Divide And Develop
B2
- Created by: Belinda
- Created on: 29-05-11 13:08
Mitosis
= division of cell nucleus to produce 2 cell nuclei with genetically identical set sof chromosomes to produce new cells for growth and replacement of tissues
1. Cell with 2 pairs of chromosomes
2. Each chromosome replicates itself
3. The copy seperates the cell now divides
4. Each new cell has the same number of chromosomes as the original cell and contains the same genes as the original cell
Happens in most parts of the body, 2 cells are made, 2 sets of chromosomes (diploid)
Meiosis
= diploid nucleus divides twice to produce 4 haploid nuclei containing half the number of chromosomes
Produces cells with genetically different sets of chromosomes and happens in sexually reproducing organisms to produce gametes
1. Each chromosome replicates itself
2. Chromosomes part company and move to opposites sides of cells with their copies
3. First cell division: 2 cells with 2 pairs of chromosomes
4. Copies now seperate and the 2nd cell division takes place
5. 4 gametes (haploid nuclei) each with half the number of chromosomes of the parental cell
4 cells are made, 1 set of chromosomes (haploid)
Growth
Three stages: Cell Division - 2 cells are form from 1, Cell expansion (elongation) - mainly when plants stretch out, Cell specialisation - unspecialised cells can be come a specific type of cell
Growth is measure by finding the total mass of an organism. Most accurate = measure the dry mass
This can only be done when the organism is dead because it inolves heating organism until water has evaporated
Wet mass is usually used as an alternative measure of growth
Wet mass = total mass of living organism
Nature and Nurture
Nature refers to the genes that are inherited by parents
Nurture refers to environmental influences e.g size
Size is a continuous variable; it can take any value within a range
Height is influenced by: Genes, hormones and nutrition
Plants needs nutrients (nitrates and phosphates) for healthy growth and development - roots absorb these from the soil
Hormones make their roots grow down into the soil and their shoots grow up into the air
Farmers use artificial hormones to stimulate this
Artificial plant hormones & performance enhancing
Auxins = naturally recurring plant homrones to control fruti initiation
Fruit growers spray unpolliated flowers with synthetic auxin to make the plants produce fruit without fertillisation recurring so they dont have seeds
Performance enhancing drugs can increase the body mass and strngth.
Athletes take them to recover from an injury more quickly, to masc pain, to be the best and win
Anabollic steroids stimnulate the development of muscle tissue
Many health problems: liver disorders, heart disease, reduced sperm production in males and altered behaviour
Regeneration in animals & stem cells & the hayflic
Plants have the ability to regenerate new leaves if old ones are lost
MOST animals cant regenerate losty body parts.
Some do as a part of a defense mechanism: Worms regenerate missing half, Immature Spiders re grow legs (not adults), and lastly reptiles shed their tales and legs
When cells become specialised its called: Differentiation
Plant cells differentiate any time but animal cells only differentiate after they are made
Stem cells are un-differentiated (unspecialised)
Hayflick limit = a limit to how many times a differeniated cell can divide by mitosis. Human stem cells limit is about 52. Stem cells have no hayflick limit. Cancer cells also have no hayfliuck limit.
Selective breeding and cloning
Selective breeding is used to increase quality, quantity and yield
Cloning:
1. The diploid nucleus is taken from a mature cell of the donor organism
2. The diploid nucleus, containing all the of the donors enetic information, is inserted in to an empty egg cell, ie: an eggcell with the nucleus removed
3. The eggcell containing the diploid nucleus is stimulated so that it begins to divide by mitosis
4. The resulting embryo is placed in the uterus of a 'surrogat mother'
5. The embryo develops into a foetus and is born as normal
One danger of this cloning is, possible ageing. Because the eggcell recieves genetic information from just one parent, defects in the DNA are more likely
Later stages of embryonicdevelopment of clones many embryos do not survive until birth
Genetic debate & gene therapy
We can determine if an individuals genes will make them more susceptible to certain illnesses
We may soon be able to remove genes and use them to replace the faulty genes
Ethnical issues: the possibility of designer babies, the possibility insurance companies can use genetic screening to refuse to cover individuals with an increased risk of disease, possibilities of increased abortion rates
Gene therapy = Experimental technique that involves transplanting genes into an individual cell to help treat inherited diseases.
Gene therapy can only provide short term relief from the symptons because genes are only transferred into target body cells, not sex cells so can't be passed onto offspring
alternative ways of fighting cancer :Introducing genes improve the patients immune responce to the disease, injecting cancer cells with genes that make them more sensitive to treatments, genes that make healthy cells more resistent to the side effects of high doses of anit-cancer drugs, by injecting cancer cells with 'suicide genes'.
Glossary
Diploid - a nucleus of a cell which contains 2 sets of chromosome; normal body cells not gametes
Haploid - a nucleus of a cell which contain 1 set of chromosomes e.g gametes
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