Cell Division, Cell Diversity and Cellular Organisation
The cell cycle...
Main stages of mitosis;
- The synthesis stage (S)
- The DNA replicates.
- It is the longest stage.
- The chromosomes condense & become visible under a light microscope.
- Each chromosome has 2 chromatids.
- The nuclear envelope breaks down.
- The centrioles duplicate and move to opposite ends of the cell to form a spindle.
- The chromosomes like up along the equator of the spindle.
- They attach to a spindle thread by their centromere.
- The replicated sister chromatides are separated when the centromere splits.
- The spindle fibres shorten, pulling the chromatids to opposite poles.
- Once separateer they are called chromosomes again.
- As the separated sister Chromatids reach the poles of the cells.
- A new nuclear envelope forms around each set of chromosomes.
- The spindle breaks down.
- The Chromosomes uncoil so they are no longer visible under a light microscope.
- The whole cell splits to down two new cells, each one identical to each other and to the parent cell.
Explain the meaning of the term homologous pair of chromosomes;
Chromosomes that have the same genes at the same loci. Members of a homologous pair of chromosomes pair up during meiosis. Diploid organisms produced by sexual reproduction have homologous pairs of choromosomes- one member of each pair from the mother and one from the father.
Significance of mitosis for growth, repair and asexual reproduction in plants and animals;
Growth- multicellular organisms produce new extra cells to grow. Each new cell is genetically identical to the parents cell, and so can perform the same function.
Repair- damaged cells need to be replaced by new ones that perform the same functions and so need to be genetically identical to the parent cell, as with growth.
Asexual reproduction- single celled organisms divide to produce two daughter cells that are separate organisms.
Some multicellular organisms produce offspring from parts of the parent.
Process of cell division by budding in yeast;
Yeast cells undergo cytokinesis by producing a small ‘bud’ that nips of the cell, a process called budding.
Cells produced as a result of meiosis are not genetically identical;
Undifferentiated cells that are capable of becoming differentiated to a number of possible cell types.
Differentiation, with reference to the production of erythrocytes (red blood cells) and neutrophils derived from stem cells in bone marrow, and the production of xylem vessels and phloem sieve tubes from cambium;
The changes occurring in the cells of a multicellular organism so that each different…