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Biology A level OCR - Eukaryotic Cell Structure Cheat Sheet (DRAFT) by

Biology A level OCR - Eukaryotic Cell Structure. This is following the OCR textbook for A level biology. The cheat sheet is on module 2, foundations in biology.

This is a draft cheat sheet. It is a work in progress and is not finished yet.


There are two fundam­ental types of cells: prokar­yotic and eukary­otic.

Prokar­yotes - unicel­lular organisms with an undivided cytoplasm. The cytoplasm is made of cytosol (water, salts and organic molecu­les).

Eukaryotic - multic­ellular organisms. Eukaryotic cells have a more complex inner structure (e.g. nucleo­plasm, cytopl­asm).

This topic is about the ultras­tru­cture of the cell (what can be observed with an electronic micros­cope).

The cytosk­eleton

A network of fibres found throughout eukaryotic cells' cytoplasm which provide stability and structure to the cell as well as hold organelles in place. It also controls cell and organelle movement.
It is made of three struct­ures:

Microf­ila­ments - Made from protein actin. Respon­sible for cell movement and cell contra­ction (during cytoki­nesis).

Microt­ubules - Determines the shape of a cell due to polyme­rised globular tubulin proteins. Used as tracks for the movement of organelles (e.g. vesicles). They also make up spindle fibres used on the separation of chromo­somes.

Interm­ediate fibres - Provide mechanical strength to cells and maintain their integrity.


Contains coded genetic info (DNA molecu­les). DNA controls protein synthesis. It is often the biggest organelles in the cell.
DNA is contained in a double membrane (nuclear envelope) which protects it from damage. Nuclear pores allow substances in and out of the nucleus. DNA molecules are too big to leave the nucleus so they are transc­ribes into RNA.

DNA + histones (proteins) = chromatin (coils and condensed to form chromo­somes).

The nucleolus

Area within the nucleus which produces ribosomes. Composed of proteins and RNA. RNA produces rRNA (ribosomal ribo nucleic acid) which combines with proteins to make ribosomes.


Membranous sacs used for storage and transport consisting of a single membrane with fluid.


Vesicles containing hydrolytic enzymes. These break down cellular waste material (including old organe­lles), pathogens absorbed by phagocytes or cells (apopt­osis).

Compar­tments for life

Metabolism - synthesis and breaking down of molecules.

Reactions take place in the cytoplasm which is separated from external enviro­nment by a cell-s­urface membrane. Organelles are membrane bound compar­tments where different reactions can take place during to the specific enviro­nments they provide.
Membranes are select­ively permeable (only allow certain substances in and out).
Some organelles are common to all Eukaryotic cells and are seen in animal cells.


Site of cellular respir­ation (produ­ction of ATP). More mitoch­ondria = more energy used.
Mitoch­ondria have a double membrane: the inner membrane is folded (forms structures called cristae) and a fluid interior (the matrix). Membrane contains the cristae contains enzymes used for respir­ation. Mitoch­ondria also contains small amounts of DNA (called mitoch­ondrial DNA or (mt)DNA). Mitoch­ondria produce their own enzymes and reproduce themse­lves.