Question

Which of the following is epidermal appendage? (a) Trichome (b) Guard cell (c) Sclereid (d) Subsidiary cell

Short answer

The epidermal appendage from the given options is Trichome.

Step-by-step solution

Understanding Epidermal Appendages

Epidermal appendages are structures that grow out of the epidermal, or outermost, layer of an organism. In plants, these can include things like hairs, glands, and stomata. So, this makes the task to identify from the given options, which one is an epidermal appendage.

Evaluating Option A - Trichome

Trichomes are hair-like outgrowths of the epidermis of plants that protect the plant from various factors. This structure fits the definition of an epidermal appendage.

Evaluating Option B - Guard Cell

Guard cells are cells surrounding each stoma in the epidermal layer. They regulate the opening and closing of the stomata but they are not appendages.

Evaluating Option C - Sclereid

Sclereids are a type of sclerenchyma cells in plants that function primarily for support. These are not epidermal appendages.

Evaluating Option D - Subsidiary Cell

Subsidiary cells are specialized plant cells that can be found associated with the guard cells. However, these cells are also not an appendage of the epidermis.

Key concepts

Trichomes

Trichomes are fascinating structures that many students may know simply as the 'hairs' on the surface of plant leaves and stems. But there's much more to trichomes than meets the eye. They play several roles in plant defense and survival, which includes deterring herbivores by being unpleasant to eat due to their texture or by trapping or poisoning insects. Trichomes can also reduce the evaporation of water from the plant surface, critical in hot and dry environments. Additionally, they reflect sunlight, reducing leaf temperature, and they can trap air to create a layer of insulation that protects against temperature extremes.

Some trichomes are glandular, meaning they secrete substances like essential oils, which contribute to a plant's scent or which can serve as a defense mechanism against pests and diseases. These diverse functions make trichomes an important topic for students to understand as they explore plant biology and the ingenious ways plants adapt to their environment.

Guard Cells

Guard cells are specialized cells in the epidermis of plants that serve a critical function in the regulation of gas exchange. They are shaped somewhat like two lips that open and close around a stoma, which is a pore on the leaf's surface. Understanding guard cells is key to understanding how plants maintain homeostasis and respond to environmental conditions.

Role in Photosynthesis and Transpiration

During photosynthesis, guard cells regulate the opening of stomata to allow carbon dioxide to enter while minimizing the loss of water through transpiration. This balancing act is a complex process influenced by light, carbon dioxide concentration, and the internal water pressure within the guard cells, known as turgor pressure. When turgor pressure is high, guard cells swell and open the stoma. When it drops, the guard cells become flaccid and the stoma closes.

Students studying plant physiology will appreciate how guard cells are an excellent example of plant adaptation, contributing to the ability of terrestrial plants to survive and thrive on land.

Plant Epidermis

The plant epidermis is the outermost layer of cells covering the entire plant body, including leaves, flowers, roots, and stems. It acts as a protective barrier between the plant and its environment and is involved in a myriad of functions that are crucial for plant survival. When thinking about the plant epidermis, it's helpful to compare it to skin, as it serves a similar purpose in many ways — protecting internal structures and regulating interactions with the surrounding world.

A single layer of tightly packed cells, the epidermis, is often coated with a waxy substance called the cuticle, which helps to conserve water by reducing transpiration rates. The presence of stomata, which are flanked by guard cells as previously described, allows for gas exchange necessary for photosynthesis, while root hair cells, which are extensions of epidermal cells in the root, increase the surface area for water and nutrient absorption.

Sclereids

Sclereids are a less commonly discussed group of cells, but they play a vital role in the structural integrity and protection of plants. They are a type of sclerenchyma cell, which are known for their toughness and rigidity, and are primarily associated with providing support to various parts of the plant. Sclereids can be found in all parts of the plant, from leaves and stems to seeds and fruits. These cells have thick, lignified cell walls that make them very hard and resistant to pressure and damage.

Variety of Forms

Sclereids come in varying shapes and sizes, which is why students may encounter them under different names such as stone cells or brachysclereids. A familiar example is in pear fruit, where sclereids create the gritty texture. By understanding sclereids and their function, students can better appreciate the intricate ways plants structure themselves to ensure both durability and adaptability to environmental stresses.