Problem 9 - Biology: The Unity and Diversity of Life

Question

Sieve tubes are part of ________. a. cortex b. mesophyll c. phloem d. xylem

Step-by-Step Solution

Answer

Sieve tubes are part of the phloem.

Step 1: Understanding the Question

We need to determine which biological structure sieve tubes are a part of. Sieve tubes are components in the plant's vascular system.

Step 2: Exploring Plant Vascular Tissues

Plants have two main types of vascular tissues: xylem and phloem. Phloem is responsible for transporting nutrients like sugars, while xylem transports water.

Step 3: Identifying Sieve Tubes

Sieve tubes are specialized cells found specifically in the phloem. They form conduits for transporting nutrients throughout the plant.

Step 4: Considering the Options

Reviewing the options provided: - Cortex: This is a part of plant tissue, but not directly involved with vascular transport. - Mesophyll: This is responsible for photosynthesis, not related to vascular transport. - Phloem: This is correct as it is where sieve tubes are found. - Xylem: This only carries water, not nutrients.

Step 5: Selecting the Correct Answer

Given the explanation above, the correct answer is option c: phloem.

Key Concepts

phloem

The phloem is a crucial part of the plant vascular system. It functions as the highway for transporting nutrients throughout the plant. Specifically, the phloem is responsible for moving organic nutrients, especially the sugars produced by photosynthesis, from the leaves down to the roots and other parts of the plant that need energy.
These nutrients provide the energy plants require to perform various functions such as growth and development. The flow within the phloem is often referred to as translocation.

• Translocation is driven by a pressure gradient created by the accumulation of sugars in the phloem.
• The phloem consists of living cells that support the active transport of nutrients.

Understanding the phloem's role helps illustrate how plants distribute nutrients effectively and ensures all parts of the plant receive the necessary resources to thrive.

sieve tubes

Sieve tubes are specialized structures within the phloem. They are essential for the transportation of sugars and other nutrients.
Sieve tubes are formed by a series of sieve tube elements aligned end-to-end to create long channels.

• These elements have sieve plates at their junctions that filter and regulate the flow of nutrients.
• Sieve tube elements lose some of their cell components, like the nucleus, to maximize space for transport.
• The companion cells play a vital role in supporting the sieve tube elements by providing them with energy and managing the transport of materials into and out of the tubes.

With these features, sieve tubes serve as the primary pathways for nutrient distribution in the plant.

xylem

The xylem is another integral component of the plant's vascular system. Its primary function is transporting water and dissolved minerals from the roots to the rest of the plant.
Unlike phloem's nutrient transport, xylem mainly moves water and features a different structure optimized for its role.

• The xylem has two types of water-conducting cells: tracheids and vessel elements.
• These cells are typically dead at maturity, forming hollow tubes that facilitate water movement through capillary action and transpiration pull.
• In addition to transport, the xylem also provides mechanical support to the plant, aiding in maintaining its structure.

By understanding the functions of both xylem and phloem, one can appreciate how they work together to ensure a balanced and efficient transport system within plants.