This is a summary of every learning objective (1.1 - 1.18) for Topic 1, LHR on the Edexcel Biology A (Salters-Nuffield) specification. I have arranged my notes answering each objective, and have given definitions, core practical information, and equations, based from the textbook.
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BIOLOGY SPECIFICATION NOTES
Edexcel Biology Salters-Nuffield A AS/A-Level
Key:
Definitions are in turquoise
Core practicals are in orange
Equations are in green
Topic 1: Lifestyle, Health and Risk (LHR)
1.1 Understand why many animals have a heart and circulation (mass transport to overcome
limitations of diffusion in meeting the requirements of organisms).
- The heart and circulation have one primary purpose - to move substances around
the body
- In very small organisms (or unicellular ones), diffusion alone is usually
enough to satisfy the organisms need to transport oxygen, carbon dioxide and
digestive products around. This is able to happen in small organisms as they have
a large surface area and a small distance to travel.
- Diffusion: The random movement of molecules from a region of high
concentration to low concentration
- More complex multicellular organisms rely on a mass transport system, to move
substances over long distances by mass flow (movement of fluids down a pressure
gradient).
- Animals usually have blood to do this, and a heart. In other words, a circulatory
system.
- There are two main types of circulatory system: open and closed. An open
circulatory system is found in insects, blood circulates in large open spaces called
cavities pumped by the heart.
- A closed circulatory system is one where the blood is in blood vessels. Animals with
these are usually larger than insects and more active.
- There are two types of closed circulatory system too: single and
double.
-A single circulatory system is found in fish. The blood only passes
through the heart once in one circuit. The heart pumps deoxygenated
blood to the gills. CO2 is transported out into the water, and O2 is
transported in. Then, the blood flows round the rest of the body and
returns to the heart. This system pumps at low pressure to allow gas
exchange; the gill capillaries cannot withstand high pressures.
High speeds can’t be maintained for too long in these creatures. A slow
flow of blood leads to low O2 levels, causing anaerobic respiration. This
, results in more lactic acid being produces, which denatures enzymes due to a lowered pH.
- A double circulatory system is found in birds
and mammals. Blood flows through the heart twice in each
circuit. This system means that the organism can respire
anaerobically for longer. The heart also gives blood returning
from the lungs an extra boost, reducing the time for blood to
circulate around the whole body, meaning organisms have a
higher metabolic rate.
1.2 Understand the importance of water as a solvent in transport, including its dipole nature.
- In animals, the transport medium for mass flow is blood. This is mainly made up of
plasma, which is mainly water and dissolved substances. Blood plays a vital role
in regulating body temperature and transferring energy around the body.
- Water is a great solvent (able to dissolve other substances) for
transport. This is because it is a dipole: it has an uneven distribution of
charge. It can form hydrogen bonds with other molecules, which gives it
some interesting properties…
- Transparent, due to small size, allowing light to penetrate it
- Liquid at room temperature due to hydrogen bonds, so it can be used as a medium
for mass transport
- High specific heat capacity, easier for organisms to maintain stable body
temperature
- High latent heat (changing state), cooling animals in the form of sweat
- Ice is less dense than water, so it can actually float on water. This provides
insulation for water below.
- High cohesion (attraction of same molecules), allowing flow of water in plant xylem
- Low viscosity (thickness), meaning less energy is needed to move through it
- Good solvent. Ionic and polar molecules dissolve in water; they react with the polar
water molecule. These molecules are hydrophilic; hydrophobic molecules cannot
dissolve in water.
1.3 Understand how the structures of blood vessels (capillaries, arteries and veins) relate to
their functions.
The order of blood vessels from the heart around the body is: artery - arteriole - capillary -
venule - vein. As the arteries branch out into arterioles and capillaries, arterial pressure is
decreased as total vessel volume is increased.
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