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54621588 Edexcel Biology AS Revision Notes .pdf



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Edexcel AS Biology Revision Notes

Written by Tim Filtness

Merchant Taylors’ School

AS Biology Revision Notes
“Science is organised knowledge. Wisdom is
organised life” - Kant

Edexcel AS Biology Revision Notes

Written by Tim Filtness

A word of caution
These revision notes are designed to help you, NOT do the job of revision
for you. Ultimately, only you can learn this material: you can’t pay, cajole
or persuade anyone to do it for you! Additionally, these notes are the bare
bones (your text book and class notes are almost certainly better sources
of information if you’re aiming for the highest grades). So treat these
notes as a minimalist approach for someone aiming for a solid B grade. At
this point you might want to get your own notes to cross-reference with
the material here. Why not add your own annotations to improve what’s
already here?

Understanding the jargon:
1. The 9 Core Practicals are not discussed here.
Don’t forget to revise them too!
2. All Key Words are given underlined in red, these
are words specifically mentioned on the syllabus!
3. There are many blue “How Science Works” boxes
in the text book. In past years these have almost
always been the basis of a number of exam
questions...

Edexcel AS Biology Revision Notes

Written by Tim Filtness

Edexcel AS Revision

Unit 1: Lifestyle, Transport, Genes &
Health
Topic 1: Lifestyle, health & Risk
1.1.2
Water molecules are polar
H = Positively charged (δ+)
O = Negatively charged (δ-)
This allows them to form Hydrogen
Bonds with other water molecules. This
gives water some useful properties;

Property
Less dense as a solid
High SHC
Present naturally in all
three states
Transparent
Cohesion
Good solvent
Immiscible with
hydrophobic molecules
High latent heat of
evaporation
Buffer

Explanation
Arctic ecosystems float, ice insulates water beneath it
etc
Cells do not heat up or cool down easily, therefore can
hold a fairly stable temp. (cf enzymes)
Allows the water cycle to function
Allows photosynthesis underwater
Generates surface tension, capillary uptake,
transpiration etc
Essential role in transport in biological systems
Allows membranes to form and, therefore, control
movement in / out of cells
Evaporation of water has a strong cooling effect and
comparatively little water is required to lose a lot of
heat
Water is capable of accepting and donating protons,
therefore acts as a buffer

Edexcel AS Biology Revision Notes

Written by Tim Filtness

1.1.3
Saccharides are made from sugar molecules, which are made from
combinations of the elements Carbon, Hydrogen and Oxygen only
Saccharides are used for;
1. Fuels for respiration (e.g. glucose)
2. Energy storage molecules (e.g. starch and glycogen)
3. Structural molecules (e.g. cellulose)
Monosaccharides – one sugar molecule only
Disaccharides – two sugar molecules joined together
Oligosaccharides – a few sugar molecules joined together
Polysaccharides – many sugar molecules joined together
Disaccharide Name
Maltose
Sucrose
Lactose

Component monosaccharides
Glucose + Glucose
Glucose + Fructose
Glucose + Galactose

You need to know the different structures of glucose. You should
be able to draw this out if requested.

OH

H

α Glucose

Β Glucose

Edexcel AS Biology Revision Notes

Written by Tim Filtness

There are three polysaccharides specifically mentioned on your
syllabus (starch, glycogen and cellulose). Cellulose is in Topic 4
(2.4.3) but is included here for reference.
Polysaccharide
Glycogen

Structure and Function
1. Made from Poly (α Glucose).
2. Found in muscle and liver cells for energy storage
3. Insoluble, so no osmotic effect in tissues
4. Lots of branches (i.e. 1-6 glycosidic bonds present),
which allows quick access to glucose
5. Compact shape, so good for storage

Starch

1. Actually made from two molecules in combination;
Amylose and Amylopectin
2. Both are made from Poly (α Glucose).
3. Found in Amyloplasts (starch grains) inside plant
cells for energy storage
4. Insoluble, so no osmotic effect in tissues
5. Amylose has no branches (i.e. 1-4 glycosidic bonds
only), so access to glucose is slow
6. Amylopectin has some branches (i.e. both 1-4 & 1-6
glycosidic bonds)

Cellulose

1. Made from Poly (β Glucose).
2. Main component of cell walls as it is a very strong
structural molecule
3. Insoluble… for obvious reasons!
4. Cellulose has no branches (i.e. 1-4 glycosidic bonds
only), so adjacent cellulose chains line up close
5. Hydrogen bonds form between adjacent chains,
creating very strong cellulose fibrils

Edexcel AS Biology Revision Notes

1.1.4

Written by Tim Filtness

Saccharides join together in condensation reactions, which produce
water. A glycosidic bond forms between the saccharide molecules.
The opposite of a condensation reaction is a hydrolysis. This
requires;
1. Heat + HCL
2. OR an enzyme (e.g. Amylase)
Tests for Sacharides:
- Iodine solution turns brown → blue/black in the presence of starch
- Benedict’s solution turns blue → brick red in the presence of a
reducing sugar
- Non reducing sugars (most disaccharides and all polysaccharides) will
give a positive result to Benedict’s if heated in acid first.

Edexcel AS Biology Revision Notes

Written by Tim Filtness

1.1.5
Triglycerides are either fats or oils. They are made from the
elements C, H & O only.
Triglycerides are used for;
1.
2.
3.
4.
5.

Long term energy storage molecules
Insulation
Protection (e.g. pericardium)
Buoyancy
Synthesis of specific hormones (e.g. steroids)
Triglycerides are formed in
condensation reactions between;
1 x glycerol
3 x fatty acid
An ester bond forms between the
fatty acid and the glycerol

Saturated triglycerides have no
C=C bonds in them. They form fats.
Unsaturated triglycerides DO have
C=C bonds in them. They form oils.

The C=C bonds form ‘kinks’ in the fatty acid chains, which push
adjacent triglycerides away from each other. This lowers the
effect of intermolecular forces (e.g. van der vaal’s forces), which
lowers the boiling and melting temp.
Test for a triglyceride (Emulsion test):
1. Add ethanol (dissolves fat)
2. Add water
3. White precipitate indicates a positive result

Edexcel AS Biology Revision Notes

Written by Tim Filtness

1.1.6
Fick’s law:
Rate of Diffusion

=

Surface Area

x

Conc Gradient

Distance
If we apply this to a cube, the rate at which O2 reaches the centre
of the cube is a product of the ratio of the Surface Area compared
to the Volume (i.e. SA:Vol)

Amoeba

Large SA:Vol ratio

Can rely on diffusion through its
surface.

Human

Small SA:Vol ratio

Diffusion through surface is too slow
to supply O2. Therefore require a mass
transport system and specialized
exchange organs

In humans the mass transport system is the circulatory system and
the heart. The specialized exchange organs include the lungs and
the digestive system.

Edexcel AS Biology Revision Notes

Written by Tim Filtness

1.1.7
You need to know;
1. the names of the 4 chambers of the heart
2. the names of the 2 arteries and 2 veins attached to the heart
3. The names of the two sets of valves in the heart
4. The cardiac cycle
5. The initiation and conduction pathways of the heartbeat

Vena Cava

Aorta

Pulmonary Artery

Semi-lunar Valve
Cuspid Valve

Vena Cava
Contraction in the heart:

Remember, the atria contract first. The L & R atria contract at
the same time. The ventricles contract second. The L & R
Ventricles contract at the same time.


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