Plant Transport and Physiology

Suberin is a waterproofing waxy layer. Its main function is to serve as a barrier to movement of water and solutes. A mature cork cell is nonliving and has cell walls that are composed of a waxy substance that is highly impermeable to gasses and water, called as suberin. Thus, option B is correct. 

• In deserts, water is scarce and saving water is a major step which plants of this region have to undertake. So in many of the desert plants like Yucca, creosote, cactus, etc, the epidermis has a thick waxy coating of cutin. 
• This restricts the loss of water through transpiration. In desert plants, the epidermis has a thick waterproof coating that is not made of suberin, elastin or chondrin. 

Therefore, the correct answer is option A.

• Cork cells are formed as a part of the bark. The waterproof waxy layer present on the cork cell is the suberin., Quercus suber. Its main function is as a barrier to the movement of water and solutes. Suberin is highly hydrophobic and a somewhat 'rubbery' material. In roots, suberin is deposited in the radial and transverse cell walls of the endodermal cells. 
• This structure, known as the Casparian strip or Casparian band, functions to prevent water and nutrients taken up by the root from entering the stele through the apoplast. Pectin, lignin, and cellulose are not hydrophobic materials. 

• The epidermis is the outermost covering and acts as a protective layer. it is formed initially by protoderm. 
• These are thin-walled as they are generally made up of parenchymatous cells. 
• The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds, and (especially in roots) absorbs water and mineral nutrients. 
• The epidermal tissue includes several differentiated cell types of epidermal cells, guard cells, subsidiary cells, and epidermal hairs (trichomes). They have thin-walled cells. 

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 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.

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.

Loading of sucrose into the phloem at the source creates a hypertonic condition (high solute concentration) rather than hypotonic, drawing water in by osmosis to generate high pressure. Therefore, statement B is factually incorrect and represents the correct choice.

Plants eliminate some waste through diffusion. During the day, excess oxygen gas produced by photosynthesis is released through the stomata. Stomata are microscopic pores in leaves. Carbon dioxide produced by respiration is normally used up during photosynthesis. At night, however, as photosynthesis slows, carbon dioxide is not used up as fast as it is produced, and it is released as a waste product. Plants also produce oxygen as a by-product of photosynthesis. The oxygen that is not used for respiration is also excreted through the stomata. Plants do not excrete gases through flowers, roots and seeds. 

In soil rich in moisture content water floods a plant root system. Leaves can retain only a finite amount of water. Excess water i.e xylem sap from the roots is given out through pores or edge of leaves in the form of droplets. This process is called guttation. As this water contains different organic and inorganic substances from the plant it is considered impure. Also, guttation is of universal occurrence. Thus the correct answer is option C.

Guttation is the phenomenon of the release of small water droplets from the pores of the plants. It is done in order to release the extra water out of the plant in very humid conditions. It is commonly seen in mesophytes.

When a well-watered shoot is cut near the base, xylem sap often exudes out due to positive hydrostatic pressure built up in the roots, known as root pressure. Guttation involves the loss of liquid water through hydathodes, and transpiration creates negative pressure (tension), not positive exudation.