F211 OCR Biology 1 (Chapter 3)

The mitotic cell cycle is made up of two main phases, interphase and mitosis (95% and 5% retrospectivly)

During interphase;

• normal cell activity takes place, (cells are not replicating) such as protein synthesis and resperation
• the DNA that make up the chromosomes is replicated during this stage so the DNA can be devided equally into the two daughter cells created in mitosis
• the chromosome becomes two chromatids 

During prophase;

• chromosmes condense and become visible - DNA molecules from the nucleus coil and supercoil becoming shorter and thicker
• when they become visable they can be seen to be composed of two strands (chromatids)
• centrioles move away from each other and spindle starts to form 
• centrioles - a pair of organelles found in animal cells which build microtubles to form spindle 
• spindle - a structure made up of microtubles that manouvers chromosomes into postition

During metaphase;

• the nuclear envelope breaks down, which allows more room for the mnouvering of chromosomes
• the chromosomes are fully condensed 
• the microtubles attach themselves to the centremeter of the chromosomes
• each centremeter is grabbed by a microtuble on each side, being pulled in opposite directions, aligning the chromosomes along the equator 
• centremeter -  the place where two chromatids are held together 

During anaphase;

• the centremeters split 
• microtubles pull the chromatids apart to either poles

During telephase;

• the two groups of chromatids reach the poles (now called chromosomes)
• the spindles disappear due to the microtubles breaking down
• new nuclear envelopes form around each group of chromosomes
• the chromsomes uncoil and become thinner again 

During cytokinesis; 

• cytoplasm splits to form two identicall daughter cells 

(the stages of mitosis)

The development of a cell become specialised for a particular function

• the zygote devides into a ball of cells known as the blastocyst
• undifferentiated cells can be obtained from bone marrow and blastocyst, these cells are the easiest to obtain (these cells are known as 'totipotent' as they can differentiate into any type of cell)
• in plants they are known as maristem cells 

Some specialised animal cells include; 

• spermatozoa - nucleus containing a hapoid set of chromosomes, 'acrosome' a specialised lyosome, mitochrodria that produce ATP for swimming, microtubles use ATP to move over each other and cause lashings 
• erythocytes - biconcave to increase surface area, small to allow through capillaries, no nucleus to make more room from haemoglobin 
• squamous epithelial cell - covers alveoli, squashed thin cells, interlocking held by basement membrane 

some examples of specialised plant cells;

• palaside cells - contain many chloroplasts, long thin and tightly packed
• xylem vessels - differentiated from cambium, thick strong cell walls containing cellulose and ligin, pits allow lateral water movement, no cytoplasm so all the space can be used to transport water 
• phloem sieve tubes - connected to each other through sieve plates so many have pores allowing sugars to be transported, companion cells provide ATP, modified cytoplasm to aid the transport of sugars  

A tissue;

• a collection of cells, together with a intercellular secretion produced by them, that is specialised to perfrom one or more particular functions (these cells are often the same type of cell)

An organ;

• a part of the body which froms a structural unit and is composed of more than one tissue

A system;

• a collection of organs with particular functions 

• 'Devison of labour' within a multicellular organism means that every cell has its own set of functions in which it specialises, communication between cells relies on cell signalling 

(meiosis vs mitosis table)