Biology11 Notes for Biology Notes

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Types of true Coelem

Types of true coelem are:

  • Schizocoel:
    Coelom formed by splitting of mesodermal bands. Annelids, arthopods, mollucs and higher chorclates have schizocoel.

  • Enterocoel:
    Coelom formed by the fusion and expansion of a linear series of pouches of archenteron. Echinoderms have enterocoel.

Body plan:-

  1. Cell aggregated body plan:
    Body contains numerous cells but each of them function independently because the cell are not organized to form tissues. E.g. sponges

  2. Blind (hollow) sac boy plan:
    Body contains a single cavity with only one opening or mouth. E.g. Coelenterates, flatworms etc.

  3. Tube-within a tube body plan:
    Body contains two tubes: One outer formed by the body wall and the inner by the digestive tract. The digestive tract is complete. E.g. annelids, vertebrates


  1. Assymetrical:
    Body cannot be divisible into two halves along any vertical plane.
    E.g. Amoeba, sponges, some mollucs, etc

  2. Symmetrical:
    Body can be divided into two similar parts through one or more planes.

    • Spherical Symmetry: Body can be divided into two equal halves by any plane passing through the centre of the body. E.g. Volvox
    • Bilateral symmetry Body can be divided into 2 equal halves through one median plane only. E.g. Humans
    • Radial symmetry Body can be divided into mirror halves by any one of many longitudinal passing through the centre. E.g. Starfish

Body Surface:

  1. Anterior End – parts usually moving forward and bearing the mouth.
  2. Posterior End – parts bearing anus or clocal aperture. It lies opposite the anterior end.
  3. Dorsal Surface – parts which are away from ground in natural position.
  4. Ventral Surface – parts towards ground
  5. Lateral surface – parts towards sides of the body
  6. Medial – parts toward the central longitudinal axis of the body.

Body Segmentation:

  1. Unsegmented: body without a linear series of segments E.g. roundworms, mollucs, echinoderms.

  2. Metamerically Segmented: body with linear series of segments and are independent to each other to work integrally. All segments are in the same stage of maturation. E.g. annelids, arthopods, chordates

  3. Pseudosegmented: Body with many false segments independent to one another. Body grows by addition of new segments from anterior end. The body segments are in different stages of maturation. E.g. tapeworms

Body temperature:

  1. Poikilothemic (cold-blooded):
    Organisms able to change their body temperature according to the surrounding temperature. E.g. fishes, amphibians

  2. Homiothermic (Warm Blooded):
    Organisms not able to change their body temperature according to the surrounding temperature. E.g. Man, aves


  1. Intracellular:
    The digestion taking place within a cell (food vacuole). E.g. in amoeba, paramecium, etc

  2. Extracellular:
    The digestion taking place outside the cell. Digestion in hydra and all animals with alimentary canal possess it.


  1. Asexual:
    binary fission, multiple fission, regeneration

  2. Sexual:
    external and internal fertilization

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