c) A student wanted to find out more about the cell cycle. The student made a slide of an onion root tip. She counted the number of cells in each stage of the cell cycle in one field of view. The table below shows the results.Stages in the cell cycleNon-dividing cells Stage 1 Stage 2 Stage 3 Stage 4 TotalNumber of cells209 4 2 1 36 Each stage of the cell cycle takes a different amount of time. Which stage is the fastest in the cell cycle? Give a reason for your answer. Stage _____________________ Reason ____________________________________________________________ ___________________________________________________________________ (2) Page 11 of 16the genetic material and subcellular organelles are duplicating and then are moving to oppositesides of the cell where the cytoplasm then then divides resulting in the formation of twodaughter cells. in photograph A the cell are beginning to form two genetically identical daughter cells but are still connected via a shared membrane(d) The cell cycle in an onion root tip cell takes 16 hours. Calculate the length of time Stage 2 lasts in a typical cell. Give your answer to 2 significant figures. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ Time in Stage 2 = ________________________ minutes (3) (e) Bacteria such as Escherichia coli undergo cell division similar to mitosis. Figure 2 shows a growth curve for E. coli grown in a nutrient broth. Figure 2What type of cell division causes the change in number of E. coli cells at P? ___________________________________________________________________ (1) Page 12 of 16(f) Suggest why the number of cells levels out at Q. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________
Question
c) A student wanted to find out more about the cell cycle. The student made a slide of an onion root tip. She counted the number of cells in each stage of the cell cycle in one field of view. The table below shows the results.Stages in the cell cycleNon-dividing cells Stage 1 Stage 2 Stage 3 Stage 4 TotalNumber of cells209 4 2 1 36 Each stage of the cell cycle takes a different amount of time. Which stage is the fastest in the cell cycle? Give a reason for your answer. Stage _____________________ Reason ____________________________________________________________ ___________________________________________________________________ (2) Page 11 of 16the genetic material and subcellular organelles are duplicating and then are moving to oppositesides of the cell where the cytoplasm then then divides resulting in the formation of twodaughter cells. in photograph A the cell are beginning to form two genetically identical daughter cells but are still connected via a shared membrane(d) The cell cycle in an onion root tip cell takes 16 hours. Calculate the length of time Stage 2 lasts in a typical cell. Give your answer to 2 significant figures. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ Time in Stage 2 = ________________________ minutes (3) (e) Bacteria such as Escherichia coli undergo cell division similar to mitosis. Figure 2 shows a growth curve for E. coli grown in a nutrient broth. Figure 2What type of cell division causes the change in number of E. coli cells at P? ___________________________________________________________________ (1) Page 12 of 16(f) Suggest why the number of cells levels out at Q. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________
Solution
c) The fastest stage in the cell cycle would be Stage 4. The reason for this is because it has the highest number of cells compared to the other stages. This suggests that cells pass through this stage more quickly than the others.
d) To calculate the length of time Stage 2 lasts in a typical cell, we need to find the proportion of cells in Stage 2 and multiply it by the total time of the cell cycle. There are 2 cells in Stage 2 out of a total of 252 cells (209 non-dividing cells + 4 in Stage 1 + 2 in Stage 2 + 1 in Stage 3 + 36 in Stage 4). So, the proportion of cells in Stage 2 is 2/252 = 0.00794. Multiply this by the total time of the cell cycle (16 hours or 960 minutes) to get the length of time Stage 2 lasts: 0.00794 * 960 = 7.62 minutes. So, Stage 2 lasts approximately 7.62 minutes.
e) The type of cell division that causes the change in number of E. coli cells at P is binary fission. This is a form of asexual reproduction and cell division used by all prokaryotic organisms.
f) The number of cells levels out at Q because the bacteria have likely exhausted the available nutrients in the broth. Without additional nutrients, the bacteria cannot continue to reproduce at the same rate, leading to a plateau in the growth curve. Additionally, waste products may have accumulated to a level that inhibits further growth.
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