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Chapter 2
Structure and Function of Cells
Looking at cells
 Living cells can be classified into 2 different kinds:
 Prokaryotic cells
 Eukaryotic cells
 All cells have an outer boundary known as the plasma
membrane (or cell membrane)
 Prokaryotic cells have very little defined internal structures.
They are very simple cells.
 This includes bacteria
 Eukaryotic cells are much more complex. They contain
membrane bound organelles. Organelles are structures that
perform the tasks that a cell needs to do.
 This includes all animals, plants, fungi, other single celled
organisms
The plasma membrane boundary
 Controls entry and exit of substances
 Is very thin (0.01µm)
 Present in prokaryotes and eukaryotes
 Is ‘partially permeable’ meaning it is selective about which
dissolved substances are allowed in or out.
 Consists of a
‘phospholipid
bilayer’
 ‘Fluid mosaic’
model describes the
form it takes
Free passage: Diffusion
 Diffusion is the net movement of a substance from a region
of high concentration to a region of low concentration.
 It is a passive process (does not require energy)
 See simulation on scootle
Osmosis: a special case of diffusion
 Osmosis is the movement of water from an area of low solute
concentration (high in water, low in dissolved substances) to
an area of high solute concentration (low in water, high in
dissolved substances) UNTIL the concentration is equal
 See simulation on scootle
Facilitated diffusion
 In some cases, movement of substances across the membrane
is assisted by carrier protein molecules (think back to the
‘fluid mosaic’ model)
 This occurs when the substances are unable to move through
the lipid bilayer.
 It is a passive process (does not require energy)
 http://highered.mcgraw-
hill.com/sites/0072495855/student_view0/chapter2/anim
ation__how_facilitated_diffusion_works.html
Paid passage: active transport
 Active transport is the movement of dissolved substances
against a concentration gradient (the OPPOSITE of
diffusion)
 It is an energy requiring process
 http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/anim
ation__how_the_sodium_potassium_pump_works.html
Bulk transport
 Endocytosis and exocytosis are two methods for moving large
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particles into and out of cells.
Endocytosis involves the cell membrane ‘engulfing’ a foreign
object and moving it into the cytosol. Eg white blood cells
Exocytosis involves a vesicle (containing whatever is to be
released) fusing with the cell membrane and release its contents
into the environment surrounding the cell
See figure 2.12 pg 30
Phagocytosis: solid material
Pinocytosis: fluid material
Surface area to Volume ratio SA:V
 Cells are small
 Some cells have folded membranes
 Cells must maintain a favourable SA:V which means that
their surface area is sufficient to take up materials essential
for cell functioning.
 Refer to biozone activity- pg 79
 See pg 44 of text
Cell walls
 Not found in ANIMAL cells
 In plants, fungi & bacteria, a cell wall exists outside the
plasma membrane
 Cell walls provide organisms with a rigid support structure
Cell organelles
The nucleus: control centre
Mitochondrion: energy
supplying organelle
 Nuclei are present in
 Mitochondria complete
eukaryotic cells
 The nucleus contains the
genetic material (DNA) of
the cell, which provides
‘instructions’ for
performing all of the tasks
that a cell needs to do.
cellular respiration in
order to provide ATP for
cellular activities.
 They are the ‘powerhouse’
of the cell
Cell Organelles (cont)
Ribosomes: protein
factories
Lysosomes: controlled
destruction
 Ribosomes makes proteins
 Programmed cell death:
for use in the cell or for
export outside the cell (eg
hormones)
apoptosis
 Lysosomes contain
digestive enzymes, which
can be released to cause the
‘self destruction’ of the cell
Transport, storage and export
Endoplasmic reticulum
Golgi complex
 Transports proteins within
 Transports substances
the cell.
 Can be called ‘rough ER’
or ‘smooth ER’
 Rough ER is surrounded
by ribosomes.
made in the cell to outside
the cell
Chloroplasts
 Found in PLANT cells only
 Site of photosynthesis: the
trapping of sunlight and
conversion to chemical
energy in the form of
glucose.
 Contain the substance
chlorophyll, a green, light
trapping pigment
Flagella & cilia: whipping
around.
 Are found in cells where
movement is required.
 Flagella are a ‘tail’ structure,
where its movement cause
the cell to move.
 Cilia are hair like structuresmovement of cilia may cause
the cell to move, or may
cause things outside the cell
to move past it. (Eg trachea)
Cells in multicellular organisms: levels
of organisation
 Cells  tissues  organs  systems
 Homework
 Biozone pgs 73, 75,76-77, 81, 83
 Plant and animal cells pgs 67- 70
 Practical report from last weeks prac
