Question

Read the following statements with 1-2 blanks in each one of them. (i) In monocot root, a large number of vascular bundies are arranged in the form of a cound the central (ii) Due to the presence of \(-\) the endodermal cells do not allow wall to wall movement of substances between cortex and pericycle, in a primary dicot root. (iii) The epidermis of stem of sunflower bears several unbranched (iw) The central portion of a dicot stem is usually occupied by comprising of thin walled parenchymatous Cells. Fill in the blanks in the above statements and select the correct option for any two of them, (a) (i) ring, pith; (i) hypodermis (b) (ii) casparian strips; (iii) unicellular (c) (i) fing, cortex; (iv) vascular bundles (d) (iii) multicellular; (iv) pith

Short answer

For (i), the correct word is 'ring' and not 'pith', making (a) incorrect. For (ii), 'casparian strips' is correct, as in (b). For (iii), the correct word is 'unicellular', making (b) a correct choice. For (iv), 'pith' is the correct answer, but 'vascular bundles' is not correct, rejecting (c). Thus, the correct options are (ii) b. casparian strips; (iii) b. unicellular.

Step-by-step solution

Identify Correct Options for Statement (i)

The statement (i) refers to the root structure of monocots. Monocot roots are characterized by the presence of vascular bundles in a certain pattern. Among the options provided, the correct word to fill the blank would be one that describes this pattern. Option (a) suggests 'ring' and 'pith'. Pith is located at the center and a 'ring' arrangement of vascular bundles is characteristic of monocot roots.

Identify Correct Option for Statement (ii)

The statement (ii) discusses the movement of substances in the root. The blank should be filled with a structure that prevents wall to wall movement. The 'casparian strips' in the endodermis of the root block the passive flow of substances from the cortex to the pericycle, only allowing regulated transport. Therefore, option (b) 'casparian strips' is correct for statement (ii).

Identify Correct Options for Statements (iii) and (iv)

Statement (iii) discusses the epidermal structures in the stem of a sunflower. The correct word to fill the blank should describe the type of epidermal structures found. Option (b) 'unicellular' is correct as sunflower stems have unicellular epidermal outgrowths known as trichomes. Statement (iv) refers to the central portion of a dicot stem which is typically occupied by 'pith', not 'vascular bundles' as the vascular bundles are arranged in a ring surrounding the pith in dicot stems. Hence, the correct option to fill the blank in the statement (iv) is 'pith' which appears in option (a).

Key concepts

Monocot Root Structure

Understanding the monocot root structure is crucial for botany students. Monocot roots, like those found in grasses and grains, have a distinctive arrangement of tissues. These roots typically lack a well-defined secondary growth stage and are characterized by the vascular bundles being arranged in a ring pattern around the center of the root, which is filled with pith. This ring configuration provides strength and stability to the plant.

The outermost layer of the monocot root is the epidermis, which helps in protection and absorption of water. Right inside the epidermis is the cortex, composed mostly of parenchyma cells, which store food and help in the diffusion of water to the center. The innermost layer of the cortex is the endodermis, acting as a checkpoint for minerals due to the presence of casparian strips.

Casparian Strips

Speaking of checkpoints, let's discuss casparian strips, an essential feature in the anatomy of roots. These are band-like structures made of a waxy substance called suberin, found in the cell walls of endodermal cells. The primary function of casparian strips is to block the passive movement of water and solutes from the soil into the vascular system of the plant, ensuring that only selected substances can pass into the vascular tissue.

This selectivity is key in maintaining the plant's internal environment and ensuring the essential nutrients are absorbed while harmful substances are excluded. As such, casparian strips are critical for the plant's ability to regulate the uptake and distribution of water and minerals from the soil.

Dicot Stem

Moving above ground, the dicot stem, such as that of a sunflower, features a more complex structure than its monocot counterparts. Dicot stems typically have an outer protective layer called the epidermis, often with hair-like structures called trichomes that can be either unicellular or multicellular.

Below the epidermis, there may be a hypodermis followed by ground tissue, which is mainly made of parenchyma cells and forms the bulk of the stem. The central part of the dicot stem is occupied by the pith, a tissue composed of soft, spongy parenchyma cells that store and transport nutrients throughout the plant. Surrounding the pith is a ring of vascular bundles, each containing both xylem and phloem, key for the transport of water, minerals, and food.

Vascular Bundles

Last but not least, let's take a closer look at vascular bundles. These are essential components of a plant's transportation system. Vascular bundles consist of xylem and phloem tissues, arranged in a specific pattern depending on whether the plant is a monocot or a dicot.

In monocots, vascular bundles are scattered throughout the stem, while in dicots, they are organized in a ring surrounding the pith. They provide support and a conduit for the flow of essential substances. Xylem transports water and dissolved minerals from the roots to the rest of the plant, and phloem distributes sugars and other nutrients from the leaves to non-photosynthetic parts of the plant. The arrangement of these bundles contributes to the overall strength and flexibility of the plant.