the leaf lamina can vary between plants, but in monocots, it's usually narrow and can be quite lengthy. The entire lamina is usually uninterrupted and unlobed, providing a continuous surface for gas exchange.

• Contains vascular bundles that are critical for transport.
• Has stomata for gas exchange.
• Facilitates a high surface area for light capture and energy absorption.

This integral part of the leaf supports the plant's survival by maximizing photosynthesis and minimizing water loss.

vascular bundles

Vascular bundles are essential components of plant vascular systems, responsible for transporting water, nutrients, and food throughout the plant. In leaves, these bundles form the vein patterns, which in the case of monocots, run parallel to each other.
Their main components are xylem and phloem:

• **Xylem** - Transports water and dissolved minerals from the roots to different parts of the plant.
• **Phloem** - Distributes the sugars and other metabolic products downward from the leaves.

In monocots, vascular bundles are evenly distributed across the leaf lamina, ensuring balanced transport of nutrients and water. The parallel arrangement allows the plant to efficiently support elongated leaf structures, characteristic of many monocots. This configuration helps optimize the plant's physiological processes, such as photosynthesis and transpiration.