Describe Endosperm formation and its function



Development of endosperm begins before that of embryo. It arises from the primary endosperm nucleus (also known as triple fusion nucleus) formed as a result of triple fusion of three nuclei i.e. two polar nuclei and a male nucleus. Primary endosperm nucleus is triploid (3N). It undergoes a series of divisions resulting in the formation of many free nuclei lying within the embryo sac. A vacuole appears in the centre so that the nuclei are pushed to the periphery. Later on unless the endosperm is absorbed by the embryo in free nuclear stage, wall formation takes place starting from the periphery towards the centre of embryo sac and by further centripetal growth, the embryo sac is filled with a compact cellular tissue around the embryo without any intercellular spaces. This tissue is endosperm occasionally as in coconut a vacuole persists in the centre of the embryo sac as it is not completely filled by the endospermic tissue. This type of endosperm development since it involves the process of free nuclear division is called the nuclear type e.g. Fritillaria biflora. This is the most common method of endosperm development. In some plants as in Silphium Lacimatum, each division of the primary endosperm nucleus is followed by wall formation, so that the endosperm is formed at once. This type of endosperm development is known as cellular type.

In some groups endosperm may develop as a few free nuclei only so that it may be regarded as suppressed as in Helobiales and orchids. Several members of Sympetalae a few families of Archichlamydae and monocotyledons show prominent endospmeric loustoria which form very efficient absorptive system.

Function of endosperm:

Endosperm serves as storage tissue as its cells are laden up with food material absorbed through the placenta. The reserve food is stored in large quantities in its cells. This may be deposited as hemi cellulose on the cell walls, when often become very thick as in date and so called vegetable ivory. In most of monocots and some dicots (e.g. castor, butter cup, cotton and all grasses) endosperm persists as permanent tissue in the seed. Such seeds are called albuminous or endospermic.

Comments

Post a Comment

Popular posts from this blog

What is the Dynamic Theory of Profit

Image
Clark's Dynamic Theory of Profit And Its Criticism The Dynamic Theory of Profit is associated with the name of an American Economist, J. B. Clark. In the world of reality, according to J. B. Clark, profit arises only in a dynamic economy. An economy is said to be dynamic when there is a change in population growth or change in the method of production or a change in the consumer’s wants, etc. A society which is without these changes is called a static society. In a static society, only monopoly profits continue to exist. All other economic profits are gradually eliminated by competition. In a dynamic society, an entrepreneur is always confronted with continuous unpredictable changes in demand for his product. The variation in demand may take place due to changes in fashions, tastes, the standard of living, distribution of income, population, new inventions, international repercussions, technological advances, etc. A prudent entrepreneur will always keep an eye on future demand
Read more

Compare the anatomy of Bifacial and Isobilateral leaves

BIFACIAL LEAF: It is also called dorsiventral leaf. This leaf is more strongly illuminated on upper surface than on lower surface. This unequal illumination induces a difference in the internal structure between upper and lower sides. Its internal structure shows: (1)        Upper Epidermis This is single layer of cells with thick cuticle which checks excessive evaporation of water from the surface. It does not contains chloroplasts, stomata are also absent. (2)        Lower Epidermis This is also single layer but with a thin cuticle. It bears many stomata, two guard cells of which contain some chloroplast, none are present in the epidermal cells. Internal to each stomata is large cavity called respiratory cavity. Lower epidermis of leaf is meant for exchange of gases (oxygen and carbon dioxide) between the atmosphere and the plant body. Excess water also evaporates from lower epidermis. (3)        Mesophyll The ground tissue lying between upper epidermis and th
Read more

osmoregulation in terrestrial and aquatic animals

Mechanism of osmoregulation is very important for all groups of animals whether inhibting land or water. Unlike plant cells, animal cells when placed in hypotonic solution burst due to the continuous absorption of water. On the contrary they would shrink and die if constantly placed in hypertonic solution. Normally uptake and loss of water are in balance for proper survival of cell. (1)        Osmoregulation in terrestrial animals: Terrestrial animals are more likely to loose water by evaporation through their permeable surfaces exposed to amsophere. Among various animal groups only Arthropods and vertebrates became the most successful land dwellers. They have developed number of strategies to maintain osmoregulation of their body fluid. (a) Water proof external coverings: To prevent water loss through external surfaces, vertebrates like reptiles, birds and mammals have water proof keratinized epidermis. Similarly the insects have developed external water proof layer called
Read more