AS Edexcel Biology Topic 1 and 2 notes

1. BIOLOGY TOPIC
1 AND 2

2. Water
• Structure of water
Water is made up of on oxygen atom and 2 hydrogen atoms
joined together by shared electrons.
Because hydrogen atoms only have one electron this is pulled
towards the oxygen atom to share electrons.
This results in the oxygen side of water having a slight
negative charge and the hydrogen end having a slight
positive charge.
This makes water a dipolar molecule.
Properties of water making it a good transport
molecule
• Water is a particularly good solvent because of its dipole
nature. This is because many substances are ionic meaning
they are made from one positive or negative atom. Therefore
the positive end of the water will be attracted to the negative
ion, and will completely surround the ion. This will make the
ion dissolve very quickly. When substances are dissolved
they cause less friction so are easier to transport.
• Water is also very cohesive. This means that molecules of the
same type attract each other, so water molecules sort of stick
together. This helps water “flow”.

3. Carbohydrates
Monosaccharides- carbohydrates such a glucose are monosaccharaides.
They are joined together using GLYCOSIDIC bonds in condensation reactions to
form Disaccharides.
Two glucose molecules join to make Maltose.
The hydrogen atom of one glucose bonds to the
hydroxyl (OH) group of another. The disaccharide
can also be broken apart in hydrolysis. In glucose
the bond is known as a 1,4 bond.
LACTOSE is another disaccharide made up of glucose and
galactose with a 1,4 glycosidic bond.
The last is SUCROSE made from glucose and fructose joined
with 1,2 glycosidic bonds.
Galactose
Galactose

4. Polysaccharides
• A polysaccharide is formed when “many” monosaccharide join
together, These are some polysaccharides:
• Starch
• The main storage molecule in plants, when energy is needed
the plant slowly breaks the starch down releasing glucose.
• Starch is made from amylose and amylopectin.
• Amylose is Glucose with 1,4 bonds and coils up so is very compact and really good
for storage because a lot can fit into a small space.
• Amylopectin is Glucose with 1,4 and 1,6 bonds so has side branches. This allows
enzymes to break down the bonds faster so releasing the glucose faster.
• Starch is also insoluble so doesn’t cause water to enter the cells via osmosis.
• Glycogen
• The main storage molecule in animals, which is broken down to release energy.
• It is made up of glucose joined using 1,4 and 1,6 glycosidic bonds, but it has even
more side branches than amylopectin meaning energy can be released very quickly.
• Like starch it is also compact and insoluble so is a good storage molecule.

5. Lipids
• Triglycerides are fat lipids.
The 3 fatty acid tails are
Hydrocarbons.
They are also HYDROPHOBIC
(water repelling)
They make the lipid insoluble.
Hydrophillic
head
How are triglycerides formed?
Like carbohydrates, they are formed using condensation reactions. Three fatty
acids and a glycerol molecule are joined using ESTER bonds.
Ester bond
The tails can also be shown with an R
= Triglyceride + Water
There are 2 types of lipids- SATURATED and UNSATURATED. The difference between
these two lipids is their tails. Saturated lipids have no double bonds between the carbon
atoms in their tails whereas unsaturated ones do. This means unsaturated lipids kink and
melt at lower temperatures they are also more healthy and are usually found in plants

6. Proteins
• A Dipeptide is made of 2 amino acids, a polypeptide of more
than 2, and a protein is made up of 1 or more polypeptide
chain.
• The general structure for an amino acid is:
The green part is the carboxyl group,
The Yellow is the amino group,
And the blue is the variable R group.
• Like lipids and carbohydrates, they are joined together in
condensation reactions with PEPTIDE bonds.

7. Structure of proteins
• Primary structure- This is the sequence of amino acids in a
straight line, held together using peptide bonds.
• Secondary structure- Now hydrogen bonds (weak bonds
between the positive hydrogen atom of one molecule and negative
atoms and groups from another molecule), form between the amino
acids making the chin coil into an a-helix or B-pleated sheet.
• Tertiary structure- The chain is coiled or folded further: Ionic
interactions form between negative and positive charges on
different parts of the molecule, Disulfide bonds form when two
cystine amino acids come close together and a sulphur molecule
from each joins, and Hydrophobic and philic interactions happen
meaning the hydrophobic molecules clump close together forcing the
hydrophilic molecules onto the outside, Lastly more hydrogen bonds
can also be formed. Some proteins are only made up of one
polypeptide chain in which case this is their final structure.
• Quaternary Structure- If the protein is made up of more than
1 polypeptide then bonds will join several chains together.
The proteins final structure and functions are all determined by
the sequence of original amino acids.

