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  • Created on: 24-05-11 10:49

Unit 2 - page 1
HGS A-level notes NCM/1/09
AQA(B) AS Unit 2
Specification 2
Polysaccharides 4
Gas exchange 6
The Circulatory System 13
Haemoglobin 20
Water Transport in Plants 23
DNA 29
DNA replication 32
Gene Expression 34
Chromosomes 37
Cell Cycle 41
Meiosis and sexual reproduction 45
Antibiotic Resistance 48
Classification 52
Biodiversity 60
Causes of diversity 62
Loss of Genetic Diversity 64
Species Diversity 67
These notes may be used freely by A level biology students and teachers,
and they may be copied and edited. I would be interested to hear of any
comments and corrections.
Neil C Millar (
Head of Biology, Heckmondwike Grammar School,
High Street, Heckmondwike WF16 0AH
Unit 2 - page 2
HGS A-level notes NCM/1/09
Unit 2 Specification
Plant Cells
There are fundamental differences between plant cells and
animal cells. The structure of a palisade cell from a leaf as
seen with an optical microscope. The appearance,
ultrastructure and function of cell wall and chloroplasts.
Explain adaptations of other plant cells. Use an optical
microscope to examine temporary mounts of plant cells,
tissues or organs.
The structures of β-glucose and the linking of β-glucose by
glycosidic bonds formed by condensation to form cellulose.
The basic structure and functions of starch, glycogen and
cellulose and the relationship of structure to function of
these substances in animals and plants.
Surface Area to Volume Ratio
The relationship between the size of an organism or
structure and surface area to volume ratio. Explain the
significance of the relationship between size and surface area
to volume ratio for the exchange of substances and of heat.
Gas Exchange
Changes to body shape and the development of systems in
larger organisms as adaptations that facilitate exchange as the
ratio reduces. Use knowledge and understanding of the
principles of diffusion to explain the adaptations of gas
exchange surfaces. Gas exchange across the body surface of
a single-celled organism; in the tracheal system of an insect
(tracheae and spiracles); across the gills of a fish (gill lamellae
and filaments including the countercurrent principle) and by
leaves of dicotyledonous plants (mesophyll and stomata).
Structural and functional compromises between the opposing
needs for efficient gas exchange and the limitation of water
loss shown by terrestrial insects.
The Circulatory system
Over large distances, efficient supply of materials is provided
by mass transport. The general pattern of blood circulation
in a mammal. Names are only required of the coronary
arteries and of blood vessels entering and leaving the heart,
liver and kidneys. The structure of arteries, arterioles and
veins in relation to their function. The structure of capillaries
and their importance in metabolic exchange. The formation
of tissue fluid and its return to the circulatory system.
Haemoglobin and Oxygen Transport
Haemoglobin is a protein with a quaternary structure. The
role of haemoglobin in the transport of oxygen. The loading,
transport and unloading of oxygen in relation to the oxygen
dissociation curve. The effects of carbon dioxide
The haemoglobins are a group…




Really good content, but the layout is a bit confusing...

Ele (moderator)



the contents at the start is confusing :S
but its good :D ** 

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