Anatomy of Flowering Plants

The maintenance of the pressure gradient in sieve tubes is crucial for the process of translocation of nutrients, primarily sugars, within the phloem of vascular plants.

Among the given options, the correct answer is: Option D Companion cells Companion cells play a vital role in the maintenance of the pressure gradient in sieve tubes.

These cells are closely associated with sieve tube elements to which they are connected by numerous plasmodesmata.

Companion cells assist in maintaining the pressure gradient through the following mechanisms: 1.

Loading and Unloading of Sugars: Companion cells actively transport sugars into and out of the sieve tubes.

This activity creates a concentration gradient, leading to osmosis which in turn generates turgor pressure within the sieve tubes.

This pressure drives the flow of sap from source tissues (where sugars are produced) to sink tissues (where sugars are utilized or stored).

2.

Metabolic Support: Companion cells provide metabolic support to the sieve tube elements, which lack a nucleus and other organelles necessary for their own metabolism, thereby maintaining the functional integrity of the sieve tubes.

Therefore, companion cells are integral in managing the pressure gradient required for efficient phloem transport, making Option D the correct choice.

Radial vascular bundles are present in roots. Monocot roots have polyarch and exarch condition of xylem.

The correct sequence of tissues in the stelar region of the stem showing secondary growth from pith towards cortex is : Primary Xylem → Secondary Xylem → Secondary Phloem → Primary Phloem

Option B : (B), (C) and (D) only Explanation : Lateral meristems are the meristems that add to the width or girth in a process known as secondary growth.

They are responsible for the secondary growth in plants and are found parallel to the sides of the plants.

1.

Axillary buds (A) are not lateral meristems; they are capable of forming branches or flowers.

2.

Fascicular vascular cambium (B) is a type of lateral meristem.

It contributes to secondary growth and produces secondary vascular tissues.

3.

Interfascicular cambium (C) is also a type of lateral meristem.

It also contributes to secondary growth in the stem.

4.

Cork cambium (D), also called phellogen, is a lateral meristem and it produces the cork, a part of the protective outer layer (periderm) in stems and roots.

5.

Intercalary meristem (E) is not a type of lateral meristem but rather a type of apical meristem located at the base of leaves or internodes on a plant stem, which is involved in primary growth and elongation of the plant.

Therefore, the correct answer is option B : Fascicular vascular cambium (B), Interfascicular cambium (C) and Cork cambium (D) only.

During secondary growth in dicot stem, the cells of medullary rays lie between the vascular bundles become dedifferentiated and give rise to new cambium called interfascicular cambium.

The girdling experiment shows that phloem is the tissue responsible for translocation of food; and that transport takes place in one direction i.e. towards the root.

The large cells around the vascular bundles of C 4 plants form bundle sheath.

These cells have large number of chloroplasts to perform calvin cycle.

Heartwood is inactive physiologically due to deposition of organic compounds and formation of tyloses so it will not conduct water and minerals.

In roots, the root hairs develops from zone of maturation. This zone is differentiated zone thus bearing root hairs.

Cells of vascular cambium divide periclinally both on the outer and inner sides to form secondary permanent tissues, i.e., secondary xylem and secondary phloem.