Plant Transport and Physiology

Light and temperature are important for the life of plants. This paves the way for the importance of photoperiodism and vernalization in flowering plants.

Plant organs can detect a change in their orientation with respect of gravity because atleast they have to be kept for a week. When it is kept for a week, slowly changes in orientation of gravity could be sensed. This sensation is shown by them as they posses several tropic movements. Geotropism makes the changes in the plant. Shoots are negatively geotropic and roots are positively geotropic.

Plants require four factors for its growth like:-

The endodermis is the central, innermost layer of cortex in some land plants. It is made of compact living cells surrounded by an outer ring of endodermal cells that are impregnated with hydrophobic substances (Casparian Strip) to restrict apoplastic flow of water to the inside. The endodermis is the boundary between the cortex and the stele. In many seedless vascular plants, the endodermis is a distinctly visible layer of cells immediately outside the vascular cylinder (stele) in roots and shoots. In most seed plants, especially woody types, an endodermis is absent from the stems but is present in roots. 

Stoma (plural stomata) is a pore, found in the epidermis of leaves, stems and other organs that is used to control gas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening. Stomata is absent in cork or phellem. A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the bark of woody stems and roots of dicotyledonous flowering plants. It functions as a pore, providing a pathway for the direct exchange of gases between the internal tissues and atmosphere through the bark, which is otherwise impermeable to gases. Cork contains lenticels. Thus, option A is correct. Passage cells are endodermal cells of older roots which have retained thin walls and Casparian strips rather than becoming suberized and waterproof like the other cells around them, to continue to allow some symplastic flow to the inside. Experimental evidence suggests that passage cells function to allow transfer of solutes such as calcium and magnesium into the stele, in order to eventually reach the transpiration system. Sieve tube elements lacks nuclei. Quiescent zone is present in root apex. 

Cellulosic materials are comprised of lignin, hemicellulose as well as cellulose. So, these are called as lignocellulosic materials. One main function of lignin is to provide structural support for the plant. Cellulose molecules are consisting of long chains of glucose molecules. This is for that the starch molecules to have a different structural configuration. So, the preparation of pure cellulose by removing lignin is an important step in the manufacture of pulp. It is for the paper industry from the woody tissues of plants to make a better quality paper.

Removal of water from the wood by prolonged heating at approximately $50^{0} C$. The other options are not relevant.

Thus, the correct answer is option D.

The epidermis is a single layer of cells found on outer layers in different parts of the plant. It forms a barrier between the underlying tissues in a plant with the surrounding environment. Therefore, it is protected from adverse environmental conditions.

The presence of stomata and guard cells in the epidermal tissue will help in the exchange of $O _{2}$ and $CO _{2}$.

Conduction of water and minerals in plants takes place in conducting vessels. It is located in the core, known as xylem. Thus conduction of water is not the function of the epidermis but, it is of xylem.

The correct option is C.

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.

• 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.