Problem 115 - Objective Biology for NEET

Question

Assertion: Growth in plant is said to be open. Reason: In plant, growth by cell division occurs throughout their life.

Step-by-Step Solution

Answer

The assertion is correct. Growth in plants is said to be 'open' because plants demonstrate open or indeterminate growth, meaning they can continue to grow throughout their lifetime. This is due to the process of cell division that occurs in plants, leading to the continuous formation of new cells, organs, and tissues.

Step 1: Understanding Open Growth

Open growth, also known as indeterminate growth, refers to the process in which plants continue to grow throughout their life. This is different from animals, which usually stop growing after reaching a certain age or size.

Step 2: Understanding Cell Division

Cell division is a process in which a parent cell divides into two or more daughter cells. In plants, this happens in meristematic cells that are present in areas like the tips of roots and stems. This process of cellular division and formation of new cells leads to the growth of the plant.

Step 3: Connecting Open Growth with Cell Division

In the case of plants, because cell division can occur throughout their life, and in particular areas (meristems) that lead to formation of new organs, plants demonstrate open growth. This means they can continue to grow throughout their lifetime due to the constant process of cell division and formation of new cells, organs, or tissues.

Key Concepts

Cell Division

Cell division is a fundamental process that underlies plant growth. It is the means by which a parent cell produces one or more daughter cells. This method is crucial for plant survival and adaptation. In plants, cell division predominantly occurs within specialized areas called meristems. These are regions at the tips of roots and shoots where high rates of division facilitate the plant’s growth.

The process involves two main types, mitosis and meiosis, but for growth, mitosis is paramount. During mitosis, a single cell divides to produce two identical cells, each with the same genetic material as the original. This ensures that as plants grow, they maintain consistent genetic information throughout their structure. This remarkable process not only aids in elongating roots and stems but also supports the plant's ability to replenish tissues and form new organs when required.

• Mitosis results in two identical daughter cells.
• Cell division occurs primarily in meristematic tissues.
• Essential for plant growth, repair, and reproduction.

Meristematic Cells

At the heart of plant growth, meristematic cells are unique cells positioned at the strategic areas of a plant such as the apex of roots and shoots. These cells are unique due to their ability to divide continuously. Unlike the cells in other parts of the plant that mainly have specific functions and seldom divide, meristematic cells are totipotent and versatile.

Meristematic tissues are classified into different types based on their location:

• Apical Meristems: Found at the tips of roots and shoots, responsible for primary growth which increases a plant's height.
• Lateral Meristems: Present along the sides of stems and roots, contributing to secondary growth to increase plant girth.
• Intercalary Meristems: Located at the base of leaf blades or between mature tissues, aiding in the rapid growth and elongation of leaves and stems.

These specialized cells enable plants to adapt and react to their environment. They add resilience and flexibility to the plant’s growth process, ensuring that it can develop new organs or tissues as needed.

Indeterminate Growth

Indeterminate growth in plants means that they can potentially keep growing indefinitely. This is a distinctive trait that contrasts notably with animals, which typically reach a mature size and then cease growing. For plants, growth continues throughout their life cycle, allowing them to expand their reach for water, nutrients, and sunlight.

This persistent growth is largely due to the activity of meristematic cells located in key areas mentioned earlier. Plants can continually add to their mass, producing new leaves, flowers, and roots as required. This adaptability is crucial for survival and reproductive strategies.

• Plants do not have a predetermined size.
• Continuous growth helps plants survive environmental changes.
• Meristematic cells play a key role in this endless growth potential.

Indeterminate growth also plays a vital role in a plant's ability to propagate and spread across various terrains. The process is not just a mechanism for individual survival, but a strategy for species propagation and colonization.