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:modification of leaf with special reference to Insectivorous plants-digieduco

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The leaf

Modification of Leaves with special reference to Insectivorous Plants:
Leaf:modification of leaf with special reference to Insectivorous plants-digieduco
A- seedling plant showing transformation of petiole into phyllode, B- phyllode of Acacia auriculoformis

1. Leaf tendris-The entire leaf is modified into a slender, coiled thread-like structure : e.g. Lathyrus aphaca (Papilionaceae). In case of Pisum sativum (Papilionaceae), terminal leaflets are modified into tendrils. In glory lily, Gloriosa superba (Liliaceae), the apex ef the leaf is metamorphosed into coily structure. Tendrils help the plant to climb up other plants or objects:


2. Spine-It is a modified leaf. In plants like Opuntia dillenii (Cactaeeae) the leaves are metamorphosed into small sharp pointed structures. The apex or margin of the leaf may be spinous as in Argemone mexicana (Papaveraceae). In Ulex, the leaves are modified into spines and the branches into hard thorns. In Citrus sp., Aegle marmelos the prophylls are spines. Spines are defensive organs, they protect the plants against attack from animals. In addition to protection they also help the plant to reduce the rate of transpiration.

3. Phyllode-It is the green, flattened or winged modified petiole of the leaf, e.g. Acacia auriculoformis (Mimosaceae). In this plant the leaflets fall off very early or they are not at all developed. A phyllode does the function of a normal leaf.

4. Fleshy leaves-These are the modifications of the normal leaves for storage of water and mucilage. These types of leaves are also called succulents. The leaves of Aloe indica (Liliaceae), Portulaca oleracea (Portulacaceae), Basella rubra (Chenopodiaceae), Bryophyllum calycinum (Crassulaceae) etc., afford good examples of fleshy leaves.

5. Hooks-Sometimes leaves are modified into hooks. This is observed in the plant Bignonia unguis-cati (Bignoniaceae), in which three terminal leaflets are modified into sharp and hard hooks. These hooks act as organs for climbing.

6. Root-like structures-The submerged leaves of the plant Myriophyllum indicum (Haloragidaceae) are modified into finely dissected root-like structures. Their function is to absorb water, because the plant does not possess true roots.

7. Pitcher plants-The morphological nature of the leaves of pitcher plant is discussed below :
Leaf:modification of leaf with special reference to Insectivorous plants-digieduco
A pitcher of Dischidia rafflesiana

Nepenthes khasiana (Nepenthaceae)- In this plant the leaf becomes modified into pitcher filled up with a liquid containing digestive juices. According to some botanists the whole leaf including the pitcher is a sessile leaf blade which is divisible into three parts, viz. the lowest expanded portion is the true lamina, the apex of the lamina is modified into tendril to some extent and finally the extreme tip into a pitcher.

Species of Sarracenia (Sanaceniaceae) occur in bogs in many parts of United States of America. These pitcher plants have a rosette of sessile pitchers.

In the climbing epiphyte Dischidia rafflesiana (Asclepiadaceae), a peculiar modification of the leaf is found. Here the leaf is modified into a pitcher with apical opening. The opening is without lid and the pitcher is not insectivorous in nature like that of Nepenthes sp. This plant is commonly found in Sunderbans (W. Bengal). After a shower, rain water is collected inside the pitcher and is absorbed by the roots developed from the nodes which enter the pitcher.

8. Insectivorous plants other than pitcher plants :

(a) Sundew (Drosera sp., Droseraceae)--The degree of modification attained by the leaves of Drosera sp. is remarkably varied. The leaf of D.burmanii is stalked, the lamina is rolled or folded to form a globular or flat structure bearing numerous tentacles, which execute movement as a response to the touch by insects. The leaves are radical and are arranged in rosettes. The tentacles secrete viscid fluid which appears as shining droplets on the tentacles and are objects of attraction for the insects.
Leaf:modification of leaf with special reference to Insectivorous plants-digieduco
A- Utricularia stellaris showing entire plant, B- an enlarged bladder of the same.

(b ) Bladderwort (Utricularia stellaris, Lentibulariaceae)--The bladders of Utricularia
stellaris form the fly catching apparatus. It is a rootless floating herb, commonly found in tanks. The bladders are borne on the segments of much dissected submerged leaves. Morphologically the bladders are extremely metamorphosed leaf segments i.e. some leaf segments are transformed into insect catching bladders. The mouth of each bladder is provided with a valve which Opens inward and closes as a result of response to stimulus conveyed by sensory hairs situated at the entrance of the mouth of the bladder. Thus each bladder is a trap for catching small aquatic animals.

(c) Aldrovanda-In Aldrovanda vesiculosa (Droseraceae) which is an aquatic herb, the leaves are metamorphosed into insect catching organs. The leaves have expanded petiole, the lamina is divided into two halves by a midrib which acts as a hinge, so that the two halves of the blade can be closed and opened along the hinge-like midrib. On the inner sides and the margins of the blade there are numerous bristle-like outgrowths which are sensitive

(d) Venus’ fly-trap (Dionaea muscipula, Droseraceae)-This insectivorous plant is
found to occur in North America bogs. The leaves of Dionaea are simple, radical and occur in rosette. The petiole of each leaf is winged and the leaf blade (lamina) is deeply notched at the apex. There are about 10-20 bristly teeth along the leaf margin. The two halves of the blade are capable of movement along the midrib like a hinge. Upper surface of the blade is also provided with several slender hairs which are sensitive to contact.










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