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Why is water important to life?
Every known form of life on earth,
from the largest mammals to the
smallest microbes, relies on water.
The most common substance found
on earth is water.
• ~ 75 % of Earth is covered by water
• Of this, 97.5% is salt water and 2.5% is fresh
• Fresh water – 70% in the polar icecaps.
– 30% is mostly present as soil moisture or lies in
underground aquifers.
– Less than 1% (about 0.007% of all water) is
accessible for use.
Properties of water
• Solubility
– Water’s ability to dissolve solute
• Universal solvent
– Used to dissolve nutrients and waste
– Used to transport substances
• Reactivity
– Most biological reactions occur in water
• High heat capacity
– Water’s ability to absorb and retain heat
– remains liquid over an extremely broad range of
• Lubricant
– Reduces friction (example movement of knees)
• Water is the only substance found naturally in
three forms: solid, liquid, and gas.
• Density
– Decreases in density when converted to solid
phase (frozen)
– consequences (that ice floats) are critical to the
evolution of life.
• Design a posters to show the importance of
water to life
• Include the following
– Properties of water and how they influence life
– State of water –solid, liquid, gas
– Water cycle