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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Bracts, Bracteoles , Inflorescence and its types-digieduco

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Bracts, Bracteoles and Inflorescence

Bracts are morphologically specialised leaves from the axil of which flowers either solitary or in clusters (on floral axis) are developed.

Bracts, Bracteoles , Inflorescence and its types-digieduco
A-bracteoles, B- petaloid bracts

Bracteoles are smaller than bracts, either thin leafy or scaly structures developing on flower stalks in between bracts and calyx.

Types of Bracts : Bracts may be of different types as follows :
Bracts, Bracteoles , Inflorescence and its types-digieduco
Types of bracts

(a) Leafy or Foliaceous bracts-When bracts are typically and ordinarily green foliage leaf-like e.g. Hibiscus sp. (Malvaceae), Acalypha indica (Euphorbiaceae) etc.

(b) Petaloid bracts-When bracts are coloured and showy like petals, e.g. Bougainvillea spectabilis (Nyctaginaceae), Euphorbia pulcherrima (Euphorbiaceae) etc.

(c) Scaly bracts-When bracts become thin and scale-like as seen in disc florets of capitulum inflorescence of Compositae.

(d) Spathy bract-Here the bracts are thick, large and boat-shaped and they either completely or partly surround the inflorescence, e. g. bracts of spadix inflorescence of Araceae, Palmae etc.

(e) Involucre of bracts-In this type, bracts are arranged in one or more whorls around the base of the flower or inflorescence, e.g. Helianthus annuus (Compositae), Daucus carota var. sativa (Umbelliferae) etc.

(f) Glumes, Lemmas etc.--These are dry, stiff and scaly bracts as seen in members of the families Gramineae and Cyperaceae. Glumes are non-flowering bracts while lemmas are flowering bracts carrying flowers at their axils.

(g) Epicalyx-It is a bracteole in nature, occurring at the base of the calyx whorl, as seen in Hibiscus rosa-sinensis and other members of the family Malvaceae.

(h) Cupule-When bracts or bracteoles grow together at the base of the flower and form a cup shaped hard body surrounding the fruit of some plants eg. Corylus sp.of Betulaceae.

Inflorescence: Inflorescence is the branch or branch-system bearing flowers "or  the arrangement of flowers on the floral axis and is a branch system”.

The stalk of the inflorescence is known as peduncle. The floral axis of an inflorescence bearing flowers is called rachis and the stalk of the individual flower is known as pedicel. Flowers having pedicels are called pedicellate and those without pedicels i.e. stalks are sessile. Sometimes the rachis instead of developing into a long axis, is condensed to form fleshy, flat or dilated structure called receptacle. The inflorescence axis (i.e. rachis) developing from an underground stem is known as scape. The small rachis of Gramineae i.e grass inflorescence produced beyond the flower is known as rachilla.

Inflorescences are mainly three types-
1)Indefinite or racemose inflorescence
2)Definite or cymose inflorescence
3)Mixed inflorescence.

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