Question

Both apical meristems and intercalary meristems are meristems. (a) primary (b) secondary (c) lateral (d) both (b) and (c)

Short answer

Both apical meristems and intercalary meristems are involved in primary growth, therefore the correct answer is (a) primary.

Step-by-step solution

Understand the concept of meristems

Meristems are regions in a plant where cells actively divide and generate new tissue. Apical meristems are found at the tips of roots and shoots, responsible for the primary growth of plants, increasing their length. Intercalary meristems are found at the base of leaves or internodes, also contributing to primary growth, but in specific parts like grasses where they enable re-growth after cutting.

Define primary and secondary growth

Primary growth in plants occurs due to the activity of the apical meristems, resulting in an increase in the length of the plant. Secondary growth is associated with lateral or secondary meristems, like the vascular cambium and the cork cambium, leading to an increase in the girth of the plant.

Determine the correct answer

Since both apical and intercalary meristems are involved in primary growth by increasing the length of the plant, the correct answer is (a) primary.

Key concepts

Understanding Apical Meristems

Apical meristems are the plant kingdom's architects of vertical growth, essential for the elongation of plants. Found at the tips of roots and shoots, these meristems are like bustling construction sites where cells divide and contribute to the primary growth of a plant. Just imagine a busy urban development area where the buildings — or in this case, the plants — get taller by the day. This is the action of apical meristems: an ongoing process that extends the plant's reach into the soil and sky.

Due to their crucial role in facilitating the plant's absorption of nutrients (through roots) and light (through shoots), apical meristems are a cornerstone of plant vitality and survival. By continuously producing new cells, they ensure the plant can adapt to its environment, find new resources, and grow efficiently.

Intercalary Meristems and Their Unique Role

Intercalary meristems may sound less familiar, but they play a vital part in the life of certain plants, particularly grasses and other monocots. These meristems are neatly tucked away at the base of leaves or the nodes of stems. Think of them as specialized units that enable plants to repair and regrow quickly, especially after traumas like grazing or mowing.

The fascinating thing about intercalary meristems is that they help a lawn rebound after cutting, making sure your garden doesn't stay bald for too long! Grasses owe their resilience to these meristems, which allow for rapid elongation and restoration in specific parts of the plant. So, when a little piece is taken away (much like a haircut), intercalary meristems are there to pick up the slack and encourage regrowth.

Primary Growth: The Key to Plant Length

Primary growth is all about lengthening, a phase when plants grow taller or roots dig deeper. Both apical and intercalary meristems are behind this push to reach greater heights and depths, driven by their ability to produce new cells at a remarkable pace. This growth can be thought of as the 'youth' stage of a plant where it grows up, much like children during their first few years of life.

Season after season, the process of primary growth allows a plant to evolve, stretching upwards to capture light and delving into the Earth to establish a strong root system. Primary growth is therefore the phase that sets the foundation for later development, as a building needs a sturdy framework before it can be expanded upon or embellished.

Secondary Growth: Expanding Girth

After establishing length, plants enter a phase of widening called secondary growth. Unlike primary growth, which increases the length of the plant, secondary growth focuses on increasing girth. It's carried out by lateral or secondary meristems, such as the vascular cambium and the cork cambium. This process is akin to a tree adding a new ring each year, gradually expanding its trunk's diameter.

While secondary growth is chiefly evident in woody plants like trees and shrubs, giving them the thick, sturdy trunks we associate with age and strength, it's not a feature in all plant species. It provides structural support, allows for more extensive transport of water and nutrients, and it further houses defensive mechanisms against environmental stressors. Secondary growth adds a new dynamic to a plant's life, contributing to its ability to survive over the long term.