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· There are two types of microscopes: light
(up to X1500 and low resolution); and
electron (up to X500 000 and high
· Resolution is how well small, close
objects can be seen separately. High
resolution produces detailed images of
cells (ultrastructure).
· Specimens need preparation to make
structures visible. Light microscopes need
stains (e.g. acetic orcein for DNA).
Electron microscopes need lead salts to
scatter electrons and produce images. The
pictures produced are called micrographs.…read more

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· Organelles; nucleus, nucleolus (makes
ribosomes), mitochondria (make ATP for
cellular energy), lysosomes (contain lytic
enzymes), chloroplasts (plant cells only),
centrioles (animal cells only, aid cell
division), cilia and flagella (beat to produce
cell movements).
· Ribosomes make proteins, rough
endoplasmic reticulum transports the
protein to Golgi apparatus which packages
and secretes it out of the cell.
· Eukaryotic cells have a true nucleus and
membrane-bound organelles. Prokaryotes
have naked DNA and small organelles with
no membranes around them.…read more

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· The fluid mosaic is a phospholipid bilayer
with scattered proteins.
· The cell surface membrane is for
transport (partially permeable) and
recognition/signalling (e.g. receptor
molecules for hormones).
· Passive transport (diffusion/facilitated
diffusion) does not use energy, while active
transport does and is against a
concentration gradient.
· Osmosis is diffusion of water from high
water potential to low across a cell
membrane. Endocytosis is bulk movement
of fluid/particles into a cell. Exocytosis is
movement to the outside of the cell.…read more

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· The life cycle of a dividing cell is the cell
cycle. It mostly involves copying and
checking genetic information. The final
small part involves mitosis which forms
two new cells.
· Cells can continue a cell cycle or they
· The main stages of mitosis are: Prophase
(chromosomes thicken, become visible);
Metaphase (chromosomes line up on the
equator); Anaphase (chromatids separate);
and Telophase (each set of chromatids
forms a new nucleus).…read more

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· New cells produced in mitosis are
genetically identical (same chromosome
combinations) to each other and the parent
cell. Cells formed by meiosis are not
genetically identical.
· Some mitosis (e.g. bone marrow)
produces stem cells. These can
differentiate into many different cell types
(e.g. red blood cells, neutrophils). They are
specialised for their function (e.g.
epithelial or guard cells).
· Cells are organised into tissues (e.g.
squamous or ciliated epithelium;
xylem/phloem) which are organised into
organ systems.…read more

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· The alveolus wall is an efficient exchange
surface as it is only one cell thick. It is
moist and is highly folded for a large
surface area.
· Alveoli are supplied with a rich network
of capillaries which carry blood close to the
alveolus wall (the exchange surface).
· Muscles move air in and out of the lungs
(ventilation). Along with the blood supply,
this keeps up a concentration gradient of
O2 & CO2.…read more

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· The trachea and bronchi have rings of
cartilage which keep them open for airflow
during ventilation.
· Smooth muscle contracts and narrows
the bronchi and bronchioles and elastic
tissue opens these airways. This controls
· Goblet cells in the lining of the trachea,
bronchi and bronchioles secrete mucus
which traps particles (e.g. pollen and
· Ciliated epithelial cells in the lining beat
upwards.…read more

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· Large multicellular animals have a small
surface area for their volume, resulting in a
large distance for diffusion of gases.
· They need a special transport (blood)
system to supply O2 and remove CO2,
especially if very active (e.g. birds,
mammals and fish).
· Single system (fish): heart ­ gills ­ body
­ heart. Double system (mammals): left
heart ­ body ­ right heart ­ lungs ­ left
heart.…read more

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· The left ventricle wall (thick) pumps
blood around the body. The right ventricle
wall (thinner) only has to pump blood to
the lungs.
· Atrial walls are very thin since they only
have to pump blood a short distance into
the ventricles.
· Cardiac cycle: chambers fill; ventricles
contract (cuspid valves close, "lub" sound);
atria contract (semi-lunar valves close,
"dub" sound).
· The Sino-Atrial Node (in right atrium)
maintains beat rhythm.…read more


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