What is the significance of an eyespot in the cell of euglena?

The significance of an eyespot in the cell of Euglena is that it allows light to be detected. An eyespot can also be referred to at stigmata, and exists only in one celled organisms. However, this is not to be confused with the use of the word lightspot (also in biology) which refers to the light-sensitive cells in the skin of some animals such as starfishes.

Primary succession is when there isn't any soil when a new community begins.

Secondary succession is when an event such as a fire destroys an area but leaves the soil.

Primary succession would transition to secondary succession by starting off without any soil. Overtime the community would begin to grow and then soil would appear and plants would start to grow. It would then change to Secondary succession whn an event destroys that area leaving just the soil behind.