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Cells and organelles
Prokaryotes and eukaryotes:
There are two main types of organism – eukaryotes and prokaryotes
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e
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Both types of cells contain organelles
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Prokaryotic cells are smaller and simpler e
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bacteria

Organelles:
Organelles are part of cells; each one has a specific function
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Animal Cells:

Plant cells:
Plant cells have all the same organelles as animal cells, but with a few added extras
 A cell wall with plasmodesmata (‘channels’ for exchanging substances between
adjacent cells)
 A ‘permanent’ vacuole (a compartment that contains cell sap)
 Chloroplasts (organelles involved in photosynthesis)

Organelles:
Organelle
Plasma membrane (also known as cell
surface membrane)
Cell wall
Nucleus

Lysosome

Ribosome

Rough endoplasmic Reticulum
Smooth endoplasmic reticulum
Vesicle

Golgi apparatus
Mitochondrion

Chloroplast

Centriole
Cilia

Flagellum

Description
Membrane found on the surface of animal
cells and just inside the cell wall of plant
cells and prokaryotic cells
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A rigid structure that surrounds plant cells
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A large organelle surrounded by a nuclear
envelope, which contains many pores
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A round organelle surrounded by a
membrane, with no clear internal
structure
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It’s made up
of proteins and RNA
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A system of membranes enclosing a fluid
filled space
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A small fluid filled sac in the cytoplasm,
surrounded by a membrane
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Vesicles are often seen at
the edges of the sacs
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It has a double
membrane – the inner one is folded to
form structures called cristae
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It’s surrounded by a double
membrane, and also has membranes
inside called thylakoid membranes
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Grana
are linked together by lamellae – thin, flat
pieces of thylakoid membrane
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Found in animal cells, but
only some plant cells
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In
cross section, they have an outer
membrane and a ring of nine pairs of
protein microtubules inside, with a single
pair of microtubules in the middle
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They stick out from the cell
surface and are surrounded by the plasma
membrane
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Function
Regulates the movement of substances
into and out of the cell
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Supports plant cells
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The pores allow substances to move
between the nucleus and the cytoplasm
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Contains digestive enzymes
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The site where proteins are made
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Some are
formed by the Golgi apparatus or the
endoplasmic reticulum, while others are
formed at the cell surface
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It also makes lysosomes
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Mitochondria are found in
very large numbers in cells that are very
active and require a lot of energy
The site where photosynthesis takes place
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The microtubules contract to make the
flagellum move
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Organelles are involved in protein production:
 Proteins are made at the ribosomes
 The ribosomes on the rough ER make proteins that are excreted or attached to cell
membrane
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 New proteins produced at the rough ER are folded and processed in the rough ER
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 At the Golgi apparatus, the proteins may undergo further processing
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E
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glycoproteins
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The cytoplasm is more than just
a solution of chemicals – it has a network of protein threads running through it
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 In eukaryotic cells these protein threads are arranged as microfilaments and
microtubules
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 They also help to strengthen the cell and maintain its shape
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 The proteins of the cytoskeleton can cause the cell to move
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coli bacterium

Eukaryotes
Larger cells (about 10-100 micrometre
diameter)
DNA is linear
Nucleus present – DNA inside nucleus
No cell wall (animals), cellulose cell wall
(plants) or chitin cell wall (fungi)
Many organelles, mitochondria and other
membrane bound organelles present
Flagella (when present) made of
microtubule proteins arranged in a ‘9+2’
formation
Larger ribosomes
Example : human liver cell

Bacterial cells are prokaryotic
 Prokaryotes like bacteria are roughly a tenth the size of eukaryotic cells
 This means that normal microscopes aren’t powerful enough to look at their internal
structure

How microscopes work
 Magnification is how much bigger the image is than the specimen
 Magnification = Image size / actual size
 Resolution is how detailed an image is
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The three types of microscope
 Light microscope
 Laser scanning confocal microscope
 Electron microscopes

Light microscope
 Light microscopes use light
 They have a resolution of 0
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 The laser causes this dye to fluoresce
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The detector will print a 3d image on a computer
 The pinhole means out of focus light is blocked, so they produce a much clearer
image than a light microscope
 They can be used to look at different depths in thick specimens

Electron microscopes
 These use electrons instead of light to from an image
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 Transmission electron microscope – use electromagnets to focus a beam of electrons,
which is transmitted through the specimen
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TEM’s produce high resolution images
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This
knocks off electrons on the specimen, which gather in a cathode ray tube to from an
image
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2 micrometres
X1500

TEM
0
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002 micrometres

Resolution
Magnification

Staining samples
 Light or electrons pass through an object
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 Sometimes the object being viewed is transparent so we need to use a stain
 For light microscopes things like methylene blue and eosin
 Electron microscopes use a heavy metal like lead
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 Place a stain next to one edge of the cover slip
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 Use tweezers to put thin slice of specimen onto a clean slide
 Put a cover slip on top



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Title: OCR A LEVEL BIOLOGY (2.1.1 - Cell Structure)
Description: All the key info for 2.1.1 on the specification for A Level Biology.

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