Thursday, November 27, 2014


1. Growth is a:
  • characteristic of all living organisms.
  • permanent irreversible increase in size of an organism
  • due to increase in its dry mass.
  • continue throughout the life of an organism (eg: woody perennial plants)
  • may cease when organism reach maturity (eg: man  or other mammals)
2. Result is irresversible:
  • increase in volume of cytoplasm
  • Increase in number of cells
  • increase in differentiation of cells
3. Growth in unicellular organisms:

  • reaches certain size – divide to form two separate cells
  • size limited - due to distance of cell over which a nucleus can exert its controlling influence.
  • division - results in growth of populations.
4. Growth in multicellular organisms:
  • originate from a single cell (the zygote)
  • cell division – increase in number of new cells produced by mitosis
  • cell expansion (cell enlargement) – increase in size, volume + mass (due to assimilation of food materials +  metabolism)
  • cell differentiation:
           i. cells undergo progressive changes in metabolic activities:
               – lead to changes in cell structures
               – produce diff specialized cells/tissues for dif functions
           ii. in higher animals:
                – produce tissues (epithelial tissue, nervous tissue, muscle tissue + connective tissue)
           iii. in higher plants:
                – produces tissues (meristematic tissue, ground tissue +  vascular tissue).
5.   Morphogenesis
      a. result from:
  • development (growth+ differentiation) of overall form of organs
  • formation of multicellular organism
      b. cell differentiation cause by:
  • differential expression of genes.
  • certain metabolites activate/repress gene in dif. cells.
  • some hormones are able to switch genes on/off (help to determine overall pattern of development)


A.    External factors affecting the rate of growth in plants are:

  1. light (intensity, wavelength and photoperiod) – affects photosynthesis, photomorphogenesis, meristemic activities and flowering.
  2. Temperature which affects enzyme activities.
  3. Oxygen – require for aerobic respiration and seed germination.
  4. Carbon dioxide – for photosynthesis, synthesis of organic molecules.
  5. Water – essential for many metabolic processes (photosynthesis, seed germination, transportation of mineral salts/soluble organic material, vacuolation, maintenance of plant cell turgidity
  6. Relative humidity of atm – affects rate of transpiration.
  7. Minerals (K+, Na+, Ca2+, NO3+) for plant metabolism/growth/development.
  8. Gravity – affects distribution of growth regulators for geotropism
  9. Seasonal influences – affect dormancy, abscission, reproduction and photoperiodism
  10. Biotic factors -pathogen-caused plant diseases, intraspecific and interspecific competition for space, sunlight, water and mineral salt).
B. Internal factors are:

  1. Genotype of the plant – determines the synthesis of specific proteins and enzymes, the type of metabolism and size.
  2. presence and absence of growth regulators/plant hormones (auxins, gibberellins, cytokinins, absciccis acid, ethene)
 C. Animal growth + development are controlled mainly by:

  1. Genotype of the animal
  2. Animal hormones (thyroxine and somathrophin).
  3. Environmental conditions (lights intensity and photoperiod, temperature, oxygen, availability of water and seasonal influences.
  4. Biotic factors.

Advantages + disadvantages
Height and length
·      easy + quick to measure.
·      growth can be measured continually
·       only measures the length in one dimension + does not take into account growth in other directions.
·       An organism not increasing in height - may continue to grow in girth or grow sideways (as in plant)
Surface area
·      more accurate measurement.
·      eg: surface area of a leaf attached to a plant can be measure at regular intervals over a period of time.
·       Dif. + impractical to carry out if the organism is irregular in shape.
·       It’s assumed that plant growth is directly proportional to the increase in the surface area of its leaves.
Volume, size
·       Suitable for measuring organisms that are spherical or cylindrical in shape.
·       Living organisms are rarely exactly spherical and cylindrical in shape
·       Not accurate measurement.
·       Dif. to carry out – complicated calculation for organism with irregular shape.
Dry mass
·       More accurate measurement of the organic materials (protein present in the body.
·       Water has to be removed by drying the organism.
·       This kills the organism, so continuous growth of the same organism cannot be measured
·       Have to use a large number of individuals from the same population which have similar age and size.
·       Dif. plants used may have dif, growth rates.
Wet mass or fresh mass
·      Easy to measure
·      No need to kill the organism.
·      Growth can be measured continuously as repetitive measurements can be carried out.
·       Measurement may be inaccurate due to fluctuations in water content in the body.
·       May be more suitable for measuring growth in animals but not for a living tree.

Thursday, August 8, 2013


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


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


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........


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


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.

     -     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.