Question

Describe the surface structures of a stem after primary growth. Where are buds located, and what are their functions?

Short answer

After primary growth, the surface structures of a stem include the protective epidermis covered by a cuticle, the cortex composed of parenchyma cells, and the vascular tissue system made up of xylem and phloem. Buds, which can be terminal, axillary, or adventitious, are responsible for growth, reproduction, adaptation and defense, and regeneration. Terminal buds contribute to primary growth at the stem tip, while axillary buds can grow into branches or side shoots, located in the leaf axil. Adventitious buds can form on other parts of the stem to help with tissue repair or new plant growth.

Step-by-step solution

Surface Structures of a Stem

After primary growth, the surface structures of a stem consist of the epidermis, which is an outer layer of cells that protects the stem. This layer is covered by a cuticle that prevents water loss and provides a barrier against pathogens. Beneath the epidermis is the cortex, composed of parenchyma cells which are responsible for storage and support. Inside the cortex is the vascular tissue system, which is made up of xylem, responsible for water transport, and phloem, responsible for transporting sugars and other nutrients. Primary growth occurs in the apical meristem and creates the basic structure of the stem.

Location of Buds

Buds can be found in various locations on a stem, depending on the plant species and the type of bud. There are three common types of buds: terminal (apical) buds, axillary (lateral) buds, and adventitious buds. Terminal buds are located at the tip of the stem and are responsible for the primary growth in length. Axillary buds are located in the axil of each leaf, which is the angle formed between the leaf and the stem. These buds can remain dormant or can grow into a branch, shoot, or flower. Adventitious buds can form on other parts of the stem, such as on roots, leaves, or wounds, and they can give rise to new plants or help in tissue repair in response to injury.

Functions of Buds

Buds serve several functions in a plant, which include: 1. Growth: Terminal buds contribute to a plant's primary growth, allowing it to grow taller or longer. Axillary buds have the potential to grow into branches or side shoots, contributing to the plant's overall structure and making the plant bushier or increasing the number of flowers or fruits it produces. 2. Reproduction: Buds can develop into reproductive structures such as flowers, which ultimately produce seeds and fruits for the plant. This enables the plant to continue its life cycle and propagate. 3. Adaptation and Defense: Buds can remain dormant when environmental conditions are not optimal, allowing the plant to conserve energy and resources. In some cases, buds can also develop into defensive structures like thorns or spines, which protect the plant from herbivores and other potential threats. 4. Regeneration: Adventitious buds can help plants regenerate damaged tissue, or even create new plants from cuttings or other separated plant parts, which is a form of asexual reproduction.

Key concepts

Primary Growth

Primary growth in plants occurs primarily through the activity of the apical meristem. This is a region of actively dividing cells located at the tips of roots and shoots.
This growth process is essential for increasing the plant's length, allowing it to reach upwards towards light and downwards into the soil.
During primary growth, the basic structure of the stem is developed. This includes the formation of the epidermis, cortex, and the initial development of the vascular tissue system.
The epidermis protects the plant by serving as a barrier against water loss and pathogens, while the cortex provides storage and support.

• Enhances vertical growth: Supports exposure to sunlight.
• Apical meristem activity: Non-stop cell division leads to stem elongation.

Stem Structure

The stem's surface structure features an outer protective layer known as the epidermis. This layer plays a critical role in safeguarding the internal tissues.
The epidermis often has a waxy cuticle that helps minimize water loss. Underneath the epidermis lies the cortex made mainly of parenchyma cells.
These cells aid in storing nutrients and providing structural support. Within the cortex, there's the vascular tissue system which consists of the xylem and phloem.

• Epidermis: Outer protective layer, often covered by a cuticle.
• Cortex: Contains supportive parenchyma cells.
• Vascular tissue: Composed of xylem and phloem, facilitating nutrient transport.

Buds Function

Buds are small structures on plants that hold great potential for growth and development. They can be found at different positions such as terminally (at the tip), axillary (at the leaf node), or adventitiously (unexpected locations like wounds).
Terminal (or apical) buds are crucial for the primary growth of plants. They contribute to increasing the length of branches or stems.
Meanwhile, axillary buds may grow into lateral branches, flowers, or shoots, significantly enhancing the plant's form and productivity.

• Growth: Ensure the plant grows taller or expands.
• Reproduction: Form flowers, aiding in seed and fruit production.
• Adaptation: Stay dormant in unfavorable conditions.

Vascular Tissue System

The vascular tissue system in plants plays a fundamental role in transport and support. This system is composed of xylem and phloem, each serving distinct but complementary functions.
Xylem is responsible for transporting water and dissolved minerals from the roots up to all parts of the plant. This upward movement is essential for maintaining plant turgor and nutrient distribution.
Phloem, on the other hand, distributes sugars and other organic compounds that are produced during photosynthesis from leaves to other growth areas in the plant.
This flow of nutrients supports growth, repair, and storage processes.

• Xylem: Moves water and minerals from roots to leaves.
• Phloem: Transports photosynthesis products to needed areas.