CELL THEORY
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All organisms are composed of cells
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The cell is the smallest unit of living matter
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Cells arise from pre-existing cells
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Information is passed on to cells in the form of DNA
PROKARYOTIC v EUKARYOTIC
Prokaryotic Cells
Eukaryotic Cells
(Bacteria)
(Plants, Animals, Fungi, Protists)
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Average diameter 0.5 – 5µm
(10 times smaller in diameter)
(100 – 1000 times smaller in volume)
DNA is circular and lies free in the cytoplasm
(circular chromosome in the nucleoid)
(rings of accessory DNA called plasmids)
Smaller ribosomes
NO Endoplasmic Reticulum (ER)
NO MEMBRANE BOUND ORGANELLES
Cell wall present (made of cross-linked peptidoglycan)
No true nucleus present
Other structures may include: flagellum, capsule,
mesosome, pili)
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Often up to 40 µm in diameter (size can vary)
(10 times larger in diameter)
(100 – 1000 times larger in volume)
DNA is not circular and is contained in the nucleus
(chromosomes)
Larger ribosomes
Endoplasmic Reticulum present (may contain
ribosomes)
CONTAINS MEMBRANE BOUND ORGANELLES
 single membrane eg: lysosomes, golgi body, vacuoles
 double membrane eg: nucleus, mitochondria
 no membrane eg: ribosomes
May have cell walls eg. Plants
NUCLEUS present with nucleus containing DNA
The Importance of compartmental organisation
o Allows cells to carry out a variety of different functions at the same time
o The membranes of the organelles have important roles themselves and often contain many of the
necessary proteins
PLANT CELLS v ANIMAL CELLS
Plant Cells
Animal Cells
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CELLULOSE CELL WALL
CHLOROPLASTS (Containing chlorophyll)
LARGE PERMANENT VACUOLE
Mitochondria
Cell membrane
Nucleus + Nucleolus
Golgi Body
ER
Ribosomes
Lysosomes
Cytoplasm
Centrioles
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NO CELL WALL
NO CHLOROPLASTS
MAY CONTAIN SMALLER TEMPORARY
VACUOLES
Mitochondria
Cell Membrane
Nucleus + Nucleolus
Golgi Body
ER
Ribosomes
Lysosomes
Cytoplasm
Centrioles
PLANT CELL
ANIMAL CELL
ORGANELLES
CELL MEMBRANE
LOCATION: - surrounding the cell and below the cell wall
in plants
FUNCTION: - gives the cell shape and
Protection from the exterior world. Regulates
the movements of substances into and out of
the cell. Has fluid type movement due to the
PHOSPHOLIPID BILAYER and contains
various proteins
PLANT CELLS:- Yes
ANIMAL CELLS:- Yes
LIGHT MICROSCOPE:- Yes
RIBOSOMES
(no membranes)
LOCATION:- Free in the cytoplasm or
attached to rough ER
FUNCTION:- Comprise of a complex
ribosomal RNA and protein and are the
site of polypeptide/protein synthesis
PLANT CELLS:- Yes
ANIMAL CELLS:- Yes
LIGHT MICROSCOPE:- No
Mitochondria
LOCATION:- In the cytoplasm enclosed
by a double membrane
FUNCTION:- Responsible for energy
production via ATP. Site of Kreb’s Cycle,
Electron Transport Chain. Contain
mitochondrial DNA. Matrix and folded
cristae are sites for cellular respiration
PLANT CELLS:- Yes
ANIMAL CELLS:- Yes
LIGHT MICROSCOPE:- No (only very
high powered light microscope)
Golgi Apparatus
(single membrane)
LOCATION:- In the cytoplasm,
associated with the smooth ER, often
close to the nucleus
FUNCTION:- Flattened sacs (cisternae)
are constantly being formed from one
end by vesicles which bud off from the
smooth ER and broken down at the other
end to form Golgi vesicles. Collects,
processes and sorts molecules (esp.
