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A common structural feature of vessel elements and sieve tube elements is :-
In plant conducting tissue xylem has an important integral cell as xylem vessel which is without nucleus. The phloem has a row of sieve tubes which are also without nucleus at maturity.
If the stoma remains surrounded by a limited number of cells which cannot be distinguished from other epidermal cells, then this type of stomata is known as.
(d) Anomocytic stomata lacking subsidiary cells surrounding the guard cells. Anisocytic stomata is characterized by the presence of three subsidiary cells of which one is distinctly smaller than the
other two. Paracytic stomata is accompanied on either side by one or more subsidiary cells which lie
parallel to the long axis of the pore and guard cells. Perigenous stomata shows an independent origin of the guard cells and the subsidiary cells.
Fascicular cambium separates the xylem and phloem in:-
(a) In dicotyledonous stems, a thin strip of primary meristem is present in between the xylem and phloem, which is termed as fascicular or vascular cambium. The cambium cells are rectangular and thin walled. Cambium is one layered. In monocot stem cambium is absent.
Epidermis is derived from:-
(d) Epidermis is the outer most covering of the plant which is in direct contact with the external environment. It is single layered or multilayered structure that helps in protection, absorption, excretion, gaseous exchange, transpiration and secretion. The epidermis is derived from dermatogen which is the outer most initial of the shoot apex.
Cork cambium results in the formation of cork which becomes impermeable to water due to the accumulation of
Cork cambium is a secondary lateral meristem that may arise from permanent living cells of hypodermis or outer cortex. It is composed of a single layer of meristematic cells. Its cells divide tangentially and periclinally towards the outer face and produce cork cells. These cells are compactly arranged and have thin cellulose walls in the beginning. As they mature there is a gradual loss of living matter and cells get elongated radially, vertically of tangentially. The cell walls become thick because of development of fatty substance called suberin, which is impervious to water.
In the sieve elements, which one of the following is the most likely function of P-proteins?
(d) Sieve elements are a component of phloem tissue and are responsible for conduction of food in plants. A sieve tube element has peripheral layer of cytoplasm without any nucleus. The central part is occupied by a network of canals which contain fibrils of p-protein. The protein is vibratite and is believed to actively participate in the transport of nutrients. One general property of its ability to form a gel and its functions as a puncture repair substance forming a plug at any site of damage in sieve element, thus preventing loss of food materials being translocated by the phloem. Thus, it is believed to have sealing function on wounding.
Select the correct pair amongst the following.
(d) The yearly growth of secondary xylem is distinct in the area which experiences two seasons, one favourable (spring or rainy season) and the other unfavourable (autumn, winter and dry summer). The wood formed in a single year consists of two types of wood, spring wood and autumn wood. The spring or early wood is much wider than the autumn or late wood. It is lighter in colour and of lower density. Spring wood consists of larger and wider xylem elements. The autumn or late wood is dark coloured and of higher density. It contains compactly arranged smaller and narrower elements Which have comparatively thicker walls. In autumn wood, tracheids and fibres are more abundant than those found in the spring wood.
As secondary growth proceeds, in a dicot stem, the thickness of.
(b) In a woody stem, due to secondary growth, secondary xylem constitutes the bulk of the stem and is commonly called wood. The secondary xylem consists of vessels, tracheids, wood parenchyma and wood fibres. Width of secondary xylem increases continuously with the age of the plant. In older stems, the wood (or secondary xylem) gets differentiated into two zones - the outer light coloured younger sapwood and the inner darker older heartwood. The xylem vessels and tracheids of heartwood become non-functional because they get filled with resins, tannins, gums etc. produced by adjacent living parenchymatous cells and due to tyloses. Changes in the nature of sapwood occur with the death of parenchyma cells and with the completion of these changes, heartwood is formed. Thus, the conversion of sapwood into heartwood is a progressive phenomenon which continues throughout the life of the plant. Initially,both sapwood and heartwood increase in size but as a tree reaches a certain age,amount of heartwood increases continuously and the amount of sapwood remains almost constant.
The desert grasses, often curls their leaf to minimise water loss due to presence of
(d) In grasses, buliform cells (large empty colourless cells) are present that make the leaves curl inwards to minimise water loss.
Tyloses are balloon-like outgrowths in the lumen of secondary xylem tracheids and vessel of duramen region. These are actually:-
Tyloses are balloon-like formation in the cavity at tracheids or vessels in the wood of trees consisting of protoplasm intruded (i.e. ingrowth) from adjacent parenchyma cells. They plug lumen, check fungal infection and increase durability of wood. With times, wall of tyloses get thick and lignified and serve as storehouse of resin, starch, gums and tannins.
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