RANSLEY FERNANDES ADMIN NO. 40202
UNIT 1O: BIOLOGICAL MOLECULES AND METABOLIC PATHWAYS
WATER
The water molecules form hydrogen
H O H bonds with another. The partial
negative charge (δ¯) on the oxygen
δ¯ atom of one molecule can create
hydrogen bond with partial positive
charge (δ+) on the hydrogen atom on
There is covalent bonding in other molecules. The water molecule
water molecule (H20) where
δ+
H is said to be polar. The water
molecule is also attracted to other
both hydrogen atoms and an
polar molecules such as ammonia,
oxygen atom share electrons
for full outer shell. O sulphur dioxide, ethanol.
δ+ H
δ¯
δ+ δ¯
H
O O H
H
H
Functions of water
The water has the ability of dissolving in
Water as a solvent various substances, which is why it is a good
solvent.
Water molecules have polar arrangement, in
which the hydrogen have positive electrical
charge on one side and oxygen atom have
negative electrical charge on other side. This
enables the molecules to attract to several
different molecules. Water can attract with
many different molecules such as salt NaCl, in
which it can disrupt attractive forces that hold
sodium and chloride together in salt molecules
and hence dissolve it.
Water is known as the universal solvent, due to the
capability of dissolving more substances compared to
other liquids. This is essential to living things on
earth, which means that wherever water goes, as
such through air, the ground or through bodies, it
takes along vital chemicals, nutrients, and minerals.
Water is the solvent of our body and it regulates The ions attract to the partial charges of water
functions, which includes the activity of dissolving molecules, so they aggregate around the water
and circulating. molecules, which makes them soluble.
, RANSLEY FERNANDES ADMIN NO. 40202
Water is a best possible medium for chemical reactions, for example, cytoplasm of cells.
The cytoplasm of cells has large
amount of water and salts. The
cytoplasm acts a medium to fill the
cells.
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Water is needed for even simple chemical reactions. Proteins wrap As we know, water is medium for
into their useful functional shape depending on how their amino many enzymatic and chemical
acid sequence reacts with water. The newly made enzymes must do reactions in our body. It moves
their chemical reactions in a medium, which in all organisms is antibodies, hormones, nutrients
water. Water is most suitable for chemical reactions as it can store and oxygen via the bloodstream
big amount of heat, it is electrically neutral and also has a pH of 7.0, and lymphatic system. Proteins and
which means it is not acidic or basic. In addition, water is involved enzymes in our body function more
in enzymatic reactions as an agent to break the bonds or by taking effectively and properly in solutions
away from a molecule to create bonds. of low viscosity.
Temperature regulator
Many hydrogen bonds take a huge amount of
energy to break when water converts from liquid
to water when sweating, which takes away heat
from our body. Therefore, this is how sweating
helps in taking away heat from our body and
blood. The hydrogen bonds in water enables it to
absorb and release heat energy more
moderately than other substances. Temperature
is a measure of kinetic energy meaning motion.
As the kinetic energy or motion increases, energy
is greater, and the temperature increase and so
the number of hydrogen bonds per water
molecule are decreased.
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regulation-mechanisms.jpg
Water has the capability to regulate the interior temperature of the body in response to the
outer temperature. Water can take in and transfer heat efficiently, so human body uses it to
balance the temperature in the body. Water has high heat capacity which means it can take in
,RANSLEY FERNANDES ADMIN NO. 40202
large amount of heat before the temperature increases. This attribute enables the water in
every cell of the body to act as buffer against quick temperature changes. Blood, which is mostly
made of water, moves heat away from the extremities and towards the essential when it
requires to preserve heat. It flows to the skin surface in order to release excess heat when
important and it transports the heat away when required. Water helps throw out excess heat
from body as water vapour from lungs and sweat on the skin.
Cohesion-tension in transpiration
The hydrogen bonds between the molecules of
water makes the cohesion forces possible,
leading to water molecules attracting with one
another. This enables the molecules of water to
move as a continual column of water which is
known as mass flow, for example in blood
vessels or phloem/xylem in plants. In addition,
it allows continual stream of transpiration in
plants. When plants lose water via their
stomata, the water is taken upwards from soil.
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The cohesion tension theory is a theory of intermolecular attraction, which describes
the procedure of water flowing upwards and against the force of gravity via the xylem
in plants.
In the cohesion tension hypothesis for water movement in xylem vessels, water goes across the
roots of plants from the soil down the water potential gradient through the apoplast and
symplast pathways.
The cohesive forces between the molecules stop the water column from breaking. Then the
water is pulled upwards in the xylem vessels. A water is pulled upwards in xylem, there will be
lower pressure at the top of xylem.
The water potential is low in the leaf cells and so water moves down the water potential
gradient. Then transpiration happens in which the water evaporates from spongy mesophyll
cells and then diffuses into the atmosphere
, RANSLEY FERNANDES ADMIN NO. 40202
Properties of water
Surface tension
The surface of water can act like an elastic sheet. Water has high surface tension, which means it can
create habitat on water surface. The molecules are affected by multiple intermolecular forces of
attraction. The molecules in the surface are not affected by molecules which are on top of them and
therefore pull together with greater power, that looks like a stretched membrane. Therefore, a
habitat can survive or live on the surface of water.
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content/uploads/Hydrogen-bonding.png
When a substance is
polar and is added
into the water, the
The molecules on thepositive
surfaceends of
sense attractive forces on just will attract
molecules
one side and thereforeto drawn
the negative
in end of
towards the liquid. water molecules and
the other way
The molecules in middle of liquid are around. Due to their
attracted equally in every direction. polarity, the water
molecules will
strongly attract with
Water does not act in the same way; it acts differently at the surface. The each other, which as
water molecules attract with each other and tend to stay together, mostly on a result will give
the surface where there is just water above. The attraction between water a high surface
molecules of water forms tension and a delicate membrane, because of which tension.
the insects like water striders walk on this membrane and can get underneath
water. The water striders have legs on which they tiny hair that fight off water
and take on air. By fighting off water, the water striders stand on the surface
of water and the air they captured enables them to float and move without
any difficulty.
The mosquito larvae use water surface tension. The
mosquito need air to breathe and they have a
particular body part known as the siphon. The
siphon uses the water’s natural surface tension to
connect for mosquitoes to breathe. The mosquito’s
tarsus leg (other 2 legs include femur and tibia) are
flexible so stiff tarsi will exert less force before
breaking through the water’s surface.
