Cell membrane function and difference-digieduco

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  Functions of cell membrane : (a) The proteins and enzymes present in the cell membrane helps in the transport of certain substances like sugar, sodium and other ions etc. across the cell membrane. (b) Cell membrane protects the internal structures of the cell and different organelles of the cytoplasm. (c) It maintains the shape of the cell. (d) It acts as a selective permeable membrane because it allows to pass certain substances while others are not, hence it helps in the transport of selective materials from and to the cells. (e) The membranes on the cytoplasmic organelles and nucleus most probably formed from the plasma membrane. (f) Other important functions of cell membrane of the cells are endocytosis and exocytosis . Endocytosis is the process by which materials are transported into the cells by the formation of vesicles. It includes two processes-phagocytosis (cell eating) and pinocytosis (cell drinking). The reverse process of endocytosis is exocytosis. During th...
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Leaf: shape of the lamina or leaf blade, prefoliation-digieduco

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The leaf

Shape of the Lamina or Leaf Blade with reference to general outline, the following types are noted :

Leaf: shape of the lamina or leaf blade, prefoliation-digieduco
Different types of leaf lamina

(A) Acicular-When the leaf blade is very long, narrow and cylindrical having the shape of a needle, e.g. Pinus sp. (Pinaceae).

(B) Linear-When the leaf blade is long, narrow and flat i.e. blades are slightly broader, e.g. in many grasses, Polyanthes tuberosa (Amaryllidaceae) etc. ‘

(C) Lanceolate-When the leaf blade has the shape like that of a lance i.e. leaf blade is wider in the middle and narrower towards the apex and base, e.g. Bambusa arundinacea (Gramineae), Polygonum barbatum (Polygonaceae), Nerium sp. (Apocynaceae) etc.

(D) Oblong-When the leaf blade is wide and long with two margins running parallel e.g. Musa sp (Musaceae), Colutea arborescens (Papilionaceae) etc.

(E) Subulate or Awl-shaped-When the leaf blade is long, narrow and gradually tapers from base to apex, e.g. Ulex europaeus (Papilionaceae), Salsola kali (Chenopodiaceae), Isoetes sp. (Pteridophyte) etc.

(F) Ovate-When the leaf blade is egg-shaped e.g. leaf blade broader at the base than at the apex, e.g. Hibiscus rosa-sinensis (Malvaceae), Solanum nigrum (Solanaceae) etc.

(G) Obovate-When the leaf blade is inversely egg-shaped i.e. leaf blade broader at the apex than at the base, e.g. Terminalia catappa (Combretaceae), Cassia obovata (Caesalpinaceae) etc.

(H) Spathulate-When the leaf blade is broad and round at the apex and tapering narrowly towards the base, e.g. Bellis perennis (Compositae), Drosera burmanni (Droseraceae), Phyla nodiflora (Verbenaceae) etc.

(I) Cordate-When the leaf blade is heart-shaped, with deep notch at the base e.g. Piper betle (Piperaceae), Sida cordifolia (Malvaceae), Ficus religiosa (Moraceae) etc.

(I) Obcordate-Opposite of cordate, i.e. when the leaf blade is inversely heart-shaped e.g. Bauhinia variegata (Caesalpinaceae), Oxalis corniculata (Oxalidaceae) etc.

(K) Sagittate-When the leaf blade is arrow-shaped i.e. the apex of the leaf blade is pointed and two basal lobes are pointed downwards, e.g. Sagittaria sagittifolia (Alismaceae), lpomoea reptans (Convolvulaceae) etc.

(L) Hastate-When the leaf blade has two pointed basal lobes directed outwards, e.g. Typhonium trilobatum (Araceae).

(M) Reniform-When the leaf blade is kidney-shaped i.e. the apex of the leaf blade is .rounded above with a deep notch at the base, e.g. Centella asiatica (Umbelliferae).

(N) Lunate-When the leaf blade has the shape like a half-moon with two pointed basal lobes, e.g. Passiflora lunata (Passifloraceae), Adiantum lunatum(pteridophyte) etc.

(O) Cuneate-When the leaf blade is wedge-shaped, flattened and broad with a narrow base e.g. Pistia stratiotes (Araceae).