8. Types of proteins
Globular
Round, compact and made up of many
polypeptides.
Hydrophilic parts facing outside and
hydrophobic facing inwards making
these proteins soluble and easily
transported.
For example haemoglobin and
enzymes.
Fibrous
Long, insoluble, polypeptide chins tightly
coiled round each other like a rope.
Strong with lots of bonds.
Often found in supportive tissues for
example collagen.

9. Enzymes
• Enzymes are biological catalysts which speed up a reaction in the
body without being used up or altered itself. For example there are
enzymes for digestion and respiration.
• They speed up reactions by lowering the activation energy needed
for the reaction to happen so it can happen at lower temperatures.
• When a substrate fits into the enzymes active site either two
substrates are held close together reducing repulsion between them,
or in breakdown reactions the active site puts strain on the bonds of
the substrate by distorting in shape putting strain on the molecule.
The lock and key theory
Enzymes are specific to certain
substrates and only the right ones fit into
the active site. The enzymes active site is
determined by its primary structure. At
first scientists thought this was because
of the specific shape of the active site-
that it was like a keyhole and the
substrate the key. However later evidence
showed that enzymes changed shape.
The induced fit theory
This helps to explain how enzymes are so
specific. Not only does the substrate have to be
the right shape but it also has to set of the
change in shape of the enzyme to fit even more
tightly around the substrate.

10. The heart and Blood vessels.
All organisms need some way to transport raw materials
such as oxygen to the cells which need it, and to
remove waste products such as carbon dioxide. In
single cellular organisms these materials can diffuse
straight across the cell membrane because of the short
distance in has to travel. However big organisms like us
need a faster way to transport these substances so we
have a heart and blood vessels.
Each part of the heart is adapted to do it’s job
efficiently.
The left ventricle has more muscular walls to
contract more powerfully and push blood all the
way round the body.
The ventricles have thicker walls than the atria to
push blood out of the heart, whereas the atria
only need to push blood down to the ventricles.
The atria-ventricular valves stop blood flowing
back into the atria when the ventricles contract.

11. Blood vessels
• Arteries- Carry blood from heart to body. They have muscular walls and
elastic tissue to cope with the high blood pressure. The endothelium (inner
lining) is folded allowing the artery to expand.
• Veins- Take deoxygenated blood back to the heart. They are wider and less
elastic than arteries because the blood is travelling at low pressures. They
contain valves to stop blood flowing backwards. Blood flow through the veins
is helped by contractions in the muscles surrounding them.
• Capillaries- Capillaries are the smallest blood vessel and are where
metabolic exchange occurs. They have very thin one cell think walls to
speed up diffusion of substances in and out of cells.

12. The cardiac cycle

13. Risk Factors of CVD

14. Cardiovascular disease
High Blood Pressure
Stretched Artery Walls
Damaged artery walls
Inflammation
White blood cells Enter
Cholesterol Accumulates
ATHEROMA
Plaque of fibrous tissue and CA salts
Artery wall narrows, hardens, and becomes less elastic
ATHERSCLEROSIS
(The hardening of the arteries because of Atheromas)

15. Cardiovascular disease
Slower blood flow
Sticky platelets
Thromboplastin and ca
salts released
Prothrombin Thrombin
Fibrin
Fibrinogen
Tangled mesh
Blood clot
THROMBOSIS

