Problem 45 - Objective Biology for NEET

Question

The primary xylem elements formed are called is called (a) protoxylem, protoxylem (b) metaxylem, metaxylem (c) protoxylem, metaxylem (d) metaxylem, protoxylem

Step-by-Step Solution

Answer

The correct answer is (a) protoxylem, protoxylem.

Step 1: Understand the Terms

Protoxylem is the first type of xylem to develop in the plant, followed by the metaxylem. In essence, 'proto-' means 'first', indicating that it forms earlier in the development of vascular tissue. 'Meta-' on the other hand, signifies something that occurs subsequently or is more advanced.

Step 2: Match the Terms with Their Definitions

Given that the primary xylem elements are formed first in the growth of the plant, the term that represents 'first' or 'early' would be the most appropriate. Hence, 'protoxylem' is the correct term for the primary xylem elements formed.

Step 3: Identify the Correct Option

By linking the definitions with the terms, the correct answer should be the one where 'protoxylem' is mentioned twice, referring to the primary xylem that is formed. This leads to option (a) which is 'protoxylem, protoxylem'.

Key Concepts

Xylem

All plants have a complex tissue called xylem. This essential tissue plays a crucial role in the plant's survival and growth. Xylem is responsible for transporting water and some nutrients from the roots throughout the plant. Think of it as the highway for water movement.

Xylem is made up of several types of cells. These include tracheids, vessel elements, xylem fibers, and xylem parenchyma. All of these components work together in unison. They ensure that water and dissolved minerals are efficiently distributed.

• Tracheids and vessel elements: These are the main conduits through which water moves.
• Xylem fibers: Provide structural support.
• Xylem parenchyma: Involved in storage and lateral transport of water and nutrients.

Understanding xylem not only aids in comprehending plant structure but also helps elucidate how plants maintain their hydration and nutrient transport.

Protoxylem

Protoxylem is the first xylem tissue formed during the initial growth phases of a plant. This means that it develops early in the life of the plant. Since it forms in young growing areas, protoxylem has to be flexible to accommodate growth.

Its flexibility is mainly due to its structure, which includes narrow vessels with spiral or annular (ring-like) thickenings. This allows the tissue to stretch without breaking as the plant elongates, particularly in stems and roots.

• The spiral and annular structures support the stretching nature.
• Located primarily in the elongating parts of the plant.
• Represents the plant’s primary plumbing system during initial growth phases.

Overall, protoxylem serves as the foundational xylem tissue, adapting to early plant growth needs and setting the stage for future development.

Metaxylem

Metaxylem represents the more mature phase of xylem development and forms after protoxylem. As the plant matures, metaxylem takes over the main job of water transport. Its cells are larger and have thicker cell walls, which differentiate it from protoxylem.

The structure of metaxylem allows it to handle more substantial volumes of water and support the plant as it increases in size and complexity. While protoxylem handles the early growth, metaxylem supports stability and sustained water transport over time.

• Metaxylem is found in parts of the plant that are no longer elongating.
• It possesses larger vessels and more efficient water-conducting capabilities.
• Ensures sustained water transport as the plant matures.

Metaxylem's role underscores the dynamics of plant growth, highlighting how plant vascular systems adapt and mature in response to development demands.