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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
CELL STRUCTURE
CELL THEORY:
Structural and functional unit of all living things
New cells arise from already existing cells
Cells contain information that instructs growth. This information can be passed onto new cells.
MICROSCOPES:
There are two main types of microscopes: Light and Electron
Electron Micrographs- shown in colour
LIGHT ELECTRON
Uses beam of light Transmission Electron Scanning Electron
Magnification = x1500 Microscope (TEM) Microscope (SEM)
Resolution = 200 nm
Wide range of specimens
can be used
Samples are fairly quick +
easy to prepare
Cheaper and safer
Limited resolution
Limited magnification
Uses electromagnets to focus Scan beam of electrons
beam of electrons across specimen
Denser parts of specimen absorb Beam bounces off surface
more electrons creating contrast of specimen
Can only be used on thin specimens Produces 3D image
Produces 2D image Magnification = x100,000
Magnification = x500,000 Resolution = 5 nm (lower)
Resolution = 0.2 nm
Advantages Disadvantages
Can produce coloured Must be used in a vacuum (no air)-
images electrons are absorbed by
Better resolution molecules in air
Better magnification Expensive
Training is required
Natural colours can't be seen
Dangerous- kills living cells
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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
STAINING:
Used to have better visualisation of cells under a microscope
Used because some cell components are transparent
ACETIC ORCEIN- stains DNA dark red
GENETIAN VIOLET- stains bacterial cell walls
IODINE- stains starch granules
METHYLENE BLUE/EOSIN- used for light microscope
Specimen dipped in METAL like lead (metal ions scatter electrons to contrast)- used for
electron microscope
SECTIONING:
Sections of tissue need to be cut into thin slices
Allows beam of light to pass through section of…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
Has receptor molecules that allows
it to respond to chemicals
(hormones)
separate cell contents from outside
the cell
separate cell components from the
cytoplasm
In cell recognition and signalling
To hold some components of
metabolic pathways in place
In regulating the transport of
materials in and out of cells
Cytoplasm Jelly-like substance Eukaryotic cells= contains
organelles
Prokaryotic cells= contains enzymes
needed for metabolic reactions.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
Vesicle Small fluid sac in Transports substances in and out cell
cytoplasm with Formed at Golgi apparatus, ER, cell
membrane surface membrane
Lysosome Round organelle Contains digestive enzymes to
surrounded by membrane break down materials
Can be used to digest invading cells
Releases enzymes to outside of cell
Mesosome Tightly-folded area of the Contains membrane bound proteins
cell membrane needed for respiration
Plasmid Small circle of DNA Exchange DNA easily and quickly
between eukaryotic cells
Used…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
Lamella (thin, flat pieces
of thylakoids)
Vacuole Filled with cell sap Keeps plant supported, rigid and
turgid
produces enzymes to destroy
bacteria
PROTEIN PRODUCTION:
This is an example of "division
of labour".
1) DNA contains
instructions to make
proteins (e.g.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
Food production e.g.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
FLUID MOSAIC MODEL:
FLUID: Lipid bilayer that is constantly moving. Membrane is the consistency of olive oil at body
temperature
MOSAIC: Protein molecules that are embedded and span the bilayer
10 nm wide
MEMBRANES AND TEMPERATURE:
Enzymes and co-enzymes attached to membrane
E.g.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
1) Cells communicate messages to each other
2) Cell releases a messenger molecule (hormone)
3) Then travels to another cell
4) Hormone is detected by cell because it binds to a
complementary receptor
5) E.g. cytokines
HORMONE RECEPTORS:
1) Proteins act as receptors for messenger molecules
2) Have specific bonding sites for specific hormone
3) Transmission of receptor is via reversible binding of hormone to receptor
4) E.g.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
THICKNESS OF MEMBRANE: Thinner membrane- faster rate of diffusion (shorter the
distance particles have to travel)
SIZE OF MOLECULES: Smaller molecules diffuse quickly than larger ones
MOVEMENT
FACILITATED DIFFUSION:
This is when large or charged molecules can't diffuse directly through membrane e.g.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
WATER POTENTIAL- The measurement of tendency of water molecules to diffuse from one
place to another
Highest water potential of pure water = ZERO
As water potential DECREASES value becomes more NEGATIVE
Measurement of water potential is "kilopascals (kPa)"
HYPOTONIC: Less concentration ­ Higher water potential ­ Net movement is INTO cell
HYPERTONIC: High concentration ­ Lower water potential ­ Net movement is OUT of cell
ISOTONIC: Same concentration ­ Same water potential ­ Net movement…read more

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