Question

Which of the following are long and narrow cells? (a) Nerve cells (b) WBC (c) Columnar epithelial cells (d) Tracheid

Short answer

The long and narrow cells among the options are nerve cells and tracheids.

Step-by-step solution

Identify Nerve Cells

Nerve cells, also known as neurons, are some of the longest cells in the body. They contain long extensions called axons, which can extend from the brain to the spinal cord or to other areas of the body.

Identify WBC

White Blood Cells, or WBC, are not naturally long and narrow. They are generally round in shape. Some types can change shape but not into a long, narrow form.

Identify Columnar Epithelial Cells

Columnar epithelial cells are named for their column-like shape. Though longer than they are wide, they are not considered 'long and narrow' in the typical sense as they are not significantly elongated.

Identify Tracheid

Tracheids are a type of water-conducting cell in vascular plants. They are long, narrow cells that help transport water and nutrients.

Key concepts

Nerve Cells

Nerve cells, commonly known as neurons, play a crucial role in the nervous system, acting as the communication framework for transmitting signals throughout the body. These cells are unique due to their structure, which supports their primary function of conveying information. A neuron consists of three main parts: the cell body, dendrites, and the axon.

The cell body, or soma, houses the nucleus and other organelles necessary for the neuron's function. Dendrites are tree-like structures that receive signals from other neurons. However, where neurons really stand out is their axon. Axons are long, slender projections that transmit signals away from the cell body. The length and narrowness of axons allow neurons to connect with distant parts of the body, such as from the brain to various limbs.

• Neurons are designed for efficient communication, facilitated by the axon's ability to reach long distances.
• The length of an axon can vary significantly, with some reaching over a meter long in humans.
• Neurons transmit electrical impulses, which are crucial for voluntary and involuntary actions.

In summary, nerve cells are specialized for quick and efficient communication over long distances, vital for the functioning of the body's systems.

Columnar Epithelial Cells

Columnar epithelial cells are a type of epithelial cell shaped like columns or cylinders, hence their name. These cells are taller than they are wide, giving them a columnar appearance, which suits their role in the body.

These cells line many organs and structures within the body, such as the intestines and respiratory tract. They often feature microvilli, small projections that increase the surface area for absorption along the intestinal lining. This adaptation allows them to process nutrients efficiently.

• Columnar cells often form a protective barrier while also permitting absorption and secretion of substances.
• They can be found in single-layered (simple) or multi-layered (stratified) arrangements depending on their location and function in the body.
• Some columnar cells are ciliated, possessing hair-like projections that help move substances along the cell surface.

The design of columnar epithelial cells makes them perfect for functions that require surface area, such as absorbing nutrients or producing mucus.

Tracheid

Tracheids are elongated cells that are a key component of the xylem, the vascular tissue that transports water and nutrients from the roots to other parts of the plant. These cells are particularly prominent in the wood of conifers but are found in all vascular plants.

The structure of tracheids is adapted for water conduction. They are long and narrow, which facilitates continuous water flow over great distances without losing efficiency. The presence of pits, which are thin areas in the cell wall, allows water to move laterally from one tracheid to another, ensuring that water can reach all parts of the plant.

• Tracheids are dead at maturity, meaning they lack cytoplasm, making them effectively tubular conduits for water transport.
• They have strong walls made of lignin, which provides structural support to the plant.
• Compared to other xylem cells, like vessel elements, tracheids are more primitive but still highly effective for transporting fluid.

In essence, the structural design of tracheids is essential for their role in water distribution and plant support, making them fundamental to a plant's vascular system.