cells

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  • Created on: 08-02-12 14:47
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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 Microscope Scanning Electron
Magnification = x1500 (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 beam Scan beam of electrons
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 molecules
Better resolution 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]
Cell Surface Membrane Made of lipids and Controls movement of substances in
proteins and out of cells
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…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
Vesicle Small fluid sac in cytoplasm Transports substances in and out cell
with membrane Formed at Golgi apparatus, ER, cell
surface membrane
Lysosome Round organelle Contains digestive enzymes to break
surrounded by membrane 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]
Grana (stack of thylakoids) Grana- carries out light dependent
Lamella (thin, flat pieces of stage of photosynthesis
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]
Prokaryotes are useful to humans:
Food production e.g.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
Membrane consist of arranged phospholipids
Head is hydrophilic- attracts water
Tail is hydrophobic- repels water
Molecules arrange themselves into a bilayer- the heads face outwards on either side of
the membrane
Centre of bilayer is hydrophobic so membrane doesn't allow water-soluble substances
through it
FLUID MOSAIC MODEL:
FLUID: Lipid bilayer that is constantly moving.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
Glycolipids Act as receptors for cell signalling, cell binding and cell recognition
Help maintain stability of membrane
COMMUNICATION AND CELL SIGNALLING:
CELL SIGNALLING:
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.…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
When molecules have evened out, they are evenly distributed
They still move around but there's no net movement
RATE OF DIFFUSION:
TEMPERATURE: Increasing the temperature increases kinetic energy- movement of
diffusion increases
CONCENTRATION GRADIENT: The higher it is the faster the rate of diffusion
SURFACE AREA: The larger the surface area the more rate of diffusion
THICKNESS OF MEMBRANE: Thinner membrane- faster rate of diffusion (shorter the
distance particles have to travel)
SIZE OF MOLECULES: Smaller…read more

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Unit One: Cells, Exchange and Transport [BIOLOGY REVISION NOTES]
Specific for certain molecules General: non-specific
Faster than simple diffusion Go at same speed as diffusion
Against concentration gradient Down a concentration gradient
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:…read more

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