(P) Rotund or Orbicular-When the leaf blade is nearly circular e.g. Nelumbo nucifera (Nymphaeaceae), Tropeolum majus (Tropaeolaceae) etc.

(Q) Elliptical-When the leaf blade is more or less like an ellipse, e.g. Lochnera rosea (Apocynaceae), Ficus elastica (Moraceae) etc.

(R) Falcate-When the leaf blade is sickle-shaped e.g. Eucalyptus globulus (Myrtaceae)
Arundinaria falcata (Gramineae).
Leaf: shape of the lamina or leaf blade, prefoliation-digieduco
Lyrate leaf lamina of Radish and pedate leaf of vitis pedata
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Leaf:stipule, STIPEL and structure of various leaf apices-digieduco


(S) lncised form-Besides the above mentioned shapes of the leaves, the shape of the leaf may be of different types due to varieties of incision of the blade. When the leaf blade has a large and rounded terminal lobe, and two or more smaller lateral lobes towards the base, it is called lyrate e.g. Raphanus sativus, Brassica nigra etc. of Cruciferae. When the lobes of the blade are arranged like the claw of a bird, it is called pedate,e.g. Vitis pedata (Vitaceae).

Prefoliation : Prefoliation is the arrangement of young leaves in the bud conditions. The manner in which the individual leaves (independent of others) are rolled or folded in the bud is called as ptyxis, whereas the arrangement of all leaves in the bud in relation to one another is known as vernation.

A. PTYXIS-Rolling or folding of individual leaves in the bud is as follows: '
Leaf: shape of the lamina or leaf blade, prefoliation-digieduco
Different types of ptyxis

1. Reclinate or lnflexed-When the upper part of the leaf blade is bent upon the lower part, e.g. Eriobotrya japonica (Rosaceae).

2. Conduplicate-When the leaf is folded lengthwise along the midrib, e.g. Magnolia
grandiflora (Magnoliaceae), Bauhunia sp. (Caesalpinaceae), Psidium sp. (Myrtaceae) etc.

3. Plicate-When the leaf is folded several times longitudinally along its main vcin, e.g. Borassus flabellifer (Palmae).

4. Circinate-When the leaf is rolled up from the apex to the base like the tail of a dog e.g. ferns, Cycas sp. (Gymnosperm).

5. Convolute-When the leaf is rolled up from one margin to the other in one direction e.g. Musa paradisiaca (Musaceae), Carma indica (Cannaceae) etc.

6. Involute-When the two margins of the leaf are rolled up in the upward direction towards the midrib e.g. Antigonon leptopus (Polygonaceae), Artocarpus heterophyllus (Moraceae), Nymphaea stellata (N ymphaeaceae) etc.

7. Revolute-When the two margins of the leaf are rolled up in the downward direction towards the midrib e.g. Nerium indicum (Apocynaceae), Terminalia catappa (combretaceae) etc.

B. VERNATION- The different types of vernation ,as seen in transverse section of the bud, are as follows:
Leaf: shape of the lamina or leaf blade, prefoliation-digieduco
Different types of vernation
1. Valvate- when the leaf margins touch each other without any overlapping e.g. calotropis procera(Asclepiadaceae), Hibiscus rosa-sinesis(Malvaceae) etc.
2. Twisted or Contorted-When the leaves are arranged in such a way that one margin is overlapped and the other margin is overlapping in regular succession, e.g. Datura Metel (Solanaceae).
3. lmbricate-When one leaf is completely internal, another leaf is completely external
and other leaves are arranged in twisted manner, e.g. Brassica nigra (Cruciferae).
4. Induplicate-This is similar to valvate type, but here the margins of leaves are slightly bent inwardly instead of merely touching one another.
5. Equitant-When the leaves overlap the next opposite ones by the two margins in a regular fashion 6. g. Acorus calamus (Araceae), Iris nepalensis (Iridaceae), Vanda roxburghii (Orchidaceae) etc.
6. Half-equitant or Obvolute-When overlapping of leaves like equitant type is incomplete so that only one half of the leaf blade remains inside the other, e. g. Salvia sp. (Labiatae).
7. Supervolute-In this type the convolute leaf completely encloses another forming a single rolled up bud, e.g. Prunus sp. (Rosaceae).






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