growth & development prepared by ms w.s.kwan what is growth ? a permanent increase in size,...
TRANSCRIPT
Growth & Development
• Prepared by Ms W.S.Kwan
What is Growth ?What is Growth ?• A permanent increase in size, weight &
complexity of an organism.
Growth is an increase in volume of individual cells & an increase in number of cells.Growth involves Cell enlargement & Cell Division
Development• Involves specialization of cells into
different cell types forming
tissues, organs & system
• Resulting in an
increase in
complexity of
an organism.
Cell level Organism level
Cell divides & expands Organism increases in size
Cell specialization (differentiation)
Organism increases in complexity
Growth in organisms
Growth & development in cells
Cell Division
Nucleardivision
Cytoplasmic Division
Resting stage
Nuclear division• Nucleus contains chromosome,
which carries genes.• At rest stage:
- Chromosomes are indistinct (not seen)
- Chromosomes appear as chromatins
• During division:- Chromosomes
become distinct
Chromatin
Chromatids During division:
Chromosomes become distinct & duplicate as a pair of chromatids
Nuclear division in Growth
• There are 2 types of nuclear division:
Mitosis & Meiosis
• Mitosis occurs when cell divides during growth.
Chromosomes appear as chromatins at resting stage
Stage of MitosisStage of Mitosis
Chromatin threads condense to form distinct chromosomes. The chromosomes duplicate (replicate) as two identica
l chromatids
Stage of MitosisStage of Mitosis
During division
Chromosomes line up in the middle part (equator) of the cell
Nuclear membrane disappeared
Stage of MitosisStage of Mitosis
Two chromatids of each chromosome separate & move to oppos
ite poles of the cell
(equal separation of chromatids)
Stage of MitosisStage of Mitosis
Stage of MitosisStage of Mitosis
-Two daughter nuclei form. -Cell splits into two daughter cells.- Each daughter cell contains same number & kinds of chromosome as the parent cell.- Daughter cells are genetically identical to the parent cell.
Summary of mitosis:
Daughter cells are identical to the parent cell.
Role & Significance of mitosis• Mitosis produces 2 daughter cells whi
ch are identical to the parent cell • Significance: Mitosis keeps chromoso
mes content constant after cell division. Genetic information is conserved.
• Role of Mitosis: It allows– cell multiplies during growth– Cell repairs / cell replacement– an organism reproduces asexually
Growth in Growth in PlantsPlants
• Primary growth– growth in length– by apical meristem
at shoot tip & root tip
meristemNote: Meristem = region of meristematic cells (i.e. cells with the ability of cell division)
Growth in PlantsGrowth in Plants• Secondary growth
– growth in diameter (thickness) (only in dicot plants)
– by cambium (meristematic cells) produce secondary xylem and secondary phloem which forms annual ring
– cork cambium : to form cork layer to replace the broken epidermis
Root Tip (L.S.)
• root cap – to protect the growing p
oint• growing point / region of ce
ll division (apical meristem)– cells multiply for growth
• region of cell elongation – cell enlarged by vacuolat
ion for growth
Root Root TipTip
Cell enlargement in plant growth• Vacuolation
Cell wall thickens &becomes rigid. Expansion stops.
Cell drawsin water byosmosis &expands.
Thin cell wall stretches & cell expands
• region of differentiation / specialization / maturation– Cells differentiate to
different specialized tissues
– various tissues fully developed
– main water absorption area
Root TipRoot Tip
Measurement of Growth in length of
the Main Root using marking ink
Do all parts of the radicle grow during the experiment ?Ans: No. Growth occurs only in the region beh
ind the tip.
pin cork
cotton wool
cork
beaker
strip of filter paperwater
radicle marked at 1mm intervals
Where is the region of maximum growth in the root ?Ans: The region of elongation which is locate
d immediately behind the tip.
pin cork
cotton wool
cork
beaker
strip of filter paperwater
radicle marked at 1mm intervals
How to Measure Growth ?How to Measure Growth ?Defect Advanta
ge
by height / length
Do not consider growth in other dimensions
?
by fresh weight
amount of water always varies
?
by dry weight
destructive (kill the organisms) & time consuming
?
Growth Patterns in PlantsGrowth Patterns in Plants
drymas
s
time
annual plant
Due to respiration of food reserves during seed germination
Dispersal of fruits & seeds
Growth Patterns in PlantsGrowth Patterns in Plants
Fresh
mass
time
Annual plant
unlimited growth
perennial woody plant
drymass
time
Growth Patterns in PlantsGrowth Patterns in Plants
Animal GrowthAnimal Growth• Cell division takes place in all parts
of the body.• Different parts have different grow
th rate
eg. the brain & head grow rapidly in baby, while the reproductive system grows fast at puberty.
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