Proteins and lipids) ready for transport
in the Golgi vesicles. Used to make
lysosomes.
PLANT CELLS:- Yes
ANIMAL CELLS:- Yes
LIGHT MICROSCOPE:- No (only very
high powered light microscope)
ROUGH
ENDOPLASMIC
RETICULUM
LOCATION:- Throughout the whole
cytoplasm often closely associated with
the nuclear envelope.
FUNCTION:- Rough endoplasmic
reticulum houses ribosomes. Membranes
form a system of flattened sacs
(cisternae) which can go on to form the
golgi apparatus. The rough ER transports
proteins formed by ribosomes
throughout the cell.
PLANT CELLS:- Yes
ANIMAL CELLS:- Yes
LIGHT MICROSCOPE:- No
CHLOROPLASTS
(double membrane)
LOCATION:-Within the cytoplasm,
particularly in the cells at the surface of
leaves in plants
FUNCTION:- The site of photosynthesis.
The light-dependant stage taking place
in the thylakoids and involves the
absorbtion of blue and red light
wavelengths that eventually energise the
electron transport system. The lightindependant stage occurs in the stroma
and produces sugar molecules via the
Calvin-Benson cycle. Contains its own
DNA.
PLANT CELLS:- YES
ANIMAL CELLS:- NO
LIGHT MICROSCOPE:- YES
CENTRIOLES
LOCATION:- Found in the cytoplasm,
usually near the nucleus
FUNCTION:- Arranged at right angles to
each other and comprising of
microtubules. The centrioles help
organise chromosomes via poles during
cell replication. They ARE NOT found in
most higher plants.
PLANT CELLS:- Variable (not in higher
plants)
ANIMAL CELLS:- YES
LIGHT MICROSCOPE:- NO
CILIA & FLAGELLA
LOCATION:- Anchored in the cell
membrane and extending outside of the
cell
FUNCTION:- Flagella are often limited
to 1 per cell and cilia may be many. They
are structures used in locomotion,
particularly in water
PLANT CELLS:- NO
ANIMAL CELLS:- YES
LIGHT MICROSCOPE:- Occasionally
(depending on the preparation)
CELLULOSE CELL
WALL
LOCATION:- Surrounds the plant cell
and sits outside the plasma membrane
FUNCTION:- Provides rigidity and
strength, supports the cell against
changes in turgor (water pressure)
PLANT CELLS:- YES
ANIMAL CELLS:- NO
LIGHT MICROSCOPE:- YES
LYSOSOMES
(single membrane)
LOCATION:- Throughout the cytoplasm
FUNCTION:- Contain digestive enzymes
which aid in the digestion of foreign
matter (eg. Bacteria) as well as the cells
own organic material. The digestive
enzymes function best at pH 5 (acidic)
and therefore cause minor damage if
small amounts are leaked. Large
amounts may cause cell death via
autodigestion
PLANT CELLS:- YES (variably, vacuoles
have lysosomal function)
ANIMAL CELLS:- YES
LIGHT MICROSCOPE:- NO
VACUOLE
(single membrane)
LOCATION:- Free in the cytoplasm
FUNCTION:- In plants they are large
and permanent and involved in storage
and support. In animal cells they are
smaller and can be formed via
phagocytosis (FOOD VACUOLES) to be
then digested by lysosomes. Also used
for storage of water, wastes and soluble
pigments
PLANT CELLS:- YES (large &
permanent)
ANIMAL CELLS:- YES (smaller & often
numerous)
LIGHT MICROSCOPE:- YES (plant cell)
NO (animal cell)
NUCLEUS
(double membrane)
LOCATION:- within the cytoplasm,
position variable
FUNCTION:- The control centre of the
cell containing the nuclear material
(DNA). Surrounded by a porous
envelope, allowing RNA into and out of
the nucleus.
PLANT CELLS:- YES
ANIMAL CELLS:- YES
LIGHT MICROSCOPE:- YES