Problem 18 - Objective Biology for NEET

Question

Which simple tissue is characterized by pits? (a) Collenchyma (b) Parenchyma (c) Sclerenchyma (d) All of these

Step-by-Step Solution

Answer

The simple tissue characterized by pits is (c) Sclerenchyma.

Step 1: Understanding Collenchyma

Collenchyma is a type of simple plant tissue that provides flexibility to the plant. It does not have pits as a characteristic feature.

Step 2: Understanding Parenchyma

Parenchyma is another type of simple plant tissue that forms the majority of leaves, stems, roots, and fruits of plants. Parenchyma cells typically have thin cell walls and are not characterized by pits.

Step 3: Understanding Sclerenchyma

Sclerenchyma is a type of simple plant tissue that provides support to the plant. It is typically characterized by the presence of thick, rigid cell walls, which can be lignified and often exhibit pits. Sclerenchyma tissue can be classified into sclereids and fibres, both of which contain pits.

Key Concepts

Collenchyma

Collenchyma cells are often found beneath the epidermis of stems and leaves, where they provide elastic support to young, growing tissues. These cells are unique because of their ability to stretch along with the plant organs, which allows for growth while providing tensile strength. Collenchyma tissue is marked by unevenly thickened cell walls, made up primarily of the carbohydrate polymer cellulose. Unlike sclerenchyma, collenchyma does not have pits, which are depressions or holes in the cell walls characteristic of other plant tissues.

These living cells continue to metabolize and can elongate if required, hence their important role in areas undergoing primary growth. Because of the lack of pits and a relatively thin primary cell wall, nutrients and water can easily move through intercellular spaces, facilitating the growth process.

Parenchyma

Parenchyma, the most common and versatile plant tissue, is involved in photosynthesis, storage, and tissue repair. These cells have thin and flexible primary cell walls that are usually not lignified, enabling the storage of water and nutrients, and allowing for gas exchange. Parenchyma cells can divide and differentiate into other cell types, aiding in the healing of wounds and regeneration of tissues.

The cells can be of various shapes, but they tend to be isodiametric, meaning they have similar dimensions in all directions. This simplicity and adaptability do not typically include characteristic pits. Parenchyma cells are alive at maturity and often exhibit large vacuoles, which help in maintaining cell turgor and storing substances.

Sclerenchyma

Sclerenchyma is known for its role in providing mechanical support and strength to the plant body, particularly in areas where growth has ceased. The cell walls of sclerenchyma are thickened due to the presence of lignin, a complex organic polymer, which provides rigidity. One of the hallmark features of sclerenchyma cells is the pits, which are small cavities in the cell wall that facilitate the transfer of water and nutrients.

Sclerenchyma tissue includes two types of cells: fibers, which are elongated and found in stems and leaves, and sclereids, which vary in shape and are often found in nutshells and seed coats. Sclerenchyma cells are dead at maturity, which means they no longer maintain their cellular metabolism but provide structural endurance to the plant.

Plant Tissue Characteristics

While individual tissues like collenchyma, parenchyma, and sclerenchyma have distinct characteristics, several overarching plant tissue characteristics can be noted. Plant tissues can be grouped into simple and complex tissues. Simple tissues like the ones mentioned have cells with similar structure and function, whereas complex tissues consist of different types of cells.

Plant tissues serve a variety of functions including support (sclerenchyma), flexibility (collenchyma), storage and repair (parenchyma), and transportation of water and nutrients (complex tissues like xylem and phloem). The diversity within plant tissues and their characteristics enable plants to survive in various environments, sustain growth, and reproduce. Structurally, plant tissues can exhibit cell walls of varying thickness and may or may not have pits depending on their function and location within the plant.