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Thursday, August 8, 2013

SEED DEVELOPMENT AND GERMINATION

1.   After fertilization:
     ·    zygote undergoes mitotic divisions
     ·    to form the embryo.


 
 2.   Endosperm muclei:
     ·    undergo mitotic divisions
     ·    to form endosperm tissue.













3.   Endospermic + embryonic development:
     ·    occur in the ovule.
     ·     integuments surrounding the ovule
     ·    will harden to form seed coat.

 
 
4.   Ovary à will become the fruit.

5.   There are two types of seeds:
     ·    monocotyledon (seeds have one cotyledon)
     ·    dicotyledon (seeds have two cotyledons)

6.   Germination:
     ·    emergence of the radicle
     ·     thru seed coat.














7.   Water:
     ·    required for germination
     ·     enters the seed by imbibition.
     ·    initiate embryo to synthesise gibberelin.


8.      Gibberelin will:
     .    diffuse thru endosperm àinto aleurone layer.
     .    initiate production of hydrolytic enzymes.

2.      Hydrolytic enzymes will:
     .    enter endosperm
     .       catalyse conversion of compound (stored in endosperm).

3.      Products (especially glucose) will be:
     .       transferred to the embryo
     .    used for respiration + germination

HUMAN FETAL DEVELOPMENT

1.   After eight weeks of development:
  • all the organs + systems à been laid down.
  •  embryo =  foetus.
 
2.   Extraembryonic membranes:
  • amnion, chorion + allantois
  • formed from embryonic cells
  • in early stages of embryonic development.
3.   Amnion:
     Ø  develops from the epiblast.
     Ø  encloses embryo in a fluid-filled amnioc sac,
     Ø  protecting embryo (foetus) from:
          ·    abrupt temperature changes
          ·    mechanical impacts.

4.    Chorion:
      Ø  develops from trophoblast.
      Ø   surrounds the embryo + other extraembryonic membranes.

5.   Aallantois:
     ·    develops from part of embryo’s archenteron.














6.   Placenta:
     ·    consists of endometrial tissue + extraembryonic membranes.
     ·    a specialized organ
     ·    allows exchange of materials
     ·    between maternal +  foetal blood streams.

7.      Foetal part of the placenta
  • arises from amniotic + chorionic membranes.
  • umbilical blood vessels àformed from allantois.
8.      Materials are exchanged across placenta by:

  • diffusion,
  • active transport
  • selective absorption.

9.      Nutrients, oxygen, water + antibodies:
  • pass from the mother’s blood
  • into the fetal blood circulatory system.










10.  Umbilical artery:
     ·    carries blood
     ·    from aorta of foetus
     ·    to placenta,

11.  Umbilical vein:
     ·    carries blood
     ·   from placenta
     ·   to posterior vena cava of foetus.

12.  Placenta is therefore:
     ·    site of gaseous exchange,
     ·    source of nutrients
     ·    excretory organ
     ·    source of antibodies.













13.  Although foetal + maternal blood streams:
      ·     flow very close to each other
      ·    but blood do not mix.

 

Wednesday, August 7, 2013

EMBRYOLOGY

1.      Embryonic development;
      ·         is triggered by fertilisation.
      ·         can be divided into three main stages:
             o   Cleavage
             o   Gastrulation,
             o   Organogenesis
 
2.      Cleavage:
      ·         division of the zygote
      ·         into daughter cells.
      ·         embryo (at the end of this stage) = blastula

 
3.      Gastrulation:
      ·         arrangement of embryonic cells
      ·         into three germ layers (ectoderm, mesoderm +  endoderm).
      ·          embryo (at the end of this stage) = gastrula.













4.      Organogenesis:
      ·         formation of organs + organ systems.
      ·         each germ layer àgives rise to different organ systems.