16. Drug treatment of CVD
• Antihypertensives- These include Beta Blockers which reduce the
strength of the hear beat, Diuretics which cause more urine to be produced, so
reducing blood volume, and Vasodilators which widen the blood vessels. All of
these reduce blood pressure.
Advantages- Different antihypertensive can be used in combination, Also blood
pressure can be monitored at home to see if the drugs are working correctly.
Disadvantages- Palpitations, fainting, headaches, irregular heart beat from too low
a blood pressure. Also depression and allergic reactions.
• Plant Statins- These reduce the amount of cholesterol absorbed into the
blood from the gut.
Advantages- Reduce the risk of developing CVD in a natural way
Disadvantages- Can reduce the absorption of so important vitamins from the gut.
• Anticoagulants- Reduce blood clot formation e.g warfarin.
Advantages- Treat people who already have blood clots.
Dissadvantages- Excessive bleeding, allergic reactions, osteoporosis and in some
cases damage to foetus
• Platelet inhibitory- Also reduce blood clots forming by preventing
platelets clumping together e.g Asprin.
Advantages- can treat people who already have clots.
Disadvantages- Rashes, diarrhoea, and liver function problems

17. Stem cells
Stem cells are unspecialised cells which can
develop into any other cell in the body. There are two types-
Totipotent- which have the ability to develop into ALL other
specialised cell including the extraembryonic cells.
Pluripotent- which can develop into all specialised cells except the
extraembyonic ones so cannot create a totally new organism.
Embryonic stem cells are the most Pluripotent, but as the embryo
grows and the stem cells replicate they become specialised to
do certain jobs such as liver cells, or red blood cells. This is
how:
All stem
cells
Contain the
Same
genes
But not all
of Them are
active.
Only in the
Right
conditions
are genes
Activated
or
deactivated.
These
changes
Caused by
The proteins
Make the
cell
Specialised.
These
Proteins
Modify the
Cell
structure
And control
Its
Processes.
So proteins
Are only
made
From the
Active
genes
mRNA is
only
Transcribed
From active
genes.

18. Genetic screening
Uses-
Identification of Carriers- this can help people to make
informed decisions about whether to have children or
carry out prenatal testing. It is usually done for people
who have a family history of certain diseases such as
Cystic Fibrosis.
Preimplantation genetic diagnosis- carried out on embryos
made in in vitro fertilisation. This avoids having babies
with genetic disorders as well as avoiding abortion.
Parental Testing- Screening foetuses of women with a family
history of genetic disorders. There are two types:
Amniocentisis Chorionic villus sampling
Carried out at
15-16 weeks,
amniotic fluid is
obtained which has
DNA which can be analysed.
Carried out at 8-12 weeks,
cells are taken from the
chorionic villi (part of the
fetus which connects it to
its mother.) These are the analysed.
MISCARRIAGE
FALSE RESULTS
UNETHICAL

19. Gene Therapy
This involves altering the alleles inside cells to cure genetic
disorders. For example Cystic Fibrosis is caused by a recessive
allele so you can add a Dominant allele to make up for it.
To do this Vectors are used to carry the correct allele into the cell.
There are three different types of vector- Plasmids which are rings
of bacterial DNA which can also carry human DNA, Altered
viruses, and liposome's which are spheres of lipids.
There are then two different types of gene therapy-
Somatic therapy Germ line therapy
This targets specific body cells
which are particularly effected by the
disorder, for example in CF only the
epithelial cells lining the lungs would
be targeted. However it means that
any offspring could still inherit the
disorder.
This is when the alleles of
the sex cells are changed
so that every single cell
produced by the offspring
will not have the disease.
However at the moment it is
illegal.

20. Effects of Cystic Fibrosis on the body
Cystic Fibrosis is caused by a mutation in the gene
which codes for the CFTR protein.
CFTR is a carrier protein which transports chloride
ions out of cells and into the mucus. This
decreases the concentration of liquid in the mucus
making water diffuse into the mucus, making it nice
and watery.
With mutant CFTR channels chloride cannot be
transported into the mucus so it is very thick and
sticky. Therefore it causes problems.
Respiratory System
•The cilia are unable to remove
mucus from the airways causing
breathing difficulties.
•The alveoli are also coated in
mucus so there is less surface
area for diffusion to happen.
Digestive System
•The tube connecting the pancreas
to the small intestine becomes
blocked stopping Digestive enzymes
reaching the small Intestine so food
can’t be digested Fully so nutrients
aren’t absorbed.
• The lining of the small intestine Is
covered in mucus so cannot absorb
So much nutrients.
Reproductive System
•In men the vas deferens
(sperm ducts) are absent or become
blocked.
•In women, thickened cervical mucus
prevents sperm reaching the egg.
•This makes it very difficult for people
With CF to reproduce and if they do it
is Likely that their children will also
have CF or be carriers.