Problem 10 - Objective Biology for NEET

Question

Find the example of lateral meristem. (a) Fascicular cambium (b) Interfascicular cambium (c) Cork-cambium (d) All of these

Step-by-Step Solution

Answer

The correct answer is (d) All of these.

Step 1: Identifying Types of Meristems

The types of meristems we have in the options are Fascicular cambium, Interfascicular cambium, and Cork cambium. Fascicular cambium and Interfascicular cambium collectively form the vascular cambium, responsible for secondary growth in plants. The Cork cambium or phellogen is also a type of lateral meristem involved in secondary growth.

Step 2: Classifying the Meristems

As seen earlier, all three types - Fascicular cambium, Interfascicular cambium and Cork cambium fall under the category of lateral meristems as they are involved in the secondary growth of plants.

Key Concepts

Secondary Growth in Plants

Secondary growth in plants is a process that results in an increase in the girth or thickness of the plant, as opposed to primary growth which increases the plant's length. It's important to understand that secondary growth occurs in woody plants and some herbaceous perennials, enabling them to become thicker and develop a sturdy structure over time.

Unlike animals, plants have the remarkable ability to grow throughout their life due to meristematic tissue � a region of plant cells capable of division and growth. Among these, the lateral meristem plays a crucial role in secondary growth, which includes the vascular cambium and cork cambium. These meristems contribute to increasing the diameter of stems and roots to support the plant as it matures.

Secondary growth begins when the vascular cambium, a cylinder of meristematic cells that runs the length of the plant, starts to produce new layers of vascular tissue. Inside the vascular cambium, new xylem tissue (wood) is produced, while phloem tissue is formed on the outside. This process not only strengthens the plant but also allows for the efficient transport of water, nutrients, and sugars throughout the plant's body.

Vascular Cambium

The vascular cambium is one of the two types of lateral meristem; the other being the cork cambium. It is a thin layer of meristematic cells located between the wood (xylem) and the bark (phloem). Its primary role is to add layers of vascular tissue called secondary xylem and secondary phloem.

The importance of the vascular cambium cannot be overstated. It gives rise to secondary xylem that forms the bulk of a mature tree's wood and is crucial for water and mineral conduction and support. The growth rings seen when a tree is cut cross-sectionally are due to the activity of the vascular cambium, with each ring generally representing one year of growth.

As the vascular cambium continues to divide, it not only increases the thickness of the stem but also changes the functional dynamics of the plant. This ability to grow year after year is what allows trees to reach substantial sizes and live for many years, sometimes even for millennia.

Cork Cambium

The cork cambium, or phellogen, is another type of lateral meristem, similar to the vascular cambium, but with a distinct function. Cork cambium arises in the outer cortex of the stem and is responsible for producing cork cells which form the bark of a tree.

As a plant undergoes secondary growth, the bark formed by the cork cambium plays a protective role. It helps to insulate the plant's tissues, minimize water loss, and defend against physical damage and pathogens. Cork cells produced by the cork cambium are filled with suberin, a waxy substance that is impermeable to water and gases, thereby providing an excellent protective barrier.

Interestingly, the cork cambium is active throughout the life of a plant, continually adding to the thickness of the bark as the plant ages. This secondary growth of the cork cambium is also what gives us cork material, harvested primarily from the cork oak tree. Sustainable harvesting involves removing the outer bark without damaging the cork cambium, allowing the tree to continue growing and producing more cork.