2.1.2 Water and its importance in plants and animals
Structure
Properties of Polar molecule
water Oxygen atoms have a more negative charge than the
hydrogen atoms
This is because there are more positive protons in oxygen
than hydrogen, so hydrogen’s electrons are pulled further
towards the oxygen
Hydrogen bonds are formed because the positive charges
are attracted to the negative charges – this is how water
molecules are attracted
Charges of oxygen and hydrogen molecules in water with the delta 𝛿
sign and a + or - alongside. (𝛿+ or 𝛿-)
Properties of water
Acts as a solvent – water is attracted to other polar and
charged particles, and they form a shell around charged ions
which prevents them from clumping together.
o Allows for transport in plasma, removal of metabolic
waste, and chemical reactions to occur inside cells
High specific heat capacity – due to hydrogen bonds
restricting movement of water molecules, this increases the
amount of energy required to break the bonds
o Prevents large temperature fluctuations in humans as
a result of changes to the environment
High latent heat of evaporation – water molecules need a
high amount of heat to become a vapour, this means that
when water evaporates it has a cooling effect
o Allows heat to be lost through sweating, cools plants
by evaporation of water from leaves
Cohesive and adhesive properties
o Cohesion – hydrogen bonds stick water molecules
together
o Adhesion – water molecules interact with other
charged particles
o These properties mean water is viscous
o Water can be used as a lubricant in the form of pleural
fluid (to minimise friction between lungs and ribcage)
and mucus (allow passage of faeces down the colon).
It is also critical for transport in the xylem
Low density as a solid – ice floats so acts as an insulator in
lakes or sea, keeping animals warm
Liquid – allows transport of nutrients and excretory product
removal
, Biofluid = any fluid produced within an organism
Biofluids
Examples of biofluids: blood, saliva, urine, semen, synovial fluid,
amniotic fluid, serum, tissue fluid, lymph, cytosol
Importance of water in biofluids
Acts as a solvent by allowing substances to dissolve in the
plasma
Takes a lot of energy to change state which stops quick
changes in the blood
Categories of biofluid
Intracellular fluids - found inside cells (eg. cytosol)
Extracellular fluids - found outside cells (eg. plasma, tissue
fluid)
The main 3 body fluids are plasma, tissue fluid, and lymph…
Blood plasma
Approx. 55% of the blood is a liquid
Plasma contains plasma proteins, absorbed nutrients,
excretory waste products, hormones, and electrolytes
Tissue fluid
Formed as hydrostatic pressure at the arteriole end of the
capillaries forces water out of the plasma into intercellular
space
The formation of tissue fluid enables capillaries to exchange
substances with every cell in the body
Lymph
Lymph is tissue fluid which has drained into the lymph
vessels
Reenters the bloodstream in the subclavian vein
Moved by the contraction of skeletal muscles and hydrostatic
pressure of tissue fluid that has left the capillaries
Lymph nodes are sites of lymphocyte multiplication found at
intervals along the lymph vessel
Urine
Waste products from metabolic reactions can contain a high
nitrogenous content and must be removed from the body
In humans, soluble waste products and excess water, sugars
and ions are excreted mainly by urine and through sweat
Serum
Blood plasma which has had the clotting factors removed
Contains electrolytes, antibodies, antigens, and hormones
Used in blood typing and diagnostic tests
Biofluids in plants
Include intracellular fluids such as the cytosol or cell sap,
