Figure 2.4 The fluid mosaic model
proposed by Singer and Nicholson
for the structure of the plasma
membrane of a red blood cell. The
lipid in the membrane is a complex
lipid known as phospholipid. What
does this name suggest about this
lipid? The carbohydrate groups in
the outer surface form part of
antigens (see chapter 3).
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The plasma membrane forms the boundary of
each living cell. It is selectively permeable.
Several different processes* exist whereby
substances may cross plasma membranes.
*( 2x diffusion, osmosis, active transport and
bulk transport)
Cell walls lie outside the plasma membrane of
plant, fungal and prokaryotic cells.
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Prokaryotic cells lack any internal membranebound organelles.
In eukaryotic cells, the nucleic acid DNA is
enclosed within the nucleus, a doublemembrane-bound organelle.
Living cells use energy all the time, principally
as chemical energy present in ATP.
Mitochondria are the major sites of ATP
production in eukaryotic cells.
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Ribosomes are tiny organelles where proteins
are produced.
The endoplasmic reticulum (ER) is a series of
membrane-bound channels, continuous with
the membrane of the outer nuclear envelope,
that transport substances within a cell.
The Golgi complex packages substances into
vesicles for export.
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Lysosomes can digest material brought into
their sacs. Lysosomes play a role in organised
cell death.
Chloroplasts are relatively large organelles
found in photosynthetic cells of plants and
algae.
Chloroplasts have an external membrane and
layers of folded internal membranes and
contain pigments called chlorophylls.
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Chloroplasts can capture the radiant energy
of sunlight and convert it to chemical energy
in sugars.
Structures known as flagella are present on
many prokaryotic cells.
Cilia or flagella are present on many
eukaryotic cells.
Flagella and cilia are cell organelles
associated with movement.
Lysoso
me
Golgi
Apparatus
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Single-celled organisms are able to carry out all
the metabolic processes necessary for life.
In multicellular organisms, cells become
differentiated to perform specialised functions.
The different levels of organisation of cells in
multicellular organisms are single cell, tissues,
organs, systems and the whole organism.
Individual cells in a group of cells must be able to
receive an adequate supply of materials and get
rid of wastes.
Each system serves the needs of other systems.