All living things are composed of cells and cell products (e.g. bone, saliva).
New cells are formed by the division of pre-existing cells.
There are basic similarities in the chemical constituents and metabolic activities of all cells.
The activity of an organism as a whole is the sum of the activities and interactions of its independent cell units.
Cell Organisation: Prokaryotic & Eukaryotic Cells
e.g. bacteria, cyanobacteria (blue-green algae)
Smaller than eukaryotes
Less complex than eukaryotes
Do not have membranes enclosing cellular components, therefore no distinct nucleus
DNA (genetic material) is on a circular chromosome in the centre of cell
Do not contain ribosomes that are involved in protein production
e.g. all cells apart from bacteria and cyanobacteria
Larger than prokaryotes
More complex than prokaryotes
Contain certain cellular components that are enclosed in membranes
Organelles in Eukaryotic Cells
Nucleus (Plural: nuclei)
Control centre of cell
Roughly spherical in shape
Contains most of the cell's DNA (Deoxyribonucleic Acid) on chromosomes
When the cell is not undergoing cell division (meiosis and mitosis), the chromosomes are less distinct strands called chromatin. Also during cell division, the nuclear membrane breaks down and reforms after cell division.
Nuclear membrane has pores to control movement of large molecules into and out of nucleus
Nucleoli (Singular: nucleolus)
Small bodies in the nucleus
Make RNA (Ribonucleic Acid)
Jelly-like material making up most of the cell
Surrounds cell and allows certain substances to pass into and out of the cell
Found in plant cells only
Made of cellulose
Situated on the outside of the cell membrane
Mitochondria (Singular: mitochondrion)
Sites of cellular respiration in the cytoplasm ('Powerhouses' of the cell)
Found at sites of highest metabolism (e.g. muscle cells) to produce energy-rich molecules of ATP (Adenosine Triphosphate)
Mitochondria have a double membrane - the outer membrane around the entire mitochondrion, and the inner membrane folded back and forth for large surface area for chemical reactions
It is thought that mitochondria in eukaryotic cells may have evolved from ancient symbiotic prokaryotic bacteria that lived inside other larger prokaryotic cells. They have their own DNA and ribosomes, and can reproduce on their own.
Small organelles containing RNA that are found in the cytoplasm
Not surrounded by membranes
'Workbenches' on which the cell's proteins (e.g. hormones, enzymes) are made
A system of membranes that help to transport chemicals such as proteins through the cell
Consist of interconnected, flattened sacs whose contents include newly-made proteins
ER sometimes buds off to form small sacs called vesicles
Rough ER has ribosomes attached
Smooth ER has no ribosomes attached
Golgi Bodies (also called Golgi Apparatus)
Serve as collecting, sorting, processing and distribution centres for proteins and carbohydrates
Particularly numerous in cells that secrete hormones or material to produce plant cell walls
Contain stacks of membranes
Various substances move into Golgi Bodies from vesicles formed from ER. Other vesicles pinch off from Golgi Bodies and carry their contents to other parts of the cell.
3 Types of Vacuoles
Mostly found in plant cells and protozoans
Plant vacuoles may contain dissolved starch
Food vacuoles in protozoa may contain food undergoing digestion
Contractile vacuoles in aquatic organisms may pump excess water out of the cell
4 Types of Plastids
Mostly found in plants
Chloroplasts contain chlorophyll for photosynthesis. Chloroplasts also have a double membrane.
Amyloplasts contain starch
Chromoplasts contain coloured pigments of flowers and fruits
Elaioplasts contain oils
Like mitochondria, plastids contain their own DNA and ribosomes, and may have once been symbiotic bacteria living inside a larger cell.
Found in animal cells and certain lower plants
At the time of cell division, these tubular structures play a role in separating the contents of the cell to aid in the division of the cell.
Cilia and Flagella
Found in many eukaryotic cells to aid in 'swimming' movement
Formed by microtubules that move side to side
Cilia (Singular: cilium) are hair-like (e.g. in protozoans such as Paramecium)
Flagella (Singular: flagellum) are whip-like (e.g. in protozoans such as Euglena)
Found in animal cells only
Digest unwanted substances within the cell by releasing digestive enzymes
Enzymes in lysosomes are responsible for the lysis of dead or dying cells, and the resorption of cells in a tadpole's tail during metamorphosis to the adult frog
Formed from Golgi Bodies that form vesicles
Maintains cell shape and provides 'anchoring' for organelles
The cytoskeleton is a complex network of both long contractile protein fibres and microtubules in the cytoplasm
Contractile proteins are responsible for movement within cells, cell contraction and cell motility.
Shortening of the microtubules is responsible for movement of chromosomes during cell division
Did You Know That...? Muscle cells contain large numbers of mitochondria because these are the respiratory 'powerhouses' of cells, and muscle cells require large quantities of energy.