Download The Importance of Water to living Organisms

“TheImportanceofWatertolivingOrganisms”
Water is a unique molecule with certain properties that make it essential
to living organisms. Your essay should look at these unique features. You
should also explore the many ways in which water is useful t o life found
on our planet.
‘A clear, colourless, tasteless liquid that is essential for plant and animal life’ (l)
Di-Hydrogen Oxide more commonly known as water, the single most
important molecule on the planets surface without it life couldn’t exist,
Biologically speaking water is the most abundant compound on this planet.
It is the most important component of the human body making up over
two thirds of total bodyweight as our cells composition is around 80%
water (2), we start life in the womb surrounded by water. Water played a
major role in the evolution of biological systems, without it respiration and
photosynthesis the very reactions of life couldn’t take place. Water is the
medium in which all cell biochemical reactions take place, be it plant or
animal. As a result of our understanding of biological systems it is widely
accepted that all life originated in water, in an ‘organic soup’ (2). It is also
true to say that organisms are so dependant on water that animal
migration and behavioural patterns closely follow water availability.
The reason why water is important as a medium for life is mainly
attributed to its wealth on the planets surface and from the five properties
it exhibits here: Solvent properties, heat capacity, surface tension, freezing
properties and transparency (2).
Between 0 and l00°C and at atmospheric pressure water is a liquid. Due to
the position of earth in relation to the sun most of the water on the
planets surface exists in a liquid state, on other planets such as Venus and
Mars water exists as a gas and a solid making it impossible for life to exist.
Water readily dissolves a wide range of inorganic and organic molecules,
creating what is known as a solution. All chemical reactions within living
cells take place in aqueous solution. Water is remarkable its properties as a
solvent are attributed to the fact that it is a polar molecule with positively
charged hydrogen atoms and a negatively charged oxygen atom, because
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of this structure other polar molecules readily dissolve. This is of great
importance as most biological molecules are of a polar nature. Another
advantage of this polar behaviour is that the individual water molecules are
attracted to one another like magnets which means that unlike other
small molecules water remains a liquid at room temperature. This
attraction is known as ‘hydrogen bonding’ (2).
Another interesting property is that it has a very high heat capacity, which
means that it takes a lot of energy to make water boil and a large amount
of energy must be removed to make water freeze. As a result of this water
in our cells and on the planets surface remains at a steady temperature
regardless of temperature fluctuations in the environment. This is
important as the range of temperatures that biochemical reactions can
operate is very small and most organisms cannot survive great variations in
temperature.
Surface tension is a very important property of water as it enables the
surface of the liquid to contract and occupy the least area; examples of this
are rain drops on a car windscreen. This is caused by the hydrogen bonds
pulling the liquid together. These forces are particularly useful in the
transport of water in the xylem vessels of plants(3).
Water is an unusual liquid as when it freezes its density lowers and its
volume increases which allows it to float on water, this is useful as it
insulates the water below it which allows aquatic life to survive in extreme
freezing temperatures(4).
The last property of water found on the surface of the earth is its
transparency this is greatly important as small photosynthesising
organisms within the water would not be able to live and as most of these
organisms are the primary producers in ocean food chains the great
ecosystems within would not exist. This means that there would be no life
on this planet, as it was stated earlier that life came from the seas. Further
benefits to the transparency of water are that a lot of aquatic animals hunt
by sight.
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Water is used by all life on this planet for the purpose of this essay two
organisms will be explained, plants and animals.
Plants are known as autotrophic which means they produce there own food
(l); they produce this by a process known as photosynthesis.
Photosynthesis is the reaction by which green plants make complex organic
molecules from carbon dioxide and water,to power this process plants
use the suns energy which is absorbed by a green pigment called
chlorophyll (5). The overall equation for photosynthesis is:
Water + Carbon Dioxide ‹ Glucose + Oxygen
During photosynthesis water is split using light energy to produce
hydrogen ions. These ions are used to reduce the Carbon Dioxide to form a
carbohydrate.
Water is also used in plants as support, this is achieved by a central large
vacuole in the centre of the cell which when turgid keeps pressure in the
cell this prevents the plant from wilting. Water enters a plant through the
roots by a process called osmosis, this is:
The net movement of water molecules across a selectively permeable
membrane from a region of high concentration to a region of low
concentration. (3)
In animals water is vastly important it has wide and varied uses, in humans
water is essential and a change in water concentration can have fatal
consequences. As earlier stated most cells in the human body contain
around 80% water. Every cell in the human body is connected via blood or
some other body fluid and any change in the composition of these fluids
will affect them in some way. In the human body water is used to
transport nutrition in and out of cells, to transport waste, to regulate
temperature, as a reactant in hydrolysis and as a medium in which
chemical reactions can take place. A reaction which is particularly
important for animals is respiration. Unlike plants, animals are not
autotrophic, they are heterotrophic which means they derive there energy
from food sources obtained outside of the body (5). Respiration occurs in
all organisms including plants, plants break down the sugars they produce
for energy. The simplified word equation for respiration is:
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Glucose + Oxygen ‹ Water + Carbon Dioxide + Energy
From this reaction we can see that water is produced and this can then be
transported off to be used elsewhere in the cell.
Fossil evidence suggests that life began around 3.5 billion years ago, at this
time according to geological evidence the earth’s atmosphere contained
four main gasses one of these being water vapour, through various
reactions life was formed, these very first organisms were crystal clays,
the very early organisms were restricted to water as they had no means of
movement. Millions of year’s later animals began to leave the seas and
venture onto the land, with this many adaptations took place for example
the gills became enclosed and evolved into air breathing organs (2). Some
animals never fully moved away from water as is seen in many amphibian
species that still return to water to breed.
The physical environment in which animals exist is also controlled by
water. For organisms, annual rainfall is very important as are its pH and
predictability; organisms living in very dry places have adapted special
devices to reduce water loss. Examples of such mechanisms to prevent
water loss can be found for example the Australian desert frog which
retains urine in its bladder for use in the dry season, it retains so much
urine that it swells up like a balloon, aborigines use these animals as
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source of water (2). Plants also show adaptations for example Marram
grass where the leaves are folded up into a spine like structure, as a result
all the stoma are on the inside therefore reducing the amount of water lost
due to transpiration (3). Other examples of adaptations can be seen in
cacti where water is stored in thick stems and branches. In addition the
epidermis is surrounded by a thick cuticle and very few stomata to
reduce transpiration. For aquatic organisms the temperature, salinity and
nutrient content of the water are essential. As well as Oxygen saturation,
wave action and the rate of current flow is important. All the above factors
govern the type of organism found in each area.
In conclusion it is clear to see water is a unique molecule unlike any other
found on this planet and due to its many characteristics and properties it
is essential to living organisms. Without water there would be no life on
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this planet, the diversity of life found on this planet is controlled by water
availability.
Bibliography
l) English Dictionary. Collins (2003) HarperCollins Publishers, ISBN 0
00 766691 8
2) Roberts, M. Reiss, M. Monger, G. Advanced Biology (2000) Nelson
Publishers, London, UK. ISBN 0 17 438732 6.
3) Feldman, C. University Access Biology Notes (2004)
4) Feldman, C. University Access Chemistry Notes (2004)
5) Rowlands, G. Biology A-Level Study Guide (2000) Pearson Education
Limited, ISBN 0 582 43177 8.
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