AS OCR Biology unit 2 (food, molecules, biodiversity and health) revision notes

Another exam period, another set of revision notes.

This was created for the June 2013 exam but can be used for later specifications.

Other notes in the series:

OCR unit 1 biology

(I also have notes for English Language, Geography and Psychology)

(Spec points missing for health and disease, and proteins otherwise COMPLETE!)

Please use responsibly and don't pass this off as your own.

Good luck for your exam!

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Preview of AS OCR Biology unit 2 (food, molecules, biodiversity and health) revision notes

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2013
AS Biology Exam
Bethany Cunningham
[ AS BIOLOGY (UNIT 2):
MOLECULES,FOOD,
BIODIVERSITY AND HEALTH]
There are also summary sheets available but do not include typical exam questions and the extra
information learnt but they do provide questions-they are good for revision. This is good for
consolidating your knowledge.

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Page 2

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APOLOGIES
Unfortunately due to a lack of time after I did not save (stupid of me I know!) I lost a lot of work, so sections are
missing. The notes are made for Monday 3rd June 2013 exam but can be used for later exams despite the change
in specifications (this is only to accommodate for the lack of January exams).
The sections that are missing are stated here:
× Health and disease; specification points E-J and L-O.…read more

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IN THE CONTEXT OF MOST EXAM QUESTIONS, TREND MEANS A CHANGE OVER TIME. EXAMINERS WILL ALWAYS EXPECT TWO PAIRS OF FIGURES,
WITH UNITS, FOR CORRECTLY DESCRIBING A CHANGE". (JUNE 2012, EXAMINER'S REPORT)
"CANDIDATES SHOULD NOT JUST REPEAT OR ADJUST WORDS THAT ARE IN THE STEM OF THE QUESTION FOR AN ANSWER ­ IT IS UNLIKELY TO BE
CREDITED". (JANUARY 2013, EXAMINER'S REPORT)
"THE USE OF `ETC' TO TRUNCATE A LIST RARELY GAINS CREDIT IN ANY ANSWER".…read more

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HIGH SPECIFIC LATENT HEAT
A great deal of heat energy is needed to make water change into water vapour. The heat needed to do this
is called LATENT HEAT. E.g. evaporation is a major cooling mechanism.
Biological effect: This occurs in transpiration in plants and in sweating/panting in animals. Water is used as
a coolant, it can be used effectively as a small amount of water absorbs much thermal energy.…read more

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B) DESCRIBE, WITH THE AID OF DIAGRAMS, THE STRUCTURE OF AN AMINO ACID;
(C) DESCRIBE, WITH THE AID OF DIAGRAMS, THE FORMATION AND BREAKAGE OF PEPTIDE BONDS IN THE SYNTHESIS AND HYDROLYSIS OF DIPEPTIDES AND POLYPEPTIDES;
(D)EXPLAIN, WITH THE AID OF DIAGRAMS, THE TERM PRIMARY STRUCTURE;
(E)EXPLAIN, WITH THE AID OF DIAGRAMS, THE TERM SECONDARY STRUCTURE WITH REFERENCE TO HYDROGEN BONDING;
(F)EXPLAIN, WITH THE AID OF DIAGRAMS, THE TERM TERTIARY STRUCTURE, WITH REFERENCE TO HYDROPHOBIC AND HYDROPHILIC INTERACTIONS, DISULFIDE BONDS AND IONIC
INTERACTIONS;
PROTEINS
EXAMINERS…read more

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Remember that there are two products of a condensation reaction-the larger molecule produced
as a result of bonding two smaller molecules, and a water molecule. Don't forget to write down
the water molecule produced.
(K) STATE THE STRUCTURAL DIFFERENCE BETWEEN ALPHA- AND BETA-GLUCOSE;
Most carbohydrates are large, complex molecules composed of long chains of monosaccharaides. Single
monosaccharaides are also carbohydrates.
Glucose is a hexose sugar- a monosaccharaide with six carbon atoms in each molecule.
ALPHA AND BETA GLUCOSE
Their isomers make a difference.…read more

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POLYSACCHARIDES
O) EXPLAIN HOW THE STRUCTURES OF GLUCOSE, STARCH (AMYLOSE), GLYCOGEN AND CELLULOSE MOLECULES RELATE TO THEIR FUNCTIONS IN LIVING ORGANISMS;
AMYLOSE
It is coiled in a spiral-straight unbranched helix and this is due to the angles of the glycosidic
bonds. This makes it compact and so easy for storage.
It is the main molecule of starch.
It is insoluble and so doesn't affect water potential or reactions.
It is metabolically inactive.
It is joined by alpha 1-4 glycosidic bonds.
Amylose is storage of energy.…read more

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ALL ARE:
1. Made of glucose.
2. Insoluble.
3. Have 1-4 glycosidic bonds.
4. Doesn't affect water potential or reactions.
TRIGLYCERIDES (LIPIDS)
(Q) EXPLAIN HOW THE STRUCTURES OF TRIGLYCERIDE, PHOSPHOLIPID AND CHOLESTEROL MOLECULES RELATE TO THEIR FUNCTIONS IN LIVING ORGANISMS;
STRUCTURE OF A TRIGLYCERIDE
They are made of carbon, hydrogen and oxygen (lower amounts than carbohydrates).
They are made of one molecule of glycerol and three fatty acids attached.
Fatty acids have long tails made of hydrocarbons.…read more

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They have a hydrocarbon ring structure attached to a hydrocarbon tail. It has a polar hydroxyl
group attached which makes it soluble,
PHOSPHOLIPIDS
This is like a triglyceride in which one of the fatty acids are
replaced by a phosphate group. The fatty acid tails of a
phospholipid are hydrophobic; however, the phosphate heads are
hydrophilic. This is because the phosphate group has a negative
charge which is attracted to the positive electrical charge on the
hydrogen atoms. In water, this forms a bilayer.…read more

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LIPIDS
Emulsion test
Lipids will dissolve in ethanol but not water.
Add lipids and shake with ethanol.
Add shaken ethanol to water.
If the solution goes cloudy, lipids are present.
Quantity measured with a colorimeter.
PROTEINS
Add biuret reagent.
This turns the solution from blue to purple if there is protein present.
Quantity measured by a colorimeter.
REDUCING SUGARS
Used for monosaccharaides and some disaccharides.
Add Benedict regant and heat (>80 degrees Celsius).
Blue brick red (due to the formation of a red precipitate).…read more

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