Here is the presentation of Water.This presentation also contains some brief description on Water and its availability for plants, Precipitation and its importance, Distribution of vegetation in relation to moisture,

1. Water

2. • Water is a most important
environmental factor. It is essential for
all life processes. The living cells have
about 80% water. It is essential for the
maintenance of turgidity of cells. It acts
as solvent for the exchanges of gases.
All physiological processes like
photosynthesis. transpiration and
respiration require water.
• Water covers about 73% of the surface
of the earth. It is present in ponds.
lakes, streams and oceans. Only I %
water is present in fresh water bodies
like ponds. river, lakes etc. 99% water is
present in oceans. It falls from the
atmosphere in form of precipitation,
and water vapours.

3. • Water availability for plants
• 1. Maximum water holding
capacity: The .moisture held by a
saturated soil is called maximum
water holding capacity. In this case,
the pore spaces in the soil are
filled with water. It varies from the
coarse texture to fine textured soil.
• Maximum water holding
capacity= Weight of saturated
soil -Weight of dried soil/Weight of
oven dried soil

4. • Field capacity of the soil: The amount
of soil moisture or water content held
in the soil after excess water has
drained away.
• It is different for different types of
soils. Field capacity varies from 5 to
35%.
• Wilting coefficient or permanent
wilting point: The amount of moisture
left in the soil alter a plant has
permanently wilt is called wilting
coefficient. Soil water is now empty for
plant. More water must be added to
the soil Otherwise, the plant will die.
The value of wilting coefficient
depends upon the nature of the soil.

5. PRECIPITATION
• Precipitation includes rain, snow, hail
and dew. Precipitation occurs due to
condensation of water vapours present
in the air. Air or wind carries these
vapours from oceans. Precipitation may
be in the form of rainfall, snow fall or
hailing.
• Precipitation is water released in the
form of rain, freezing rain, snow or hail.

6. • Rain
• The geography of the region and
weather system determines the amount
of rain fall. The air is saturated with
water over oceans. It blows off the
ocean. The air moves upward. There is
low temperature there. The water
vapours condense to firm droplets. Thus
clouds are formed.

7. • Snow
• Snow is also a kind of precipitation.
Snow fall mostly occur on high
mountains. There is a freezing
temperature on the high -
mountains. Therefore, water
vapours are frozen to form snow.
Snow deposits on the mountains
and form glaciers.

8. • Hail
• Some of the drops of rain solidified
due to very low temperature
(below 0°c). They form hail stones.
They fall on the surface of earth.
Hail is not beneficial for the plants.
It destroys different part of the
plants. It destroys the seedling of
the plants.

9. • Dew
• Dew is water in the form of droplets
that appear on the thin, exposed
objects in the morning and evening
due to condensation.
• Sometimes, the temperature is below
freezing point. Therefore, the dew
drops freeze. Such frozen dews are
called frost. It occurs in temperate
regions. Dew adds water content to
the soil. It also increases humidity.
• Dew has little effect on most of
vegetations. But it has great effect in
deserts. There is night cooling in the
deserts. It causes heavy dew
formation. This dew is important for
plant life.

10. Importance of precipitation
• Rain is a major source of soil moister
for the plants.
• Rain increases the humidity of air. Thus
it reduces the rate of transpiration in
plants. It affects many physiological
functions of the plant.
• The amount of rain determines the
different vegetation zones. The
deserts, grass lands and forest are
formed due to different amount of
rain.
• Snow is important for driving rivers.
• Snow may cause ice crystal formation
in plant cells. It kills the plants.
• Hail storm destroy the standing
crops
• Dew has great significance for
desert plants.

11. Distribution of vegetation
in relation to moisture
• Plants are divided into four groups in relation
to moisture. These groups are hydrophytes,
amphibiophytes. Mesophytes and xerophytes.
1. Hydrophytes
• The plants grow in water reservoirs like
ponds, lakes streams or rivers are called
hydrophytes. These plants live in habits with
abundance of water. They may be submerged
hydrophytes. free floating hydrophytes. fixed
floating hydrophytes.
• (a)Submerged hydrophytes: these plants are
fully submerged in water. They may be
rootless. Their stem is soft and tender. Cuticle
is absent in them. Vascular tissues are poorly
developed. Mesophyll of the leave is not
differentiated into palisade and spongy. They
have special type of stomata
called hydathodes. Its example is Hydrilla.

12. • (b)Free floating plants: They are not
anchored in the soil. Roots are absent
in them. Hydathodes are present only
on the dorsal surface. Its examples are
wolffia, Pistia.
• (c)Fixed floating plants: They are
anchored in the soil and their leaves
are free floating on the surface of
water. They occur in shallow water.
They have well developed roots. The
stern is present in the form of rhizome.
Its example is Marsilea.

13. 2. Amphibiophytes
• The moisture loving plants are amphibiophytes. They grow on very moist
and swampy places. These places are present on the sides of ponds. lakes
and rivers. Their roots and part of stem are embedded in the mud. Most of
their characteristics are intermediate between hydrophytes and
mesophytes. They have well developed mechanical and conducting tissues.
Their endodermis is thick walled. They have system of air space in the
body. Their example is sagittaria.

14. 3. Mesophytes
• The land plants which grow in places which
are neither dry not wet are called
mesophytes. They are intermediate between
hydrophytes and mesophytes. Many of the
cultivated, ornamental and evergreen plants
belong to this group. They have well
developed tap root and adventitious roots.
The stem is erect. The leaves are large with
waxy coating. Stomata are present on the
lower.surface of the leaves. The leaves are
dark green in colour. They readily wilt even in
slight water deficiency.

15. 4. Xerophytes . .
• The desert plants are called xerophytes. They face
the extreme shortage of water. They have following
adaptation to reduce the rate of transpiration.
• (i). Many xerophytes posses small, thick leaves. It
reduces the surface are proportional to volume of the
plants. Thus it reduces the loss of water by
transpiration.
• (ii). They have thick, waxy and leathery cuticle.
• (iii). The stomata are on the lower surface of the
leaves. These stomata are present in depressions.
• (iv). Some plants like cacti shed their leaves during
the dry seasons. Therefore, the transpiration is
stopped completely. They have stem as their
photosynthetic organ. Their stem store water in the
rainy season and use it in dry condition.
• (v). Most of their body is composed of water
storing cells. Such plants are called succulents.