Biological Molecules: Water and Carbohydrates

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Boardworks AS Biology
Biological Molecules: Water and Carbohydrates
Learning Outcomes
Topic 3 Water and Organic Molecules
After studying this topic you should be able
to:
•Draw the structure of a water molecule and
describe its polar nature.
•Explain what a hydrogen bond is and how they
contribute to the cohesion of water molecules.
•Explain how water acts as the solvent of life.
 CEB Textbook Chapter 2, pages 29-35 and
Chapter 3, pages 38 and 39.
 Mastering Biology, Chapters 2 and 3
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•Explain what is meant by the term “organic
molecules” (study notes).
X You are not required to study the section How water moderates
temperature on page 30 of your CEB textbook nor the section Acids,
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Bases and
Structure of Water
Water (H2O) is a compound that consists of
two hydrogen atoms covalently bonded to one δ–
δ+
oxygen atom.
Each hydrogen shares a pair of
electrons with the oxygen. The
oxygen has a greater affinity (stronger
pull) for electrons than the hydrogens, δ+
104.5 °
so it ‘pulls’ the electrons closer.
This makes the oxygen slightly negative (indicated by δ–)
and the hydrogens slightly positive (indicated by δ+).
Because of its V shape (H’s on one side and O on the
other....
Water is a polar molecule = A molecule containing polar
covalent bonds (having opposite charges on opposite
ends).
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Hydrogen Bonds
Hydrogen Bonds
Many of the properties of water are due to its ability to form
hydrogen bonds.
The slight negative charge on the oxygen atom makes it
attract the slightly positive hydrogen atom of another water
molecule.
hydrogen
bond
The numerous hydrogen bonds in water make it a very
stable structure.
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Covalent bonding vs. Hydrogen bonding
Hold
water molecules
together.
Each
water molecule can
form a maximum of 4
hydrogen bonds
The
hydrogen bonds
joining water molecules are
weak, about 1/20th as
strong as covalent bonds.
Covalent Bond
They
form, break, and
reform with great frequency
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Hydrogen Bond
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Boardworks AS Biology
Biological Molecules: Water and Carbohydrates
Hydrogen Bonds - Effects
Extraordinary Properties that are a result of
hydrogen bonds.
1. Cohesion-tension theory
Water is
a polar molecule, meaning
that its positive and negative charges are
not evenly distributed.
This
means that, in a thin tube (such as
a plant vessel), water molecules
spontaneously arrange so that positive
and negatively charged poles lie next
to each other
1. Cohesive behavior
2. Resists changes in temperature
3. High heat of vaporization
This
causes the molecules to cohere, or
stick together by hydrogen bonding, so
that as some leave a plant by
evaporation (leaves), others are pulled
up behind them.
4. Expands when it freezes
5. Universal solvent
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Organisms Depend on
Cohesion!
water
Cohesion among
molecules plays a key role in the
transport of water against
gravity in plants
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Capillary Action
Because water has both adhesive
and cohesive properties, capillary
action is present.
Capillary Action = Water is attracted to
another charged material e.g. glass by
adhesion and then through cohesion,
other water molecules move with it.
Adhesion,
clinging
of one substance to
another, contributes
too, as water adheres
to the wall of the
vessels.
e.g. water in a straw
Cohesion = The attraction between molecules of the same
kind e.g. Water molecules by hydrogen bonding
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Adhesion and Cohesion Cause Capillary
Action
e.g. water moves through trees this way
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Adhesion Also Causes Water to …
Which gives water the ability to “climb” structures.
Why does the liquid climb higher in the thinner tube?
Form
spheres
& hold onto
plant leaves
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Attach to a
silken spider
web
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Boardworks AS Biology
Biological Molecules: Water and Carbohydrates
Activity!
Try to float a paperclip on water.
How is this possible?
What will happen if you touch the surface
with detergent?
Surface Tension
Surface tension, a measure of
the force necessary to stretch or
break the surface of a liquid, is
related to cohesion.
Water has a greater surface
tension than most other liquids
because hydrogen bonds
among surface water molecules
resist stretching or breaking the
surface
VIDEOS – Surface Tension
http://www.youtube.com/watch?v=ynk4vJa-VaQ – Surface tension boat
http://www.youtube.com/watch?v=M6ypoyZRTkg – Jesus Christ Lizard
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Water doesn’t cling to Oxygen and Nitrogen in
Air
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Activity! Making a surface tension speed boat.
