BIO BOTANY [2 Mark Questions]

A hydathode is a type of epidermal pore, commonly found in higher plants. Structurally, hydathodes are modified stomata, usually located at leaf tips or margins, especially at the teeth. Hydathodes occur in the leaves of submerged aquatic plants such as ranunculus fluitans as well as in many herbaceous land plants.q

Some of the epidermal cells of the grass are filled with silica. They are called silica cells.

Cambium consists of brick shaped and thin walled meristematic cells. It is one to four layers in thickness. These cells are capable of forming new cells during secondary growth.

All the tissues inside the endodermis comprise the stele. This includes pericycle, vascular system and pith.

Xylem and phloem are present on different radii alternating with each other. The bundles are separated by parenchymatous tissue. (Monocot and Dicot roots).

The cytoplasmic nucleated parenchyma, is associated with the sieve cells of Gymnosperms. Albuminous cells in Conifers are analogous to companion cells of Angiosperms. It also called as strasburger cells.

In true root endodermis, radial and inner tangential walls of endodermal cells possess thickenings of lignin, suberin and some other carbohydrates in the form of strips they are called casparian strips.

Sometimes in young stem, chloroplasts develop in peripheral cortical cells, which is Called chlorenchyma.

Two functions of epidermal tissue system in plants:

1. This system in the shoot checks excessive loss of water due to the presence of cuticle.
2. Epidermis protects the underlying tissues.

In some Xerophytic plants (eg: Cycas, Nerium), stomata is sunken beneath the abaxial leaf surface within stomatal crypts. The sunken stomata reduce water loss by transpiration.

Some cells of upper epidermis (eg: Grasses) are larger and thin walled. They are called bulliform cells or motor cells. These cells are helpful for the rolling and unrolling of the leaf according to the weather change.

It is made up of single layer of parenchyma cells which are arranged compactly without intercellular spaces. It is devoid of epidermal pores and cuticle. Root hair is always single celled, it absorbs water and mineral salts from the soil. The another important function of piliferous layer is protection.

Phloem consists of four types of Cells: Sieve elements Companion cells Phloem parenchyma Phloem fibres.

Protoxylem lies towards the .centre and meta xylem towards the periphery this condition is called Endarch. It is seen in stems.

These fibres are present in the phloem. Natural Bast fibres are strong and cellulosic. Fibres obtaining from the phloem or outer bark of jute, kenaf, flax and hemp plants. The so called pericyclic fibres are actually phloem fibres.

Between Libriform fibres and Fibre tracheids:

Libriform fibres	Fibre tracheids
1. These fibres have slightly lignified secondary walls with simple pits. These fibres are long and narrow.	1. These are shorter than the libriform fibres with moderate secondary thickenings in the cell walls. Pits are simple or bordered.

The sclereids are present in the leaf lamina of Olea europaea. They are very much elongated fibre like and about 1mm length.

Isodiametric sclereids, with hard cell wall. It is found in bark, pith cortex, hard endosperm and fleshy portion of some fruits. eg: Pulp of Pyrus.

It is the most common type of collenchyma with irregular arrangement and thickening at the angles where cells meet., eg: Hypodermis of Datum and Nicotiana.

Apical cell theory is proposed by Nageli. The single apical cell or apical initial composes the root meristem. The apical initial is tetrahedral in shape and produces root cap from one side. The remaining three sides produce epidermis, cortex and vascular tissues. It is found in vascular cryptogams.

It is the inner zone of shoot apex,that forms cortex and stele of shoot.

Present in apices of root and shoot. It is responsible for increase in the length of the plant, it is called as primary growth.

Two characters of meriste – matic tissue:

1. The meristematic cells are isodiametric and they may be, oval, spherical or polygonal in shape.
2. They have generally dense cytoplasm with prominent nucleus.

The two types of principal groups are:

1. Meristematic tissues
2. Permanent tissues.

A tissue is a group of cells that are alike in origin, structure and function. The study of tissue is called Histology.