Chapter+3

toc

=Dbq P36 Cell Size and cycle=

1. (a) 24.00 to 01.00 about 50% 0f the population in S phase (not sure about the time scales rather small)

(b) I read G2 + M peaks around 05.00, 03.00 and 06.00 (three peaks)

2. G1

3. Cell size decreases during the later part of the day when the light levels are falling. Cell size increases during the main day light period. If cell size is a measure of the capcity to carry out cellular process such as photosynthesis thn the data is consistent with the hypothesis.

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I- G1 since, non-dividing cells will be in the early interphase (G1) and will not be DNA replicating (s) or preparing for division (G2). The frequency of cells with this amount of DNA will therefore be high.

II- S, as this phase is shorter than either G1 or G2 then the frequency of cell found in the phase will be lower. There should be an increased quantity of DNA per nucleus as these cells will be at various stages of DNA replication. Note that stage II has more DNA than the non replicating cells which act as a control.

III - G2 for two reasons. a) The mass of DNA per nucleus is double that of I (G1) which is consistent with the idea that ALL cell have completed DNA replication and doubled the mass of DNA. b) Frequency of the cells in III is greater than II (s) as this stage is longer than the S phasebut shorter than I (G1).

b) Prophase (one nucleus) the chromosomes are represented by a pair of sister chromatids such that the mass of DNA would be double the norm(G1) this is consistent with phase III (G2) approx 14 pg/ Nucleus

Telophase (two nuclei forming) would have half the DNA mass of the G2 phase which is consistent with the measurement of the non-dividing or G1 dividing cell at 7pg/ nucleus