Tag: kinds of plant tissue

The epidermis is the outermost cellular layer which covers the whole plant structure, i.e., it covers roots, stem, leaves, flowers and fruit. It is composed of a single layer of living cells, although there are exceptions. Epidermis is usually closely packed, without intercellular spaces or chloroplasts. The outer walls, which are exposed to the atmosphere and usually thickened and may be covered by a waxy, waterproof cuticle which are made up of cutin. So, their side walls stick together due to the wax secretion. 

The epidermis is the outermost cellular layer which covers the whole plant structure, i.e., it covers roots, stem, leaves, flowers and fruit. It is composed of a single layer of living cells, although there are exceptions.

A conspicuous part of the primary structure of many roots is the endodermis, the innermost layer of the cortex, the walls of which often become conspicuously thickened, plus strips of suberized tissue on the radial walls called as 'Casparian strips.'

The epidermis is a single layer of cells that covers the leaves, flowers, roots and stems of plants. It forms a boundary between the plant and the external environment. Its main function is protection. It has small opening known as stomata.

• Epidermis is the outermost layer of the plant body. It carries out functions as follows:

1. It covers the body from outside and protects from pathogen attack and atmosphere changes.  
2. It shows the presence of stomata (minute pore-like structure) on leaves. Stomata are involved in gaseous exchange (oxygen, carbon dioxide) with the atmosphere. It also shows the presence of lenticels on the woody stem for gaseous exchange. 
3. The stomata present on leaves are also involved in transpiration (water evaporation from plant body). Stomata are guarded by guard cells, which close and open the stomata as per requirement. Therefore, epidermis bearing stomata also check for water loss from the plant body. 
4. The epidermis is protected by cuticle at some parts of the tree and it helps to stop water loss by evaporation.

• Lignin is a substance, which is impermeable to water. It is absent in cork cells.
• Pectin is not present in cork cells. 
• Hemicellulose is permeable to water and gases.
• Cork cells are dead and have cell walls composed of a waxy substance "suberin", which is highly impermeable to gases and water. This substance prevents water loss from the stem. 

Bulliform cells or motor cells are large, bubble-shaped epidermal cells that occur in groups on the upper surface of the leaves of many grasses. Loss of turgor pressure in these cells causes leaves to roll up during water stress. During drought, the loss of moisture through vacuoles induces bulliform cells to cause the leaves of many grass species to close as the two edges of the grass blade fold up toward each other. Once adequate water is available, these cells enlarge and the leaves open again. Folded leaves offer less exposure to sunlight, so they are heated less thus, reducing evaporation and conserving the remaining water in the plant and occur on the leaves of many monocotyledons but are probably best known in grasses. They are thought to play a role in the unfolding of developing leaves and in the rolling and unrolling of mature leaves in response to alternating wet and dry periods. So, motor cells helps in inward rolling of leaves and not in transpiration or guttation. 
Thus, the correct answer is option A.

The periderm is the secondary protective dermal tissue that replaces the epidermis during growth in thickness of stems and roots of gymnosperms and dicotyledons i.e., secondary growth.