Organelles

The nucleus is a membrane bound organelle found in eukaryotic cells. It contains most of the cells genetic material, organised as multiple long linear DNA molecules with a large variety of proteins to form chromosomes. The function of the nucleus is to maintain the reliability of the genes and to control the activities of the cell by regulating gene expressions. Therefore the nucleus is the control centre of the cell. 

The nucleolus (plural nucleoli) is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus of a cell. its function is to transcribe ribosomal RNA and assemble it within the nucleolus. three Major components of the nucleolus are reconised : the fibrillar centres, the dense fibillar components and the granular components.

The Golgi apparatus is found in most cells. It is another packaging organelle.The Golgi apparatus gathers simple molecules and combines them to make molecules that are more complex. It then takes those big molecules such as horemones, packages them in vesicles, and either stores them for later use or sends them out of the cell. It is also the organelle that builds lysosomes (cell digestion machines). Cisternae is flattened membrane disks

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SER has a variety of functions such as the synthesis of lipids including steroid horemones. In the liver cell the toxins are broken down my SER. It has NO ribosomes on it.

The outer membrane of the rough ER is covered in ribosomes. proteins are manufactured/synthesised in the rough ER e.g. antibodies in response to a bacterial infection. It is a network of membranes enclosing spaces called cisternae. the manufactured proteins enter the cisternae which break up to form small membrane -bound sacks called vesicles. these move towards the golgi apparatus.

The cell surface membrane controls what enters and leaves the cell eg. water and oxygen can difuse through it. many other substances can only pass through special transporter proteins in the cell surface membrane. It is selectively permeable.

mitochondria is the site of aerobic respiration. in respiration glucose molecules are broken down to make ATP molecules. chemical energy from the glucose is transferred to chemical energy in ATP.ATP leaves the mitochondrion and can be used by other parts of the cell when energy is needed.

Chloroplasts trap energy from sunlight using it to make water and co2 which react together to form glucose and oxygen (photosynthesis). they are only found in plant cells. They are surrounded by 2 membranes. There are stacks of membranes  (Grana) inside the chloroplast which contain chlorophyll