Theory question 103
Cell Division(a) What is a cell?
(b) Describe briefly the structure of DNA
(c) Describe the process of mitosis
(d) what is the importance of mitosis to living organisms?
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(a) A cell is the basic unit of structure and function of a living organism, consisting of protoplasm (nucleus and cytoplasm) surrounded by a membrane
(b) DNA is made of two long strands of nucleotides twisted into a double helix; each nucleotide has deoxyribose sugar, a phosphate group and a base; bases are adenine, thymine, guanine, cytosine; the strands are joined by hydrogen bonds between paired bases (A with T, G with C), like rungs of a ladder
(c) Interphase: chromosomes copied
Prophase: chromosomes shorten and thicken, each of two chromatids; nuclear membrane and nucleolus disappear; spindle forms
Metaphase: chromosomes line up on the equator attached to spindle fibres by centromeres
Anaphase: centromeres split; chromatids pulled to opposite poles
Telophase: nuclear membranes re-form; cytoplasm divides (furrowing in animals, cell plate in plants) giving two identical daughter cells
(d) Growth; repair and replacement of worn-out cells; asexual reproduction; keeps chromosome number constant and gives genetically identical cells
Describe the stages of mitosis in their correct order.