Chromosomes and Mitosis

Question 1

what are chromosomes?

Answer 1

•tightly coiled strands of DNA molecules
•found in the nucleus of a cell
•carries a large number of genes

Question 2

what are genes?

Answer 2

•sections of DNA that code for a protein
•different genes contain the development of different characteristics e.g. hair colour

Question 3

how are chromosomes arranged in the nucleus of a body cell?

Answer 3

•in pairs e.g. humans have 23 pairs so 46 altogether
•body cells normally have 2 copies of each chromosome- one from the organisms ‘mother’ and one from its ‘father’

Question 4

why is cell division by mitosis important?

Answer 4

•for growth and repair of multicellular organisms
• for replacing worn out or damaged cells/ repairing damaged tissue

Question 5

what are some examples of contexts where mitosis is occuring?

Answer 5

•growth of embryos into foetus and beyond
•regular replacement of skin cells, blood cells and cells lining the digestive system
•plant roots/shoot tips

Question 6

what is the definition of the cell cycle?

Answer 6

*a series of stages in which a cell divides

Question 7

what happens during the different stages of cell division?

Answer 7

Stage 1- Growth and DNA replication
•Before it divides, the cell had to grow and increase the amount of sub cellular structures e.g. ribosomes or mitochondria
•DNA then replicates to form 2 copies of each chromosome

Stage 2- mitosis
•the chromosomes line up at the centre of the cell and cell fibres pull them apart.
•The two arms of each chromosomes go to opposite ends of the cell
•membranes form around each of the sets of chromosomes which then become nuclei of the two new cells (the nucleus has divided)

Stage 3- Cytokensis
•the cytoplasm and cell membrane divide
•2 genetically identical cells are formed