1. Break a popsicle stick in half and place a small amount
of detergent on the end.
2. Place on a plate of water.
You only get one shot at this so enjoy
http://www.youtube.com/watch?v=Hm52rkh68JA
Water Molecules sticking to
themselves because they
are polar
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2. Water Resists Changes in Temperature
It takes much more
energy to raise the
temperature of water
compared to other
solvents. Why?
Why is this
property
so
important
for life?
Because hydrogen
bonds hold the water
molecules together!
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High Specific Heat Capacity
Water resists temperature
change, both for heating
and cooling.
Water can absorb or
release large amounts of
heat energy with little
change in actual
temperature.
High Specific
Heat Capacity =
Amount of heat
needed to raise
or lower 1g of a
substance 1° C.
Water has a high specific
heat capacity.
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Boardworks AS Biology
Biological Molecules: Water and Carbohydrates
3. High heat of vaporization
In order for water to
evaporate, hydrogen bonds
must be broken.
As water evaporates, it
removes a lot of heat with
it.
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High Heat of
Vaporization =
Amount of energy
to convert 1g or a
substance from a
liquid to a gas
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In late fall / early winter, the temperatures
near the sea coast are usually higher
because the oceans are still releasing
stored energy from the summer.
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The high specific heat of water means that
a lake won’t freeze or heat up suddenly.
This gives aquatic organisms a chance to
adjust to temperature changes slowly.
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Effects of High Specific Heat Capacity
In late autumn / early winter, the temperatures near
the sea coast are usually higher because the
oceans are still releasing stored energy from the
summer.
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In late fall / early winter, the temperatures
near the sea coast are usually higher
because the oceans are still releasing
stored energy from the summer.
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Many people rely on the high specific heat
property of water to heat their home.
Water is warmed in the boiler and then
piped throughout the house before
returning.
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Boardworks AS Biology
Biological Molecules: Water and Carbohydrates
4. Water Expands When it Freezes
4. Water Expands When it Freezes
Ice is about 10% less dense than water at 4oC.
Therefore it will float on water! (e.g. it has fewer
molecules of water per unit volume because of the
spacious crystal lattice structure)
When water reaches
0oC, water becomes
locked into a crystalline
lattice with each
molecule bonded to the
maximum of four
partners.
As ice starts to melt, some
of the hydrogen bonds
break and some water
molecules can slip closer
together than they can
while in the ice state.
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4. Water Expands When it Freezes
The density of water:
1.
Prevents water from freezing
from the bottom up.
2.
Ice forms on the surface
first—the freezing of the
water releases heat to the
water below creating
insulation.
3.
Solute – substance dissolved
in a solvent to form a solution
Why is this
property so
important for
life?
Solvent – fluid that dissolves
solutes
Example: Ice Tea – water is
the solvent and tea and sugar
the solutes the result is a
aqueous solution
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5. Water is a Universal Solvent
Water (solvent) can dissolve
many ionic solids e.g. salts,
sugars, because water
molecules are polar
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5. Water is a Universal Solvent
Water is the solvent of Life!
Why is this
property so
important for
life?
Makes transition between
season less abrupt.
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Water as a Solvent
Why is this
property so
important for
life?
The water molecules attach to
the ionic solids (solutes) due
to hydrogen bonding and pull
them into the solution
Can you think of some examples
in the body where this would be
important?
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Boardworks AS Biology
Biological Molecules: Water and Carbohydrates
Properties and biological roles of water
Summary Quiz
1.Why is water a polar
molecule?
2.What is a hydrogen
bond?
3.What are the 5 life
supporting properties
of water?
4.The tendency of
water molecules of the
same kind to stick
together is called....
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Key words
Aqueous solution
Carbon skeletons
Cohesion
Digestion
Hydrocarbon
Hydrogen bond
Hydrolysis
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Homework
Macromolecule
Monomer
Organic Molecule
Polar molecule
Polymer
Solute
Solution
Solvent
Synthesis
1.Complete handout question on water.
