Transcript Growth & Development

What is Growth ?
• a permanent increase in size, weight & complexity
of an organism
• involves Cell Division (Mitosis) & Cell Enlargement
What is Mitosis ?
• Mitosis occurs when…
– cell divides during growth
– an organism reproduces asexually
– repairing a damage part of body
• 2 daughter cells have exactly the same
number & kinds of chromosomes as the parent
cell
• significance: keep the number of
chromosomes constant after cell division
Stage of Mitosis
Chromosomes appear as
chromatins at resting stage
Stage of Mitosis
Chromatin threads condense to form
distinct chromosomes. The chromosomes
become shorter & thicker - each seems to
consist of two identical chromatids
Stage of Mitosis
Chromosomes line up in the middle part
(equatorial region) of the cell
Stage of Mitosis
Two chromatids of each
chromosome separate & move to
opposite poles of the cell
Stage of Mitosis
The chromatids become chromosomes
of the two daughter cells
Growth in Plants
• Primary growth
– grow in length
• by apical meristem (the
plant tissue that retain
the ability for cell
division)
meristem
Growth in Plants
• Secondary growth
– grow in diameter
(only in dicotyledonous plants)
– by cambium
to produce secondary xylem and
secondary phloem
which forms annual ring
– cork cambium : to form cork layer
to replace the broken epidermis
(6-yrs)
Root Tip
• root cap
– to protect the growing point
• region of cell division (growing point)
– to increase the number of cells for growth
• region of cell elongation
– actual cell elongation region (growth)
– about 2 to 4 mm from the tip
Root Tip (L.S.)
Root Tip
• region of differentiation
– similar cells differentiate to
different tissues
• region of root hair (maturation)
– various tissues fully developed
– main water absorption area
Root Tip (L.S.)
Measurement of Growth
in length of the Main
Root using marking ink
pin
radicle marked
at 1mm intervals
cork
cotton
wool
cork
beaker
strip of
filter paper
water
Do all parts of the radicle grow during the experiment ?
Ans: No. Growth occurs only in the region behind the
tip.
pin
radicle marked
at 1mm intervals
cork
cotton
wool
cork
beaker
strip of
filter paper
water
Where is the region of maximum growth in the root ?
Ans: The region of elongation which is located
immediately behind the tip.
Growth Patterns in Plants
dry
mass
annual plant
time
Growth Patterns in Plants
dry
mass
biennial plant
time
Growth Patterns in Plants
dry
mass
unlimited
growth
perennial plant
time
Animal Growth
• different parts have different growth
rate
• eg. the brain grows first in baby
• eg. the reproductive system grows
only at puberty
Animal Growth
relative
growth
head & brain
general body
limited growth
reproductive system
age
How to Measure Growth ?
• by height / length
– defect : do not take into account the growth
in other dimensions
• by fresh weight
– defect : the amount of water always varies
• by dry weight
– defect : too destructive (the organisms die)
– defect : too time consuming
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