AS Biology OCR F211 revision notes

AS Biology OCR F211 revision notes :)

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UNIT 1 Cells, exchange and transport
Module 1 Cells
Magnification = the degree to which the size of an image is larger than the object itself
Resolution = the degree to which it is possible to distinguish between two objects that are very
close together (more detail)
Robert Hooke > microscope with several lenses
Sheliden and Schwann > Cell Theory
Light microscope
use of lens to magnify specimen
magnification up to x1500
resolution up to 200nm (magnitude of wavelength of light)
wide range of specimens, but not detailed
prep staining (e.g. acetic orcein stains DNA) / sectioning (embed in wax, no distortion)
micrometre (m) 106m
nanometre (nm) 109m
IAM triangle Actual size = Image size/Magnification
Transmission electron microscope (TEM)
electron beam passes through thin prepared sample
magnification up to x500 000
two dimensional image
Scanning electron microscope (SEM)
electrons `bounced off' sample
magnification up to x100 000
three dimensional image
Electron microscopes
resolution up to 0.1nm
detailed images of structures inside cells
v. expensive
high degree of skill and training
prep fix in glutaraldehyde to make firm, dehydrate, embed in resin, cut using diamond
knife, stain with lead salts, mount onto copper grid, place in vacuum
MRS GREN
Cytoskeleton

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Golgi apparatus)
USES ATP
Undulipodia + cilia
hair like extensions that stick out form the surface of cells
cylinder 9+2 arrangement
undulipodia longer
e.g.…read more

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ER, may add sugar molecules
packages modified proteins into vesicles to be transported
modified proteins may go to surface of cell
Mitochondria
spherical or sausageshaped
two membranes separated by fluidfilled space
inner membrane highly folded (cristae)
central part called matrix
where ATP (adenosine triphosphate) produced during respiration
Chloroplasts
have two membranes separated by fluidfilled space
inner membrane continuous
network of flattened membrane sacs (thylakoids) stack of these called granum
chlorophyll molecules present on membranes
site of photosynthesis
Lysosomes
spherical sacs surrounded by a single membrane…read more

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Eukaryotes
have true nucleus
Prokaryotes
bacteria
smaller than eukaryotes
no membranebound organelles
surrounded by cell wall (made of peptidoglycan)
ribosomes are smaller
DNA in form of single loop, small loops of DNA plasmids
free DNA, in nucleoid area
ATP production in mesosomes (infolded regions of cell surface membrane)
some have flagella
Phospholipids two hydrophobic fatty acid tails and hydrophillic phosphate head
two tramlines separated by pale area
Specialise => muscle cell membranes contain a large number of channels that allow rapid
uptake of glucose to…read more

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Ions (e.g. sodium ions) > channel proteins
Endo inwards
Exo outwards
Phago solid material
Pino liquid material
Bulk transport endocytosis and exocytosis (via vesicles)
e.g.…read more

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Module 2 Exchange and transport
Exchange surfaces
large surface area so more space folding walls and membranes
thin barrier to reduce diffusion distance
steep diffusion gradient fresh supply on one side, removal on other
Inhale diaphragm contracts, flatter, intercostal muscles contract to raise ribs volume of chest
cavity increases, pressure in chest drops below atmospheric pressure
trachea have thick ring of cartilage
cartilage > supports trachea and bronchi, not complete ring so some flexibility
smooth muscle > contracts to constrict airway
elastic fibres > recoils…read more

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PURKYNE TISSUE AND ATRIOVENTRICULAR /NODE
P excitation of atria Increase in ST bit indicates a heart attack
QRS excitation of ventricles
T diastole…read more

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Carriage of oxygen
oxygen + haemoglobin > oxyhaemoglobin
four subunits = each has a polypeptide chain and a haem group (contains a single iron atom)
and can attract and hold an oxygen molecule
oxyhaemoglobin dissociation curve
when one oxygen molecules diffuses into the haemoglobin molecule + associates with haem
group, then conformational change so more easy to associate, so steeper curve
difficult to achieve 100% saturation because harder for 4th haem group to associate
fetal haemoglobin has higher affinity for oxygen so curve on the…read more

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Bohr effect > because hydrogen ions taken up by haemoglobin, less space for oxygen so
oxyhaemoglobin releases more oxygen
more carbon dioxide, more acidic, haemoglobin less saturated with oxygen
Transport in plants
roots have water, leaves have sugars
water and minerals move up in xylem
sugars move up or down in phloem
vascular bundles in young root > circle, cross of xylem and phloem in areas around it
around bundle is endodermis, gets water into xylem, just inside endodermis is meristem cells
vascular bundles in…read more

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Water moves up stem:
1 root pressure > water moves into xylem through osmosis because minerals moved into
xylem
2 transpiration pull > water molecules attracted to each other through cohesion, column,
so transpiration stream
3 capillary action > adhesion to sides of xylem vessel
Transpiration = number of leaves, number and size and position of stomata, presence cuticle,
light, temperature, humidity, wind, amount of water
Transpiration unavoidable because photosynthesis
Xerophytes adapted to dry/arid conditions
small leaves
thicker waxy cuticle
close stomata when water availability…read more

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