Question

when a cell stops growing because it touches another cell, thats called...
m. contact inhibition
n. metastasis
o. cancer
p. invasive growth
what happens during the s phase of interphase?*
s. nuclear envelope disappears
t. it is the last checkpoint before mitosis
u. dna replicates
v. it is a phase of rest for the cell where nothing occurs
which of the following is an example of an external checkpoint of the cell cycle?*
p. g1 checkpoint
q. g2 checkpoint
r. m checkpoint

Explanation:

• First question: Contact inhibition is the phenomenon where normal cells stop growing when they come into contact with other cells. Metastasis is the spread of cancer cells. Cancer is a general term for a group of diseases. Invasive growth is related to abnormal cell growth. So, when a cell stops growing because it touches another cell, it's contact inhibition.
• Second question: In the S phase (synthesis phase) of interphase, DNA replicates. The nuclear envelope disappears in mitosis (prophase). The last checkpoint before mitosis is the G2 checkpoint. The cell is not at rest in the S phase as DNA replication is occurring.
• Third question: G1, G2, and M checkpoints are internal checkpoints of the cell cycle. There seems to be an error in the options provided as none of P, Q, R are external checkpoints. But if we assume it's a mis - labeling (maybe the intended external checkpoint was not listed correctly, but among the given options, if we consider the context of cell cycle checkpoints knowledge, and if we assume it's a wrong - option - set case), but based on standard knowledge, external checkpoints could be factors like growth factors (not in these options). However, if we go by the given options and the fact that maybe it's a misprint (for example, if it was supposed to be a question about internal checkpoints, but the label was wrong), but strictly by the question's ask (external checkpoint example), there is an error. But if we assume it's a wrong - option - labelling and we have to choose from the given (maybe it was a mistake in question creation), but in reality, G1, G2, M are internal.

Answer:

• First question: M. Contact inhibition
• Second question: U. DNA replicates
• Third question: There is an error in the options as G1 (P), G2 (Q), and M (R) checkpoints are internal. But if forced to choose from the given (assuming a mis - label in question creation), no correct external option is present. However, if we consider it as a wrong - labelling (maybe it was about internal, but said external), but based on the question's current state, it's an incorrect option set for the external checkpoint question. But if we ignore the 'external' mis - match (if it was a typo and meant internal), all three (P, Q, R) are internal checkpoints. But as per the question's exact ask (external), no answer. But following the multiple - choice format and assuming some error, if we have to pick (even though wrong), no valid external from P, Q, R. But if we consider the first two questions:
• First: M. Contact inhibition
• Second: U. DNA replicates