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Polygonum Type - Monosporic Embryo Sacs
The embryo sac is formed from the chalazal megaspore in the tetrad and is eight-nucleate. The development of the embryo sac begins with elongation of the functional megaspore. Initially, the megaspore cytoplasm is non-vacuolated but later small vacuoles appear which fuse to form a large vacuole. The spindle of the nuclear division in the megaspore is oriented along the long axis of the cell. Wall is not formed after the nucleus divides.
A large central vacuole appears between the two daughter nuclei. It expands and pushes the nuclei towards the opposite poles of the cell. Both the nuclei divide to form four nuclei, two at each pole. By a further division an eight nucleate condition is reached. This is followed by cellular organisation of the embryo sac. Out of the four nuclei at the micropylar end of the sac, three organize into egg apparatus and the fourth is left free in the cytoplasm of the central cell as the upper polar nucleus. Similarly, three nuclei of the chalazal quartet form three antipodal cells; the fourth one functions as the lower polar nucleus. Eventually, the latter comes to lie close to the upper polar nucleus.
What is Organelles? Organelles : Eukaryotic cells contain various membrane-bound structures called organelles, in contrast to prokaryotes, which lack a definite internal or
Q. What are the effects of somatostatin for the pancreatic hormonal secretion? Somatostatin inhibits both glucagon and insulin secretions.
Closed Type of Circulatory Systems Some non-chordates, like cephalopods (octopuses, squids), earthworms, polychactes and all vertebrates have a closed circulation along with b
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ONSE T OF PUBERTY IN FEMALE - Attains at the age of 13 by estrogen hormone. It includes - 1. Growt h of breasts 2. Growth
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VARI A TION S - Defined as "dissimilarities of features among members of the same species". Offsprings of same parent are different and also differ from their parent.
Compare the teeth of Australopithecus afaensis and Homo sapiens. a)Describe the similarities and differences between the two species. b) Write a hypothesis about dietary difference
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