3.24c stages of mitosis

the nucleus of the cell contains the chromosomes, during the resting stage of the cell cycle known as the interphase the chromosomes are copied in  a process known as DNA replication, this process creates two copies of each chromosome which are held together by a structure known as the centromere.

stages of mitosis includes ::
the nucleus membrane breaks down in the process of cell division, called prophase. chromosomes become visible as a pair of chromatids.
a network of of protein molecules appear called spindles the chromosome will move towards the spindle during the late prophase and will move finally join onto a spindle fibre at the centromere known as the metaphase, in this phase the chromosomes are in the middle arranged across the equator of the cell.
the next phase is the amaphase where the spindle fibre shortens so the chromatids gets pulled apart to opposite poles of the cell.
telophase is the end of mitosis where the nucleus begins to reform around the chromosomes at the end of the phase two nuclei are formed at opposite ends of the cell.
cytokinesis is not considered a stage of mitosis but it is where the cell splits to form two cells, each with one chromosome in, identical to the parental cell.

3.24a mitosis

mitosis, a form of cell division which results in growth because of a n increase in the number of cells.

diploid(2n) is the number of chromosomes in a nucleus.
e.g. for humans 2n=46 ( the diploid number for humans is 46)

In the process of the mitosis a cell will divide into two cells each with a diploid nucleus, they can be described as identical or daughter cells. They are 'identical' because they have the same number of chromosomes and the same set of chromosomes.

3.16 structure of the DNA molecule

3.16 a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T) and the cytosine (C) with guanine (G)

the two strands of helixes are called the ‘sugar-phosphate backbone’ they are linked together by pairs of four different types of bases (two pairs).

the order of the bases on one side of the double helix, are what is called the gene. 

3.15 the gene is a section of a molecule of DNA

The gene is located in the nucleus of a molecule of DNA, it carries the information of the characteristics of the organism like the blood type or the petal colour. This information is then passed on to the cytoplasm where the genetic information is turned into a protein in which controls the production of the characteristics of the organism.

3.14 the nucleus of the cell contains chromosomes on which genes are located

The chromosomes are the genetic information within the cell

Within the nucleus à chromosomes are found à they are composed of DNA(in a shape known as the double helix) à sections of the DNA are called genes, these carry the information for the construction of à proteins which controls the production of  à the characteristics (e.g. blood type)

Different organisms have different numbers of chromosomes, Humans have 46 whilst cats have 38.

Chromosomes operate in pairs known as the homologous pairs, the homologous nature is based on the length of the chromosome. There are 2 versions each characteristic contained in the gene, which can be found in the same place within the homologous pair.

3.1 Sexual and Asexual reproduction

3.1 differences in sexual and asexual reproduction

1. organisms that have sexual reproduction show sexes that is when they can be identified as a male or female. In asexual reproduction organisms do not have sexes.

2. sexually reproducing organisms produce cells called gametes, this take the form of the male in the sperm cell and the female in the egg cell. asexually reproducing organisms have no gametes.

3. the type of cell division that produces gametes is called Meiosis which halves the number of adult chromosomes through cell division in the gamete cell. in an organism that shows asexual reproduction there is mitosis and binary fission, in this process the number of chromosomes is maintained constantly and are identical.

4. In sexually reproducing populations we find the process of fertilisation in which the sperm cell from the male and the egg from the female fuse. The are no gametes in asexual reproduction therefore no fusion of the cells and no fertilisation occurs.

5. in the population of sexually reproducing organisms there is a broad variety in the individuals of this population whereas in asexual reproduction show small amounts of variations in the individuals in this population.