Problem 134 - Objective Biology for NEET

Question

Periderm is made up of (a) Phellem (b) Phellogen (c) Phelloderm (d) All of these

Step-by-Step Solution

Answer

The correct answer is (d) All of these. The Periderm is composed of Phellem, Phellogen and Phelloderm.

Step 1: Explore the components of Periderm

Understand that the Periderm is a part of the plant's bark and is made of three primary layers which are: Phellem, Phellogen, and Phelloderm. Each of these layers serve a specific function.

Step 2: Analysing the options given in the question

Analyse each of the listed entities in the options (a) Phellem, (b) Phellogen, (c) Phelloderm and (d) All of these, in relation to the composition of the Periderm.

Step 3: Matching components with options

Having analysed each of the options, it can be inferred that they all correspond to the layers that make up the Periderm.

Key Concepts

Periderm

The Periderm is a protective tissue layer that forms in the stems and roots of woody plants. It replaces the epidermis, which is the plant's original protective layer, when that layer is damaged or when the plant requires more robust protection as it grows. Its formation is crucial for plant survival, particularly in harsh environmental conditions, because it helps in reducing water loss and shielding against pathogens.

• It acts as a secondary protective barrier.
• Comprises three main layers: Phellem, Phellogen, and Phelloderm.

Peridermal layers are especially important in trees and shrubs, where they contribute to the toughness of the plant's exterior.

Phellem

Phellem, also known as cork, is one of the essential components of the Periderm. It is formed on the outer side of Phellogen.

• It consists of tightly packed cells filled with suberin, a waxy substance that provides waterproofing.
• Acts as an insulator protecting against temperature fluctuations.
• Prevents infection by bacteria and fungi.

The formation of Phellem is a vital process, enabling plants to survive adverse environmental conditions by preventing excessive water loss.

Phellogen

Phellogen, commonly referred to as the cork cambium, is the middle layer of the Periderm and serves as the generative tissue. It is responsible for the continuous production of both Phellem and Phelloderm.

• Made up of meristematic cells, which means they are capable of division and growth.
• Functions as a living dividing layer that regenerates the external parts of the Periderm.
• Directly contributes to the thickening of stems and roots over time.

Understanding the role of Phellogen is essential for comprehending how plants adapt and protect themselves through growth.

Phelloderm

Phelloderm is the innermost layer of the Periderm, found on the internal side of the Phellogen. It consists of living parenchyma cells and is similar in function to the cortical tissue found in plants.

• Works together with cortical tissues in storing nutrients.
• Facilitates gas exchange by keeping the innermost tissues flexible and viable.
• Helps in repairing tissues in case of damage.

Phelloderm is less substantial than Phellem but plays a critical role in maintaining the health of the plant by ensuring nutrient storage and recovery after injury.