Question

Select the incorrect statement from the following: (a) End walls of sieve tube have sieve plates. (b) Sieve tube and companion cells are connected by pit present between common longitudinal wall. (c) Companion cells are specialized parenchymatous cells having nucleus which controls the function of sieve tubes (d) Phloem parenchyma is present in most of the monocots.

Short answer

The incorrect statement is (d) 'Phloem parenchyma is present in most of the monocots.'

Step-by-step solution

Analyze Statement (a)

Statement (a) says 'End walls of sieve tube have sieve plates.' Sieve plates are indeed found at the end walls of sieve tubes, this is a correct statement.

Analyze Statement (b)

Statement (b) says 'Sieve tube and companion cells are connected by pit present between common longitudinal wall.' This statement is also correct. Sieve tubes and companion cells are interconnected by plasmodesmata, small channels occurring at pit fields.

Analyze Statement (c)

Statement (c) says 'Companion cells are specialized parenchymatous cells having nucleus which controls the function of sieve tubes.' This statement is true, companion cells do control the function of sieve tubes and they have a nucleus while sieve tubes do not.

Analyze Statement (d)

Statement (d) says 'Phloem parenchyma is present in most of the monocots.' This is however incorrect. Phloem parenchyma is absent or very scarce in most monocotyledons, thus making this statement false.

Key concepts

Sieve Tubes

Sieve tubes are a critical component of the phloem, a type of plant tissue responsible for transporting nutrients throughout the plant. The primary function of sieve tubes is to conduct soluble organic compounds, primarily sugars, which are produced during photosynthesis in the leaves to other parts of the plant that require energy.
Sieve tubes are composed of multiple sieve tube elements, which are living cells that lack a nucleus at maturity. Because of this, they need to be closely associated with companion cells. One unique feature of sieve tubes is the presence of sieve plates. Sieve plates are located at the end walls of sieve tube elements and consist of clusters of pores. These pores allow for the free movement of phloem sap between adjacent sieve tube elements, facilitating efficient nutrient transport. The arrangement and function of sieve plates are crucial for the plant's overall health and efficiency in nutrient distribution.

Companion Cells

Companion cells are specialized parenchymatous cells found in the phloem of angiosperms. They play a vital role in the functioning of sieve tubes. While sieve tubes lack a nucleus at maturity, companion cells maintain their nucleus and other organelles, allowing them to support and control the activities of sieve tubes.
These cells are connected to sieve tube elements via plasmodesmata, which are microscopic channels that enable the transfer of materials and signals between the two cells. This connection is essential because it allows companion cells to aid in the maintenance of the sieve tube elements, facilitating their function in nutrient transport.
By controlling what substances enter and leave the sieve tubes, companion cells help regulate the flow of nutrients across the plant. Their presence ensures that the plant's nutritional needs are met efficiently.

Monocotyledons

Monocotyledons, often referred to as monocots, are a large group of flowering plants characterized by having a single embryonic leaf or cotyledon. Some common examples include grasses, lilies, and orchids. Their unique structure differentiates them from dicotyledons (dicots), which have two cotyledons.
One of the distinctive features of monocots is their vascular structure. In many monocots, phloem parenchyma, a type of supportive cell found in the phloem, is either absent or present in very limited quantities. This contrasts with dicots, where phloem parenchyma is more consistently present.
The scarcity or absence of phloem parenchyma in monocots influences how these plants are structured and function. Their vascular bundles are more dispersed throughout the stem, which can affect how nutrients and water are transported.

Phloem Parenchyma

Phloem parenchyma cells are an important component of the phloem tissue found mainly in dicotyledons. These cells play a supportive role in the transport of nutrients within the plant. They are living cells that help in the lateral transport of nutrients and contribute to the overall structure and stability of the plant.
Unlike other phloem cells such as sieve tubes and companion cells, phloem parenchyma cells are not directly involved in long-distance nutrient transport. Instead, they provide a supportive environment that facilitates the overall function of the phloem.
While the presence and density of phloem parenchyma vary across different plant types, they are typically more prominent in dicots than in monocots. The absence or limited presence of these cells in monocots highlights their unique vascular bundle configuration which differs from the more organized structure found in dicots.