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Cell Structure
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Magnification: how many times bigger the image is produced
Resolution: ability to distinguish between 2 points that are close together as
separate structures

Optical microscopes:
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Use light to form an image- limits the resolution of the microscope
Produce a colour image
Maximum resolution: 200nm
Can be used to observe eukaryotic cells (living or dead), their nuclei
and maybe mitochondria and chloroplast
Cant be used to observe smaller organelles i
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ribosomes, ER or
lysosomes
Maximum magnification: x1500

Electron microscopes:
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Uses electrons to form an image
Vacuum needed for electron microscopes
Maximum resolution: 0
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5nm
• Allows internal structures within cells to be seen
▪ Disadvantages:
• Can only be used with very thin specimens
• Cannot be used to observe live specimens
• Lengthy treatment to prepare specimens
• Don’t produce a colour image
o SEM: electrons scanned across the surface of the specimen
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• A laser scanning confocal microscope moves a single
spot of focused light across a specimen (point
illumination)- causes fluorescence from the components
with dye
• Emitted light from the specimen is filtered through a
pinhole aperture
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Dry mount: specimens viewed whole or cut into very thin slices with a sharp bladesectioning
Specimen is placed on the centre of the slide and a cover slip is placed over the
sample
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Squash slide: wet mount is first prepared, then a lens tissue is used to gently press
down the coverslip
Potential damage to a coverslip can be avoided by squashing the sample inbetween
two microscopic slides
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Then iodine which fixes the dye
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Then stained with
safranin dye- counter stain
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The nuclear envelope contains nuclear pores which allows molecules to move
into or out of the nucleus
Nucleolus: area within the nucleus which produces ribosomes- contains ribosomes
and RNA
Mitochondria: have a double membrane
o Inner- highly folded membrane to form the cristae
o Fluid- matrix
o Membrane forming the cristae contains the enzymes used in aerobic
respiration
o Contains small amounts of DNA- mitochondrial DNA, can produce their own
enzymes and reproduce themselves
Vesicles: membranous sacs that have storage and transport roles
Lysosomes: specialized forms of vesicles that contain hydrolytic enzymesresponsible for breaking down waste materials in cells including old organelles
o Play a role in immune system as theyre responsible for breaking down pathogens
ingested by phagocytic cells

o Play an important role in programmed cell death (apoptosis)
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Cytoskeleton: network of fibres necessary for the shape and stability of a cell
o Organelles held in place by the cytoskeleton and it controls cell movement and
organelle movement
o 3 components:
▪ Microfilaments: for cell movement and cell contraction during cytokinesis

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Microtubules: track for the movement of organelles- determines the shape
of the cell
Intermediate fibres: mechanicalstrength to cells and help maintain their
integrity

Centrioles: component of the cytoskeleton composed of microtubules
o 2 associated centrioles form the centrosome, which is involved in the
assembly and organization of the spindle fibres during cell division

Organisms with flagella and cilia- centrioles are thought to play a role in the positioning of
these structures
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Flagella and cilia: flagella are longer than cilia but cilia are usually present in much
greater numbers
o Flagella-cell motility
oCilia- mobile/ stationary
▪ Stationary cilia present on the surface of many cells and have an
important function in sensory organs such as the nose
▪ Mobile cilia: beat in a rhythmic manner, creating a current, cause
fluids or objects adjacent to the cell to move
▪ Each cilium contains two central microtubules surrounded by 9 pairs
of microtubules arranged like a “wheel”- 9+2 movement
▪ Pairs of parallel microtubules slide over each other causing the cilia to
move in a beating motion
Endoplasmic reticulum: network of membranes enclosing flattened sacs called
cisternae- connected to the outer membrane of the nucleus
o 2 types:
▪ SER: lipid and carbohydrate synthesis and storage
▪ RER: ribosomes bound to the surface and is responsible for the
synthesis and transport of proteins
Ribosomes: constructed of RNA molecules made in the nucleus of the cell- site of
protein synthesis
Golgi apparatus: compact structure formed of cisternae and doesn’t contain
ribosomes- role in modifying and packaging proteins (packaging proteins into vesicles
either secretory vesicles if to leave the cell, or lysosomes- stay in cell)

Protein production
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Proteins are synthesized in the ribosomes bound to the RER
Pass into the cisternae and are packaged into transport vesicles
Vesicles containing the newly synthesized proteins moves towards the Golgi
apparatus via the transport function of cytoskeleton
Vesicles fuse with the cis face of the Golgi apparatus and the proteins enter
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Some vesicles form lysosomes-contain enzymes for use in the cell

Plant cell organelles

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• Cellulose cell wall: defence mechanism,
protecting the contents of the cell against
pathogens
• Vacuole: contains cell sap- maintenance
of turgor so that the contents of the cell
push against the cell wall and maintain a
turgid framework for the cell surface
membrane
oSelectively permeable
oIf vacuoles appear in animal cells, they
are small and transient (not permanent)
Chloroplasts: responsible for photosynthesis
o Stroma: fluid
o Thylakoids: internal network of membranes which form flattened sacs
o Granum: several thylakoids stacked together
o Lamellae: membranes joining the grana
o Grana contain the chlorophyll pigments- light dependent reactions occur
during photosynthesis
o Starch produced by photosynthesis is present as starch grains

Prokaryotic cells

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• Have a cell wall made up of peptidoglycan- also known as murein
• Cell wall is a complex polymer made up from amino acids and sugars
• Flagella of prokaryotes are tinner than the equivalent structure of
eukaryotes and doesn’t have the 9=2 arrangement
• Flagellum is attached to the cell membrane of a bacterium by a basal
body and rotated by a molecular motor
• Basal body attaches the filament comprising the flagellum to the cell
surface membrane of a bacterium
A molecular motor causes the flagellum to rotate giving the filament a whip like
movement, which propels the cell



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