Divide and Develop B2

Mitosis is the division of a cell nucleus to produc two nuclei with genetically identical sets of chromosomes. This happens to produce new cells for growth and for the replacement of tissues.

1. Cell with two pairs of chromosomes

2. Each cell replicates itself

3. The copies seperate. Cell no divides.

4. Each cell has the same number of chromosomes as the orginal cell and contains the same genes as the orginal cell.

In meisos a diplois nucleus divides twice to produce four haploid nuclei which contain half the number of chomosome. A diploid nucleus contains two setsof chromosomes. A haploid only contains one.This process produces cells with genetically different sets of chromosomes and happens in gametes (sex cells ova an sperm)

Growth is the permanent increase in the size of an organism; cell division, cell expansion, cell specialisation.

Growth can be measured via; length, total mass, dry mass, wet mass.

Nature-refers to inherited genes

Nurture-refers to environmental influences.

Auxins are naturally occurring plant hormones which control the fruit iniation. (development of fruit). To ensure fruit is avaliable all year round fruit growers sprat unpollinated flowers with synthetic auxin. This will make plants produce fruit without fertlisation occurring.

Performance enchancing drugs- act on the bosy in a similar way to natural growth hormones.

Sports players are not allowed to use them- but some takes risk use them to

• to recover quikly from a injury
• mask pain so they can perform
• to improve on natural ability
• to win
  

is when an organism has the ability to regenerate new leaves if they are lost of a new leg if it comes off.

Animals that can replace body parts do so as a defence mechanism.

eg worms, spiders, reptiles, star fish.

STEM CELLS

Differentiation- the process by which stem cells become specialised to do a certain job.

Stem cells are undifferentiated. This means they could differentiate into any type of cell- and could potentially be developed to replace damaged celld and tissues as well as used in the treatment of diseases.

...there is a limit to how may times a differentaited cell can divide by mitosis

In a human cell the Hayflick limit is about 52 divisions.

Stem cells have not differentiated, meaning they have not got a Hayflick limit.

Cancer cells also have no hayflick limit...which is why they are so dangerous...

Selective Breeding

• increses quality
• increases quantity
• increases yield

cloning ... genetically identical

Gene Therapy

Is the name given to an experimental technique that invovles transplanting genes into an indivuals cells to help treat inherited diseases eg cystic fibrosis

Nuclear Transfer-the process where a donor nucleus is transfered into an empty egg cell.

Phototropism- a plant growth response to light

Elongation- when a plant cell becomes longr during the process of differentiationa