Question

Which of the following cell types stay alive when they mature? Choose all that apply. a. companion cells c. tracheids b. sieve elements d. vessel elements

Short answer

Companion cells and sieve elements stay alive when mature.

Step-by-step solution

Understanding the Options

We need to identify which cell types, among the options given, remain alive once they mature. Let's examine each cell type: companion cells, sieve elements, tracheids, and vessel elements.

Analyzing Companion Cells

Companion cells are part of the phloem and are alive when mature. They support the metabolic functions of sieve tube elements by providing the necessary molecules that sieve elements require to function.

Analyzing Sieve Elements

Sieve elements are also part of the phloem and remain alive when mature. Although they lose some organelles during maturation, they stay functionally alive due to their connection with companion cells.

Analyzing Tracheids

Tracheids are part of the xylem tissue. They become dead when they mature. Their role is to conduct water, and their cell walls, strengthened by lignin, support this function after they die.

Analyzing Vessel Elements

Vessel elements, like tracheids, are part of the xylem. They also die upon maturation and form part of the tube-like structure to efficiently transport water throughout the plant.

Conclusion

Based on the analysis: companion cells and sieve elements remain alive when mature, while tracheids and vessel elements do not.

Key concepts

Companion Cells

Companion cells are crucial components of the phloem in plant tissue. These cells stay alive when they mature, and this vitality is essential for their primary function. Companion cells are closely associated with sieve elements, and their main role is to support these cells through various metabolic processes.

They provide the necessary nutrients and molecules that sieve elements need but can't produce on their own. This support includes supplying ATP and aiding in the transport of photosynthesis products. The relationship between companion cells and sieve elements is symbiotic because neither cell type can function optimally without the other.

• They retain their nucleus and other organelles, helping maintain cellular functions.
• They facilitate the loading and unloading of the sieve tubes.

Sieve Elements

Sieve elements, another integral component of phloem, are interesting because they remain alive, yet they lose many functions as they mature. While developing, they lose their nucleus, ribosomes, and vacuoles, which is unusual for cells that remain alive. Despite this loss, they continue to function due to their dependency on companion cells.

Sieve elements are responsible for the transportation of sugars and nutrients within plants. Their structure allows them to form long tubes, known as sieve tubes, which extend throughout the plant.

• They have sieve plates at both ends to aid the flow of nutrients.
• Stay functionally alive by relying on companion cells for metabolic assistance.

This unique partnership is vital for the plant's ability to distribute the nutritional products of photosynthesis. Without sieve elements working in tandem with companion cells, plants wouldn't be able to transport sugars from leaves to other parts.

Xylem

Xylem is a fundamental tissue responsible for water and nutrient conduction from roots to the rest of the plant. Unlike phloem components like companion cells and sieve elements, xylem tissue contains cells that die when they mature.

Tracheids and vessel elements, the primary cells found in xylem, are dead at maturity. This might seem counterintuitive for tissue with such an essential role, but the death of these cells is crucial.

• Tracheids are elongated cells that help support the plant.
• Vessel elements form tubes for efficient water transport.
• Both cell types have lignified walls that remain rigid and facilitate the movement of water through capillary action.

Thus, the strength and durability of dead tracheids and vessels are vital for maintaining structure and facilitating water movement within the plant.

Phloem

Phloem works alongside xylem to conduct substances within the plant, but whereas xylem transports water, phloem's primary duty is to distribute the sugars and nutrients created during photosynthesis. Phloem consists of live cells like sieve elements and companion cells, which collaborate to perform its functions.

Due to the complexity of transporting organic compounds, the symbiotic relationship between sieve elements and companion cells becomes even more critical. The phloem is versatile and flexible, unlike the rigid structure of xylem.

• Allows the movement of nutrients upwards and downwards through the plant.
• Consists of living tissues, ensuring active transport of substances.
• Sieve plates facilitate the directional flow of nutrients.

By balancing the transport system alongside xylem, phloem ensures that nutrients and energy produced in certain areas, like leaves, are available throughout the plant.