Biology Unit 1 Edexcel notes

  • Transport systems
  • Arteries, capillaries and veins
  • The heart
  • Blood pressure 
  • Gas exchange
  • Cell membrane

Might add more stuff to it later.

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  • Created by: Niki :)
  • Created on: 06-05-12 08:43
Preview of Biology Unit 1 Edexcel notes

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Niki's Notes
Transport systems
Simple organisms
Organisms such as Amoeba can rely on simple diffusion to get all of the substances they
need. Nutrients and oxygen can diffuse into the cell and waste can diffuse out. This is because these
organisms have a large surface area to volume ratio. Because the Amoeba is a single cell, there is
less distance for substances to travel, and diffusion is much quicker.
Remember: the
bigger the organism,
the smaller the SA :
Vol ratio!
Large organisms
These organisms are made of lots of cells, so substances need to travel long distances from
the outside to the cytoplasm of all the cells. Simple diffusion would not be suitable for this as
nutrients would not be able to reach the cells fast enough. Humans use the heart and circulatory
system as a mass transport system to do this. Substances are transported through the in the flow of
a fluid with a mechanism for moving it around the body. Processes such as osmosis, diffusion and
active transport are involved as well.
Mass transport system: Features
A suitable transport medium
A system of vessels to carry substances
A way of ensuring that substances are moved in the right direction
A quick way of moving materials to meet the needs of the organism or a way of maintaining
a concentration gradient.

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Water in living organisms
Water has the chemical formula HO. Water molecules are described as slightly polarised because
they have a slight positive charge at one end of the molecule and a slight negative charge at the
other end. As a result, individual molecules form hydrogen bonds with each other.
Water is an important solvent in living organisms because most biochemical reactions take place in
aqueous solution.…read more

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The Heart (Cardiac cycle)
All arteries (except the pulmonary arteries) take oxygenated blood away from the heart.
The valves close up to stop blood from going back into the heart.
Mammals have a double circulation consisting of a pulmonary (to lungs) and systemic (to the rest of
the body) circulations. Blood is transferred to and from the heart twice.…read more

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1. The heart is at rest and the myocardium is relaxed.
2. The atria and ventricles passively fill with blood (AV valves)
3. The aortic and pulmonary artery semilunar valves are closed, bi and tri are open
Atrial Systole:
1. The atria contract and the ventricles relax
2. Remaining blood is forced into the ventricles
3. The bicuspid and tricuspid are open, semi-lunar valves closed
1. The atria contract and eject the final amount of blood into the ventricles.
2.…read more

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SA node ­ pacemaker, because it determines the rate of contraction of the rest of the cardiac
muscle (Where the vena cava enters the right atrium)
Intrinsic rhythmicity ­ In early embryo cells that are destined to become the heart, begin
contracting long before the heart forms.…read more

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Factors that affect membrane fluidity
1. Temperature ­ at lower temps, lipids have less kinetic energy so are packed more tightly,
decreasing fluidity. High temps = loose lipids, more fluidity.
2. Lipids ­ Long with saturated tails have a high melting point, which decreases fluidity. The
straight unkinked fatty acid chains mean the lipid molecules can pack together more tightly.
3. Cholesterol ­ (Normal body temp) Low levels can make the membrane too fluid, and may
cause the cell to burst.…read more

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Diffusion and gas exchange
Facilitated diffusion ­ proteins in the membrane allow only specific substances to move through
passively down their concentration gradient.
Hypotonic ­ The osmotic concentration of solutes is lower than that in the cytoplasm of the cells.
Water enters the cell.
Isotonic ­ There is no net gain or loss of water. The solution has the same osmotic concentration as
the cell.
Hypertonic ­ The osmotic concentration of solutes is higher than that in the cytoplasm.…read more

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Plasma - mostly water with dissolved nutrients, salts, hormones and proteins
Largely water
Contains fibrinogen, a substance vital for blood clotting
Contains a range of dissolve substances
Platelets ­ cell fragments involved in blood clotting
Tiny fragments of larger cells called megakaryocytes found in bone marrow
White Blood cells (leucocytes) ­ help fight infection
Much larger than erythrocytes but can change their shape to fit through small blood vessels
Between 4000 and 10000 per cubic ml of blood
Most are formed I…read more

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The vessels
They carry blood away from the heart
(except pulmonary artery)
Arteries near the heart have the most
elastic fibres to withstand high blood
Blood pressure in the arteries
decreases the further away it is from
the heart
The diameter of the lumen changes.…read more

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Gas exchange in the alveoli
Inhalation (active)
The muscles around the diaphragm contract and it is lowered and flattened.
The intercostals muscles between the ribs also contract, raising the rib cage upwards and
The volume of the chest cavity increases, reducing the pressure in the cavity.
This pressure is now lower than the pressure of the atmospheric air outside, so to equalise
the pressure, air moves in through the trachea, bronchi and bronchioles into the lungs.…read more



Just wanted to say these notes are incredibly helpful as my textbook hasn't arrived so using your notes as a refresher from class. Really recommend them, Thank you!

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