Biology AS AQA Unit 2 The Variety of Life

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created by: Chelcie
  • Created on: 02-09-13 12:51
Preview of Biology AS AQA Unit 2 The Variety of Life

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The Variety of Life
HAEMOGLOBIN MOLECULES
PRIMARY STRUCTURE
Consisting of 4 polypeptide chains.
SECONDARY STRUCTURE
Polypeptide chains are coiled into a helix.
TERTIARY STRUCTURE
Polypeptides are folded into a precise shape-
importantly to carry O
QUATERNY STRUCTURE
All polypeptides are linked to form a spherical
molecule.
Each polypeptide is associated with a haem group
which contains a ferrous (Fe2+)
Each ferrous can combine with an O molecule making a total of 4 O molecules in 1 haemoglobin.
ROLE OF HAEMOGLOBIN
To transport O.
They must readily associate with O at the surface where gas exchange takes place.
Haemoglobin must readily dissociate from O at tissues requiring it.
Haemoglobin changes its affinity for O under different conditions. It does this by changing its shape
at the presence of certain substances (e.g. CO)
In CO, the new shape of haemoglobin binds more loosely with O therefore O is released readily-
low affinity.
O concentration CO Affinity for O Result
concentration
Gas exchange High Low High O attached
surface
Respiring Low High Low O released
tissues
WHY DO WE HAVE DIFFERENT HAEMOGLOBIN?
Haemoglobins with a high affinity for O take O easily but less readily release it.
Haemoglobins with a low affinity for O take O less easily but readily release it.
ENVIRONMENTAL CONDITIONS
An environment with little O requires haemoglobin with a high affinity (to readily combine with O)
As the metabolic rate is not high in this organism, there is no need for a fast release.
HIGH METABOLIC RATE
Organisms will have haemoglobins with low affinity to release O easily to respiring tissues.
Provided there is plenty of O in environment, release of O is most important factor.

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WHY DO DIFFERENT HAEMOGLOBINS HAVE DIFFERENT AFFINITIES?
Different haemoglobin have different sequences of amino acids and therefore shapes. Its affinity
for O depends on the shape.
LOADING/ASSOCIATING
When haemoglobin combines with O in lungs
UNLOADING/DISSOCIATING
When haemoglobin releases O at tissues
OXYGEN DISSOCIATION CURVES
At low partial pressure of oxygen, the 4
polypeptides are closely united so have difficulty
absorbing the first O molecule.…read more

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LOADING, TRANSPORT, UNLOADING OF O
At gas exchange surface, pH is high due to the low levels of CO
The higher the pH changes, the higher affinity of O. This is due to a shape change to enable
ready loading of O so that it is not able to easily release O, so it is not lost in transport.
In tissues, CO is high. As CO is acidic in solution, the pH is lowered.…read more

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STARCH
Polysaccharide
Chains of a-glucose monosaccharides linked by glycosidic bonds that are formed in
condensation reactions.
Wound into a coil to make more compact.
Starch is a good energy store because:
It is insoluble so it doesn't draw water into the cell by osmosis
Compact
When hydrolysed it forms a-glucose which is easily transported and ready for use in
respiration.
CELLULOSE
Monomers of b-glucose
Position of ­H group in a-glucose and ­OH group in B-glucose is reversed.…read more

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Chloroplast envelope:
Double plasma membrane that surrounds the organelles. Highly selective to what enters/leaves
chloroplast.
Grana:
Stacks up to 100 thylakoids (disc like structures) where 1st stage of photosynthesis occurs.
Chlorophyll:
Has photosynthesis pigment. Found within thylakoids.
Some thylakoids have tubular extensions that join with thylakoids in adjacent Grana.
Adaption:
Granal membranes provide a large surface area for attachment of chlorophyll, electron
carriers, and enzymes that carry out 1st stage of photosynthesis. The chemicals are attached
to the membrane in a highly ordered fashion.…read more

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