Which component of the transport system in plants is primarily responsible for the movement of water and minerals from the roots to the leaves?
Phloem
Xylem
Sieve tubes
Companion cells
Correct Answer:B
Explanation
Correct Option: B. Xylem
Detailed Explanation:
Understanding Plant Transport Systems:
Plants have a complex transport system that consists of two main types of vascular tissues: xylem and phloem. Each of these tissues has distinct functions in the plant.
Role of Xylem:
The xylem is primarily responsible for the transport of water and dissolved minerals from the roots to the leaves. This process is crucial for plant survival as it helps in photosynthesis, nutrient transport, and maintaining turgor pressure (the pressure of the cell contents against the cell wall).
Mechanism of Water Transport:
Water is absorbed by the roots from the soil through root hairs. Once in the root, water travels through the xylem vessels, which are specialized tubes that facilitate this upward movement.
The movement of water in the xylem occurs mainly through a process called transpiration. As water evaporates from the stomata (tiny openings on the leaves), it creates a negative pressure that pulls more water upward from the roots through the xylem. This is often referred to as the "cohesion-tension theory."
Why Other Options Are Incorrect:
A. Phloem: The phloem is responsible for transporting sugars and other organic nutrients produced during photosynthesis from the leaves to other parts of the plant. It does not transport water and minerals; hence, it is not the correct answer.
C. Sieve tubes: Sieve tubes are part of the phloem and are specifically involved in the transport of sugars. They do not play a role in the movement of water and minerals, making this option incorrect.
D. Companion cells: Companion cells are also associated with the phloem and assist in the transport of nutrients by supporting sieve tubes. They do not transport water and minerals, so this option is also incorrect.
Summary of Xylem Function:
The xylem consists of various cell types, including tracheids and vessel elements, which are designed to facilitate the efficient movement of water. The structure of xylem cells allows for minimal resistance to water flow, making them highly effective for their role.
Revision Summary:
The xylem is responsible for transporting water and minerals from the roots to the leaves.
Water movement in the xylem is driven by transpiration and the cohesion-tension theory.
Phloem, sieve tubes, and companion cells are involved in the transport of nutrients, not water.
Understanding the distinct roles of xylem and phloem is crucial for grasping plant physiology.