Problem 34 - Objective Biology for NEET

Question

Hard lignified thick-walled long and pointed cells of a plant are (a) Parenchyma (b) Sclerenchyma fibers (c) Collenchymas (d) Sclereids

Step-by-Step Solution

Answer

'Sclerenchyma fibers' is the correct answer.

Step 1: Read and Understand the problem

The exercise is describing the properties of a plant's cell which are Hard, lignified, thick-walled, long and pointed. The task is to find out the type of the cell from the given options.

Step 2: Compare the described cell with the Options

The properties of the cell match well with the characteristics of Sclerenchyma fibers. Parenchyma are not hard or lignified, collenchyma are not hard or lignified and sclereids are not usually long and pointed.

Step 3: Choose the Correct Answer

Based on the comparisons, it is found that the described cell matches with the sclerenchyma fibers. So, the answer to this exercise is 'Sclerenchyma fibers'.

Key Concepts

Sclerenchyma fibers

Sclerenchyma fibers are one of the primary types of support cells in plants. They are known for their ability to provide structural support due to their thick cell walls, which are often lignified. These fibers are long, slender, and typically pointed at both ends.
This unique structure allows them to effectively strengthen various parts of the plant, including the stems and leaves. Sclerenchyma fibers are dead at maturity, meaning they lose their cytoplasm and organelles, becoming hollow tubes that can effectively resist external pressures. This makes them particularly useful in textile production, where plant fibers like hemp and flax are derived from sclerenchyma tissues.

Lignification

Lignification is the process by which lignin, a complex organic polymer, is deposited within the cell walls of plants. This process is crucial in strengthening plant tissues, as lignin provides rigidity and resistance against various environmental factors.
The deposition of lignin occurs predominantly in mature plant cells like sclerenchyma fibers, making them hard and less flexible. Lignin also plays a pivotal role in water transportation within the plant, as it makes the cell walls hydrophobic, thereby reducing water loss.
Lignification is an essential step in the transition of plant cells from being flexible and soft to becoming hard and sturdy, enabling them to fulfill their role in providing structural support.

Plant tissue types

Plant tissues are categorized based on their structure and function, playing different roles in the plant's survival and growth. Among the primary tissue types are:

• Parenchyma: These are versatile cells found throughout the plant, involved in photosynthesis, storage, and tissue repair.
• Collenchyma: Known for providing support in young growing organs, these cells have cell walls that are thicker and often have a pectin layer.
• Sclerenchyma: Another support tissue, sclerenchyma cells are divided into fibers and sclereids, both known for their rigid cell walls due to lignification.

Each type of tissue is specialized, contributing to the plant's ability to grow, reproduce, and adapt to its environment.

Cell wall structure

The structure of a plant cell wall is vital for the overall strength and function of plant cells. The cell wall is a complex matrix made up of cellulose, hemicellulose, and pectin, and in some cells, lignin.

• Primary wall: This is the initial thin and flexible layer formed while the cell is growing. It contains a mix of cellulose and pectin, allowing for some flexibility and growth.
• Secondary wall: Formed after the cell has matured, this layer is much thicker and is often lignified, which gives it significant mechanical strength.

The cell wall is crucial not only for maintaining the cell's shape and ensuring structural integrity but also for its role in protecting against pathogens and controlling the transport of substances in and out of the cell.