External stimulus. The rain is something out of your control while you're waiting. Rain is not something you are doing nor is it a response to you waiting for the bus.
Answer:
<u>Option- D: </u>Is the best choice to choose from the given options.
Now, let us explain the term Cell cycle in a more comprehensive way.
<u>As the cell cycle is controlled at three checkpoints.</u>
- The integrity of the DNA is assessed at the G₁ checkpoint.
- Proper chromosome duplication is assessed at the G₂ checkpoint.
- Attachment of each kinetochore to a spindle fiber is assessed at the M checkpoint.
Explanation:
The cell cycle is controlled by three internal checkpoints that evaluate the condition of the genetic information.
- <u>The G₁ Checkpoint</u>:This stage determines whether all conditions are favorable for cell division to proceed. The cell can halt the cycle and attempt to remedy the problematic condition, or the cell can advance into G₀ (inactive) phase and await further signals when conditions improve.
- <u>The G₂ Checkpoint:</u> The most important role of the G₂ checkpoint is to ensure that all of the chromosomes have been accurately replicated without mistakes or damage.
- <u>The M Checkpoint:</u>It occurs near the end of the meta-phase stage of mitosis. it determines whether all the sister chromatids are correctly attached to the spindle micro-tubules
The development of the human embryo follows fertilization, and continues as fetal development. By the end of the tenth week of gestational age the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where many organs become fully developed.
