Divide And Develop

B2

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  • 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)

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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)

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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

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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

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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

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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.

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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

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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'.

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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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