WELCOME..... TO .....HIGH SCHOOL BIOLOGY BLOG !!!

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.

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.

Sunday, September 16, 2012

Experiment 4 : Effect of temperature on enzymatic activity

Experiment 4 by L6ScZeta 2012
Enough or not?...enough or not??.....
 


One drop...two drops...three drops........

















Now...see this...this is how to hold it...





Where is the reading???








 
 
 
 
 
 
 
 
 
 



Wow....this stop watch is awesome!



 Experiment 4 by L6ScGamma 2012



L6ScGamma in action.......

Is this mine?...I think this is yours.........wait......I think.......
Give a BIG smile!...you're on candid camera........


Huh!....Oh..oh.!.caught in action........



Ohhhh.....so......sweet........


OK! Everybody! Time's up! Stop smiling and start working.......

One drop...two drops...three drops....... Oh oh..no more already!


I think mine is overcooked...How about yours? Oh!...mine is well done!


Hemmm....how come mine is still dark blue.....???


Now...add saliva to the starch slowwwww...ly.......and..... stir fast!







Experiment 1: Measurement of cell size using microscope


Experiment 1 by L6ScBeta 2012

Light microscope was used in the experiment. What are the magnification of eyepiece and all the objective lenses?
The Lower Six Science Beta students were trying out the microscope.
The students were listening to the instructions given by the teacher.

Saturday, September 15, 2012

HORMONES IN REPRODUCTION II

1.   Early pregnancy:
     -     trophoblastic cells secrete HCG
     -     which signals the corpus luteum
     -     to continue its secretion of oestrogen + progesterone.














2.   Later in pregnancy:
     -     secretion of oestrogen +  progesterone
     -     is taken over by the placenta.












 3.   Progesterone + oestrogen:
     -     develop + maintain endometrium (of the uterus)
     -     throughout pregnancy.
     -     ostrogen - promotes uterine contraction, while
     -     progesterone - inhibits it.

4.   In late pregnancy - oestrogen levels increase with respect to progesterone.











5.   Prior to birth:
     -     oxytocin stimulates uterine wall contractions
     -     causing the baby to be delivered.

6.   During pregnancy:
     -     the effect of prolactin (which promotes milk production)
     -     is inhibited by high levels of oestrogen + progesterone.

7.   After birth:
     -     When oestrogen + progesterone levels drop
     -     prolactin causes the breast to produce milk

8.   The interaction between hormones:
     -     oestrogen + oxytocin
     -     and local regulators (prostaglandins)
     -     induce + regulate labour.

 
9.   Oestrogens:
     -      which reach their highest level
     -     during the last weeks of pregnancy
     -     trigger the formation of oxytocin receptors on the uterus.

10.Oxytocin:
     -     stimulates powerful contractions of the uterus.
     -     also stimulates placenta to secrete prostagladins.

11.  Prostaglandins:
     -     enhance the contractions or the uterus,
     -     making them more powerful
     -      and more frequent.

12.  Physical + emotional stresses:
      -     in turn, stimulate the release of more oxytocin + prostaglandins.

13.  This positive feedback system à underlies the three stages of labour.

HORMONES IN REPRODUCTION I


1.   Menstrual cycle:
     -     lasts an average of 28 days
     -      controlled by the brain
     -      via hormones produced by the pituitary.

 
2.   Hypothalamus:
     -     produces GnRH
     -     which stimulates anterior pituitary
     -     to secrete FSH + LH into the blood.

3.   FSH:
     -     stimulates ovarian follicle growth
     -      which in turn secretes oestrogen.
     -      to stimulates the regrowth of the lining of uterus.













4.   Early in the cycle:
     -     low level of oestrogen à  inhibits secretion of FSH + LH  X.

5.   Middle of the cycle:
     -      high levels oestrogen à stimulates a surge of FSH + LH .
     -     surge of LH à triggers ovulation.
     -     ruptured follicle à develops into corpus luteum.
     -     corpus luteum à secretes oestrogen + progesterone.

 
6.   After ovulation:
     -          high levels of both oestrogen + progesterone levels to drop.

7.   At the end of the cycle:
     -     drop in oestrogen + progesterone blood levels
     -     causes uterine lining to disintegrate.
     -     frees pituitary from inhibition
     -     thus triggering the secretion of FSH + LH,
     -     which stimulates development of a new follicle.














8.   Menstrual cycle:
     -     refers to changes that occur in the uterus
     -     which begins with menstrual flow phase
     -     followed by proliferative phase,
     -     last phase - secretory phase.

9.   Ovarian cycle = running parallel to the menstrual cycle
     -     which begins with the follicular phase,
     -      followed by ovulation
     -     later, the luteal phase.

10.  Changes in the ovary + uterus:
      -     are correlated
      -     with the changing pituitary + ovarian hormone levels
      -   in menstrual cycle.