Question

Outside to inside the layer of monocot root are (a) Endodermis - Epidermis - Cortex - Pith-Vascular bundle-Pericycle (b) Pith-Epidermis-Endodermis-Cortex-Pericycle-Vascular bundle (c) Epidermis-Cortex-Endodermis-Pericycle-Vascular bundle-Pith (d) Pericycle-Vascular bundle-Cortex-Pith-Epidermis-Endodermis

Short answer

The correct sequence of layers in a monocot root from outside to inside is 'Epidermis-Cortex-Endodermis-Pericycle-Vascular bundle-Pith', hence the correct answer is option (c).

Step-by-step solution

Understand the basic structure of a monocot root

A monocot root typically has the following layers from outside to inside: Epidermis, Cortex, Endodermis, Pericycle, Vascular bundle and Pith.

Compare this structure to the options

Option (a), (b) and (d) don't correspond to the right sequence of layers in a monocot root. Option (c) provides the correct sequence: 'Epidermis-Cortex-Endodermis-Pericycle-Vascular bundle-Pith'

Choosing the right option

Based on the comparison in Step 2, option (c) is the correct answer.

Key concepts

Epidermis

The epidermis is the outermost layer of the monocot root. It primarily serves as a protective barrier against the environment. This layer consists of tightly packed cells that protect the root from physical damage and help prevent water loss. Most importantly, it aids in the absorption of water and minerals from the soil. These cells lack chloroplasts as they are not involved in photosynthesis, but they do play a crucial role in the initial uptake of nutrients.

In many monocot roots, the epidermis also has root hairs. These root hairs increase the surface area of the root, allowing for more effective absorption of water and nutrients. Their presence highlights the critical role of the epidermis in the plant's ability to gather sustenance from its environment.

Cortex

Moving inward, the next layer is the cortex. This layer is located between the epidermis and the endodermis and is mainly composed of parenchyma cells. These cells are generally loose, facilitating the easy movement of water and nutrients across the root. The cortex functions as a storage site and provides cushioning to the inner parts of the root.

The large intercellular spaces found within the cortex allow gases to circulate and provide space for storage in some roots. This storage could be in the form of starch or other nutrients. Additionally, the cortex aids in the transport of water by channeling it towards the endodermis.

Vascular Bundle

Within the root structure, the vascular bundle is the central part responsible for the transport of water, nutrients, and food throughout the plant. In a monocot root, the vascular bundles are usually arranged in a ring. This bundle consists of two main types of tissues: xylem and phloem.

The xylem is responsible for the transport of water and dissolved minerals from the roots upwards to the rest of the plant. In contrast, the phloem distributes the sugars produced during photosynthesis from the leaves to other parts of the plant. This balanced transport system is crucial for plant health and sustenance, maintaining a steady flow of necessary substances.

Endodermis

The endodermis is a single layer of cells that defines the boundary between the cortex and the pericycle. This layer serves as a selective barrier that regulates the flow of substances into the vascular bundle. The endodermal cells possess a unique structure known as the Casparian strip.

The Casparian strip is a band of cell wall material composed mainly of lignin and suberin, which makes these cells relatively impermeable to water. This ensures that all water and nutrients must pass through the cytoplasm of endodermal cells through a process of active transport, allowing the plant to control the uptake of nutrients efficiently.

Pericycle

Directly beneath the endodermis lies the pericycle. This is a crucial layer as it plays essential roles in root growth and development. The pericycle is involved in the formation of lateral roots, contributing to the extensive root system typical of monocot plants.

This layer can also contribute to the secondary growth in plants that undergo such processes. Cells in the pericycle can differentiate to form part of the vascular cambium and the cork cambium. This ability to regenerate and develop additional plant structures underscores the significance of the pericycle in plant growth and propagation.

Pith

At the center of the monocot root structure is the pith. Interestingly, in many monocot roots, the pith is well-developed, unlike in dicot roots where it is usually absent. The pith mainly consists of parenchyma cells that act as a storage tissue.

This central part of the root stores nutrients and starches that can be utilized by the plant when external supplies are limited. While it does not play a direct role in transport like the vascular bundle, the pith supports the root's structural integrity and offers a stable center for nutrient accumulation. By providing storage and structural support, the pith exemplifies the complexity and interdependence of the root’s internal structure.