Transcript Growth & Development

Growth & Development
•
Prepared by Ms W.S.Kwan
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.
Growth &
development in cells
Growth in
organisms
Cell level
Organism level
Cell divides & expands
Organism increases in
size
Cell specialization
(differentiation)
Organism increases in
complexity
Cell Division
Resting stage
Nuclear
division
Cytoplasmic
Division
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.
Stage of Mitosis
Chromosomes appear as
chromatins at resting stage
Stage of Mitosis
During
division
Chromatin threads condense to form
distinct chromosomes. The chromosomes
duplicate (replicate) as two identical
chromatids
Stage of Mitosis
Chromosomes line up in the middle part
(equator) of the cell
Nuclear membrane disappeared
Stage of Mitosis
Two chromatids of each
chromosome separate & move to
opposite poles of the cell
(equal separation of chromatids)
Stage 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 which
are identical to the parent cell
• Significance: Mitosis keeps chromosomes
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 Plants
• Primary growth
– growth in length
– by apical meristem at
shoot tip & root tip
meristem
Note: Meristem = region of meristematic cells
(i.e. cells with the ability of cell division)
Growth 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
• root cap
– to protect the growing
point
• growing point / region of cell
division (apical meristem)
– cells multiply for growth
• region of cell elongation
– cell enlarged by
vacuolation for growth
Root Tip (L.S.)
Cell enlargement in plant growth
• Vacuolation
Thin cell wall stretches
& cell expands
Cell draws
in water by
osmosis &
expands.
Cell wall thickens &becomes
rigid. Expansion stops.
Root Tip
• region of differentiation /
specialization / maturation
– Cells differentiate to
different specialized
tissues
– various tissues fully
developed
– main water absorption
area
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.
How to Measure Growth ?
Defect
by height /
length
by fresh
weight
by dry
weight
Do not consider growth
in other dimensions
amount of water always
varies
destructive (kill the
organisms) & time
consuming
Advantage
?
?
?
Growth Patterns in Plants
dry
mass
Dispersal
of fruits
& seeds
Due to
respiration of
food reserves
during seed
germination
annual plant
time
Growth Patterns in Plants
Fresh
mass
Annual plant
time
Growth Patterns in Plants
dry
mass
unlimited
growth
perennial woody plant
time
Animal Growth
• Cell division takes place in all parts of
the body.
• Different parts have different growth
rate
eg. the brain & head grow rapidly in
baby, while the reproductive system
grows fast at puberty.
~END~