Plants-The growth of plants

The starting point in the life of many types
of plants begins from a seed.Transformation
and development of seeds into a full grown
plant is an extraordinary process which
necessitates cell division,cell enlargement
growth,the formation of such parts as roots,
stems,leaves,flowers and a long series of
complex changes.The final appearance of
plants is also affted by the gentic pattern
of the fertilized ovule and environmental
factors.

Seed is a live plant which has not grown and
acts as a bridge among generations of plants.
Each seed is made up of embryo,tissues of
storing materials,enzymes and a seed coat.
When seeds are in suitable environment from
the point of view of moisture , oxygen,
temperature and light they begin to
germinate. During the germination process,
it first absorbs water and as a result of
the production and the activities of special
enzymes inside the seed undissolved nutrients
change into dissolvable ones. The materials
thus produced are transferred into embryo
meristem and provides the necessary energy
for the growth of the plant and eventually
causes the crack in the seed coat and the
emergence of a seedling.

Embryo is in fact a tiny plant which has
a main axis and two growth points at its
each end.On one end there are the embryonic
roots called radicle and on the other end
there are the embryonic stems called plumule.
The embryo also contains one or more hidden
leaves called cotyledon.Generally,the speed
at which radicle grows is more than that of
plumule,therefore,radicle is the first part
to come out of the broken seed coat.
This is a big advantage for the survival of
seedlings . Main roots appear later than
radicles.

Roots help the growth of plants through
supporting the plant in soil,absorbtion
of water and minerals and transferring
them to the stem and in some cases by
storing nutrients.

Plumules also have an apical meristem at
their ends the cells of which divide quickly,
grow upward and are pushed out of soil a
generative layer forms in stems between
xylem and phloem tissues which through
fast division produce cells in two
directions,these cells are eventually turned
into phloem and xylem.

Leaves are also lateral projections produced
from the apical meristems.Leaves have two
main parts : leaf stalk or petiol and leaf
blade or flat part.

Leaves play their role in the life of the
plant through photosynthesis,respiration,
evaporation and transpiration.Photosynthesis
is a process during which green plants
produce glucose and release oxygen in the
presence of sunlight by using the CO2
existing in the air and water.A portion of
the glucose produced is used to make complex
organic compounds such as starch,celloluse,
lipids,proteins,vitamins and hormones,and
another portion is used in the process of
plant respiration,thus the necessary energy
for other plant activities are produced.
Outstanding transformations in the life cycle
of plants occur when they get from vegetative
phase to reproduction phase.In this phase the
apical meristems produce the earliest designs
of flowers consisting of sepals , petals,
stamens and carpels.Plants reproduction takes
place with the appearce of flowers.

Reproductive parts produce gametes of male
(pollen( and female) ovule(.The two male and
female reproductive cells in plants meet and
unite,and following fertilization and egg
cell formation,fruit and seed are produced.
They,then grow and spread,which in fact when
suitable environmental conditions are met,
a new plant life cycle begins.