Tag: structure of a leaf

leaf is a green outgrowth of a stem. It performs photosynthesis and provides food to the rest of the plant body. There are different types of leaves found due to climate, water availability, etc. A leaf consists of lamina and petiole, leaves can be monocot or dicot. It contains stomate which helps in gaseous exchange.

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. A hydathode is a type of secretory tissue in leaves, usually found in angiosperms, that secretes water through pores in the epidermis or margin of leaves, typically at the tip of a marginal tooth or serration.
Hydathodes are mainly found in aquatic plants and in some herbaceous plants growing in moist places.
A stoma (plural stomata) is a pore, found in the epidermis of leaves, stems and other organs that is used to control gas exchange.
Aerenchyma is the spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root.
Thus, the correct answer is option A.

Marginal meristem is the meristem located along the margin of a leaf primordium and forming the leaf blade. The apical meristem or growing tip, is a completely undifferentiated meristematic tissue found in the buds and growing tips of roots in plants.
Intercalary meristems are capable of cell division, and they allow for rapid growth and regrowth of many monocots. Intercalary meristems at the nodes of bamboo allow for rapid stem elongation, while those at the base of most grass leaf blades allow damaged leaves to rapidly regrow.
In mass meristem the cells divide in all planes to form bulk of tissue. this type of meristem takes part in the formation of cortex, pith, endosperm and sporangia.
Therefore, the correct answer is option D.

A hydathode is a type of secretory tissue in leaves, usually found in angiosperms, that secretes water through pores in the epidermis or margin of leaves, typically at the tip of a marginal tooth or serration. 

• A leaf is said to be hypostomatous where stomata are present on abaxial surface only (lower surface). Most tree species of dicotyledons possess such leaves. Ex. Ficus, Nerium etc.
• Hypostomatous plants are non-aquatic plants in which stomata are present on the lower surface because their function is to regulate the amount of water in the leaf and being on the bottom prevents it from absorbing too much water in the rain or transpirating too much in the sun.

Lenticels and hydathodes both lack guard cells and hence, their openings are not regulated. Hydathodes are openings at end of vascular supply to leaves and are involved in the process of guttation, which is loss of water in liquid form. Lenticels are lens shaped openings in big woody trunks of trees for gaseous exchange.

Palisade tissues are present just beneath the epidermis and are composed of elongated cells arranged parallel to each other in one to three layers. These cells are marked by the presence of abundant chloroplast and thus provide the site for photosynthesis. Loosely arranged irregular cells with large intercellular spaces make the spongy parenchyma, which is present just beneath the palisade tissue. They contain less chloroplast as compared to that of palisade tissue. Thus, the correct answer is option A.

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. The shape of lenticels is one of the characteristics used for tree identification. So, lenticels helps in gaseous exchange and not in transpiration or vegetative propagation. 

The cortex is the outermost layer of the stem or root of a plant, bounded on the outside by the epidermis and on the inside by the endodermis. In plants, it is composed mostly of differentiated cells, usually large thin-walled parenchyma cells of the ground tissue system. The outer cortical cells often acquire irregularly thickened cell walls, and are called as collenchyma cells. Some of the outer cortical cells may contain chloroplasts but usually these cells lacks chloroplast. It is responsible for the transportation of materials into the central cylinder of the root through diffusion and may also be used for food storage in the form of starch. cortex, in plants, tissue of unspecialized cells lying between the epidermis and the vascular or conducting, tissues of stems and roots.
Cortical cells may contain stored carbohydrates or other substances such as resins, latex, essential oils, and tannins. Cells of cortex are living and contains nucleus and nucleolus.
Thus, the correct answer is option A.

Plants have three types of meristems, the apical meristem, the intercalary meristem and the lateral meristem. Leaves are derived from shoot apical meristem which swells to form undifferentiated leaf primordium which divides into two systems that develop leaf blades and leaf sheaths. The growth of leaf blades occurs due to cells division but is mainly from cell elongation. The flattened blade form is derived from the marginal meristem present at the margins of leaf axis. Meristem present at the sides and causes increase in girth of the plant is termed as lateral meristem and is not involved in leaf formation.
Therefore, the correct answer is option C.