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Yogita Ingle 6 years, 3 months ago
Industrial melanism. It is an example of natural selection shown by peppered moth Biston betularia. The moth had a dull grey coloured body before industrial revolution in England. The colour of moth enabled it to adapt to the light coloured background. After the industrial revolution the environment changed with the deposition of tar soot on the bark of the trees. As a result, light coloured species of moth were easily detected by the predators against the dark bark of trees while the black coloured moth Biston carbonaria increased in number. The change enabled the animal to adjust with the changed environment.
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Yogita Ingle 6 years, 3 months ago
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Primary sewage treatment |
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Secondary sewage treatment |
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It is a mechanical process involving the removal of coarse solid materials. |
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It is a biological process involving the action of microbes. |
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It is inexpensive and relatively less complicated. |
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It is a very expensive and complicated process. |
Gambhir Acharya 6 years, 3 months ago
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Yogita Ingle 6 years, 3 months ago
10% law is followed in detritus food chain as most of the energy is lost as heat and only 10% is transferred from one trophic level to the next. However most of the detritus food chains are small sized and therefore the law is not as evident as in other larger food chains.
Posted by Kamal Narayan 5 years, 8 months ago
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Meghna Thapar 5 years, 8 months ago
Fertilization is a sequence of coordinated molecular events involving the merging of the sperm with the egg, the fusion of the pronuclei and the intermingling of the maternal and paternal chromosomes. The first form of human life is the zygote (a diploid cell) from which the new organism will result.
Fertilization can be internal (inside the body of female) or external (outside the body of female). Fertilization performs two basic functions in the process of embryonic development.
(a) Upon fertilization, the secondary oocyte completes meiotic division and produces a second polar body, which degenerates.
(b) A diploid zygote is formed, which undergoes cleavage to form a morula and then a blastocyst, which implants in the endometrium.
A. Approximation of sperm and ovum:
This can be done by fertilizin-antifertilizin compatibility reaction. Fertilizin (glycoprotein) of egg interacts with antifertilizin (composed of acidic amino acids) of a sperm of the same species. This interaction makes the sperms stick to the egg surface.
B. Penetration of structures surrounding the ovum:
1. The spermatozoa acrosome aids the sperm in penetrating the layers around the ovum. The acrosome is highly modified lysosomes, derived from the Golgi apparatus during spermatogenesis. It consists of a membrane-bound sac of hydrolytic enzymes and is completely enclosed within the plasma membrane of the sperm cell.
2. As the sperm cells approach the egg, the acrosome reaction occurs to prepare the sperm to fertilize ovum (called capaciation).
a. The acrosomal membrane fuses with the plasma membrane of the sperm cell.
b. The enzymes within the acrosome are released into the milieu surrounding the sperm and egg.
3. Acrosome contents and their functions
a. Hyaluronidase is a hydrolytic enzyme:
(1) It lyses the glycosaminoglycans in the extracellular matrix holding the cells of the corona radiata together. As the coronal cells become more loosely associated, sperm cells can propel themselves inward, toward the zona pellucida by making a receptive cone or fertilization cone through the cytoplasm of the egg
(2) Hyaluronidase may also be involved in breaking down the zona pellucida.
b. Neuraminidase, also a hydrolytic enzyme, removes neuraminic acid (sialic acid) from glycoproteins. In experimental studies, a neuraminidase-treated zona pellucida cannot be penetrated by sperm cells. Thus, the acrosomal neuraminidase may aid in preventing more than one sperm from entering an ovum (polyspermy).
c. Zona lysins are proteolytic enzymes that are capable of degrading the zona pellucida, perhaps easing the passage of sperm cells through to the ovum.
4. Once the sperm cell has penetrated the corona radiata and zona pellucida, its unit membrane fuses with the unit membrane surrounding the egg cytoplasm. Just after the entry of sperm into the egg, a fertilization membrane is formed (by zona pellucida) in the egg. This fertilization membrane prevents polyspermic fertilization (penetration of many sperms into an ovum simultaneously). A previtelline space is formed between the fertilization membrane and the plasma membrane.
C. Activation of ovum:
As sperm enters the ovum (actually a secondary oocyte) it gets activated and undergoes the second meiotic division. As a result of this the oocyte produces an ovum and a secondary polar body. The polar bodies ultimately degenerate and the ovum contains the haploid number of chromosomes.
Then the ‘chromosome of sperms and egg are set free by the breakdown of their nuclear envelopes. Mixing up the chromosomes of a sperm and an ovum is known as karyogamy or amphimixis. The latter results in the formation of diploid zygote nucleus which contains both the maternal and paternal chromosomes.
Posted by Kamal Narayan 6 years, 3 months ago
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Yogita Ingle 6 years, 3 months ago
The follicular phase is known as the Proliferative phase because the primary follicle grows into the mature Graafian follicle and the endometrium of the uterus regenerates through proliferation simultaneously. The hormones LH and FSH stimulate follicular development.
Posted by Ritika Yadav 6 years, 3 months ago
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Yogita Ingle 6 years, 3 months ago
HIV is a member of a group of viruses called retrovirus,which has an envelope enclosing the RNA genome.Bacteriophage virus has an envelope enclosing the DNA genome. It is divided into three parts, head,neck and tail.
Posted by Ritika Yadav 6 years, 3 months ago
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Yogita Ingle 6 years, 3 months ago
Several fossil discoveries have been made which are of organisms better known as 'missing links' but there is no living representative which could be said an intermediate between reptiles and birds.
Most well known of these missing links is the one which was discovered first, in 1861: the Archaeopteryx.
This impression fossil displayed a typical lizard like tail, there were digits ending in claws, in both the limbs but most amazing feature was the feathers covering its body. There was a beak as well.
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Yogita Ingle 6 years, 3 months ago
Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In such plants, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2). The CO2 is stored as the four-carbon acid malate, and then used during photosynthesis during the day.
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R Saravanan 6 years, 3 months ago
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