Question:

Stoma opens, when

Updated On: Jul 29, 2022
  • guard cells swell due to an increase in their water potential
  • guard cells swell by endosmosis due to influx of hydrogen ions (protons)
  • guard cells swell by endosmosis due to efflux of potassium ions
  • guard cells swell due to a decrease in their water potential
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The Correct Option is D

Solution and Explanation

During day time, photosynthesis occurs in guard cells because they contain chloroplast. The soluble sugar formed by this process decreases the water potential of guard cells and hence, resulting in stomatal opening.
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Concepts Used:

The Tissue System

Epidermal Tissue System:

The epidermal tissue system forms the outer-most covering of the whole plant body and comprises epidermal cells, stomata, and the epidermal appendages – the trichomes and hairs. The epidermis is the outermost layer of the primary plant body. It is made up of elongated, compactly arranged cells, which form a continuous layer. The epidermis is usually single-layered.

Ground Tissue System:

All tissues except the epidermis and vascular bundles constitute the ground tissue. It consists of simple tissues such as parenchyma, collenchyma, and sclerenchyma. Parenchymatous cells are usually present in the cortex, pericycle, pith, and medullary rays, in the primary stems and roots. In leaves, the ground tissue consists of thin-walled chloroplast-containing cells and is called mesophyll.

Vascular Tissue System:

The vascular system consists of complex tissues, the phloem, and the xylem. The xylem and phloem together constitute vascular bundles. In dicotyledonous stems, cambium is present between phloem and xylem. Such vascular bundles because of the presence of cambium possess the ability to form secondary xylem and phloem tissues and hence are called open vascular bundles. In the monocotyledons, the vascular bundles have no cambium present in them. Hence, since they do not form secondary tissues they are referred to as closed.

Read More: Plant Tissue