Problem 20 - Objective Biology for NEET

Question

Secondary growth of plant occurs due to (a) Lateral meristems (b) Vascular cambium (c) Cork cambium (d) All of these

Step-by-Step Solution

Answer

The correct answer to the exercise is (d) All of these. All parts mentioned, Lateral meristems, Vascular cambium, and Cork cambium, are involved in the secondary growth of plants.

Step 1: Understand the Lateral meristems

Lateral meristems are a type of meristem, or tissue, in plants that are responsible for secondary growth. They are found parallel to the sides of the plant. Lateral meristems include the vascular cambium and the cork cambium. Hence, lateral meristems are involved in the secondary growth of a plant.

Step 2: Understand Vascular cambium

Vascular cambium is a type of lateral meristem that contributes to secondary growth in plants. It is the layer of plant tissue located between the xylem and the phloem in the stem and root of a plant, that is responsible for the production of secondary xylem and phloem, thus contributing to the increase in the girth of the plant.

Step 3: Understand Cork cambium

Cork cambium, also known as the phellogen, is another type of lateral meristem and is responsible for producing the cork, a tough protective material. It contributes to the secondary growth of the plant by increasing the girth and providing protection against physical damage and water loss.

Step 4: Conclusion

After examining each part and their roles, it is clear that all of them - lateral meristems, vascular cambium, and cork cambium - are involved in secondary growth of a plant. Therefore, the correct answer is (d) All of these.

Key Concepts

Lateral Meristems

Lateral meristems are essential tissues in plants, helping them grow wider rather than taller. Imagine the rings you see when you cut a tree log; these rings are a result of lateral growth! This growth happens parallel to the plant's surface, making the stem and roots thicker over time.

Lateral meristems are crucial for plants that need stability and support as they increase in size. These meristems are composed of two types: the vascular cambium and the cork cambium. Both types play a distinct role but work together to aid the plant in secondary growth.

• Vascular Cambium: Mainly responsible for the production of new layers of xylem and phloem.
• Cork Cambium: Builds protective layers to safeguard the plant.

Understanding lateral meristems helps you see how plants maintain their structural integrity and protect themselves from environmental damage.

Vascular Cambium

The vascular cambium is like the plant's internal builder. It is a thin layer situated between the xylem and phloem within the stems and roots. This crucial tissue generates cells that form new layers of xylem and phloem as the plant grows.

One of the major roles of the vascular cambium is to increase the diameter of the plant stem. As new secondary xylem is added to the inside and secondary phloem to the outside, the stem becomes thicker. This thickness is essential for supporting the plant as it grows upward and needs to transport more water and nutrients.

• Secondary Xylem: This forms the strengthening wood of the plant.
• Secondary Phloem: Helps in the movement of nutrients within the plant.

The continuous division and regeneration of cells in the vascular cambium are what enable a tree to survive for hundreds of years, growing bit by bit each season.

Cork Cambium

Cork cambium, also known as phellogen, is like the plant's shield. This lateral meristem forms an outer protective layer as the plant expands. Located beneath the surface, the cork cambium produces cork cells that eventually make up the bark.

The primary function of the cork cambium is to protect the plant. It does this by minimizing water loss, warding off pests, and insulating the trunk and branches from temperature extremes. The cells generated are waterproof and can resist decay, contributing to the plant's long-term survival in various environments.

• Environmental Protection: Acts as a defense layer against environmental stressors.
• Contribution to Girth: Adds to the thickness of the plant, enhancing structural strength.

Through its production of cork, the cork cambium not only protects the plant but also supports its growth by allowing the stem to increase in girth without damaging underlying tissues.