Anatomy of Flowering Plants Test - 3

Root apex (root apical meristem) is found at the tip of main root and its branches. Root apical meristem is subterminal because it is covered by root cap. In many cases, a quiescent centre (Clowes, 1961) is found in the centre of the root apex. Differential division in various parts of root apical meristem gives rise to 3-4 regions-protoderm, procambium, ground meristem and calyptrogen. Calyptrogen differentiates only in monocots. It gives rise to root cap. Protoderm forms epiblema/epidermis procambium forms vascular tissues and ground meristem gives rise to pith, endodermis and cortex.

Meristematic cells are small immature cells, which possess ability to grow and divide rapidly. Cytoplasm of these cells is dense with conspicuous nucleus. Walls are thin, elastic and made of cellulose, rate of respiration is very high. ER is small, poorly developed mitochondria have simple structure and proplastids are present instead of plastids.

The given figure represents the longitudinal sector vegetative shoot apex, Shoot apical meristem is derived meristem present in plumule of embryo. Shoot apex or at the tip of stem and its branches as terminal bud. apex is conical or dome shaped in outline. Leaf prime are produced periodically on the flanks. Some cells of apical meristem are left behind during the formation leaves and elongation of the stern. They constitute all buds.

Sclerenchyma is asimple supportive tissue of highly thick-walled cells with little or no protoplasm. Sclerenchyma cells are generally dead, thesecells are empty. Wall thickeninig is uniformwhich can bemade up of cellulose,lignin or both pits are usually simple and oblique, they may be branched.

Both apical meristem and intercalary meristem are 'primary' meristems as they appear early in the life of a plant and helps in the formation of the primary plant body. So, the correct answer is 'primary'.

In the given figure, companion cells are labelled as ‘C’. These cells are narrow, elongated and thin walled living cells. They lie on the sides of sieve tubes and are closely associated with them through compound plasmodesmata.
Companion cells are replaced by modified parenchyma cells albuminous cells) in non-flowering plants. 'A' represents sieve Plate and 'B' represents sieve tube cell. Vessels are absent in gymnosperms and pteridophytes with some exceptions e.g., Selaginella, etc.

Phloem parenchyma is absent in most of the monocots and some herbaceous dicots. Gymnosperms lack companion cells, instead they possess albuminous cells. Gynmosperms lack vessels (except Gnetum etc.) but possess tracheids. Infact, tracheids constitute 90−95% of wood in gymnosperms.

Sclereids are highly thickened dead sclerenchyma cells with very narrow cavities. Steroids may be isodiametric polyhedral, spherical, oval, short or cylindrical. Sclereids may occur singly or in groups. They provide stiffness to the parts in which they occur. Sclereids are present in grit of guava, sapota, apple and pear, epidermal covering of legume seeds, petiole of lotus, fruit walls of nuts, etc.

Root hair zone (or Zone of cell maturation) also represents the zone of differentiation because different types of primary tissues differentiate or mature in this region (viz, xylem, phloem, pericycle, endodermis, cortex, epiblema, etc.). 
Zone of elongation is about 4-8 mm in length. It lies behind the growing point. The cells of this region are newly formed cells which lose the power of division. They elongate rapidly. 
Meristematic zone is about 1 mm in length. The growing point of the root is subterminal and lies protected below the root cap. It is made up of compactly or closely arranged small thin walled isodiametric and meristematic cells which have dense protoplasm.

Primary growth is the increase in the length of root and shoot. It is the result of cell division of apical meristem.

Increase in girth or thickness of the axis of plant takes place due to the activity of secondary lateral meristems like vascular cambium and cork cambium. It is called secondarygrowth.

Phloem is a complex permanent tissue that transports organic food inside the plant. Xylem is a complex permanent tissue that performs the function of ascent of sap ie., transport of inorganic nutrients (water and minerals) inside the plant.

Meristematic cells are actively dividing cells characterized by absence of intercellular spaces.

Meristematic region is the region of active mitotic division in plants, from which permanent tissues are derived. It comprises of cells which are packed close to one another without any intercellular spaces. Meristematic cells are found in root and shoot tip regions. 

Xylem vessels become dead and lose their protoplasm due to deposition of lignified secondary wall. Mature sieve tube elements are living cells without nucleus.

Xylem is made up of three types of dead cells (vessels, tracheids, xylem fibres). There are only one type of living cells (xylem parenchyma). It stores food and helps in the one lateral conduction of water or sap.

Collenchyma is a simple permanent tissue of refractile non lignified living cells which possess pectocellulose thickenings in specific area of their walls. It provides mechanical strength to young dicot stems, petioles and leaves. Collenchyma also provides flexibility to the organs and allows their bending e.g., Cucurbita stems.

Idioblasts are specialized non-greenlarge-sized parenchyma cells which possess inclusions or ingredients like tannins, oils, crystals, etc.

Vessels are present in almost all angiosperms, but there are 10 woody genera belonging to 5 families viz Winteraceae (e.g., Wintera). Tetracentraceae (e.g., Tetracentron). Trochodendraceae (e.g., Trochodendron). Amborellaceae (Amborella) and Chloranthaceae in which vessels are absent.

A quiescent centre is found in the centre of the root apex. Cell divisions are very few in the quiescent centre as there is very little synthesis of new proteins. Cells of quiescent centre have small nuclei and light cytoplasm.