Due this Friday
2.Answer question 5 and 6 in unit
assessment 1
3. Read Study notes and DEFINE ‘organic
molecule’. Add to your glossary for the
topic
4.WATCH this video for excellent revision
of this topic
Recap –Water Liquid Awesome Video
http://www.youtube.com/watch?v=HVT3Y3_gHGg
Or just search WATER LIQUID AWESOME on youtube!
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• Which is polar, and which is non-polar?
Wax Paper
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What did the molecules attach to? Why?
Answer: Because the water molecules are polar,
they attached to themselves and stayed in a
drop. The wax paper is non-polar, so the water
did not mix with it.
= Non-Polar -/Water Droplets
 Polar +/-
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Water Droplets
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Biological Molecules: Water and Carbohydrates
Many products use polarity to help
waterproof materials.
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Answer: When two (Non-polar) oil bubbles
meet, they join together to form a large
bubble.
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Oil and Water don’t…________?
Add a few drops of vegetable oil to a clear Petridish using an overhead projector.
What happens?
What happens when two oil bubbles meet?
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Where have we seen the picture below?
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Oil and water don’t mix. An oil spill can cause severe
damage to aquatic systems because of this property.
OIL IS WHAT WE CALL A HYDROCARBON
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Boardworks AS Biology
Biological Molecules: Water and Carbohydrates
Organic Chemistry and
Hydrocarbons
“Hydrocarbon Compounds”
• “Organic” originally
(C4H10)
Learning Outcomes
•Describe hydrocarbons and their
main function.
•Describe the synthesis and
digestion of polymers.
referred to any chemicals
that came from
organisms
• 1828 - German chemist
Friedrich Wohler
synthesized urea in a lab
• Today, organic chemistry
is the chemistry of virtually
all compounds containing
the element carbon
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Organic Chemistry and Hydrocarbons
Friedrich
Wohler


• Over a million organic
compounds, with a
dazzling array of
properties
• Why so many?
Carbon’s unique
bonding ability!
• Let’s start with the
simplest of the organic
compounds. These
are the Hydrocarbons
1800 – 1882
Used
inorganic
substances to
synthesize urea, a
carbon compound
found in urine.
This
re-defined
organic chemistry.
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Organic Chemistry and Hydrocarbons
Organic Chemistry and Hydrocarbons
• Hydrocarbons contain
only two elements:
1) Hydrogen, and
2) Carbon
• The simplest
hydrocarbons are called
“alkanes”, which contain
only carbon to carbon
single covalent bonds
(CnH2n+2)
• Methane (CH4) with one
carbon is the simplest
alkane. It is the major
component of natural gas
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• Carbon has 4 valence
electrons, thus forms 4
covalent bonds
not only with other
elements, but also
forms bonds WITH
ITSELF (nonpolar)
• Ethane (C2H6) is the
simplest alkane with a
carbon to carbon bond
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Boardworks AS Biology
Biological Molecules: Water and Carbohydrates
Hydrocarbon - Alkanes
Hydrocarbons
• Many hydrocarbons
used for fuels:
methane, propane,
butane, octane
• As the number of
carbons increases, so
does the boiling and
melting pt. e.g.The first
4 are gases; #5-15 are
liquids; higher alkanes
are solids
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Since the electrons are shared equally,
the molecule is nonpolar thus, not
attracted to water oil (a hydrocarbon)
not soluble in H2O “like dissolves like”
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Coal
Hydrocarbons - Natural Gas
• Formed from huge
fern trees and
mosses decaying
millions of years ago
under great pressure
of rocks / soil.
• Coal may be found
close to the surface
(strip-mined), or
deep within the earth
• Pollutants from coal
are common; soot
and sulfur problems
• Fossil fuels (hydrocarbons)
provide much of the world’s
energy
• Natural gas and petroleum
contain mostly the aliphatic
(or straight-chain)
hydrocarbons – formed
from marine life buried in
sediment of the oceans
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BIG
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BRUTUS
Dragline used
VIDEO - Formation of Polymers
Polymerisation 4.37
to remove the
overburden of a
strip mining coal
field near West
Mineral, Kansas.
http://www.youtube.com/watch?v=UNsNGV
SVDMk
Note
the size of
the man standing
next to it.
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