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Biology - AS Level - 10.1 - Biological Molecules - .7 - Organic Elements and Wat


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How many elements approx naturally occur in the earth's crust?
How many elements are essential for life?
What are the 4 most common elements in organisms?
C, H, N, O.
What elements are commonly found in organisms in smaller quantities (8)?
Phosphorus, Sulphur, Na, K, Mg, Cl, Ca, Fe.
Why are HONC biologically significant?
They can form more stable covalent bonds than any other elements with the same valencies (1 2 3 4 respectively).
Carbon's special property:
It's tetravalent - can form 4 covalent bonds with other atoms. Can be other Cs or from other elements. Bonds point towards tetrahedron vertices - v stable arrangement.
Carbon bonds:
C-C bonds v strong. Long chains rings or branched chains can exist in a single molecule. They can also form double bonds i.e. >C=C< or >C=O, >C=N-), hence there is an enormous variety of C-containing molecules.
Structure and formula of glycerol:

| | |
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Structure of glycine:
\ | #
/ | \
Structure of glucose:
H C--O H
\/H OH\/
/ \OH H/ \
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The human body is about ... water:
Polar molecule because:
Shared electrons are pulled towards the O atom giving it a slightly negative charge and leaving each H atom with a slightly positive charge.
Hydrogen bonds make water such an important factor for living organisms because:
negative and positive molecule ends attract each other so the molecules tend to stick together.

||| between two atoms ie H|||O = hydrogen bonds. Say hydrogen not H-bond in exam.
Why is water the universal solvent?
So many things dissolve.
Ionic substances carry + and - charges so they are attracted to the charges on the H2O Molecules. Water surrounds separated molecules.
Other polar substances eg some sugars and alcohols also dissolve in the same day.
- ion - hs surrond
+ ion - os surround
Why is water's use as a solvent relevant?
Solution - molecules and ions free to move - more chemically reactive. Maj of cell reactions take place aqueous sols.Also, good transport medium because of solvent properties.
Why is it relevant that non-polars and water will not mix?
eg Lipids will not mix and usually group together in its presence - important for membrane stability.
What is surface tension?
Water mols more attracted to each other than to surrounding air.
Attraction between mols of sim subst called cohesion.Not easily broken, water has greater surface tension than most liquids.
Apart from itself, water tension in:
Can form H bonds with other polars - stick to each other but also other surfaces IE side of container.
Relevance of surface tension:
Significant in cells and translocation in plants. Important for many small organisms who rely on surface tension in order to settle on water or skate over its surface.
Specific heat capacity:
the amount of heat energy (J) required to raise the temp of 1kg of water by 1C.
Water has high shc - gain much to raise, lose much to lower. Buffer against extreme temp flucts in environ.
Latent heat of vaporization:
Water has high lhv - lot J (heat) needed to evap. When, draws much heat energy out of the material underneath - cooling effect (sweating, panting, plant cooling) - much heat lost without much water loss.
Latent heat of fusion:
Water must losse a lot of heat J before it forms ice crystals. Cells and environs are less likely to freeze (ice crystals v damaging in cells).
What is the difference between adhesion and cohesion?
Adhesion is for different substances, cohesion is for the same substance.
When is water most dense? What happens afterwards?
4C - Density decreases as it feezes so ice floats.
Why does ice float?
Gets less dense - in liquid H bonds constantly form and reform - when frozen forms H bonds with 4 other mols - rigid lattic holds mols further apart than in liquid - expands and becomes less dense.
Why is it important that ice floats?
Insulates water below it - allows nutrient cycling in larged bodies of water - life can survive to greater depth.
Important that transparent and colourless:
Aquatic plants can get sunlight and photo. - O2 into water, feeds fish etc. (plants are producers).
Has relatively high density compared with air:
Large animals can float. Dispersal of repro structures eg larvae and large fruits.
Difficult to compress:
Shock absorber in mammalian joints - allows movement via synovial fluid. Important structural agent. Plants remain turgid, support for hydroskeletal animals.
Conducts electricity
Nervous response
How good an electrical conductor is water?
Pure has low but dissolved ions make good
Good that water is liquid at room temp:
transport in cells, synovial fluid allows to move
What is a reagent? Why is it good that water is one?
Takes part in chemical reaction. Photosynthesis, hydrolysis (digestive system etc) - many take place in water.
Low viscosity:
Can change shape so things can be dissolved (more reactive), can get through narrow vessesl (blood and xylem), lubricant (mucus and saliva for swallowing).
Water columns do not break or pull apart easily:
transport in plant and animal bloodstreams - continuous column can be pulled up to tree top.
Water is universal solvent
dissolving good for transport as main transport medium - also makes more reactive.
Ice less dense than water
Heat not lost in convection - water animals can survive, ditto nutrients and nutrient cycling.
High surface tension
Pond skaters
Translocation in plants and cvells - can move up stem.

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