Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Release of Microspores
Up to the tetrad stage, there is no cellulosic wall around the microspores. As you will come to know in the next unit, a unique feature of the pollen is the ornamentation of the pollen wall. This ornamentation is seen on the outer layer of the pollen or exine. The exine is made up of sporopollenin, one of the most resistant (to physical and biological decomposition) substances known in the biological world. Pollen grains of prehistoric plants are well preserved as fossils because of their exine. There is enormous variation in the ornamentation of the exine, and it is a characteristic feature of a given species. Often pollen grains of particular group of plants can be identified on the basis of their exine pattern.
The blue print of exine, termed primexine is laid down below the callose wall after the basic structural features of the exine including the position of the germ pore (a region in the pollen wall through which the pollen tube emerges) are demarcated in the primexine. This important morphogenetic event takes place while the microspores are still enclosed in the callose wall, in groups of four or at the tetrad stage. Thus, the pattern of mature exine is laid down before the spores are set free. The callose wall seems to play an important role in the orderly deposition of primexine. You will read more about this in the next unit. After the development of exine, the callose wall dissolves. The enzyme callase which dissolves the callose wall is produced by the surrounding tapetal cell pen plasmodium. The development of the male gametophyte begins after the liberation of individual microspores.
Q. Are organic solvents like benzene and ether non-polar or polar substances? the ethers and Benzene are molecules without electrically charged portions and thus they are non-p
Which are plant tissues responsible for the supporting of the plant? The plant supporting tissues are the sclerenchyma and the collenchyma. The collenchyma is made of elonga
State four characteristics of an efficient respiratory surface. Four characteristics of an well-organized respiratory surface are: a) thin epithelium, b) large surface ar
Q. How are gases exchanged in sponges? The gas exchange in sponges happens by diffusion from the exterior to the cells that absorb molecular oxygen and liberate carbon dioxide.
CONCLUSION OF PHYLUM ANNELIDA
Q. Describe some Food borne disease? Food borne diseases are caused by the ingestion of foods containing toxic or infectious agents. In India, the diseases transmitted by foo
Q. How is the excretory system of molluscs characterized? Molluscs have one or two pair of spongelike nephridia, similar to kidneys
RESPIR A T ORY ORGANS IN ANIMALS - In Protozoa plasmalemma functions as respiratory surface. In Porifera, respiration occur through body wall. In Coelentrata resp
How we attempt a question of phylum mollusca?
#question.sir please explain amoeba as in example of protozoa
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd