An overview of the Systemic Aterial System

 





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14.6 ECOLOGICAL SUCCESSION

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14.6 ECOLOGICAL SUCCESSION You have learnt in Chapter 13, the characteristics of population and community and also their response to environment and how such responses vary from an individual response.  Let us examine another aspect of community response to environment over time.  Bcological succession:   The gradual and fairly predictable change in the species composition of a given area is called ecological succession. An important characteristic of all communities is that composition and structure constantly change in response to the changing environmental conditions.  This change is orderly and sequential, parallel with the changes in the physical environment.  These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community.   Sere(s):  The entire sequence of communities that successively change in a given area are called sere(s).  The individual transitiona...
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Figure 7.9 A sketch of the evolution of plant forms through geological periods NEET

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Figure 7.9 A sketch of the evolution of plant forms through geological periods NEET Expectations/ practice 1. Match the following 2. Find the correct sequence Coenozoic    Quaternary Angiosperm (flowering plants) Monocotyledons Tertiary Bryophytes Measozoic    Cretaceous Shenopsids (horsetails), Ginkgos, Gnetales, Dicotes Jurassic Herbaceous lycopods, Ferns, Conifers and Cycads Triassic Paleozoic Permian Arborescent lycopods Carboniferous Seed ferns Devonian Progynmnosperm Silurian Zosterophyllum Chlorophyte ancestors > Tracheophyte ancestor > Rhynia-type Plants > Psilophyton Chlorophyte ancestor > Bryophytes Chlorophyte ancestors > Tracheophyte ancestor > Zosterophyllum > Arborescent lycopods > Herbaceous lycopods Chlorophyte > Tracheophyte > Rhynia-type Plants > Psilophyton > Shenopsids (horsetails) Chlorophyte > Tracheophyte > Rhynia-type Pla...
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8.3 AIDS

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8.3 AIDS The word AIDS stands for Acquired Immuno Deficiency Syndrome.  This means deficiency of immune system, acquired during the lifetime of an individual indicating that it is not a congenital disease. ‘Syndrome’ means a group of symptoms.  AIDS was first reported in 1981 and in the last twenty-five years or so, it has spread all over the world killing more than 25 million persons.  AIDS is caused by the Human Immuno deficiency Virus (HIV), a member of a group of viruses called retrovirus , which have an envelope enclosing the RNA genome.   Human Immuno deficiency Virus (HIV) Structure & its Genome:   It is roughly spherical with a diameter of about 120  nm , around 60 times smaller than a  red blood cell . It is composed of two copies of positive- sense   single-stranded   RNA  that codes for the virus's nine  genes  enclosed by a conical  capsid  composed of 2,000 copies...
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