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 this p
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Leaf:Fibonacci series, simple and compound leaves-digieduco

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Fibonacci series: In alternate or spiral phyllotaxy the leaves are arranged with the divergence of 1/2, 1/3, 2/5, 3/8,5/13,8/21,13/34 etc.

In this series it is observed that in each fraction the numerations and denominators are the sums of two preceding fractions. Thus
1/2, 1/3, 1+1/2+3=2/5, 1+2/3+5=3/8, 2+3/5+8=5/13, 3+5/8+13=8/21 etc.

The value of the different fractions varies accordingly between 1/2 and 1/3 the angular divergence between two consecutive leaves bearing 371/2°on the average. The great majority of spiral leaf arrangements can be expressed by the terms of divergence known as Fibonacci series. Hence, in the arrangement of leaves there is a mathematical calculation.

The mean angular divergence of successive leaves is known as tibonacci angle. This fibonacci series was discovered by Carl Schimper and A. Brown. Hence this series is also known as Schimper-Brown series of divergence after the name of discoverer.

It shows a rational relation of the divergence to circumference of the stem. So that with the increase in number of leaves there occurs the location of definite number of leaves one above the other. Wienar has shown that in a fibonacci series of arrangement equal distribution of leaves takes place in a minimised space.
Leaf:Fibonacci series, simple and compound leaves-digieduco
Simple and compound leaves

Simple and Compound Leaves:

There are two types of leaves, e.g. (a) simple and (b) compound.

(A) SIMPLE LEAF-A leaf is said to be simple when it possesses one articulation and consists of a single leaf blade or lamina-this is due to the union of membranes of the midrib and its branches. The margin of the leaf blade may be entire or incised to any depth (therefore only lobed) but the incision never touches the base of the midrib or the petiole.

(B) COMPOUND LEAF-A leaf is said to be compound when it possesses two or more articulations and the leaf blade is broken up into a number of small segments, called leaflets, due to several incisions of the blade which touch the base of the non-membranous midrib or the petiole. The leafiets are free from one another and arranged on the axis i.e.
 midrib known as rachis. The leaflets may be situated rachis either laterrally on the sides of the rachis or terminally i.e. at the apex of the rachis (petiole).
Leaf:Fibonacci series, simple and compound leaves-digieduco
Different types of compound pinnate leaves

Types of Compound leaf-Compound leaves are of two types, viz. (i) Pinnate and (ii) Palmate.

1. PINNATELY COMPOUND LEAF :
In pinnate type of compound leaf, the leaflets are arranged either alternately or in an opposite manner on both sides of the rachis directly or on the branches of the rachis. This type of compound leaf looks like pinnae of a bird’s feather.

Types of pinnately compound leaf,

(a) Unipinnate-When the midrib i.e. rachis bears the leaflets directly, it is termed as unipinnate. Unipinnate type again may be of two kinds e.g. :

(i) Paripinnate-When the leaflets are arranged in pairs i.e. rachis bears even number of leaflets, e.g. species of Sesbania, Saraca, Cassia, Tamarindus indica (Caesalpinaceae) etc.

(ii) Imparipinnate-When leaflets are arranged on the rachis in such a way that the terminal end of the rachis bears a single leaflet-so the rachis bears at the apex an unpaired odd leaflet, e.g. Clitoria ternata (Papilionaceae), Rosa centifolia (Rosaceae), Azadirachta indica (Meliaceae) etc.

(b) Bipirnnate-In this case secondary branches are produced from the rachis which bear smaller Ieaflets called pinnules, i.e. in bipinnate the pinnately compound leaf is twice
pinnate. Examples-Acacia arabica, Mimosa pudica (Mimosaceae), Caesalpinia pulcherrima (Caesalpinaceae).
Leaf:Fibonacci series, simple and compound leaves-digieduco
Different types of pinnate compound leaves

(c) Tripinnate-In this type, the rachis produces secondary branches, which in turn again produce tertiary branches bearing leaflets. Hence in tripinnate type the leaf is thrice pinnate e.g. Moringa olifera (Moringaceae), Oroxylon sp. (Bignoniaceae).

(d) Decompound-When the leaf is more than thrice pinnate i.e. when the incision goes beyond the tripinnate condition, e.g. Daucus carota var. sativa, Foeniculum vulgare, Coriandrum sativum (Umbelliferae), species of Cosmos (Compositae) etc.
Leaf:Fibonacci series, simple and compound leaves-digieduco
Different types of pinnate compound leaves

2. PALMATELY COMPOUND LEAF :

A palmately compound leaf is formed when the petiole bears terminally and articulated to it a number of leanets which seem to be radiating from a common point like fingers of a palm. In palmately compound leaves, the rachis does not develop at all -hence leaflets are articulated to the petiole.

Types of palmately compound leaf :

(a) Umifoliate-When one leaflet is articulated to the apex of the winged petiole, e.g. Citrus aurantium, Citrus limon (Rutaceae) etc.

(b) Bifoliate-When two leaflets are articulated to the apex of the petiole, e.g. Balanites aegyptica (Zygophyllaceae), Bignonia grandiflora (Bignoniaceae), Hardwickia binata (Caesalpinaceae) etc.

(c) Trifoliate-When three leaflets are articulated to the apex of the petiole, e.g.Vitex negundo (Verbenaceae), Oxalis corniculata (Oxalidaceae), Aegle marmelos (Rutaceae) etc.

(d) Quadrifoliate-When four leaflets are articulated to the apex of 'the petiole, e.g. Marsilea quadrifolia (pteridophyte).

(e) Digitate or Multifoliate-When more than four leaflets are articulated to the apex of the petiole, e.g. Bombax ceiba (Bombacaceae), Gynandropsis gynandra (Capparidaceae) etc.




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