Edexcel A-Level Biology I Unit 2 Cells
Viruses Reproduction I Primrose Kitten
2024 Exam Comprehensive Review
A-Level biology key words for Edexcel Unit 2. These
are really important to learn, as definition in
biology can get you loads of marks in an exam. Full
glossary booklet with revision crosswords available
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ORGANELLE - Answer>>A specialised part of a cell that
performs a particular function.
MAGNIFICATION - Answer>>The ability of a lens to enlarge the
size of an object. Calculated by dividing the image size by the real
size of the object.
RESOLUTION - Answer>>The ability of a microscope to
distinguish two adjacent points as separate from each other.
MICROMETER μm - Answer>>An SI unit of measurement
which is one thousandth of a millimeter
NANOMETER nm - Answer>>An SI unit of measurement which
is one thousandth of a micrometer
TRANSMISSION ELECTRON MICROSCOPE - Answer>>A
beam of electrons focussed by electromagnets pass through
,ultra-thin dead tissue samples. Capable of a maximum
magnification of x500 000 and a resolution of 0.2nm.
SCANNING ELECTRON MICROSCOPE - Answer>>A
focussed beam of electrons is passed across the surface of the
specimen to produce a three dimensional view of the surface.
Maximum magnification is x100 000 and maximum resolution is
10nm.
LASER SCANNING COFOCAL MICROSCOPE -
Answer>>Based on a conventional optical microscopy and used
to enhance optical resolution. Cells are stained with fluorescent
dyes. A thick section of tissue or small living organism is scanned
with a laser beam, which is reflected by the dyes to produce a
computerised 3D image.
EYE PIECE GRATICULE - Answer>>A circular disc fitted into
the eyepiece of a microscope, which has a scale marked on it
with equal divisions in arbitrary units. The length of each division
varies as the objective lens is changed.
STAGE MICROMETER - Answer>>This is used to calibrate the
scale on the eye piece graticule for each objective lens used. The
micrometer slide has a scale engraved into it, calibrated in known
divisions e.g. 0.1mm.
CALIBRATE - Answer>>To determine, rectify or mark the
graduations of a measuring instrument. e.g. using a stage
micrometer to determine the length of each divison on an eye
piece graticule.
NUCLEUS - Answer>>Present in eukaryotic cells and consists
of chromatin. Chromatin is a complex of DNA and histone
proteins. DNA, provides the template for making RNA. The
, nucleus indirectly controls the activities of the cell. Chromatin
exists in two forms: lighter, less condensed euchromatin and
darker, motre condensed heterochromatin.
NUCLEOLUS - Answer>>A darkly stained region within the
nucleus, responsible for the manufacture of ribosomal RNA and
hence ribosomes.
ROUGH ENDOPLASMIC RETICULUM - Answer>>An
elaborate three dimensional series of sheet like membranes
which are continous with the outer nuclear envelope, which form a
system of flattened cisternae. RER has ribosomes present on the
outer surfaces of the cisternae to produce proteins destined for
transport and secretion. RER provides a large surgace area for
protein and glycoprotein synthesis as well as a pathway for the
transport of materials especially proteins to the Golgi apparatus
for further processing.
SMOOTH ENDOPLASMIC RETICULUM - Answer>>SER lacks
ribosomes on its surface and is often more tubular in appearance.
Its functions are to (i) synthesise, store and transport lipids and
phospholipids (ii) synthesise steroids such as cholesterol and
reproductive hormones. (iii) synthesise, store and transport
carbohydrates; (iv) detoxify lipid soluble drugs.
GOLGI APPARATUS - Answer>>Consists of a series of
unconnected flattened membranous sacs called cisternae and
Golgi vesicles. The functions of the Golgi apparatus is to (i)
modify proteins and lipids from the RER and prepare them for
secretion. (ii) produce secretory enzymes (iii) form lysosomes
CISTERNA - Answer>>Pleural is cisternae. A series of flattened
tubular membranes found in the endoplasmic reticulum and Golgi
apparatus.
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