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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Pollination: definition, types of pollination, advantage and disadvantage of self and cross pollination-digieduco

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Definition : PolIination is the transference of pollen grains from the anther to the stigma whether of the same flower or of a different flower.

Types of Pollination : Pollination is of two types, viz :

(a) Self-pollination or Autogamy-In this type the transference of pollen grains from
the anther of a flower to the stigma of the same flower takes place. Bisexual flowers are generally seif-poliinated.

Sometimes self-poliination is also applicable in the transference of pollens from the anther of male or of bisexual flower to the stigma of female or another bisexual flower occurring on the same plant-this process is called geitonogamy. According to this concept, only one parent plant is concerned in seif-pollination.

(b) Cross-pollination or Allogamy-It is the transference of pollens from the anther
of one flower to the stigma of another flower borne by a different plant of the same or different species. All unisexual flowers are generally cross-pollinated.

Cross-poliination when takes place within the same species is called xenogamy and
between two different species is called hybridism; hybrids are produced as a result of hybridism.

Advantages and Disadvantages of Self and Cross-pollination :

In self-pollination, there is least possibility of failure and an almost universal phenomenon in bisexual flowers. For self-pollination plants are not to depend on external agents to carry Pollens that is why the process is easily Secured. Disadvantage of self pollination is that if self-pollination is continued generation after generation, it results in weaker progeny,

Cross-pollination has many advantages, such as:

(a) it produces healthy progeny, (b) it results in the production of more viable seeds, (c) plants are better adapted in nature and (d) the possibility in the production of new varieties.

Most important disadvantage is that for cross-pollination, plants have to depend on various external agents and there is wastage of pollens, specially in anemophily.

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