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the nucleus
The nucleus controls the cell’s activities and contains a
cytoplasm like substance called nucleoplasm
DNA is bound to proteins and is called
chromatin – this condenses to form the
chromosomes during cell division
Within the nucleus are 1 or 2
bodies – each called a
nucleolus these make rRNA
and assemble ribosomes
The nuclear membrane is a double
membrane structure containing pores that
allow the transport of mRNA and nucleotides

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Mitochondria
Mitochondria are formed from 2
membranes separated by a narrow
inter-membrane space
The inner membrane is folded to
increase its surface area into
extensions called cristae
The biochemical reactions of aerobic
respiration take place in the
mitochondria and they release
chemical energy in the form of ATP

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Golgi apparatus
The golgi apparatus was named after its discoverer Camillo
Golgi. It is similar in structure to smooth ER but has a more
compact form
It is a collection of flattened membrane sacs that are
constantly forming on one side and budding off as vesicles on
the other
Its functions are:
• to package proteins for secretion
•to secrete carbohydrates
•to produce glycoproteins
• to transport and store lipids
• to form lysosomes

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Lysosomes
Lysosomes contain and isolate digestive enzymes –
they are needed to prevent the rest of the cell being
digested by these enzymes
Several lysosomes may empty their contents into
one membrane lined vacuole containing a worn out
organelle

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Centrioles
Centrioles arise from a region
of the cytoplasm called the
centrosome and consist of 2
hollow cylinders
At cell division they migrate to
opposite poles of the cell and
produce the microtubules of the
spindles that pull chromosomes
apart

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Endoplasmic reticulum
The endoplasmic reticulum (ER) is an elaborate system of
membrane bound sacs (cisternae) – these are often
continuous with the nuclear envelope and the golgi body
Rough endoplasmic
reticulum (rER) has
ribosomes lining it
and is involved with
protein synthesis as
a transport system
Smooth
endoplasmic
reticulum (sER)
lacks
ribosomes – it
is involved with
the synthesis
and transport of
lipids

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Ribosomes
Ribosomes are involved in protein synthesis –
they move along molecules of mRNA and
read the nucleotide code to produce proteins
mRNA
U U U C G A U G C A U C G C A A C U C G C
aa1 aa2 aa3 aa4
C G U
aa5
U G A
aa6
Ribosomes are made of rRNA
(produced by the nucleolus) and
protein – they consist of one
large and one small sub-unit
large sub-unit
small sub-unit

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Cytoplasm
The cytoplasm is the matrix that contains all of the different
organelles
It is an aqueous mixture of chemicals either in solution or as
colloids including:
• simple ions such as sodium (Na+
) and chloride (Cl-
)
• organic molecules such as amino-acids, ATP and sugars
• storage materials such as fat droplets
It can be seen to be moving – this is called cytoplasmic
streaming

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Proteins also totally
penetrate and appear on the
inner and outer surfaces of
the membrane
Cell membrane
The main function of a cell membrane is to function as a
boundary between the cell and its environment – it
controls entry and exit into and from the cell
A phospholipid
bilayer forms
the majority of
the membrane
This “fluid-mosaic”
model was proposed
in 1972 by J Singer
and G Nicholson

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Chloroplasts
found only in plant cells – chloroplasts are
bounded by a double membrane known as the
chloroplast envelope
inside is a colourless matrix – the stroma
floating in the stroma are thylakoids
these stack together to form a granum
the grana can be interconnected by tubular
extensions called intergranal lamellae
also present are starch grains
which act as temporary stores
for the carbohydrates formed
during photosynthesis

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Vacuole
the vacuole is a large fluid filled sac
it is surrounded by a membrane called the
tonoplast
it functions as a storage site and provides
support for plant cells by creating a pressure
potential through osmosis

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The cell wall is made of cellulose microfibrils
contained in a polysaccharide matrix
The cell wall provides strength and support and
provides a pathway for water to move through
the plant – the apoplast pathway
Cell wall

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Plasmodesmata
There are gaps in the cell wall that allow
neighbouring cells to link together
There is a continuation of cytoplasm from
cell to cell and the endoplasmic reticulum
can also be linked
cell 1
cell 2