Topic 2 - CELLS + CONTROL

2.1- Stages of Mitosis

Mitosis is part of the cell cycle and has 6 stages:

• INTER.- Before the cell can divide to produce an identical daughter cell, it must produce a copy of its DNA
• PRO. - Chromosomes condense and the nuclear envelope breaks down
• Metaphase - The chromosomes then line up in the equator of the cell and the spindle fibres attach to them
• ANA. - one copy goes to each pole of the cell and is pulled by the spindle fibres
• TELO. - membranes form around each of the sets of chromosomes. These then become the nuclei of the two cells - the nucleus has divided
• CYTO- Before telophase ends, the cytoplasm and cell membrane divide to produce two identical daughter cells.

2.2- Mitosis in Growth, Repair and As.Rep.

• DEVELOPMENT + GROWTH -  the formation of a multicellular organism from a single fertilized egg and an increase in size through the division of cells by mitosis. 
• CELL REPAIR - many cells within a multicellular organism are constantly dying and being replaced by mitosis. 
• ASEXUAL REP. – some organisms (e.g. Plants and bacteria) can reproduce asexually so that only one parent is needed.

2.3 - Mitosis Description

Mitosis is the production of two daughter cells each with identical sets of chromosomes in the nucleus to the parent cell, this results in the formation of two genetically identical diploid body cells.

 2.4 - Cancer

A cancerous growth is when cells start to divide uncontrollably without any cell death due to a change/mutation in the gene These cells are not specialized and will cause problems if this happens in an important organ as they take over the space and prevent the organ from working.

2.5- Cell division and growth

Plants and animals both grow due to these processes:

• CELL DIFFERENTIATION - the process by which cells become specialised to complete different tasks. There is one type of cell that can be used to make any cell.
• CELL DIVISION - cells need to divide in order to grow and repair themselves
• CELL ELONGATION - This is where a plant expands, making it bigger and so making it grow. ONLY in plants

• All growth in animals happens by division. They tend to grow whilst young, reach full growth and then stop, from then on most cell division is for repair.
• In plants, growth in height is mainly due to enlongation. Cell division happens at the tips of roots and shoots. Plants grow continously. Therefore plants continue to differentiate.

2.6- Importance of differentiation

Differentiation allows specialised cells to distinguish between each other, to perform specific functions and in turn, creates variation among and between species.

2.7- Percentile Charts

• They are used to define an overall pattern in development and to highlight potential problems
• 'Percentile'- eg. a baby is in the 75th percentile of average mass this means that 75% of babies are lighter and 25% are …