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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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8.1 COMMON DISEASES IN HUMANS NEET

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8.1 COMMON DISEASES IN HUMANS A wide range of organisms belonging to bacteria, viruses, fungi, protozoans, helminths, etc., could cause diseases in man.  Such disease causing organisms are called pathogens. Most parasites are therefore pathogens as they cause harm to the host by living in (or on) them.  The pathogens can enter our body by various means, multiply and interfere with normal vital activities, resulting in morphological and functional damage.  Pathogens have to adapt to life within the environment of the host.  For example, the pathogens that enter the gut must know a way of surviving in the stomach at low pH and resisting the various digestive enzymes.  A few representative members from different groups of pathogenic organisms are discussed here along with the diseases caused by them.  Preventive and control measures against these diseases in general, are also briefly described. Typhoid:  Salmonella typhi is a pathogenic b...
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